This document defines the Web Application Messaging Protocol (WAMP). WAMP is a routed protocol that provides two messaging patterns: Publish & Subscribe and routed Remote Procedure Calls. It is intended to connect application components in distributed applications. WAMP uses WebSocket as its default transport, but can be transmitted via any other protocol that allows for ordered, reliable, bi-directional, and message-oriented communications.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This document is also available in these normative formats: RFC (TXT format) and RFC (HTML format)
This Internet-Draft will expire on October 20, 2018.
,------. ,------.
| Peer | | Peer |
`--+---' TCP established `--+---'
|<----------------------------------------->|
| |
| TLS established |
|+<--------------------------------------->+|
|+ +|
|+ WebSocket established +|
|+|<------------------------------------->|+|
|+| |+|
|+| WAMP established |+|
|+|+<----------------------------------->+|+|
|+|+ +|+|
|+|+ +|+|
|+|+ WAMP closed +|+|
|+|+<----------------------------------->+|+|
|+| |+|
|+| |+|
|+| WAMP established |+|
|+|+<----------------------------------->+|+|
|+|+ +|+|
|+|+ +|+|
|+|+ WAMP closed +|+|
|+|+<----------------------------------->+|+|
|+| |+|
|+| WebSocket closed |+|
|+|<------------------------------------->|+|
|+ +|
|+ TLS closed +|
|+<--------------------------------------->+|
| |
| TCP closed |
|<----------------------------------------->|
,--+---. ,--+---.
| Peer | | Peer |
`------' `------'
### Protocol errors {#protocol_errors}
WAMP implementations MUST close sessions (disposing all of their resources such as subscriptions and registrations) on protocol errors caused by offending peers.
Following scenarios have to be considered protocol errors:
- Receiving `WELCOME` message, after session was established.
- Receiving `HELLO` message, after session was established.
- Receiving `CHALLENGE` message, after session was established.
- Receiving `GOODBYE` message, before session was established.
- Receiving `ERROR` message, before session was established.
- Receiving `ERROR` message with invalid REQUEST.Type.
- Receiving `SUBSCRIBED` message, before session was established.
- Receiving `UNSUBSCRIBED` message, before session was established.
- Receiving `PUBLISHED` message, before session was established.
- Receiving `RESULT` message, before session was established.
- Receiving `REGISTERED` message, before session was established.
- Receiving `UNREGISTERED` message, before session was established.
- Receiving `INVOCATION` message, before session was established.
- Receiving protocol incompatible message, such as empty array, invalid WAMP message type id, etc.
- Catching error during message encoding/decoding.
- Any other exceptional scenario explicitly defined in any relevant section of this specification below (such as receiving a second `HELLO` within the lifetime of a session).
In all such cases WAMP implementations:
1. MUST send an `ABORT` message to the offending peer, having reason `wamp.error.protocol_violation` and optional attributes in ABORT.Details such as a human readable error message.
2. MUST close the WAMP session by disposing any allocated subscriptions/registrations for that particular client and without waiting for or processing any messages subsequently received from the peer,
3. SHOULD also drop the WAMP connection at transport level (recommended to prevent denial of service attacks)
# Messages {#messages}
All WAMP messages are a `list` with a first element `MessageType` followed by one or more message type specific elements:
```
[MessageType|integer, ... one or more message type specific
elements ...]
```
The notation `Element|type` denotes a message element named `Element` of type `type`, where `type` is one of
* `uri`: a string URI as defined in [URIs](#uris)
* `id`: an integer ID as defined in [IDs](#ids)
* `integer`: a non-negative integer
* `string`: a Unicode string, including the empty string
* `bool`: a boolean value (`true` or `false`) - integers MUST NOT be used instead of boolean value
* `dict`: a dictionary (map) where keys MUST be strings, keys MUST be unique and serialization order is undefined (left to the serializer being used)
* `list`: a list (array) where items can be again any of this enumeration
*Example*
A `SUBSCRIBE` message has the following format
```
[SUBSCRIBE, Request|id, Options|dict, Topic|uri]
```
Here is an example message conforming to the above format
```
[32, 713845233, {}, "com.myapp.mytopic1"]
```
## Extensibility
Some WAMP messages contain `Options|dict` or `Details|dict` elements. This allows for future extensibility and implementations that only provide subsets of functionality by ignoring unimplemented attributes. Keys in `Options` and `Details` MUST be of type `string` and MUST match the regular expression `[a-z][a-z0-9_]{2,}` for WAMP predefined keys. Implementations MAY use implementation-specific keys that MUST match the regular expression `_[a-z0-9_]{3,}`. Attributes unknown to an implementation MUST be ignored.
## No Polymorphism
For a given `MessageType` and number of message elements the expected types are uniquely defined. Hence there are no polymorphic messages in WAMP. This leads to a message parsing and validation control flow that is efficient, simple to implement and simple to code for rigorous message format checking.
## Structure
The application payload (that is call arguments, call results, event payload etc) is always at the end of the message element list. The rationale is: Brokers and Dealers have no need to inspect (parse) the application payload. Their business is call/event routing. Having the application payload at the end of the list allows Brokers and Dealers to skip parsing it altogether. This can improve efficiency and performance.
## Message Definitions
WAMP defines the following messages that are explained in detail in the following sections.
The messages concerning the WAMP session itself are mandatory for all Peers, i.e. a Client MUST implement `HELLO`, `ABORT` and `GOODBYE`, while a Router MUST implement `WELCOME`, `ABORT` and `GOODBYE`.
All other messages are mandatory per role, i.e. in an implementation that only provides a Client with the role of Publisher MUST additionally implement sending `PUBLISH` and receiving `PUBLISHED` and `ERROR` messages.
### Session Lifecycle
#### HELLO
Sent by a Client to initiate opening of a WAMP session to a Router attaching to a Realm.
```
[HELLO, Realm|uri, Details|dict]
```
#### WELCOME
Sent by a Router to accept a Client. The WAMP session is now open.
```
[WELCOME, Session|id, Details|dict]
```
#### ABORT
Sent by a Peer*to abort the opening of a WAMP session. No response is expected.
```
[ABORT, Details|dict, Reason|uri]
```
#### GOODBYE
Sent by a Peer to close a previously opened WAMP session. Must be echo'ed by the receiving Peer.
```
[GOODBYE, Details|dict, Reason|uri]
```
#### ERROR
Error reply sent by a Peer as an error response to different kinds of requests.
```
[ERROR, REQUEST.Type|int, REQUEST.Request|id, Details|dict,
Error|uri]
[ERROR, REQUEST.Type|int, REQUEST.Request|id, Details|dict,
Error|uri, Arguments|list]
[ERROR, REQUEST.Type|int, REQUEST.Request|id, Details|dict,
Error|uri, Arguments|list, ArgumentsKw|dict]
```
### Publish & Subscribe
#### PUBLISH
Sent by a Publisher to a Broker to publish an event.
```
[PUBLISH, Request|id, Options|dict, Topic|uri]
[PUBLISH, Request|id, Options|dict, Topic|uri,
Arguments|list]
[PUBLISH, Request|id, Options|dict, Topic|uri,
Arguments|list, ArgumentsKw|dict]
```
#### PUBLISHED
Acknowledge sent by a Broker to a Publisher for acknowledged publications.
```
[PUBLISHED, PUBLISH.Request|id, Publication|id]
```
#### SUBSCRIBE
Subscribe request sent by a Subscriber to a Broker to subscribe to a topic.
```
[SUBSCRIBE, Request|id, Options|dict, Topic|uri]
```
#### SUBSCRIBED
Acknowledge sent by a Broker to a Subscriber to acknowledge a subscription.
```
[SUBSCRIBED, SUBSCRIBE.Request|id, Subscription|id]
```
#### UNSUBSCRIBE
Unsubscribe request sent by a Subscriber to a Broker to unsubscribe a subscription.
```
[UNSUBSCRIBE, Request|id, SUBSCRIBED.Subscription|id]
```
#### UNSUBSCRIBED
Acknowledge sent by a Broker to a Subscriber to acknowledge unsubscription.
```
[UNSUBSCRIBED, UNSUBSCRIBE.Request|id]
```
#### EVENT
Event dispatched by Broker to Subscribers for subscriptions the event was matching.
```
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict]
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict, PUBLISH.Arguments|list]
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict, PUBLISH.Arguments|list,
PUBLISH.ArgumentsKw|dict]
```
> An event is dispatched to a Subscriber for a given `Subscription|id` only once. On the other hand, a Subscriber that holds subscriptions with different `Subscription|id`s that all match a given event will receive the event on each matching subscription.
>
### Routed Remote Procedure Calls
#### CALL
Call as originally issued by the Caller to the Dealer.
```
[CALL, Request|id, Options|dict, Procedure|uri]
[CALL, Request|id, Options|dict, Procedure|uri, Arguments|list]
[CALL, Request|id, Options|dict, Procedure|uri, Arguments|list,
ArgumentsKw|dict]
```
#### RESULT
Result of a call as returned by Dealer to Caller.
```
[RESULT, CALL.Request|id, Details|dict]
[RESULT, CALL.Request|id, Details|dict, YIELD.Arguments|list]
[RESULT, CALL.Request|id, Details|dict, YIELD.Arguments|list,
YIELD.ArgumentsKw|dict]
```
#### REGISTER
A Callees request to register an endpoint at a Dealer.
```
[REGISTER, Request|id, Options|dict, Procedure|uri]
```
#### REGISTERED
Acknowledge sent by a Dealer to a Callee for successful registration.
```
[REGISTERED, REGISTER.Request|id, Registration|id]
```
#### UNREGISTER
A Callees request to unregister a previously established registration.
```
[UNREGISTER, Request|id, REGISTERED.Registration|id]
```
#### UNREGISTERED
Acknowledge sent by a Dealer to a Callee for successful unregistration.
```
[UNREGISTERED, UNREGISTER.Request|id]
```
#### INVOCATION
Actual invocation of an endpoint sent by Dealer to a Callee.
```
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict]
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict, C* Arguments|list]
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict, CALL.Arguments|list, CALL.ArgumentsKw|dict]
```
#### YIELD
Actual yield from an endpoint sent by a Callee to Dealer.
```
[YIELD, INVOCATION.Request|id, Options|dict]
[YIELD, INVOCATION.Request|id, Options|dict, Arguments|list]
[YIELD, INVOCATION.Request|id, Options|dict, Arguments|list,
ArgumentsKw|dict]
```
## Message Codes and Direction
The following table lists the message type code for all 25 messages defined in the WAMP basic profile and their direction between peer roles.
Reserved codes may be used to identify additional message types in future standards documents.
> "Tx" indicates the message is sent by the respective role, and "Rx" indicates the message is received by the respective role.
| Cod | Message | Pub | Brk | Subs | Calr | Dealr | Callee| |-----|----------------|------|------|------|-------|-------|-------| | 1 | `HELLO` | Tx | Rx | Tx | Tx | Rx | Tx | | 2 | `WELCOME` | Rx | Tx | Rx | Rx | Tx | Rx | | 3 | `ABORT` | Rx | TxRx | Rx | Rx | TxRx | Rx | | 6 | `GOODBYE` | TxRx | TxRx | TxRx | TxRx | TxRx | TxRx | | | | | | | | | | | 8 | `ERROR` | Rx | Tx | Rx | Rx | TxRx | TxRx | | | | | | | | | | | 16 | `PUBLISH` | Tx | Rx | | | | | | 17 | `PUBLISHED` | Rx | Tx | | | | | | | | | | | | | | | 32 | `SUBSCRIBE` | | Rx | Tx | | | | | 33 | `SUBSCRIBED` | | Tx | Rx | | | | | 34 | `UNSUBSCRIBE` | | Rx | Tx | | | | | 35 | `UNSUBSCRIBED` | | Tx | Rx | | | | | 36 | `EVENT` | | Tx | Rx | | | | | | | | | | | | | | 48 | `CALL` | | | | Tx | Rx | | | 50 | `RESULT` | | | | Rx | Tx | | | | | | | | | | | | 64 | `REGISTER` | | | | | Rx | Tx | | 65 | `REGISTERED` | | | | | Tx | Rx | | 66 | `UNREGISTER` | | | | | Rx | Tx | | 67 | `UNREGISTERED` | | | | | Tx | Rx | | 68 | `INVOCATION` | | | | | Tx | Rx | | 70 | `YIELD` | | | | | Rx | Tx |## Extension Messages WAMP uses type codes from the core range [0, 255]. Implementations MAY define and use implementation specific messages with message type codes from the extension message range [256, 1023]. For example, a router MAY implement router-to-router communication by using extension messages. ## Empty Arguments and Keyword Arguments Implementations SHOULD avoid sending empty `Arguments` lists. E.g. a `CALL` message ``` [CALL, Request|id, Options|dict, Procedure|uri, Arguments|list] ``` where `Arguments == []` SHOULD be avoided, and instead ``` [CALL, Request|id, Options|dict, Procedure|uri] ``` SHOULD be sent. Implementations SHOULD avoid sending empty `ArgumentsKw` dictionaries. E.g. a `CALL` message ``` [CALL, Request|id, Options|dict, Procedure|uri, Arguments|list, ArgumentsKw|dict] ``` where `ArgumentsKw == {}` SHOULD be avoided, and instead ``` [CALL, Request|id, Options|dict, Procedure|uri, Arguments|list] ``` SHOULD be sent when `Arguments` is non-empty. # Sessions The message flow between Clients and Routers for opening and closing WAMP sessions involves the following messages: 1. `HELLO` 2. `WELCOME` 3. `ABORT` 4. `GOODBYE` ## Session Establishment ### HELLO After the underlying transport has been established, the opening of a WAMP session is initiated by the Client sending a `HELLO` message to the Router ``` [HELLO, Realm|uri, Details|dict] ``` where * `Realm` is a string identifying the realm this session should attach to * `Details` is a dictionary that allows to provide additional opening information (see below). The `HELLO` message MUST be the very first message sent by the Client after the transport has been established. In the WAMP Basic Profile without session authentication the Router will reply with a `WELCOME` or `ABORT` message.
