synapse/docs/specification.rst

Matrix Specification

WARNING

Warning

The Matrix specification is still very much evolving: the API is not yet frozen and this document is in places incomplete, stale, and may contain security issues. Needless to say, we have made every effort to highlight the problem areas that we're aware of.

We're publishing it at this point because it's complete enough to be more than useful and provide a canonical reference to how Matrix is evolving. Our end goal is to mirror WHATWG's Living Standard approach except right now Matrix is more in the process of being born than actually being living!

Table of Contents

Introduction

Matrix is a new set of open APIs for open-federated Instant Messaging and VoIP functionality, designed to create and support a new global real-time communication ecosystem on the internet. This specification is the ongoing result of standardising the APIs used by the various components of the Matrix ecosystem to communicate with one another.

The principles that Matrix attempts to follow are:

• Pragmatic Web-friendly APIs (i.e. JSON over REST)
• Keep It Simple & Stupid
  • provide a simple architecture with minimal third-party dependencies.
• Fully open:
  • Fully open federation - anyone should be able to participate in the global Matrix network
  • Fully open standard - publicly documented standard with no IP or patent licensing encumbrances
  • Fully open source reference implementation - liberally-licensed example implementations with no IP or patent licensing encumbrances
• Empowering the end-user
  • The user should be able to choose the server and clients they use
  • The user should be control how private their communication is
  • The user should know precisely where their data is stored
• Fully decentralised - no single points of control over conversations or the network as a whole
• Learning from history to avoid repeating it
  • Trying to take the best aspects of XMPP, SIP, IRC, SMTP, IMAP and NNTP whilst trying to avoid their failings

The functionality that Matrix provides includes:

• Creation and management of fully distributed chat rooms with no single points of control or failure
• Eventually-consistent cryptographically secure synchronisation of room state across a global open network of federated servers and services
• Sending and receiving extensible messages in a room with (optional) end-to-end encryption
• Extensible user management (inviting, joining, leaving, kicking, banning) mediated by a power-level based user privilege system.
• Extensible room state management (room naming, aliasing, topics, bans)
• Extensible user profile management (avatars, displaynames, etc)
• Managing user accounts (registration, login, logout)
• Use of 3rd Party IDs (3PIDs) such as email addresses, phone numbers, Facebook accounts to authenticate, identify and discover users on Matrix.
• Trusted federation of Identity servers for:
  • Publishing user public keys for PKI
  • Mapping of 3PIDs to Matrix IDs

The end goal of Matrix is to be a ubiquitous messaging layer for synchronising arbitrary data between sets of people, devices and services - be that for instant messages, VoIP call setups, or any other objects that need to be reliably and persistently pushed from A to B in an interoperable and federated manner.

Architecture

Clients transmit data to other clients through home servers (HSes). Clients do not communicate with each other directly.

How data flows between clients
==============================

{ Matrix client A }                             { Matrix client B }
^          |                                    ^          |
|  events  |                                    |  events  |
|          V                                    |          V
+------------------+                            +------------------+
|                  |---------( HTTP )---------->|                  |
|   Home Server    |                            |   Home Server    |
|                  |<--------( HTTP )-----------|                  |
+------------------+        Federation          +------------------+

A "Client" typically represents a human using a web application or mobile app. Clients use the "Client-to-Server" (C-S) API to communicate with their home server, which stores their profile data and their record of the conversations in which they participate. Each client is associated with a user account (and may optionally support multiple user accounts). A user account is represented by a unique "User ID". This ID is namespaced to the home server which allocated the account and looks like:

@localpart:domain

The localpart of a user ID may be a user name, or an opaque ID identifying this user. They are case-insensitive.

A "Home Server" is a server which provides C-S APIs and has the ability to federate with other HSes. It is typically responsible for multiple clients. "Federation" is the term used to describe the sharing of data between two or more home servers.

Data in Matrix is encapsulated in an "event". An event is an action within the system. Typically each action (e.g. sending a message) correlates with exactly one event. Each event has a type which is used to differentiate different kinds of data. type values MUST be uniquely globally namespaced following Java's package naming conventions <http://docs.oracle.com/javase/specs/jls/se5.0/html/packages.html#7.7>, e.g. com.example.myapp.event. The special top-level namespace m. is reserved for events defined in the Matrix specification. Events are usually sent in the context of a "Room".

Room structure

A room is a conceptual place where users can send and receive events. Rooms can be created, joined and left. Events are sent to a room, and all participants in that room with sufficient access will receive the event. Rooms are uniquely identified internally via a "Room ID", which look like:

!opaque_id:domain

There is exactly one room ID for each room. Whilst the room ID does contain a domain, it is simply for globally namespacing room IDs. The room does NOT reside on the domain specified. Room IDs are not meant to be human readable. They ARE case-sensitive.

The following diagram shows an m.room.message event being sent in the room !qporfwt:matrix.org:

{ @alice:matrix.org }                             { @bob:domain.com }
        |                                                 ^
        |                                                 |
Room ID: !qporfwt:matrix.org                 Room ID: !qporfwt:matrix.org
Event type: m.room.message                   Event type: m.room.message
Content: { JSON object }                     Content: { JSON object }
        |                                                 |
        V                                                 |
+------------------+                          +------------------+
|   Home Server    |                          |   Home Server    |
|   matrix.org     |<-------Federation------->|   domain.com     |
+------------------+                          +------------------+
         |       .................................        |
         |______|           Shared State          |_______|
                | Room ID: !qporfwt:matrix.org    |
                | Servers: matrix.org, domain.com |
                | Members:                        |
                |  - @alice:matrix.org            |
                |  - @bob:domain.com              |
                |.................................|

Federation maintains shared state between multiple home servers, such that when an event is sent to a room, the home server knows where to forward the event on to, and how to process the event. State is scoped to a single room, and federation ensures that all home servers have the information they need, even if that means the home server has to request more information from another home server before processing the event.

Room Aliases

Each room can also have multiple "Room Aliases", which looks like:

#room_alias:domain

.. TODO
    - Need to specify precise grammar for Room Aliases

A room alias "points" to a room ID and is the human-readable label by which rooms are publicised and discovered. The room ID the alias is pointing to can be obtained by visiting the domain specified. They are case-insensitive. Note that the mapping from a room alias to a room ID is not fixed, and may change over time to point to a different room ID. For this reason, Clients SHOULD resolve the room alias to a room ID once and then use that ID on subsequent requests.

When resolving a room alias the server will also respond with a list of servers that are in the room that can be used to join via.

GET    
#matrix:domain.com      !aaabaa:matrix.org
 |                    ^
 |                    |
_______V____________________|____
|          domain.com            |
| Mappings:                      |
| #matrix >> !aaabaa:matrix.org  |
| #golf   >> !wfeiofh:sport.com  |
| #bike   >> !4rguxf:matrix.org  |
|________________________________|

Identity

Users in Matrix are identified via their user ID. However, existing ID namespaces can also be used in order to identify Matrix users. A Matrix "Identity" describes both the user ID and any other existing IDs from third party namespaces linked to their account.

Matrix users can link third-party IDs (3PIDs) such as email addresses, social network accounts and phone numbers to their user ID. Linking 3PIDs creates a mapping from a 3PID to a user ID. This mapping can then be used by other Matrix users in order to discover other users, according to a strict set of privacy permissions.

In order to ensure that the mapping from 3PID to user ID is genuine, a globally federated cluster of trusted "Identity Servers" (IS) are used to perform authentication of the 3PID. Identity servers are also used to preserve the mapping indefinitely, by replicating the mappings across multiple ISes.

Usage of an IS is not required in order for a client application to be part of the Matrix ecosystem. However, by not using an IS, discovery of users is greatly impacted.

API Standards

The mandatory baseline for communication in Matrix is exchanging JSON objects over RESTful HTTP APIs. HTTPS is mandated as the baseline for server-server (federation) communication. HTTPS is recommended for client-server communication, although HTTP may be supported as a fallback to support basic HTTP clients. More efficient optional transports for client-server communication will in future be supported as optional extensions - e.g. a packed binary encoding over stream-cipher encrypted TCP socket for low-bandwidth/low-roundtrip mobile usage.

For the default HTTP transport, all API calls use a Content-Type of application/json. In addition, all strings MUST be encoded as UTF-8.

Clients are authenticated using opaque access_token strings (see Registration and Login for details), passed as a query string parameter on all requests.

Any errors which occur on the Matrix API level MUST return a "standard error response". This is a JSON object which looks like:

{
  "errcode": "<error code>",
  "error": "<error message>"
}

The error string will be a human-readable error message, usually a sentence explaining what went wrong. The errcode string will be a unique string which can be used to handle an error message e.g. M_FORBIDDEN. These error codes should have their namespace first in ALL CAPS, followed by a single _. For example, if there was a custom namespace com.mydomain.here, and a FORBIDDEN code, the error code should look like COM.MYDOMAIN.HERE_FORBIDDEN. There may be additional keys depending on the error, but the keys error and errcode MUST always be present.