,------. ,------.
|Client| |Router|
`--+---' `--+---'
| HELLO |
| ---------------->
| |
| WELCOME |
| <----------------
,--+---. ,--+---.
|Client| |Router|
`------' `------'
A WAMP session starts its lifetime when the Router has sent a `WELCOME` message to the Client, and ends when the underlying transport closes or when the session is closed explicitly by either peer sending the `GOODBYE` message (see below).
It is a [protocol error](#protocol_errors) to receive a second `HELLO` message during the lifetime of the session and the Peer MUST close the session if that happens.
#### Client: Role and Feature Announcement
WAMP uses *Role & Feature announcement* instead of *protocol versioning* to allow
* implementations only supporting subsets of functionality
* future extensibility
A Client must announce the roles it supports via `Hello.Details.roles|dict`, with a key mapping to a `Hello.Details.roles.
,------. ,------.
|Client| |Router|
`--+---' `--+---'
| HELLO |
| ---------------->
| |
| ABORT |
| <----------------
,--+---. ,--+---.
|Client| |Router|
`------' `------'
*Example*
```
[3, {"message": "The realm does not exist."},
"wamp.error.no_such_realm"]
```
* After session is opened, when protocol violation happens (see "Protocol errors" section).
*Examples*
* Router received second HELLO message.
```
[3, {"message":
"Received HELLO message after session was established."},
"wamp.error.protocol_violation"]
```
* Client peer received second WELCOME message
```
[3, {"message":
"Received WELCOME message after session was established."},
"wamp.error.protocol_violation"]
```
## Session Closing
A WAMP session starts its lifetime with the Router sending a `WELCOME` message to the Client and ends when the underlying transport disappears or when the WAMP session is closed explicitly by a `GOODBYE` message sent by one Peer and a `GOODBYE` message sent from the other Peer in response.
```
[GOODBYE, Details|dict, Reason|uri]
```
where
* `Reason` MUST be an URI.
* `Details` MUST be a dictionary that allows to provide additional, optional closing information (see below).
,------. ,------.
|Client| |Router|
`--+---' `--+---'
| GOODBYE |
| ---------------->
| |
| GOODBYE |
| <----------------
,--+---. ,--+---.
|Client| |Router|
`------' `------'
,------. ,------.
|Client| |Router|
`--+---' `--+---'
| GOODBYE |
| <----------------
| |
| GOODBYE |
| ---------------->
,--+---. ,--+---.
|Client| |Router|
`------' `------'
*Example*. One Peer initiates closing
```
[6, {"message": "The host is shutting down now."},
"wamp.close.system_shutdown"]
```
and the other peer replies
```
[6, {}, "wamp.close.goodbye_and_out"]
```
*Example*. One Peer initiates closing
```
[6, {}, "wamp.close.close_realm"]
```
and the other peer replies
```
[6, {}, "wamp.close.goodbye_and_out"]
```
### Difference between ABORT and GOODBYE
The differences between `ABORT` and `GOODBYE` messages is that `ABORT` is never replied to by a Peer, whereas `GOODBYE` must be replied to by the receiving Peer.
> Though `ABORT` and `GOODBYE` are structurally identical, using different message types serves to reduce overloaded meaning of messages and simplify message handling code.
### Session Statechart
The following state chart gives the states that a WAMP peer can be in during the session lifetime cycle.
+--------------+
+--------(6)-------------> |
| | CLOSED <--------------------------+
| +------(4)-------------> <---+ |
| | +--------------+ | |
| | | | |
| | (1) (7) |
| | | | |
| | +--------v-----+ | (11)
| | | +---+ |
| | +------------+ ESTABLISHING +----------------+ |
| | | | | | |
| | | +--------------+ | |
| | | | (10) |
| | | (9) | |
| | | | | |
| | (2) +--------v-----+ +--------v-------+ |
| | | | | | | |
| | | +------> FAILED <--(13)-+ CHALLENGING / +-+
| | | | | | | AUTHENTICATING |
| | | | +--------------+ +----------------+
| | | (8) |
| | | | |
| | | | |
| | +-------v-------+ |
| | | <-------------------(12)-------------+
| | | ESTABLISHED |
| | | +--------------+
| | +---------------+ |
| | | |
| | (3) (5)
| | | |
| | +-------v-------+ +--------v-----+
| | | +--+ | |
| +-+ SHUTTING DOWN | | | CLOSING |
| | |(14) | |
| +-------^-------+ | +--------------+
| |----------+ |
+----------------------------------+
| # | State |
|----|---------------------------------------------------------------|
| 1 | Sent HELLO |
| 2 | Received WELCOME |
| 3 | Sent GOODBYE |
| 4 | Received GOODBYE |
| 5 | Received GOODBYE |
| 6 | Sent GOODBYE |
| 7 | Received invalid HELLO / Send ABORT |
| 8 | Received HELLO or AUTHENTICATE |
| 9 | Received other |
| 10 | Received valid HELLO [needs authentication] / Send CHALLENGE |
| 11 | Received invalid AUTHENTICATE / Send ABORT |
| 12 | Received valid AUTHENTICATE / Send WELCOME |
| 13 | Received other |
| 14 | Received other / ignore |
# Agent Identification
When a software agent operates in a network protocol, it often identifies itself, its application type, operating system, software vendor, or software revision, by submitting a characteristic identification string to its operating peer.
Similar to what browsers do with the `User-Agent` HTTP header, both the `HELLO` and the `WELCOME` message MAY disclose the WAMP implementation in use to its peer:
```
HELLO.Details.agent|string
```
and
```
WELCOME.Details.agent|string
```
*Example: A Client "HELLO" message.*
```
[1, "somerealm", {
"agent": "AutobahnJS-0.9.14",
"roles": {
"subscriber": {},
"publisher": {}
}
}]
```
*Example: A Router "WELCOME" message.*
```
[2, 9129137332, {
"agent": "Crossbar.io-0.10.11",
"roles": {
"broker": {}
}
}]
```
# Publish and Subscribe
All of the following features for Publish & Subscribe are mandatory for WAMP Basic Profile implementations supporting the respective roles, i.e. *Publisher*, *Subscriber* and *Broker*.
## Subscribing and Unsubscribing
The message flow between Clients implementing the role of Subscriber and Routers implementing the role of Broker for subscribing and unsubscribing involves the following messages:
1. `SUBSCRIBE`
2. `SUBSCRIBED`
3. `UNSUBSCRIBE`
4. `UNSUBSCRIBED`
5. `ERROR`
,---------. ,------. ,----------.
|Publisher| |Broker| |Subscriber|
`----+----' `--+---' `----+-----'
| | |
| | |
| | SUBSCRIBE |
| | <---------------------
| | |
| | SUBSCRIBED or ERROR |
| | --------------------->
| | |
| | |
| | |
| | |
| | UNSUBSCRIBE |
| | <---------------------
| | |
| | UNSUBSCRIBED or ERROR|
| | --------------------->
,----+----. ,--+---. ,----+-----.
|Publisher| |Broker| |Subscriber|
`---------' `------' `----------'
A Subscriber may subscribe to zero, one or more topics, and a Publisher publishes to topics without knowledge of subscribers.
Upon subscribing to a topic via the `SUBSCRIBE` message, a Subscriber will receive any future events published to the respective topic by Publishers, and will receive those events asynchronously.
A subscription lasts for the duration of a session, unless a Subscriber opts out from a previously established subscription via the `UNSUBSCRIBE` message.
> A Subscriber may have more than one event handler attached to the same subscription. This can be implemented in different ways: a) a Subscriber can recognize itself that it is already subscribed and just attach another handler to the subscription for incoming events, b) or it can send a new `SUBSCRIBE` message to broker (as it would be first) and upon receiving a `SUBSCRIBED.Subscription|id` it already knows about, attach the handler to the existing subscription
>
### SUBSCRIBE
A Subscriber communicates its interest in a topic to a Broker by sending a `SUBSCRIBE` message:
```
[SUBSCRIBE, Request|id, Options|dict, Topic|uri]
```
where
* `Request` MUST be a random, ephemeral ID chosen by the Subscriber and used to correlate the Broker's response with the request.
* `Options` MUST be a dictionary that allows to provide additional subscription request details in a extensible way. This is described further below.
* `Topic` is the topic the Subscriber wants to subscribe to and MUST be an URI.
*Example*
```
[32, 713845233, {}, "com.myapp.mytopic1"]
```
A Broker, receiving a `SUBSCRIBE` message, can fullfill or reject the subscription, so it answers with `SUBSCRIBED` or `ERROR` messages.
### SUBSCRIBED
If the Broker is able to fulfill and allow the subscription, it answers by sending a `SUBSCRIBED` message to the Subscriber
```
[SUBSCRIBED, SUBSCRIBE.Request|id, Subscription|id]
```
where
* `SUBSCRIBE.Request` MUST be the ID from the original request.
* `Subscription` MUST be an ID chosen by the Broker for the subscription.
*Example*
```
[33, 713845233, 5512315355]
```
> Note. The `Subscription` ID chosen by the broker need not be unique to the subscription of a single Subscriber, but may be assigned to the `Topic`, or the combination of the `Topic` and some or all `Options`, such as the topic pattern matching method to be used. Then this ID may be sent to all Subscribers for the `Topic` or `Topic` / `Options` combination. This allows the Broker to serialize an event to be delivered only once for all actual receivers of the event.
> In case of receiving a `SUBSCRIBE` message from the same Subscriber and to already subscribed topic, Broker should answer with `SUBSCRIBED` message, containing the existing `Subscription|id`.
### Subscribe ERROR
When the request for subscription cannot be fulfilled by the Broker, the Broker sends back an `ERROR` message to the Subscriber
```
[ERROR, SUBSCRIBE, SUBSCRIBE.Request|id, Details|dict,
Error|uri]
```
where
* `SUBSCRIBE.Request` MUST be the ID from the original request.
* `Error` MUST be an URI that gives the error of why the request could not be fulfilled.
*Example*
```
[8, 32, 713845233, {}, "wamp.error.not_authorized"]
```
### UNSUBSCRIBE
When a Subscriber is no longer interested in receiving events for a subscription it sends an `UNSUBSCRIBE` message
```
[UNSUBSCRIBE, Request|id, SUBSCRIBED.Subscription|id]
```
where
* `Request` MUST be a random, ephemeral ID chosen by the Subscriber and used to correlate the Broker's response with the request.
* `SUBSCRIBED.Subscription` MUST be the ID for the subscription to unsubscribe from, originally handed out by the Broker to the Subscriber.
*Example*
```
[34, 85346237, 5512315355]
```
### UNSUBSCRIBED
Upon successful unsubscription, the Broker sends an `UNSUBSCRIBED` message to the Subscriber
```
[UNSUBSCRIBED, UNSUBSCRIBE.Request|id]
```
where
* `UNSUBSCRIBE.Request` MUST be the ID from the original request.
*Example*
```
[35, 85346237]
```
### Unsubscribe ERROR
When the request fails, the Broker sends an `ERROR`
```
[ERROR, UNSUBSCRIBE, UNSUBSCRIBE.Request|id, Details|dict,
Error|uri]
```
where
* `UNSUBSCRIBE.Request` MUST be the ID from the original request.
* `Error` MUST be an URI that gives the error of why the request could not be fulfilled.
*Example*
```
[8, 34, 85346237, {}, "wamp.error.no_such_subscription"]
```
## Publishing and Events
The message flow between Publishers, a Broker and Subscribers for publishing to topics and dispatching events involves the following messages:
1. `PUBLISH`
2. `PUBLISHED`
3. `EVENT`
4. `ERROR`
,---------. ,------. ,----------.
|Publisher| |Broker| |Subscriber|
`----+----' `--+---' `----+-----'
| PUBLISH | |
|------------------> |
| | |
|PUBLISHED or ERROR| |
|<------------------ |
| | |
| | EVENT |
| | ------------------>
,----+----. ,--+---. ,----+-----.
|Publisher| |Broker| |Subscriber|
`---------' `------' `----------'
### PUBLISH
When a Publisher requests to publish an event to some topic, it sends a `PUBLISH` message to a Broker:
```
[PUBLISH, Request|id, Options|dict, Topic|uri]
```
or
```
[PUBLISH, Request|id, Options|dict, Topic|uri, Arguments|list]
```
or
```
[PUBLISH, Request|id, Options|dict, Topic|uri, Arguments|list,
ArgumentsKw|dict]
```
where
* `Request` is a random, ephemeral ID chosen by the Publisher and used to correlate the Broker's response with the request.
* `Options` is a dictionary that allows to provide additional publication request details in an extensible way. This is described further below.
* `Topic` is the topic published to.
* `Arguments` is a list of application-level event payload elements. The list may be of zero length.
* `ArgumentsKw` is an optional dictionary containing application-level event payload, provided as keyword arguments. The dictionary may be empty.
If the Broker allows and is able to fulfill the publication, the Broker will send the event to all current Subscribers of the topic of the published event.
By default, publications are unacknowledged, and the Broker will not respond, whether the publication was successful indeed or not. This behavior can be changed with the option `PUBLISH.Options.acknowledge|bool` (see below).