Some standard error codes are below:

M_FORBIDDEN

Forbidden access, e.g. joining a room without permission, failed login.

M_UNKNOWN_TOKEN

The access token specified was not recognised.

M_BAD_JSON

Request contained valid JSON, but it was malformed in some way, e.g. missing required keys, invalid values for keys.

M_NOT_JSON

Request did not contain valid JSON.

M_NOT_FOUND

No resource was found for this request.

M_LIMIT_EXCEEDED

Too many requests have been sent in a short period of time. Wait a while then try again.

Some requests have unique error codes:

M_USER_IN_USE

Encountered when trying to register a user ID which has been taken.

M_ROOM_IN_USE

Encountered when trying to create a room which has been taken.

M_BAD_PAGINATION

Encountered when specifying bad pagination query parameters.

M_LOGIN_EMAIL_URL_NOT_YET

Encountered when polling for an email link which has not been clicked yet.

The C-S API typically uses HTTP POST to submit requests. This means these requests are not idempotent. The C-S API also allows HTTP PUT to make requests idempotent. In order to use a PUT, paths should be suffixed with /{txnId}. {txnId} is a unique client-generated transaction ID which identifies the request, and is scoped to a given Client (identified by that client's access_token). Crucially, it only serves to identify new requests from retransmits. After the request has finished, the {txnId} value should be changed (how is not specified; a monotonically increasing integer is recommended). It is preferable to use HTTP PUT to make sure requests to send messages do not get sent more than once should clients need to retransmit requests.

Valid requests look like:

POST /some/path/here?access_token=secret
{
  "key": "This is a post."
}

PUT /some/path/here/11?access_token=secret
{
  "key": "This is a put with a txnId of 11."
}

In contrast, these are invalid requests:

POST /some/path/here/11?access_token=secret
{
  "key": "This is a post, but it has a txnId."
}

PUT /some/path/here?access_token=secret
{
  "key": "This is a put but it is missing a txnId."
}

Receiving live updates on a client

Clients can receive new events by long-polling the home server. This will hold open the HTTP connection for a short period of time waiting for new events, returning early if an event occurs. This is called the Event Stream. All events which are visible to the client will appear in the event stream. When the request returns, an end token is included in the response. This token can be used in the next request to continue where the client left off.

When the client first logs in, they will need to initially synchronise with their home server. This is achieved via the /initialSync_ API. This API also returns an end token which can be used with the event stream.

Registration and Login

Clients must register with a home server in order to use Matrix. After registering, the client will be given an access token which must be used in ALL requests to that home server as a query parameter 'access_token'.

If the client has already registered, they need to be able to login to their account. The home server may provide many different ways of logging in, such as user/password auth, login via a social network (OAuth2), login by confirming a token sent to their email address, etc. This specification does not define how home servers should authorise their users who want to login to their existing accounts, but instead defines the standard interface which implementations should follow so that ANY client can login to ANY home server. Clients login using the /login_ API. Clients register using the /register_ API. Registration follows the same general procedure as login, but the path requests are sent to and the details contained in them are different.

In both registration and login cases, the process takes the form of one or more stages, where at each stage the client submits a set of data for a given stage type and awaits a response from the server, which will either be a final success or a request to perform an additional stage. This exchange continues until the final success.

In order to determine up-front what the server's requirements are, the client can request from the server a complete description of all of its acceptable flows of the registration or login process. It can then inspect the list of returned flows looking for one for which it believes it can complete all of the required stages, and perform it. As each home server may have different ways of logging in, the client needs to know how they should login. All distinct login stages MUST have a corresponding type. A type is a namespaced string which details the mechanism for logging in.

A client may be able to login via multiple valid login flows, and should choose a single flow when logging in. A flow is a series of login stages. The home server MUST respond with all the valid login flows when requested by a simple GET request directly to the /login or /register paths:

{
  "flows": [
    {
      "type": "<login type1a>",
      "stages": [ "<login type 1a>", "<login type 1b>" ]
    },
    {
      "type": "<login type2a>",
      "stages": [ "<login type 2a>", "<login type 2b>" ]
    },
    {
      "type": "<login type3>"
    }
  ]
}

The client can now select which flow it wishes to use, and begin making POST requests to the /login or /register paths with JSON body content containing the name of the stage as the type key, along with whatever additional parameters are required for that login or registration type (see below). After the flow is completed, the client's fully-qualified user ID and a new access token MUST be returned:

{
  "user_id": "@user:matrix.org",
  "access_token": "abcdef0123456789"
}

The user_id key is particularly useful if the home server wishes to support localpart entry of usernames (e.g. "user" rather than "@user:matrix.org"), as the client may not be able to determine its user_id in this case.