*Example*
```
[16, 239714735, {}, "com.myapp.mytopic1"]
```
*Example*
```
[16, 239714735, {}, "com.myapp.mytopic1", ["Hello, world!"]]
```
*Example*
```
[16, 239714735, {}, "com.myapp.mytopic1", [], {"color": "orange",
"sizes": [23, 42, 7]}]
```
### PUBLISHED
If the Broker is able to fulfill and allowing the publication, and `PUBLISH.Options.acknowledge == true`, the Broker replies by sending a `PUBLISHED` message to the Publisher:
```
[PUBLISHED, PUBLISH.Request|id, Publication|id]
```
where
* `PUBLISH.Request` is the ID from the original publication request.
* `Publication` is a ID chosen by the Broker for the publication.
*Example*
```
[17, 239714735, 4429313566]
```
### Publish ERROR
When the request for publication cannot be fulfilled by the Broker, and `PUBLISH.Options.acknowledge == true`, the Broker sends back an `ERROR` message to the Publisher
```
[ERROR, PUBLISH, PUBLISH.Request|id, Details|dict, Error|uri]
```
where
* `PUBLISH.Request` is the ID from the original publication request.
* `Error` is an URI that gives the error of why the request could not be fulfilled.
*Example*
```
[8, 16, 239714735, {}, "wamp.error.not_authorized"]
```
### EVENT
When a publication is successful and a Broker dispatches the event, it determines a list of receivers for the event based on Subscribers for the topic published to and, possibly, other information in the event.
Note that the Publisher of an event will never receive the published event even if the Publisher is also a Subscriber of the topic published to.
> The Advanced Profile provides options for more detailed control over publication.
>
When a Subscriber is deemed to be a receiver, the Broker sends the Subscriber an `EVENT` message:
```
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict]
```
or
```
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict, PUBLISH.Arguments|list]
```
or
```
[EVENT, SUBSCRIBED.Subscription|id, PUBLISHED.Publication|id,
Details|dict, PUBLISH.Arguments|list, PUBLISH.ArgumentKw|dict]
```
where
* `SUBSCRIBED.Subscription` is the ID for the subscription under which the Subscriber receives the event - the ID for the subscription originally handed out by the Broker to the Subscribe*.
* `PUBLISHED.Publication` is the ID of the publication of the published event.
* `Details` is a dictionary that allows the Broker to provide additional event details in a extensible way. This is described further below.
* `PUBLISH.Arguments` is the application-level event payload that was provided with the original publication request.
* `PUBLISH.ArgumentKw` is the application-level event payload that was provided with the original publication request.
*Example*
```
[36, 5512315355, 4429313566, {}]
```
*Example*
```
[36, 5512315355, 4429313566, {}, ["Hello, world!"]]
```
*Example*
```
[36, 5512315355, 4429313566, {}, [], {"color": "orange",
"sizes": [23, 42, 7]}]
```
# Remote Procedure Calls
All of the following features for Remote Procedure Calls are mandatory for WAMP Basic Profile implementations supporting the respective roles.
## Registering and Unregistering
The message flow between Callees and a Dealer for registering and unregistering endpoints to be called over RPC involves the following messages:
1. `REGISTER`
2. `REGISTERED`
4. `UNREGISTER`
5. `UNREGISTERED`
6. `ERROR`
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| | |
| | |
| | REGISTER |
| | <---------------------
| | |
| | REGISTERED or ERROR |
| | --------------------->
| | |
| | |
| | |
| | |
| | |
| | UNREGISTER |
| | <---------------------
| | |
| | UNREGISTERED or ERROR|
| | --------------------->
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
### REGISTER
A Callee announces the availability of an endpoint implementing a procedure with a Dealer by sending a `REGISTER` message:
```
[REGISTER, Request|id, Options|dict, Procedure|uri]
```
where
* `Request` is a random, ephemeral ID chosen by the Callee and used to correlate the Dealer's response with the request.
* `Options` is a dictionary that allows to provide additional registration request details in a extensible way. This is described further below.
* `Procedure`is the procedure the Callee wants to register
*Example*
```
[64, 25349185, {}, "com.myapp.myprocedure1"]
```
### REGISTERED
If the Dealer is able to fulfill and allowing the registration, it answers by sending a `REGISTERED` message to the `Callee`:
```
[REGISTERED, REGISTER.Request|id, Registration|id]
```
where
* `REGISTER.Request` is the ID from the original request.
* `Registration` is an ID chosen by the Dealer for the registration.
*Example*
```
[65, 25349185, 2103333224]
```
### Register ERROR
When the request for registration cannot be fulfilled by the Dealer, the Dealer sends back an `ERROR` message to the Callee:
```
[ERROR, REGISTER, REGISTER.Request|id, Details|dict, Error|uri]
```
where
* `REGISTER.Request` is the ID from the original request.
* `Error` is an URI that gives the error of why the request could not be fulfilled.
*Example*
```
[8, 64, 25349185, {}, "wamp.error.procedure_already_exists"]
```
### UNREGISTER
When a Callee is no longer willing to provide an implementation of the registered procedure, it sends an `UNREGISTER` message to the Dealer:
```
[UNREGISTER, Request|id, REGISTERED.Registration|id]
```
where
* `Request` is a random, ephemeral ID chosen by the Callee and used to correlate the Dealer's response with the request.
* `REGISTERED.Registration` is the ID for the registration to revoke, originally handed out by the Dealer to the Callee.
*Example*
```
[66, 788923562, 2103333224]
```
### UNREGISTERED
Upon successful unregistration, the Dealer sends an `UNREGISTERED` message to the Callee:
```
[UNREGISTERED, UNREGISTER.Request|id]
```
where
* `UNREGISTER.Request` is the ID from the original request.
*Example*
```
[67, 788923562]
```
### Unregister ERROR
When the unregistration request fails, the Dealer sends an `ERROR` message:
```
[ERROR, UNREGISTER, UNREGISTER.Request|id, Details|dict,
Error|uri]
```
where
* `UNREGISTER.Request` is the ID from the original request.
* `Error` is an URI that gives the error of why the request could not be fulfilled.
*Example*
```
[8, 66, 788923562, {}, "wamp.error.no_such_registration"]
```
## Calling and Invocations
The message flow between Callers, a Dealer and Callees for calling procedures and invoking endpoints involves the following messages:
1. `CALL`
2. `RESULT`
3. `INVOCATION`
4. `YIELD`
5. `ERROR`
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| ----------------> |
| | |
| | INVOCATION |
| | ---------------->
| | |
| | YIELD or ERROR |
| | <----------------
| | |
| RESULT or ERROR | |
| <---------------- |
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
The execution of remote procedure calls is asynchronous, and there may be more than one call outstanding. A call is called outstanding (from the point of view of the Caller), when a (final) result or error has not yet been received by the Caller.
### CALL
When a Caller wishes to call a remote procedure, it sends a `CALL` message to a Dealer:
```
[CALL, Request|id, Options|dict, Procedure|uri]
```
or
```
[CALL, Request|id, Options|dict, Procedure|uri, Arguments|list]
```
or
```
[CALL, Request|id, Options|dict, Procedure|uri, Arguments|list,
ArgumentsKw|dict]
```
where
* `Request` is a random, ephemeral ID chosen by the Caller and used to correlate the Dealer's response with the request.
* `Options` is a dictionary that allows to provide additional call request details in an extensible way. This is described further below.
* `Procedure` is the URI of the procedure to be called.
* `Arguments` is a list of positional call arguments (each of arbitrary type). The list may be of zero length.
* `ArgumentsKw` is a dictionary of keyword call arguments (each of arbitrary type). The dictionary may be empty.
*Example*
```
[48, 7814135, {}, "com.myapp.ping"]
```
*Example*
```
[48, 7814135, {}, "com.myapp.echo", ["Hello, world!"]]
```
*Example*
```
[48, 7814135, {}, "com.myapp.add2", [23, 7]]
```
*Example*
```
[48, 7814135, {}, "com.myapp.user.new", ["johnny"],
{"firstname": "John", "surname": "Doe"}]
```
### INVOCATION
If the Dealer is able to fulfill (mediate) the call and it allows the call, it sends a `INVOCATION` message to the respective Callee implementing the procedure:
```
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict]
```
or
```
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict, CALL.Arguments|list]
```
or
```
[INVOCATION, Request|id, REGISTERED.Registration|id,
Details|dict, CALL.Arguments|list, CALL.ArgumentsKw|dict]
```
where
* `Request` is a random, ephemeral ID chosen by the Dealer and used to correlate the *Callee's* response with the request.
* `REGISTERED.Registration` is the registration ID under which the procedure was registered at the Dealer.
* `Details` is a dictionary that allows to provide additional invocation request details in an extensible way. This is described further below.
* `CALL.Arguments` is the original list of positional call arguments as provided by the Caller.
* `CALL.ArgumentsKw` is the original dictionary of keyword call arguments as provided by the Caller.
*Example*
```
[68, 6131533, 9823526, {}]
```
*Example*
```
[68, 6131533, 9823527, {}, ["Hello, world!"]]
```
*Example*
```
[68, 6131533, 9823528, {}, [23, 7]]
```
*Example*
```
[68, 6131533, 9823529, {}, ["johnny"], {"firstname": "John",
"surname": "Doe"}]
```
### YIELD
If the Callee is able to successfully process and finish the execution of the call, it answers by sending a `YIELD` message to the Dealer:
```
[YIELD, INVOCATION.Request|id, Options|dict]
```
or
```
[YIELD, INVOCATION.Request|id, Options|dict, Arguments|list]
```
or
```
[YIELD, INVOCATION.Request|id, Options|dict, Arguments|list,
ArgumentsKw|dict]
```
where
* `INVOCATION.Request` is the ID from the original invocation request.
* `Options`is a dictionary that allows to provide additional options.
* `Arguments` is a list of positional result elements (each of arbitrary type). The list may be of zero length.
* `ArgumentsKw` is a dictionary of keyword result elements (each of arbitrary type). The dictionary may be empty.
*Example*
```
[70, 6131533, {}]
```
*Example*
```
[70, 6131533, {}, ["Hello, world!"]]
```
*Example*
```
[70, 6131533, {}, [30]]
```
*Example*
```
[70, 6131533, {}, [], {"userid": 123, "karma": 10}]
```
### RESULT
The Dealer will then send a `RESULT` message to the original Caller:
```
[RESULT, CALL.Request|id, Details|dict]
```
or
```
[RESULT, CALL.Request|id, Details|dict, YIELD.Arguments|list]
```
or
```
[RESULT, CALL.Request|id, Details|dict, YIELD.Arguments|list,
YIELD.ArgumentsKw|dict]
```
where
* `CALL.Request` is the ID from the original call request.
* `Details` is a dictionary of additional details.
* `YIELD.Arguments` is the original list of positional result elements as returned by the Callee.
* `YIELD.ArgumentsKw` is the original dictionary of keyword result elements as returned by the Callee.
*Example*
```
[50, 7814135, {}]
```
*Example*
```
[50, 7814135, {}, ["Hello, world!"]]
```
*Example*
```
[50, 7814135, {}, [30]]
```
*Example*
```
[50, 7814135, {}, [], {"userid": 123, "karma": 10}]
```
### Invocation ERROR
If the Callee is unable to process or finish the execution of the call, or the application code implementing the procedure raises an exception or otherwise runs into an error, the Callee sends an `ERROR` message to the Dealer:
```
[ERROR, INVOCATION, INVOCATION.Request|id, Details|dict,
Error|uri]
```
or
```
[ERROR, INVOCATION, INVOCATION.Request|id, Details|dict,
Error|uri, Arguments|list]
```
or
```
[ERROR, INVOCATION, INVOCATION.Request|id, Details|dict,
Error|uri, Arguments|list, ArgumentsKw|dict]
```
where
* `INVOCATION.Request` is the ID from the original `INVOCATION` request previously sent by the Dealer to the Callee.
* `Details` is a dictionary with additional error details.
* `Error` is an URI that identifies the error of why the request could not be fulfilled.
* `Arguments` is a list containing arbitrary, application defined, positional error information. This will be forwarded by the Dealer to the Caller that initiated the call.
* `ArgumentsKw` is a dictionary containing arbitrary, application defined, keyword-based error information. This will be forwarded by the Dealer to the Caller that initiated the call.
*Example*
```
[8, 68, 6131533, {}, "com.myapp.error.object_write_protected",
["Object is write protected."], {"severity": 3}]
```
### Call ERROR
The Dealer will then send a `ERROR` message to the original Caller:
```
[ERROR, CALL, CALL.Request|id, Details|dict, Error|uri]
```
or
```
[ERROR, CALL, CALL.Request|id, Details|dict, Error|uri,
Arguments|list]
```
or
```
[ERROR, CALL, CALL.Request|id, Details|dict, Error|uri,
Arguments|list, ArgumentsKw|dict]
```
where
* `CALL.Request` is the ID from the original `CALL` request sent by the Caller to the Dealer.
* `Details` is a dictionary with additional error details.
* `Error` is an URI identifying the type of error as returned by the Callee to the Dealer.
* `Arguments` is a list containing the original error payload list as returned by the Callee to the Dealer.
* `ArgumentsKw` is a dictionary containing the original error payload dictionary as returned by the Callee to the Dealer
*Example*
```
[8, 48, 7814135, {}, "com.myapp.error.object_write_protected",
["Object is write protected."], {"severity": 3}]
```
If the original call already failed at the Dealer **before** the call would have been forwarded to any Callee, the Dealer will send an `ERROR` message to the Caller:
```
[ERROR, CALL, CALL.Request|id, Details|dict, Error|uri]
```
*Example*
```
[8, 48, 7814135, {}, "wamp.error.no_such_procedure"]
```
# Predefined URIs
WAMP pre-defines the following error URIs for the basic and for the advanced profile. WAMP peers MUST use only the defined error messages.
## Basic Profile
### Incorrect URIs
When a Peer provides an incorrect URI for any URI-based attribute of a WAMP message (e.g. realm, topic), then the other Peer MUST respond with an `ERROR` message and give the following *Error URI*:
```
wamp.error.invalid_uri
```
### Interaction
Peer provided an incorrect URI for any URI-based attribute of WAMP message, such as realm, topic or procedure
```
wamp.error.invalid_uri
```
A Dealer could not perform a call, since no procedure is currently registered under the given URI.
```
wamp.error.no_such_procedure
```
A procedure could not be registered, since a procedure with the given URI is already registered.
```
wamp.error.procedure_already_exists
```
A Dealer could not perform an unregister, since the given registration is not active.
```
wamp.error.no_such_registration
```
A Broker could not perform an unsubscribe, since the given subscription is not active.
```
wamp.error.no_such_subscription
```
A call failed since the given argument types or values are not acceptable to the called procedure. In this case the Callee may throw this error. Alternatively a Router may throw this error if it performed *payload validation* of a call, call result, call error or publish, and the payload did not conform to the requirements.
```
wamp.error.invalid_argument
```
### Session Close
The Peer is shutting down completely - used as a `GOODBYE` (or `ABORT`) reason.
```
wamp.close.system_shutdown
```
The Peer want to leave the realm - used as a `GOODBYE` reason.
```
wamp.close.close_realm
```
A Peer acknowledges ending of a session - used as a `GOODBYE` reply reason.
```
wamp.close.goodbye_and_out
```
A Peer received invalid WAMP protocol message (e.g. `HELLO` message after session was already established) - used as a `ABORT` reply reason.
```
wamp.error.protocol_violation
```
### Authorization
A join, call, register, publish or subscribe failed, since the Peer is not authorized to perform the operation.
```
wamp.error.not_authorized
```
A Dealer or Broker could not determine if the Peer is authorized to perform a join, call, register, publish or subscribe, since the authorization operation *itself* failed. E.g. a custom authorizer did run into an error.
```
wamp.error.authorization_failed
```
Peer wanted to join a non-existing realm (and the Router did not allow to auto-create the realm).
```
wamp.error.no_such_realm
```
A Peer was to be authenticated under a Role that does not (or no longer) exists on the Router. For example, the Peer was successfully authenticated, but the Role configured does not exists - hence there is some misconfiguration in the Router.
```
wamp.error.no_such_role
```
## Advanced Profile
A *Dealer* or *Callee* canceled a call previously issued
```
wamp.error.canceled
```
A *Peer* requested an interaction with an option that was disallowed by the *Router*
```
wamp.error.option_not_allowed
```
A *Dealer* could not perform a call, since a procedure with the given URI is registered, but *Callee Black- and Whitelisting* and/or *Caller Exclusion* lead to the exclusion of (any) *Callee* providing the procedure.
```
wamp.error.no_eligible_callee
```
A *Router* rejected client request to disclose its identity
```
wamp.error.option_disallowed.disclose_me
```
A *Router* encountered a network failure
```
wamp.error.network_failure
```
# Ordering Guarantees
All WAMP implementations, in particular Routers MUST support the following ordering guarantees.
> A WAMP Advanced Profile may provide applications options to relax ordering guarantees, in particular with distributed calls.
>
## Publish & Subscribe Ordering
Regarding **Publish & Subscribe**, the ordering guarantees are as follows:
If *Subscriber A* is subscribed to both **Topic 1** and **Topic 2**, and *Publisher B* first publishes an **Event 1** to **Topic 1** and then an **Event 2** to **Topic 2**, then *Subscriber A* will first receive **Event 1** and then **Event 2**. This also holds if **Topic 1** and **Topic 2** are identical.
In other words, WAMP guarantees ordering of events between any given *pair* of Publisher and Subscriber.
Further, if *Subscriber A* subscribes to **Topic 1**, the `SUBSCRIBED` message will be sent by the *Broker* to *Subscriber A* before any `EVENT` message for **Topic 1**.
There is no guarantee regarding the order of return for multiple subsequent subscribe requests. A subscribe request might require the *Broker* to do a time-consuming lookup in some database, whereas another subscribe request second might be permissible immediately.
## Remote Procedure Call Ordering
Regarding **Remote Procedure Calls**, the ordering guarantees are as follows:
If *Callee A* has registered endpoints for both **Procedure 1** and **Procedure 2**, and *Caller B* first issues a **Call 1** to **Procedure 1** and then a **Call 2** to **Procedure 2**, and both calls are routed to *Callee A*, then *Callee A* will first receive an invocation corresponding to **Call 1** and then **Call 2**. This also holds if **Procedure 1** and **Procedure 2** are identical.
In other words, WAMP guarantees ordering of invocations between any given *pair* of Caller and Callee.
There are no guarantees on the order of call results and errors in relation to *different* calls, since the execution of calls upon different invocations of endpoints in Callees are running independently. A first call might require an expensive, long-running computation, whereas a second, subsequent call might finish immediately.
Further, if *Callee A* registers for **Procedure 1**, the `REGISTERED` message will be sent by *Dealer* to *Callee A* before any `INVOCATION` message for **Procedure 1**.
There is no guarantee regarding the order of return for multiple subsequent register requests. A register request might require the *Broker* to do a time-consuming lookup in some database, whereas another register request second might be permissible immediately.
# Security Model
The following discusses the security model for the Basic Profile. Any changes or extensions to this for the Advanced Profile are discussed further on as part of the Advanced Profile definition.
## Transport Encryption and Integrity
WAMP transports may provide (optional) transport-level encryption and integrity verification. If so, encryption and integrity is point-to-point: between a Client and the Router it is connected to.
Transport-level encryption and integrity is solely at the transport-level and transparent to WAMP. WAMP itself deliberately does not specify any kind of transport-level encryption.
Implementations that offer TCP based transport such as WAMP-over-WebSocket or WAMP-over-RawSocket SHOULD implement Transport Layer Security (TLS).
WAMP deployments are encouraged to stick to a TLS-only policy with the TLS code and setup being hardened.
Further, when a Client connects to a Router over a local-only transport such as Unix domain sockets, the integrity of the data transmitted is implicit (the OS kernel is trusted), and the privacy of the data transmitted can be assured using file system permissions (no one can tap a Unix domain socket without appropriate permissions or being root).
## Router Authentication
To authenticate Routers to Clients, deployments MUST run TLS and Clients MUST verify the Router server certificate presented. WAMP itself does not provide mechanisms to authenticate a Router (only a Client).
The verification of the Router server certificate can happen
1. against a certificate trust database that comes with the Clients operating system
2. against an issuing certificate/key hard-wired into the Client
3. by using new mechanisms like DNS-based Authentication of Named Enitities (DNSSEC)/TLSA
Further, when a Client connects to a Router over a local-only transport such as Unix domain sockets, the file system permissions can be used to create implicit trust. E.g. if only the OS user under which the Router runs has the permission to create a Unix domain socket under a specific path, Clients connecting to that path can trust in the router authenticity.
## Client Authentication
Authentication of a Client to a Router at the WAMP level is not part of the basic profile.
When running over TLS, a Router MAY authenticate a Client at the transport level by doing a *client certificate based authentication*.
### Routers are trusted
Routers are *trusted* by Clients.
In particular, Routers can read (and modify) any application payload transmitted in events, calls, call results and call errors (the `Arguments` or `ArgumentsKw` message fields).
Hence, Routers do not provide confidentiality with respect to application payload, and also do not provide authenticity or integrity of application payloads that could be verified by a receiving Client.
Routers need to read the application payloads in cases of automatic conversion between different serialization formats.
Further, Routers are trusted to **actually perform** routing as specified. E.g. a Client that publishes an event has to trust a Router that the event is actually dispatched to all (eligible) Subscribers by the Router.
A rogue Router might deny normal routing operation without a Client taking notice.
# Advanced Profile
While implementations MUST implement the subset of the Basic Profile necessary for the particular set of WAMP roles they provide, they MAY implement any subset of features from the Advanced Profile. Implementers SHOULD implement the maximum of features possible considering the aims of an implementation.
> Note: Features listed here may be experimental or underspecced and yet unimplemented in any implementation. This part of the specification is very much a work in progress. An approximate status of each feature is given at the beginning of the feature section.
## Messages
The Advanced Profile defines the following additional messages which are explained in detail in separate sections.
### Message Definitions
The following 4 additional message types MAY be used in the Advanced Profile.
#### CHALLENGE
The `CHALLENGE` message is used with certain Authentication Methods. During authenticated session establishment, a **Router** sends a challenge message.
```
[CHALLENGE, AuthMethod|string, Extra|dict]
```
#### AUTHENTICATE
The `AUTHENTICATE` message is used with certain Authentication Methods. A **Client** having received a challenge is expected to respond by sending a signature or token.
```
[AUTHENTICATE, Signature|string, Extra|dict]
```
#### CANCEL
The `CANCEL` message is used with the Call Canceling advanced feature. A *Caller* can cancel and issued call actively by sending a cancel message to the *Dealer*.
```
[CANCEL, CALL.Request|id, Options|dict]
```
#### INTERRUPT
The `INTERRUPT` message is used with the Call Canceling advanced feature. Upon receiving a cancel for a pending call, a *Dealer* will issue an interrupt to the *Callee*.
```
[INTERRUPT, INVOCATION.Request|id, Options|dict]
```
### Message Codes and Direction
The following table list the message type code for **the OPTIONAL messages** defined in this part of the document and their direction between peer roles.
| Cod | Message | Pub | Brk | Subs | Calr | Dealr | Callee| |-----|----------------|------|------|------|-------|--------|-------| | 4 | `CHALLENGE` | Rx | Tx | Rx | Rx | Tx | Rx | | 5 | `AUTHENTICATE` | Tx | Rx | Tx | Tx | Rx | Tx | | 49 | `CANCEL` | | | | Tx | Rx | | | 69 | `INTERRUPT` | | | | | Tx | Rx |> "Tx" ("Rx") means the message is sent (received) by a peer of the respective role. ## Features Support for advanced features must be announced by the peers which implement them. The following is a complete list of advanced features currently defined or proposed. Status | Description -------|-------------------------------------------------- sketch | There is a rough description of an itch to scratch, but the feature use case isn't clear, and there is no protocol proposal at all. alpha | The feature use case is still fuzzy and/or the feature definition is unclear, but there is at least a protocol level proposal. beta | The feature use case is clearly defined and the feature definition in the spec is sufficient to write a prototype implementation. The feature definition and details may still be incomplete and change. stable | The feature definition in the spec is complete and stable and the feature use case is field proven in real applications. There are multiple, interoperable implementations. ### RPC Features
| Feature | Status | P | B | S | Cr | D | Ce| |----------------------------|--------|---|---|---|----|---|---| | progressive_call_results | beta | | | | X | X | X | | progressive_calls | sketch | | | | X | X | X | | call_timeout | alpha | | | | X | X | X | | call_canceling | alpha | | | | X | X | X | | caller_identification | alpha | | | | X | X | X | | call_trustlevels | alpha | | | | | X | X | | registration_meta_api | beta | | | | | X | | | pattern_based_registration | beta | | | | | X | X | | shared_registration | beta | | | | | X | X | | sharded_registration | alpha | | | | | X | X | | registration_revocation | alpha | | | | | X | X | | procedure_reflection | sketch | | | | | X | |### PubSub Features
| Feature | Status | P | B | S | Cr | D | Ce | |-------------------------------|--------|---|---|---|----|---|----| | subscriber_blackwhite_listing | stable | X | X | | | | | | publisher_exclusion | stable | X | X | | | | | | publisher_identification | alpha | X | X | X | | | | | publication_trustlevels | alpha | | X | X | | | | | subscription_meta_api | beta | | X | | | | | | pattern_based_subscription | beta | | X | X | | | | | sharded_subscription | alpha | | X | X | | | | | event_history | alpha | | X | X | | | | | topic_reflection | sketch | | X | | | | |### Other Advanced Features
| Feature | Status | |---------------------------------------|--------| | challenge-response authentication | beta | | cookie authentication | beta | | ticket authentication | beta | | rawsocket transport | stable | | batched WS transport | sketch | | longpoll transport | beta | | session meta api | beta |## Advanced RPC Features ### Progressive Call Results #### Feature Definition A procedure implemented by a *Callee* and registered at a *Dealer* may produce progressive results. Progressive results can e.g. be used to return partial results for long-running operations, or to chunk the transmission of larger results sets. The message flow for progressive results involves:
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| -----------------> |
| | |
| | INVOCATION |
| | ---------------->
| | |
| | YIELD (progress)|
| | <----------------
| | |
| RESULT (progress)| |
| <----------------- |
| | |
| | YIELD (progress)|
| | <----------------
| | |
| RESULT (progress)| |
| <----------------- |
| | |
| | |
| ... | ... |
| | |
| | YIELD or ERROR |
| | <----------------
| | |
| RESULT or ERROR | |
| <----------------- |
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
A *Caller* indicates its willingness to receive progressive results by setting
```
CALL.Options.receive_progress|bool := true
```
*Example.* Caller-to-Dealer `CALL`
```json
[
48,
77133,
{
"receive_progress": true
},
"com.myapp.compute_revenue",
[2010, 2011, 2012]
]
```
If the *Callee* supports progressive calls, the *Dealer* will forward the *Caller's* willingness to receive progressive results by setting
```
INVOCATION.Details.receive_progress|bool := true
```
*Example.* Dealer-to-Callee `INVOCATION`
```json
[
68,
87683,
324,
{
"receive_progress": true
},
[2010, 2011, 2012]
]
```
An endpoint implementing the procedure produces progressive results by sending `YIELD` messages to the *Dealer* with
```
YIELD.Options.progress|bool := true
```
*Example.* Callee-to-Dealer progressive `YIELDs`
```json
[
70,
87683,
{
"progress": true
},
["Y2010", 120]
]
```
```json
[
70,
87683,
{
"progress": true
},
["Y2011", 205]
]
```
Upon receiving an `YIELD` message from a *Callee* with `YIELD.Options.progress == true` (for a call that is still ongoing), the *Dealer* will **immediately** send a `RESULT` message to the original *Caller* with
```
RESULT.Details.progress|bool := true
```
*Example.* Dealer-to-Caller progressive `RESULTs`
```json
[
50,
77133,
{
"progress": true
},
["Y2010", 120]
]
```
```json
[
50,
77133,
{
"progress": true
},
["Y2011", 205]
]
```
and so on...