If the flow has multiple stages to it, the home server may wish to create a session to store context between requests. If a home server responds with a session key to a request, clients MUST submit it in subsequent requests until the flow is completed:

{
  "session": "<session id>"
}

This specification defines the following login types:

• m.login.password
• m.login.oauth2
• m.login.email.code
• m.login.email.url
• m.login.email.identity

Password-based

Type

m.login.password

Description

Login is supported via a username and password.

To respond to this type, reply with:

{
  "type": "m.login.password",
  "user": "<user_id or user localpart>",
  "password": "<password>"
}

The home server MUST respond with either new credentials, the next stage of the login process, or a standard error response.

OAuth2-based

Type

m.login.oauth2

Description

Login is supported via OAuth2 URLs. This login consists of multiple requests.

To respond to this type, reply with:

{
  "type": "m.login.oauth2",
  "user": "<user_id or user localpart>"
}

The server MUST respond with:

{
  "uri": <Authorization Request URI OR service selection URI>
}

The home server acts as a 'confidential' client for the purposes of OAuth2. If the uri is a sevice selection URI, it MUST point to a webpage which prompts the user to choose which service to authorize with. On selection of a service, this MUST link through to an Authorization Request URI. If there is only 1 service which the home server accepts when logging in, this indirection can be skipped and the "uri" key can be the Authorization Request URI.

The client then visits the Authorization Request URI, which then shows the OAuth2 Allow/Deny prompt. Hitting 'Allow' returns the redirect URI with the auth code. Home servers can choose any path for the redirect URI. The client should visit the redirect URI, which will then finish the OAuth2 login process, granting the home server an access token for the chosen service. When the home server gets this access token, it verifies that the cilent has authorised with the 3rd party, and can now complete the login. The OAuth2 redirect URI (with auth code) MUST respond with either new credentials, the next stage of the login process, or a standard error response.

For example, if a home server accepts OAuth2 from Google, it would return the Authorization Request URI for Google:

{
  "uri": "https://accounts.google.com/o/oauth2/auth?response_type=code&
  client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&scope=photos"
}

The client then visits this URI and authorizes the home server. The client then visits the REDIRECT_URI with the auth code= query parameter which returns:

{
  "user_id": "@user:matrix.org",
  "access_token": "0123456789abcdef"
}

Email-based (code)

Type

m.login.email.code

Description

Login is supported by typing in a code which is sent in an email. This login consists of multiple requests.

To respond to this type, reply with:

{
  "type": "m.login.email.code",
  "user": "<user_id or user localpart>",
  "email": "<email address>"
}

After validating the email address, the home server MUST send an email containing an authentication code and return:

{
  "type": "m.login.email.code",
  "session": "<session id>"
}

The second request in this login stage involves sending this authentication code:

{
  "type": "m.login.email.code",
  "session": "<session id>",
  "code": "<code in email sent>"
}

The home server MUST respond to this with either new credentials, the next stage of the login process, or a standard error response.

Email-based (url)

Type

m.login.email.url

Description

Login is supported by clicking on a URL in an email. This login consists of multiple requests.

To respond to this type, reply with:

{
  "type": "m.login.email.url",
  "user": "<user_id or user localpart>",
  "email": "<email address>"
}

After validating the email address, the home server MUST send an email containing an authentication URL and return:

{
  "type": "m.login.email.url",
  "session": "<session id>"
}

The email contains a URL which must be clicked. After it has been clicked, the client should perform another request:

{
  "type": "m.login.email.url",
  "session": "<session id>"
}

The home server MUST respond to this with either new credentials, the next stage of the login process, or a standard error response.

A common client implementation will be to periodically poll until the link is clicked. If the link has not been visited yet, a standard error response with an errcode of M_LOGIN_EMAIL_URL_NOT_YET should be returned.

Email-based (identity server)

Type

m.login.email.identity

Description

Login is supported by authorising an email address with an identity server.

Prior to submitting this, the client should authenticate with an identity server. After authenticating, the session information should be submitted to the home server.

To respond to this type, reply with:

{
  "type": "m.login.email.identity",
  "threepidCreds": [
    {
      "sid": "<identity server session id>",
      "clientSecret": "<identity server client secret>",
      "idServer": "<url of identity server authed with, e.g. 'matrix.org:8090'>"
    }
  ]
}

N-Factor Authentication

Multiple login stages can be combined to create N-factor authentication during login.