An invocation MUST *always* end in either a *normal* `RESULT` or `ERROR` message being sent by the *Callee* and received by the *Dealer*.
*Example.* Callee-to-Dealer final `YIELD`
```json
[
70,
87683,
{},
["Total", 490]
]
```
*Example.* Callee-to-Dealer final `ERROR`
```json
[
4,
87683,
{},
"com.myapp.invalid_revenue_year",
[1830]
]
```
A call MUST *always* end in either a *normal* `RESULT` or `ERROR` message being sent by the *Dealer* and received by the *Caller*.
*Example.* Dealer-to-Caller final `RESULT`
```json
[
50,
77133,
{},
["Total", 490]
]
```
*Example.* Dealer-to-Caller final `ERROR`
```json
[
4,
77133,
{},
"com.myapp.invalid_revenue_year",
[1830]
]
```
In other words: `YIELD` with `YIELD.Options.progress == true` and `RESULT` with `RESULT.Details.progress == true` messages may only be sent *during* a call or invocation is still ongoing.
The final `YIELD` and final `RESULT` may also be empty, e.g. when all actual results have already been transmitted in progressive result messages.
*Example.* Callee-to-Dealer `YIELDs`
```
[70, 87683, {"progress": true}, ["Y2010", 120]]
[70, 87683, {"progress": true}, ["Y2011", 205]]
...
[70, 87683, {"progress": true}, ["Total", 490]]
[70, 87683, {}]
```
*Example.* Dealer-to-Caller `RESULTs`
```
[50, 77133, {"progress": true}, ["Y2010", 120]]
[50, 77133, {"progress": true}, ["Y2011", 205]]
...
[50, 77133, {"progress": true}, ["Total", 490]]
[50, 77133, {}]
```
The progressive `YIELD` and progressive `RESULT` may also be empty, e.g. when those messages are only used to signal that the procedure is still running and working, and the actual result is completely delivered in the final `YIELD` and `RESULT`:
*Example.* Callee-to-Dealer `YIELDs`
```
[70, 87683, {"progress": true}]
[70, 87683, {"progress": true}]
...
[70, 87683, {}, [["Y2010", 120], ["Y2011", 205], ...,
["Total", 490]]]
```
*Example.* Dealer-to-Caller `RESULTs`
```
[50, 77133, {"progress": true}]
[50, 77133, {"progress": true}]
...
[50, 77133, {}, [["Y2010", 120], ["Y2011", 205], ...,
["Total", 490]]]
```
> Note that intermediate, progressive results and/or the final result MAY have different structure. The WAMP peer implementation is responsible for mapping everything into a form suitable for consumption in the host language.
*Example.* Callee-to-Dealer `YIELDs`
```
[70, 87683, {"progress": true}, ["partial 1", 10]]
[70, 87683, {"progress": true}, [], {"foo": 10,
"bar": "partial 1"}]
...
[70, 87683, {}, [1, 2, 3], {"moo": "hello"}]
```
*Example.* Dealer-to-Caller `RESULTs`
```
[50, 77133, {"progress": true}, ["partial 1", 10]]
[50, 77133, {"progress": true}, [], {"foo": 10,
"bar": "partial 1"}]
...
[50, 77133, {}, [1, 2, 3], {"moo": "hello"}]
```
Even if a *Caller* has indicated its expectation to receive progressive results by setting `CALL.Options.receive_progress|bool := true`, a *Callee* is **not required** to produce progressive results. `CALL.Options.receive_progress` and `INVOCATION.Details.receive_progress` are simply indications that the *Caller* is prepared to process progressive results, should there be any produced. In other words, *Callees* are free to ignore such `receive_progress` hints at any time.
#### Progressive Call Result Cancellation
Upon receiving a `YIELD` message from a *Callee* with `YIELD.Options.progress == true` (for a call that is still ongoing), if the original *Caller* is no longer available (has left the realm), then the *Dealer* will send an `INTERRUPT` to the *Callee*. The `INTERRUPT` will have `Options.mode` set to `"killnowait"` to indicate to the client that no response should be sent to the `INTERRUPT`. This `INTERRUPT` in only sent in response to a progressive `YIELD` (`Details.progress == true`), and is not sent in response to a normal or final `YIELD`.
```
[INTERRUPT, INVOCATION.Request|id, Options|dict]
```
Options:
```
INTERRUPT.Options.mode|string == "killnowait"
```
Progressive call result cancellation closes an important safety gap: In cases where progressive results are used to stream data to *Callers*, and network connectivity is unreliable, *Callers* my often get disconnected in the middle of receiving progressive results. Recurring connect, call, disconnect cycles can quickly build up *Callees* streaming results to dead *Callers*. This can overload the router and further degrade network connectivity.
The message flow for progressive results cancellation involves:
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| -----------------> |
| | |
| | INVOCATION |
| | ---------------->
| | |
| | YIELD (progress)|
| | <----------------
| | |
| RESULT (progress)| |
| <----------------- |
,--+---. | |
|Caller| | |
`------' | YIELD (progress)|
(gone) | <----------------
| |
| INTERRUPT |
| ---------------->
| |
,--+---. ,--+---.
|Dealer| |Callee|
`------' `------'
Note: Any `ERROR` returned by the *Callee*, in response to the `INTERRUPT`, is ignored (same as in call canceling when mode="killnowait"). So, it is not necessary for the *Callee* to send an `ERROR` message.
#### Callee
A *Callee* that does not support progressive results SHOULD ignore any `INVOCATION.Details.receive_progress` flag.
A *Callee* that supports progressive results, but does not support call canceling is considered by the *Dealer* to not support progressive results.
#### Feature Announcement
Support for this advanced feature MUST be announced by *Callers* (`role := "caller"`), *Callees* (`role := "callee"`) and *Dealers* (`role := "dealer"`) via
```
HELLO.Details.roles.
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| ----------------> |
| | |
| | INVOCATION |
| | ---------------->
| | |
| CANCEL | |
| ----------------> |
| | |
| | INTERRUPT |
| | ---------------->
| | |
| | ERROR |
| | <----------------
| | |
| ERROR | |
| <---------------- |
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
Message flow during call canceling when *Callee* does not support this feature or mode is `skip`
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| ----------------> |
| | |
| | INVOCATION |
| | ----------------> |
| | |
| CANCEL | |
| ----------------> |
| | |
| ERROR | |
| <---------------- |
| | |
| | RESULT (skipped) |
| | <---------------- |
| | |
| | or ERROR (skipped)|
| | <-----------------
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
Message flow during call canceling when *Callee* supports this feature and mode is `killnowait`
,------. ,------. ,------.
|Caller| |Dealer| |Callee|
`--+---' `--+---' `--+---'
| CALL | |
| ----------------> |
| | |
| | INVOCATION |
| | ---------------->
| | |
| CANCEL | |
| ----------------> |
| | |
| ERROR | |
| <---------------- |
| | INTERRUPT |
| | ---------------->
| | |
,--+---. ,--+---. ,--+---.
|Caller| |Dealer| |Callee|
`------' `------' `------'
A *Caller* cancels a remote procedure call initiated (but not yet finished) by sending a `CANCEL` message to the *Dealer*:
```
[CANCEL, CALL.Request|id, Options|dict]
```
A *Dealer* cancels an invocation of an endpoint initiated (but not yet finished) by sending a `INTERRUPT` message to the *Callee*:
```
[INTERRUPT, INVOCATION.Request|id, Options|dict]
```
Options:
```
CANCEL.Options.mode|string == "skip" | "kill" | "killnowait"
```
Note: After the *Dealer* sends an `INTERRUPT` when mode="killnowait", any responses from the *Callee* are ignored. This means that it is not necessary for the *Callee* to respond with an `ERROR` message, when mode="killnowait", since the *Dealer* ignores it.
#### Feature Announcement
Support for this feature MUST be announced by *Callers* (`role := "caller"`), *Callees* (`role := "callee"`) and *Dealers* (`role := "dealer"`) via
```
HELLO.Details.roles.
,------. ,------.
|Client| |Router|
`--+---' `--+---'
| HELLO |
| ---------------->
| |
| CHALLENGE |
| <----------------
| |
| AUTHENTICATE |
| ---------------->
| |
| WELCOME or ABORT|
| <----------------
,--+---. ,--+---.
|Client| |Router|
`------' `------'
Concrete use of `CHALLENGE` and `AUTHENTICATE` messages depends on the specific authentication method.
See [WAMP Challenge-Response Authentication](#wampcra) or [ticket authentication](#ticketauth) for the use in these authentication methods.
If two-factor authentication is desired, then two subsequent rounds of `CHALLENGE` and `RESPONSE` may be employed.
##### CHALLENGE
An authentication MAY be required for the establishment of a session. Such requirement MAY be based on the `Realm` the connection is requested for.
To request authentication, the Router MUST send a `CHALLENGE` message to the *Endpoint*.
```
[CHALLENGE, AuthMethod|string, Extra|dict]
```
##### AUTHENTICATE
In response to a `CHALLENGE` message, the Client MUST send an `AUTHENTICATE` message.
```
[AUTHENTICATE, Signature|string, Extra|dict]
```
If the authentication succeeds, the Router MUST send a `WELCOME` message, else it MUST send an `ABORT` message.
#### Transport-level Authentication
##### Cookie-based Authentication
When running WAMP over WebSocket, the transport provides HTTP client cookies during the WebSocket opening handshake. The cookies can be used to authenticate one peer (the client) against the other (the server). The other authentication direction cannot be supported by cookies.
This transport-level authentication information may be forward to the WAMP level within `HELLO.Details.transport.auth|any` in the client-to-server direction.
##### TLS Certificate Authentication
When running WAMP over a TLS (either secure WebSocket or raw TCP) transport, a peer may authenticate to the other via the TLS certificate mechanism. A server might authenticate to the client, and a client may authenticate to the server (TLS client-certificate based authentication).
This transport-level authentication information may be forward to the WAMP level within `HELLO.Details.transport.auth|any` in both directions (if available).
#### Challenge Response Authentication {#wampcra}
WAMP Challenge-Response ("WAMP-CRA") authentication is a simple, secure authentication mechanism using a shared secret. The client and the server share a secret. The secret never travels the wire, hence WAMP-CRA can be used via non-TLS connections. The actual pre-sharing of the secret is outside the scope of the authentication mechanism.
A typical authentication begins with the client sending a `HELLO` message specifying the `wampcra` method as (one of) the authentication methods:
```javascript
[1, "realm1",
{
"roles": ...,
"authmethods": ["wampcra"],
"authid": "peter"
}
]
```
The `HELLO.Details.authmethods|list` is used by the client to announce the authentication methods it is prepared to perform. For WAMP-CRA, this MUST include `"wampcra"`.
The `HELLO.Details.authid|string` is the authentication ID (e.g. username) the client wishes to authenticate as. For WAMP-CRA, this MUST be provided.
If the server is unwilling or unable to perform WAMP-CRA authentication, it MAY either skip forward trying other authentication methods (if the client announced any) or send an `ABORT` message.
If the server is willing to let the client authenticate using WAMP-CRA, and the server recognizes the provided `authid`, it MUST send a `CHALLENGE` message:
```javascript
[4, "wampcra",
{
"challenge": "{ \"nonce\": \"LHRTC9zeOIrt_9U3\",
\"authprovider\": \"userdb\", \"authid\": \"peter\",
\"timestamp\": \"2014-06-22T16:36:25.448Z\",
\"authrole\": \"user\", \"authmethod\": \"wampcra\",
\"session\": 3251278072152162}"
}
]
```
The `CHALLENGE.Details.challenge|string` is a string the client needs to create a signature for. The string MUST BE a JSON serialized object which MUST contain:
1. `authid|string`: The authentication ID the client will be authenticated as when the authentication succeeds.
2. `authrole|string`: The authentication role the client will be authenticated as when the authentication succeeds.
3. `authmethod|string`: The authentication methods, here `"wampcra"`
4. `authprovider|string`: The actual provider of authentication. For WAMP-CRA, this can be freely chosen by the app, e.g. `userdb`.
5. `nonce|string`: A random value.
6. `timestamp|string`: The UTC timestamp (ISO8601 format) the authentication was started, e.g. `2014-06-22T16:51:41.643Z`.
7. `session|int`: The WAMP session ID that will be assigned to the session once it is authenticated successfully.
The client needs to compute the signature as follows:
```
signature := HMAC[SHA256]_{secret} (challenge)
```
That is, compute the HMAC-SHA256 using the shared `secret` over the `challenge`.
After computing the signature, the client will send an `AUTHENTICATE` message containing the signature, as a base64-encoded string:
```javascript
[5, "gir1mSx+deCDUV7wRM5SGIn/+R/ClqLZuH4m7FJeBVI=", {}]
```
The server will then check if
* the signature matches the one expected
* the `AUTHENTICATE` message was sent in due time
If the authentication succeeds, the server will finally respond with a `WELCOME` message:
```javascript
[2, 3251278072152162,
{
"authid": "peter",
"authrole": "user",
"authmethod": "wampcra",
"authprovider": "userdb",
"roles": ...
}
]
```
The `WELCOME.Details` again contain the actual authentication information active.
If the authentication fails, the server will response with an `ABORT` message.
##### Server-side Verification
The challenge sent during WAMP-CRA contains
1. random information (the `nonce`) to make WAMP-CRA robust against replay attacks
2. timestamp information (the `timestamp`) to allow WAMP-CRA timeout on authentication requests that took too long
3. session information (the `session`) to bind the authentication to a WAMP session ID
4. all the authentication information that relates to authorization like `authid` and `authrole`
##### Three-legged Authentication
The signing of the challenge sent by the server usually is done directly on the client. However, this is no strict requirement.
E.g. a client might forward the challenge to another party (hence the "three-legged") for creating the signature. This can be used when the client was previously already authenticated to that third party, and WAMP-CRA should run piggy packed on that authentication.
The third party would, upon receiving a signing request, simply check if the client is already authenticated, and if so, create a signature for WAMP-CRA.
In this case, the secret is actually shared between the WAMP server who wants to authenticate clients using WAMP-CRA and the third party server, who shares a secret with the WAMP server.
This scenario is also the reason the challenge sent with WAMP-CRA is not simply a random value, but a JSON serialized object containing sufficient authentication information for the third party to check.
##### Password Salting
WAMP-CRA operates using a shared secret. While the secret is never sent over the wire, a shared secret often requires storage of that secret on the client and the server - and storing a password verbatim (unencrypted) is not recommended in general.
WAMP-CRA allows the use of salted passwords following the [PBKDF2](http://en.wikipedia.org/wiki/PBKDF2) key derivation scheme. With salted passwords, the password itself is never stored, but only a key derived from the password and a password salt. This derived key is then practically working as the new shared secret.
When the password is salted, the server will during WAMP-CRA send a `CHALLENGE` message containing additional information:
```javascript
[4, "wampcra",
{
"challenge": "{ \"nonce\": \"LHRTC9zeOIrt_9U3\",
\"authprovider\": \"userdb\", \"authid\": \"peter\",
\"timestamp\": \"2014-06-22T16:36:25.448Z\",
\"authrole\": \"user\", \"authmethod\": \"wampcra\",
\"session\": 3251278072152162}",
"salt": "salt123",
"keylen": 32,
"iterations": 1000
}
]
```
The `CHALLENGE.Details.salt|string` is the password salt in use. The `CHALLENGE.Details.keylen|int` and `CHALLENGE.Details.iterations|int` are parameters for the PBKDF2 algorithm.
#### Ticket-based Authentication {#ticketauth}
With *Ticket-based authentication*, the client needs to present the server an authentication "ticket" - some magic value to authenticate itself to the server.
This "ticket" could be a long-lived, pre-agreed secret (e.g. a user password) or a short-lived authentication token (like a Kerberos token). WAMP does not care or interpret the ticket presented by the client.
> Caution: This scheme is extremely simple and flexible, but the resulting security may be limited. E.g., the ticket value will be sent over the wire. If the transport WAMP is running over is not encrypted, a man-in-the-middle can sniff and possibly hijack the ticket. If the ticket value is reused, that might enable replay attacks.
>
A typical authentication begins with the client sending a `HELLO` message specifying the `ticket` method as (one of) the authentication methods:
```javascript
[1, "realm1",
{
"roles": ...,
"authmethods": ["ticket"],
"authid": "joe"
}
]
```
The `HELLO.Details.authmethods|list` is used by the client to announce the authentication methods it is prepared to perform. For Ticket-based, this MUST include `"ticket"`.
The `HELLO.Details.authid|string` is the authentication ID (e.g. username) the client wishes to authenticate as. For Ticket-based authentication, this MUST be provided.
If the server is unwilling or unable to perform Ticket-based authentication, it'll either skip forward trying other authentication methods (if the client announced any) or send an `ABORT` message.
If the server is willing to let the client authenticate using a ticket and the server recognizes the provided `authid`, it'll send a `CHALLENGE` message:
```javascript
[4, "ticket", {}]
```
The client will send an `AUTHENTICATE` message containing a ticket:
```javascript
[5, "secret!!!", {}]
```
The server will then check if the ticket provided is permissible (for the `authid` given).
If the authentication succeeds, the server will finally respond with a `WELCOME` message:
```javascript
[2, 3251278072152162,
{
"authid": "joe",
"authrole": "user",
"authmethod": "ticket",
"authprovider": "static",
"roles": ...
}
]
```
where
1. `authid|string`: The authentication ID the client was (actually) authenticated as.
2. `authrole|string`: The authentication role the client was authenticated for.
3. `authmethod|string`: The authentication method, here `"ticket"`
4. `authprovider|string`: The actual provider of authentication. For Ticket-based authentication, this can be freely chosen by the app, e.g. `static` or `dynamic`.
The `WELCOME.Details` again contain the actual authentication information active. If the authentication fails, the server will response with an `ABORT` message.
#### Salted Challenge Response Authentication Mechanism {#wamp-scram}
The WAMP Salted Challenge Response Authentication Mechanism ("WAMP-SCRAM"), is a password-based authentication method where the shared secret is neither transmitted nor stored as cleartext. WAMP-SCRAM is based on [RFC5802](https://tools.ietf.org/html/rfc5802) (_Salted Challenge Response Authentication Mechanism_) and [RFC7677](https://tools.ietf.org/html/rfc7677) (_SCRAM-SHA-256 and SCRAM-SHA-256-PLUS_).
WAMP-SCRAM supports the Argon2 ([draft-irtf-cfrg-argon2](https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2/)) password-based key derivation function, a memory-hard algorithm intended to resist cracking on GPU hardware. PBKDF2 ([RFC2898](https://tools.ietf.org/html/rfc2898)) is also supported for applications that are required to use primitives currently approved by cryptographic standards.
##### Security Considerations
With WAMP-SCRAM, if the authentication database is stolen, an attacker cannot impersonate a user unless they guess the password offline by brute force.
In the event that the server's authentication database is stolen, and the attacker either eavesdrops on one authentication exchange or impersonates a server, the attacker gains the ability to impersonate that particular user on that server. If the same salt is used on other servers, the attacker would gain the ability to impersonate that user on all servers using the same salt. That's why it's important to use a per-user random salt.
An eavesdropper that captures a user authentication exchange has enough information to mount an offline, brute-force dictionary attack for that particular user. If passwords are sufficiently strong, the cost/time needed to crack a password becomes prohibitive.
Note that when HTML/JavaScript assets are served to a web browser, WAMP-SCRAM does not safeguard against a man-in-the-middle tampering with those assets. Those assets could be tampered with in a way that captures the user's password and sends it to the attacker.
In light of the above security concerns, a secure TLS transport is therefore advised to prevent such attacks. The channel binding feature of SCRAM can be used to ensure that the TLS endpoints are the same between client and router.
##### Deviations from RFC5802
1. To simplify parsing, SCRAM attributes in the authentication exchange messages are encoded as members of the `Options`/`Details` objects without escaping the `,` and `=` characters. However, the `AuthMessage` used to compute the client and server signatures DOES use the exact syntax specified in [RFC5802, section 7](https://tools.ietf.org/html/rfc5802#section-7). This makes it possible to use existing test vectors to verify WAMP-SCRAM implementations.
2. Hashing based on the weaker SHA-1 specified in [RFC5802](https://tools.ietf.org/html/rfc5802) is intentionally not supported by WAMP-SCRAM, in favor of the stronger SHA-256 specified in [RFC7677](https://tools.ietf.org/html/rfc7677).
3. The [Argon2](https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2) key derivation function MAY be used instead of PBKDF2.
4. Nonces are required to be base64-encoded, which is stricter than the `printable` syntax specification of [RFC5802](https://tools.ietf.org/html/rfc5802).
5. The `"y"` channel binding flag is not used as there is currently no standard way for WAMP routers to announce channel binding capabilities.
6. The use of `authzid` for user impersonation is not supported.
##### authmethod Type String
`"wamp-scram"` SHALL be used as the `authmethod` type string for WAMP-SCRAM authentication. Announcement by routers of WAMP-SCRAM support is outside the scope of this document.
##### Conventions
###### Base64 encoding
Base64 encoding of octet strings is restricted to canonical form with no whitespace, as defined in [RFC4648](https://tools.ietf.org/html/rfc4648) (_The Base16, Base32, and Base64 Data Encodings_).
###### Nonces
In WAMP-SCRAM, a _nonce_ (number used once) is a base64-encoded sequence of random octets. It SHOULD be of sufficient length to make a replay attack unfeasible. A length of 16 octets (128 bits) is recommended for each of the client and server-generated nonces.
See [RFC4086](https://tools.ietf.org/html/rfc4086) (_Randomness Requirements for Security_) for best practices concerning randomness.
###### Salts
A _salt_ is a base64-encoded sequence of random octets.
To prevent rainbow table attacks in the event of database theft, the salt MUST be generated randomly by the server **for each user**. The random salt is stored with each user record in the authentication database.
###### Username/Password String Normalization
Username and password strings SHALL be normalized according to the _SASLprep_ profile described in [RFC4013](https://tools.ietf.org/html/rfc4013), using the _stringprep_ algorithm described in [RFC3454](https://tools.ietf.org/html/rfc3454).
While SASLprep preserves the case of usernames, the server MAY choose to perform case insensitive comparisons when searching for a username in the authentication database.
##### Channel Binding
_Channel binding_ is a feature that allows a higher layer to establish that the other end of an underlying secure channel is bound to its higher layer counterpart. See [RFC5056](https://tools.ietf.org/html/rfc5056) (_On the Use of Channel Bindings_) for an in-depth discussion.
[RFC5929](https://tools.ietf.org/html/rfc5929) defines binding types for use with TLS transports, of which `tls-unique` and `tls-server-end-point` are applicable for WAMP-SCRAM. For each channel binding type, there is a corresponding definition of the _channel binding data_ that must be sent in response to the authentication challenge.
Negotiation and announcement of channel binding is outside the scope of this document. [RFC5929 section 6](https://tools.ietf.org/html/rfc5929#section-6) recommends that application protocols use `tls-unique` exclusively, except perhaps where server-side proxies are commonly deployed.
Note that WAMP-SCRAM channel binding is not generally possible with web browser clients due to the lack of a suitable API for this purpose.
###### The tls-unique Channel Binding Type
The `tls-unique` channel binding type allows the WAMP layer to establish that the other peer is authenticating over the same, unique TLS connection. The channel binding data for this type corresponds to the bytes of the first TLS Finished message, as described in [RFC5929, section 3](https://tools.ietf.org/html/rfc5929#section-3). [RFC5929 section 10.2](https://tools.ietf.org/html/rfc5929#section-10.2) addresses the concern of disclosing this data over the TLS channel (in short, the TLS Finished message would already be visible to eavesdroppers).
To safeguard against the _triple handshake attack_ described in [RFC7627](https://tools.ietf.org/html/rfc7627), this channel binding type MUST be used over a TLS channel that uses the _extended master secret_ extension, or over a TLS channel where session resumption is not permitted.
###### The tls-server-end-point Channel Binding Type
The `tls-server-end-point` channel binding type allows the WAMP layer to establish that the other peer is authenticating over a TLS connection to a server having been issued a Public Key Infrastructure Certificate. The channel binding data for this type is a hash of the TLS server's certificate, computed as described in [RFC5929, section 4.1](https://tools.ietf.org/html/rfc5929#section-4.1). The certificate is hashed to accommodate memory-constrained implementations.
##### Authentication Exchange
WAMP-SCRAM uses a single round of challenge/response pairs after the client authentication request and before the authentication outcome.
The mapping of RFC5802 messages to WAMP messages is as follows:
```
SCRAM Message | WAMP Message
---------------------- | ------------
`client-first-message` | `HELLO`
`server-first-message` | `CHALLENGE`
`client-final-message` | `AUTHENTICATE`
`server-final-message` with `verifier` | `WELCOME`
`server-final-message` with `server-error` | `ABORT`
```
###### Initial Client Authentication Message
WAMP-SCRAM authentication begins with the client sending a `HELLO` message specifying the `wamp-scram` method as (one of) the authentication methods:
```javascript
[1, "realm1",
{
"roles": ...,
"authmethods": ["wamp-scram"],
"authid": "user",
"authextra":
{
"nonce": "egVDf3DMJh0=",
"channel_binding": null
}
}
]
```
where:
```
1. `authid|string`: The identity of the user performing authentication. This corresponds to the `username` parameter in RFC5802.
2. `authextra.nonce|string`: A base64-encoded sequence of random octets, generated by the client. See [Nonces](#nonces).
3. `authextra.channel_binding|string`: Optional string containing the desired channel binding type. See [Channel Bindings](#channel-binding).
Upon receiving the `HELLO` message, the server MUST terminate the authentication process by sending an `ABORT` message under any of the following circumstances:
* The server does not support the WAMP-SCRAM `authmethods`, and there are no other methods left that the server supports for this `authid`.
* The the server does not support the requested `channel_binding` type.
* (Optional) The server does not recognize the given `authid`. In this case, the server MAY proceed with a mock `CHALLENGE` message to avoid leaking information on the existence of usernames. This mock `CHALLENGE` SHOULD contain a generated `salt` value that is always the same for a given `authid`, otherwise an attacker may discover that the user doesn't actually exist.
###### Initial Server Authentication Message
If none of the above failure conditions apply, and the server is ready to let the client authenticate using WAMP-SCRAM, then it SHALL send a `CHALLENGE` message:
```javascript
[4, "wamp-scram",
{
"nonce": "egVDf3DMJh0=SBmkFIh7sSo=",
"salt": "aBc+fx0NAVA=",
"kdf": "pbkdf2",
"iterations": 4096,
"memory": null
}
]
```
where:
1. `nonce|string`: A server-generated nonce that is appended to the client-generated nonce sent in the previous `HELLO` message. See [Nonces](#nonces).
2. `salt|string`: The base64-encoded salt for this user, to be passed to the key derivation function. This value is stored with each user record in the authentication database. See [Salts](#salts).
3. `kdf`: The key derivation function (KDF) used to hash the password. This value is stored with each user record in the authentication database. See [Key Derivation Functions](#key-derivation-functions).
4. `iterations|integer`: The execution time cost factor to use for generating the `SaltedPassword` hash. This value is stored with each user record in the authentication database.
5. `memory|integer`: The memory cost factor to use for generating the `SaltedPassword` hash. This is only used by the Argon2 key derivation function, where it is stored with each user record in the authentication database.
The client MUST respond with an ABORT message if `CHALLENGE.Details.nonce` does not begin with the client nonce sent in `HELLO.Details.nonce`.
The client SHOULD respond with an ABORT message if it detects that the cost parameters are unusually low. Such low-cost parameters could be the result of a rogue server attempting to obtain a weak password hash that can be easily cracked. What constitutes unusually low parameters is implementation-specific and is not covered by this document.
###### Final Client Authentication Message
Upon receiving a valid `CHALLENGE` message, the client SHALL respond with an `AUTHENTICATE` message:
```javascript
[5, "dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=",
{
"nonce": "egVDf3DMJh0=SBmkFIh7sSo=",
"channel_binding": null,
"cbind_data": null
}
]
```
where:
```
1. `Signature|string` argument: The base64-encoded `ClientProof`, computed as described in the [SCRAM-Algorithms](#scram-algorithms) section.
2. `nonce|string`: The concatenated client-server nonce from the previous `CHALLENGE` message.
3. `channel_binding|string`: Optional string containing the channel binding type that was sent in the original `HELLO` message.
4. `cbind_data|string`: Optional base64-encoded channel binding data. MUST be present if and only if `channel_binding` is not `null`. The format of the binding data is dependent on the binding type. See [Channel Binding](#channel-binding).
Upon receiving the `AUTHENTICATE` message, the server SHALL then check that:
* The `AUTHENTICATE` message was received in due time.
* The `ClientProof` passed via the `Signature|string` argument is validated against the `StoredKey` and `ServerKey` stored in the authentication database. See [SCRAM Algorithms](#scram-algorithms).
* `nonce` matches the one previously sent via `CHALLENGE`.
* The `channel_binding` matches the one sent in the `HELLO` message.
* The `cbind_data` sent by the client matches the channel binding data that the server sees on its side of the channel.
###### Final Server Authentication Message - Success
If the authentication succeeds, the server SHALL finally respond with a `WELCOME` message:
```javascript
[2, 3251278072152162,
{
"authid": "user",
"authrole": "frontend",
"authmethod": "wamp-scram",
"authprovider": "static",
"roles": ...,
"authextra":
{
"verifier":
"v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4="
}
}
]
```
where:
1. `authid|string`: The authentication ID the client was actually authenticated as.
2. `authrole|string`: The authentication role the client was authenticated for.
3. `authmethod|string`: The authentication method, here `"wamp-scram"`.
4. `authprovider|string`: The actual provider of authentication. For WAMP-SCRAM authentication, this can be freely chosen by the app, e.g. static or dynamic.
5. `authextra.verifier|string`: The base64-encoded `ServerSignature`, computed as described in the [SCRAM Algorithms](#scram-algorithms) section.
The client SHOULD check the `verifier` for mutual authentication, terminating the session if invalid.
###### Final Server Authentication Message - Failure
If the authentication fails, the server SHALL respond with an `ABORT` message.
The server MAY include a SCRAM-specific error string in the `ABORT` message as a `Details.scram` attribute. SCRAM error strings are listed in [RFC5802, section 7](https://tools.ietf.org/html/rfc5802#section-7), under `server-error-value`.
##### SCRAM Algorithms
_This section is non-normative_.
[RFC5802](https://tools.ietf.org/html/rfc5802) specifies the algorithms used to compute the `ClientProof`, `ServerSignature`, `ServerKey`, and `StoredKey` values referenced by this document. Those algorithms are summarized here in pseudocode for reference.
###### Notation
* `"="`: The variable on the left-hand side is the result of the expression on the right-hand side.
* `"+"`: String concatenation.
* `IfNull(attribute, value, else)`: If the given `attribute` is absent or null, evaluates to the given `value`, otherwise evaluates to the given `else` value.
* `Decimal(integer)`: The decimal string representation of the given `integer`.
* `Base64(octets)`: Base64 encoding of the given octet sequence, restricted to canonical form with no whitespace, as defined in [RFC4648](https://tools.ietf.org/html/rfc4648).
* `UnBase64(str)`: Decode the given Base64 string into an octet sequence.
* `Normalize(str)`: Normalize the given string using the SASLprep profile [RFC4013](https://tools.ietf.org/html/rfc4013) of the "stringprep" algorithm [RFC3454](https://tools.ietf.org/html/rfc3454).
* `XOR`: The exclusive-or operation applied to each octet of the left and right-hand-side octet sequences.
* `SHA256(str)`: The SHA-256 cryptographic hash function.
* `HMAC(key, str)`: Keyed-hash message authentication code, as defined in [RFC2104](https://www.ietf.org/rfc/rfc2104.txt), with SHA-256 as the underlying hash function.
* `KDF(str, salt, params...)`: One of the supported key derivations function, with the output key length the same as the SHA-256 output length (32 octets). `params...` are the additional parameters that are applicable for the function: `iterations` and `memory`.
* `Escape(str)`: Replace every occurrence of "`,`" and "`=`" in the given string with "`=2C`" and "`=3D`" respectively.
###### Data Stored on the Server
For each user, the server needs to store:
1. A random, per-user salt.
2. The type string corresponding to the key derivation function (KDF) used to hash the password (e.g. `"argon2id13"`). This is needed to handle future revisions of the KDF, as well as allowing migration to stronger KDFs that may be added to WAMP-SCRAM in the future. This may also be needed if the KDF used during user registration is configurable or selectable on a per-user basis.
3. Parameters that are applicable to the key derivation function : `iterations` and possibly `memory`.
4. The `StoredKey`.
5. The `ServerKey`.
where `StoredKey` and `ServerKey` are computed as follows:
```javascript
SaltedPassword = KDF(Normalize(password), salt, params...)
ClientKey = HMAC(SaltedPassword, "Client Key")
StoredKey = SHA256(ClientKey)
ServerKey = HMAC(SaltedPassword, "Server Key")
```
Note that `"Client Key"` and `"Server Key"` are string literals.
The manner in which the `StoredKey` and `ServerKey` are shared with the server during user registration is outside the scope of SCRAM and this document.
###### AuthMessage
In SCRAM, `AuthMessage` is used for computing `ClientProof` and `ServerSignature`. `AuthMessage` is computed using attributes that were sent in the first three messages of the authentication exchange.
```javascript
ClientFirstBare = "n=" + Escape(HELLO.Details.authid) + "," +
"r=" + HELLO.Details.authextra.nonce
```
ServerFirst = "r=" + CHALLENGE.Details.nonce + "," +
"s=" + CHALLENGE.Details.salt + "," +
"i=" + Decimal(CHALLENGE.Details.iterations)
CBindName = AUTHENTICATE.Extra.channel_binding
CBindData = AUTHENTICATE.Extra.cbind_data
CBindFlag = IfNull(CBindName, "n", "p=" + CBindName)
CBindInput = CBindFlag + ",," +
IfNull(CBindData, "", UnBase64(CBindData))
ClientFinalNoProof = "c=" + Base64(CBindInput) + "," +
"r=" + AUTHENTICATE.Extra.nonce
AuthMessage = ClientFirstBare + "," + ServerFirst + "," +
ClientFinalNoProof
```
###### ClientProof
`ClientProof` is computed by the client during the authentication exchange as follows:
```javascript
SaltedPassword = KDF(Normalize(password), salt, params...)
ClientKey = HMAC(SaltedPassword, "Client Key")
StoredKey = SHA256(ClientKey)
ClientSignature = HMAC(StoredKey, AuthMessage)
ClientProof = ClientKey XOR ClientSignature
```
The `ClientProof` is then sent to the server, base64-encoded, via the `AUTHENTICATE.Signature` argument.
The server verifies the `ClientProof` by computing the `RecoveredStoredKey` and comparing it to the actual `StoredKey`:
```javascript
ClientSignature = HMAC(StoredKey, AuthMessage)
RecoveredClientKey = ClientSignature XOR ReceivedClientProof
RecoveredStoredKey = SHA256(RecoveredClientKey)
```
Note that the client MAY cache the `ClientKey` and `StoredKey` (or just `SaltedPassword`) to avoid having to perform the expensive KDF computation for every authentication exchange. Storing these values securely on the client is outside the scope of this document.
###### ServerSignature
`ServerSignature` is computed by the server during the authentication exchange as follows:
```javascript
ServerSignature = HMAC(ServerKey, AuthMessage)
```
The `ServerSignature` is then sent to the client, base64-encoded, via the `WELCOME.Details.authextra.verifier` attribute.
The client verifies the `ServerSignature` by computing it and comparing it with the `ServerSignature` sent by the server:
```javascript
ServerKey = HMAC(SaltedPassword, "Server Key")
ServerSignature = HMAC(ServerKey, AuthMessage)
```
##### Key Derivation Functions
SCRAM uses a password-based key derivation function (KDF) to hash user passwords. WAMP-SCRAM supports both [Argon2](https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2/) and [PBKDF2](https://tools.ietf.org/html/rfc2898) as the KDF. Argon2 is recommended because of its memory hardness and resistance against GPU hardware. PBKDF2, which does not feature memory hardness, is also supported for applications that are required to use primitives currently approved by cryptographic standards.
The following table maps the `CHALLENGE.Details.kdf` type string to the corresponding KDF.
KDF type string | Function
--------------- | --------
`"argon2id13"` | Argon2id variant of Argon2, version 1.3
`"pbkdf2"` | PBKDF2
To promote interoperability, WAMP-SCRAM client/server implementations SHOULD support both of the above KDFs. During authentication, there is no "negotiation" of the KDF, and the client MUST use the same KDF than the one used to create the keys stored in the authentication database.
Which KDF is used to hash the password during user registration is up to the application and/or server implementation, and is not covered by this document. Possibilities include:
* making the KDF selectable at runtime during registration,
* making the KDF statically configurable on the server, or,
* hard-coding the KDF selection on the server.
###### Argon2
The Argon2 key derivation function, proposed in [draft-irtf-cfrg-argon2](https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2/), is computed using the following parameters:
* `CHALLENGE.Details.salt` as the cryptographic salt,
* `CHALLENGE.Details.iterations` as the number of iterations,
* `CHALLENGE.Details.memory` as the memory size (in kibibytes),
* 1 as the parallelism parameter,
* Argon2id as the algorithm variant, and,
* 32 octets as the output key length.
For WAMP-SCRAM, the parallelism parameter is fixed to 1 due to the password being hashed on the client side, where it is not generally known how many cores/threads are available on the client's device.
Section 4 of the Argon2 internet draft recommends the general procedure for selecting parameters, of which the following guidelines are applicable to WAMP-SCRAM:
* A 128-bit salt is recommended, which can be reduced to 64-bit if space is limited.
* The `memory` parameter is to be configured to the maximum amount of memory usage that can be tolerated on client devices for computing the hash.
* The `iterations` parameter is to be determined experimentally so that execution time on the client reaches the maximum that can be tolerated by users during authentication. If the execution time is intolerable with `iterations` = 1, then reduce the `memory` parameter as needed.
###### PBKDF2
The PBKDF2 key derivation function, defined in [RFC2898](https://tools.ietf.org/html/rfc2898), is used with SHA-256 as the pseudorandom function (PRF).
The PDBKDF2 hash is computed using the following parameters:
* `CHALLENGE.Details.salt` as the cryptographic salt,
* `CHALLENGE.Details.iterations` as the iteration count, and,
* 32 octets as the output key length (`dkLen`), which matches the SHA-256 output length.
[RFC2898 section 4.1](https://tools.ietf.org/html/rfc2898) recommends at least 64 bits for the salt.
The `iterations` parameter SHOULD be determined experimentally so that execution time on the client reaches the maximum that can be tolerated by users during authentication. [RFC7677 section 4](https://tools.ietf.org/html/rfc7677#section-4) recommends an iteration count of at least 4096, with a significantly higher value on non-mobile clients.
### Alternative Transports
The only requirements that WAMP expects from a transport are: the transport must be message-based, bidirectional, reliable and ordered. This allows WAMP to run over different transports without any impact at the application layer.
Besides the WebSocket transport, the following WAMP transports are currently specified:
* [RawSocket Transport](#rawsocket)
* [Batched WebSocket Transport](#batchedwebsocket)
* [LongPoll Transport](#longpoll)
* [Multiplexed Transport](#multiplexed)
> Other transports such as HTTP 2.0 ("SPDY") or UDP might be defined in the future.
#### RawSocket Transport {#rawsocket}
**WAMP-over-RawSocket** is an (alternative) transport for WAMP that uses length-prefixed, binary messages - a message framing different from WebSocket.
Compared to WAMP-over-WebSocket, WAMP-over-RawSocket is simple to implement, since there is no need to implement the WebSocket protocol which has some features that make it non-trivial (like a full HTTP-based opening handshake, message fragmentation, masking and variable length integers).
WAMP-over-RawSocket has even lower overhead than WebSocket, which can be desirable in particular when running on local connections like loopback TCP or Unix domain sockets. It is also expected to allow implementations in microcontrollers in under 2KB RAM.
WAMP-over-RawSocket can run over TCP, TLS, Unix domain sockets or any reliable streaming underlying transport. When run over TLS on the standard port for secure HTTPS (443), it is also able to traverse most locked down networking environments such as enterprise or mobile networks (unless man-in-the-middle TLS intercepting proxies are in use).
However, WAMP-over-RawSocket cannot be used with Web browser clients, since browsers do not allow raw TCP connections. Browser extensions would do, but those need to be installed in a browser. WAMP-over-RawSocket also (currently) does not support transport-level compression as WebSocket does provide (`permessage-deflate` WebSocket extension).
##### Endianess
WAMP-over-RawSocket uses *network byte order* ("big-endian"). That means, given a unsigned 32 bit integer
```
0x 11 22 33 44
```
the first octet sent out to (or received from) the wire is `0x11` and the last octet sent out (or received) is `0x44`.
Here is how you would convert octets received from the wire into an integer in Python:
```python
import struct
octets_received = b"\x11\x22\x33\x44"
i = struct.unpack(">L", octets_received)[0]
```
The integer received has the value `287454020`.
And here is how you would send out an integer to the wire in Python:
```python
octets_to_be_send = struct.pack(">L", i)
```
The octets to be sent are `b"\x11\x22\x33\x44"`.
##### Handshake
**Client-to-Router Request**
WAMP-over-RawSocket starts with a handshake where the client connecting to a router sends 4 octets:
```
MSB LSB
31 0
0111 1111 LLLL SSSS RRRR RRRR RRRR RRRR
```
The *first octet* is a magic octet with value `0x7F`. This value is chosen to avoid any possible collision with the first octet of a valid HTTP request (see [here](http://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html#sec5.1) and [here](http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.2)). No valid HTTP request can have `0x7F` as its first octet.
> By using a magic first octet that cannot appear in a regular HTTP request, WAMP-over-RawSocket can be run e.g. on the same TCP listening port as WAMP-over-WebSocket or WAMP-over-LongPoll.
The *second octet* consists of a 4 bit `LENGTH` field and a 4 bit `SERIALIZER` field.
The `LENGTH` value is used by the *Client* to signal the **maximum message length** of messages it is willing to **receive**. When the handshake completes successfully, a *Router* MUST NOT send messages larger than this size.
The possible values for `LENGTH` are:
```
0: 2**9 octets
1: 2**10 octets
...
15: 2**24 octets
```
This means a *Client* can choose the maximum message length between **512** and **16M** octets.
The `SERIALIZER` value is used by the *Client* to request a specific serializer to be used. When the handshake completes successfully, the *Client* and *Router* will use the serializer requested by the *Client*.
The possible values for `SERIALIZER` are:
{align="left"}
0: illegal
1: JSON
2: MessagePack
3 - 15: reserved for future serializers
Here is a Python program that prints all (currently) permissible values for the *second octet*:
```python
SERMAP = {
1: 'json',
2: 'messagepack'
}
## map serializer / max. msg length to RawSocket handshake
## request or success reply (2nd octet)
##
for ser in SERMAP:
for l in range(16):
octet_2 = (l << 4) | ser
print("serializer: {}, maxlen: {} =>
0x{:02x}".format(SERMAP[ser], 2 ** (l + 9), octet_2))
```
The *third and forth octet* are **reserved** and MUST be all zeros for now.
**Router-to-Client Reply**
After a *Client* has connected to a *Router*, the *Router* will first receive the 4 octets handshake request from the *Client*.
If the *first octet* differs from `0x7F`, it is not a WAMP-over-RawSocket request. Unless the *Router* also supports other transports on the connecting port (such as WebSocket or LongPoll), the *Router* MUST **fail the connection**.
Here is an example of how a *Router* could parse the *second octet* in a *Clients* handshake request:
```python
## map RawSocket handshake request (2nd octet) to
## serializer / max. msg length
##
for i in range(256):
ser_id = i & 0x0f
if ser_id != 0:
ser = SERMAP.get(ser_id, 'currently undefined')
maxlen = 2 ** ((i >> 4) + 9)
print("{:02x} => serializer: {}, maxlen: {}".
format(i, ser, maxlen))
else:
print("fail the connection: illegal serializer value")
```
When the *Router* is willing to speak the serializer requested by the *Client*, it will answer with a 4 octets response of identical structure as the *Client* request:
```
MSB LSB
31 0
0111 1111 LLLL SSSS RRRR RRRR RRRR RRRR
```
Again, the *first octet* MUST be the value `0x7F`. The *third and forth octets* are reserved and MUST be all zeros for now.
In the *second octet*, the *Router* MUST echo the serializer value in `SERIALIZER` as requested by the *Client*.
Similar to the *Client*, the *Router* sets the `LENGTH` field to request a limit on the length of messages sent by the *Client*.
During the connection, *Router* MUST NOT send messages to the *Client* longer than the `LENGTH` requested by the *Client*, and the *Client* MUST NOT send messages larger than the maximum requested by the *Router* in its handshake reply.
If a message received during a connection exceeds the limit requested, a *Peer* MUST **fail the connection**.
When the *Router* is unable to speak the serializer requested by the *Client*, or it is denying the *Client* for other reasons, the *Router* replies with an error:
```
MSB LSB
31 0
0111 1111 EEEE 0000 RRRR RRRR RRRR RRRR
```
An error reply has 4 octets: the *first octet* is again the magic `0x7F`, and the *third and forth octet* are reserved and MUST all be zeros for now.
The *second octet* has its lower 4 bits zero'ed (which distinguishes the reply from an success/accepting reply) and the upper 4 bits encode the error:
```
0: illegal (must not be used)
1: serializer unsupported
2: maximum message length unacceptable
3: use of reserved bits (unsupported feature)
4: maximum connection count reached
5 - 15: reserved for future errors
```
> Note that the error code `0` MUST NOT be used. This is to allow storage of error state in a host language variable, while allowing `0` to signal the current state "no error"
Here is an example of how a *Router* might create the *second octet* in an error response:
```python
ERRMAP = {
0: "illegal (must not be used)",
1: "serializer unsupported",
2: "maximum message length unacceptable",
3: "use of reserved bits (unsupported feature)",
4: "maximum connection count reached"
}
## map error to RawSocket handshake error reply (2nd octet)
##
for err in ERRMAP:
octet_2 = err << 4
print("error: {} => 0x{:02x}").format(ERRMAP[err], err)
```
The *Client* - after having sent its handshake request - will wait for the 4 octets from *Router* handshake reply.
Here is an example of how a *Client* might parse the *second octet* in a *Router* handshake reply:
```python
## map RawSocket handshake reply (2nd octet)
##
for i in range(256):
ser_id = i & 0x0f
if ser_id:
## verify the serializer is the one we requested!
## if not, fail the connection!
ser = SERMAP.get(ser_id, 'currently undefined')
maxlen = 2 ** ((i >> 4) + 9)
print("{:02x} => serializer: {}, maxlen: {}".
format(i, ser, maxlen))
else:
err = i >> 4
print("error: {}".format(ERRMAP.get(err,
'currently undefined')))
```
##### Serialization
To send a WAMP message, the message is serialized according to the WAMP serializer agreed in the handshake (e.g. JSON or MessagePack).
The length of the serialized messages in octets MUST NOT exceed the maximum requested by the *Peer*.
If the serialized length exceed the maximum requested, the WAMP message can not be sent to the *Peer*. Handling situations like the latter is left to the implementation.
E.g. a *Router* that is to forward a WAMP `EVENT` to a *Client* which exceeds the maximum length requested by the *Client* when serialized might:
* drop the event (not forwarding to that specific client) and track dropped events
* prohibit publishing to the topic already
* remove the event payload, and send an event with extra information (`payload_limit_exceeded = true`)
##### Framing
The serialized octets for a message to be sent are prefixed with exactly 4 octets.
```
MSB LSB
31 0
RRRR RTTT LLLL LLLL LLLL LLLL LLLL LLLL
```
The *first octet* has the following structure
```
MSB LSB
7 0
RRRR RTTT
```
The five bits `RRRRR` are reserved for future use and MUST be all zeros for now.
The three bits `TTT` encode the type of the transport message:
```
0: regular WAMP message
1: PING
2: PONG
3-7: reserved
```
The *three remaining octets* constitute an unsigned 24 bit integer that provides the length of transport message payload following, excluding the 4 octets that constitute the prefix.
For a regular WAMP message (`TTT == 0`), the length is the length of the serialized WAMP message: the number of octets after serialization (excluding the 4 octets of the prefix).
For a `PING` message (`TTT == 1`), the length is the length of the arbitrary payload that follows. A *Peer* MUST reply to each `PING` by sending exactly one `PONG` immediately, and the `PONG` MUST echo back the payload of the `PING` exactly.
For receiving messages with WAMP-over-RawSocket, a *Peer* will usually read exactly 4 octets from the incoming stream, decode the transport level message type and payload length, and then receive as many octets as the length was giving.
When the transport level message type indicates a regular WAMP message, the transport level message payload is unserialized according to the serializer agreed in the handshake and the processed at the WAMP level.
#### Batched WebSocket Transport for WAMP {#batchedwebsocket}
*WAMP-over-Batched-WebSocket* is a variant of WAMP-over-WebSocket where multiple WAMP messages are sent in one WebSocket message.
Using WAMP message batching can increase wire level efficiency further. In particular when using TLS and the WebSocket implementation is forcing every WebSocket message into a new TLS segment.
WAMP-over-Batched-WebSocket is negotiated between Peers in the WebSocket opening handshake by agreeing on one of the following WebSocket subprotocols:
* `wamp.2.json.batched`
* `wamp.2.msgpack.batched`
Batching with JSON works by serializing each WAMP message to JSON as normally, appending the single ASCII control character `\30` ([record separator](http://en.wikipedia.org/wiki/Record_separator#Field_separators)) octet `0x1e` to *each* serialized messages, and packing a sequence of such serialized messages into a single WebSocket message:
```
Serialized JSON WAMP Msg 1 | 0x1e |
Serialized JSON WAMP Msg 2 | 0x1e | ...
```
Batching with MessagePack works by serializing each WAMP message to MessagePack as normally, prepending a 32 bit unsigned integer (4 octets in big-endian byte order) with the length of the serialized MessagePack message (excluding the 4 octets for the length prefix), and packing a sequence of such serialized (length-prefixed) messages into a single WebSocket message:
```
Length of Msg 1 serialization (uint32) |
serialized MessagePack WAMP Msg 1 | ...
```
With batched transport, even if only a single WAMP message is to be sent in a WebSocket message, the (single) WAMP message needs to be framed as described above. In other words, a single WAMP message is sent as a batch of length **1**. Sending a batch of length **0** (no WAMP message) is illegal and a *Peer* MUST fail the transport upon receiving such a transport message.
#### A HTTP Longpoll Transport for WAMP {#longpoll}
The *Long-Poll Transport* is able to transmit a WAMP session over plain old HTTP 1.0/1.1. This is realized by the Client issuing HTTP/POSTs requests, one for sending, and one for receiving. Those latter requests are kept open at the server when there are no messages currently pending to be received.
**Opening a Session**
With the Long-Poll Transport, a Client opens a new WAMP session by sending a HTTP/POST request to a well-known URL, e.g.
```
http://mypp.com/longpoll/open
```
Here, `http://mypp.com/longpoll` is the base URL for the Long-Poll Transport and `/open` is a path dedicated for opening new sessions.
The HTTP/POST request SHOULD have a `Content-Type` header set to `application/json` and MUST have a request body with a JSON document that is a dictionary:
```javascript
{
"protocols": ["wamp.2.json"]
}
```
The (mandatory) `protocols` attribute specifies the protocols the client is willing to speak. The server will chose one from this list when establishing the session or fail the request when no protocol overlap was found.
The valid protocols are:
* `wamp.2.json.batched`
* `wamp.2.json`
* `wamp.2.msgpack.batched`
* `wamp.2.msgpack`
> The request path with this and subsequently described HTTP/POST requests MAY contain a query parameter `x` with some random or sequentially incremented value:
>
> http://mypp.com/longpoll/open?x=382913
>
> The value is ignored, but may help in certain situations to prevent intermediaries from caching the request.
>
Returned is a JSON document containing a transport ID and the protocol to speak:
```javascript
{
"protocol": "wamp.2.json",
"transport": "kjmd3sBLOUnb3Fyr"
}
```
As an implied side-effect, two HTTP endpoints are created
```
http://mypp.com/longpoll/