This can be achieved by responding with the next login type on completion of a previous login stage:

{
  "next": "<next login type>"
}

If a home server implements N-factor authentication, it MUST respond with all stages when initially queried for their login requirements:

{
  "type": "<1st login type>",
  "stages": [ <1st login type>, <2nd login type>, ... , <Nth login type> ]
}

This can be represented conceptually as:

_______________________
|    Login Stage 1      |
| type: "<login type1>" |
|  ___________________  |
| |_Request_1_________| | <-- Returns "session" key which is used throughout.
|  ___________________  |     
| |_Request_2_________| | <-- Returns a "next" value of "login type2"
|_______________________|
         |
         |
_________V_____________
|    Login Stage 2      |
| type: "<login type2>" |
|  ___________________  |
| |_Request_1_________| |
|  ___________________  |
| |_Request_2_________| |
|  ___________________  |
| |_Request_3_________| | <-- Returns a "next" value of "login type3"
|_______________________|
         |
         |
_________V_____________
|    Login Stage 3      |
| type: "<login type3>" |
|  ___________________  |
| |_Request_1_________| | <-- Returns user credentials
|_______________________|

Fallback

Clients cannot be expected to be able to know how to process every single login type. If a client determines it does not know how to handle a given login type, it should request a login fallback page:

GET matrix/client/api/v1/login/fallback

This MUST return an HTML page which can perform the entire login process.

Rooms

Creation

To create a room, a client has to use the /createRoom_ API. There are various options which can be set when creating a room:

visibility

Type:

String

Optional:

Yes

Value:

Either public or private.

Description:

A public visibility indicates that the room will be shown in the public room list. A private visibility will hide the room from the public room list. Rooms default to public visibility if this key is not included.

room_alias_name

Type:

String

Optional:

Yes

Value:

The room alias localpart.

Description:

If this is included, a room alias will be created and mapped to the newly created room. The alias will belong on the same home server which created the room, e.g. !qadnasoi:domain.com >>> #room_alias_name:domain.com

name

Type:

String

Optional:

Yes

Value:

The name value for the m.room.name state event.

Description:

If this is included, an m.room.name event will be sent into the room to indicate the name of the room. See Room Events for more information on m.room.name.

topic

Type:

String

Optional:

Yes

Value:

The topic value for the m.room.topic state event.

Description:

If this is included, an m.room.topic event will be sent into the room to indicate the topic for the room. See Room Events for more information on m.room.topic.

invite

Type:

List

Optional:

Yes

Value:

A list of user ids to invite.

Description:

This will tell the server to invite everyone in the list to the newly created room.

Example:

{
  "visibility": "public", 
  "room_alias_name": "the pub",
  "name": "The Grand Duke Pub",
  "topic": "All about happy hour"
}

The home server will create a m.room.create event when the room is created, which serves as the root of the PDU graph for this room. This event also has a creator key which contains the user ID of the room creator. It will also generate several other events in order to manage permissions in this room. This includes:

• m.room.power_levels : Sets the power levels of users.
• m.room.join_rules : Whether the room is "invite-only" or not.
• m.room.add_state_level: The power level required in order to add new state to the room (as opposed to updating exisiting state)
• m.room.send_event_level : The power level required in order to send a message in this room.
• m.room.ops_level : The power level required in order to kick or ban a user from the room.

See Room Events for more information on these events.

Modifying aliases

Note

This section is a work in progress.

Permissions

Note

This section is a work in progress.

Permissions for rooms are done via the concept of power levels - to do any action in a room a user must have a suitable power level.

Power levels for users are defined in m.room.power_levels, where both a default and specific users' power levels can be set. By default all users have a power level of 0, other than the room creator whose power level defaults to 100. Power levels for users are tracked per-room even if the user is not present in the room.

State events may contain a required_power_level key, which indicates the minimum power a user must have before they can update that state key. The only exception to this is when a user leaves a room.

To perform certain actions there are additional power level requirements defined in the following state events:

• m.room.send_event_level defines the minimum level for sending non-state events. Defaults to 50.
• m.room.add_state_level defines the minimum level for adding new state, rather than updating existing state. Defaults to 50.
• m.room.ops_level defines the minimum levels to ban and kick other users. This defaults to a kick and ban levels of 50 each.

Joining rooms

Users need to join a room in order to send and receive events in that room. A user can join a room by making a request to /join/<room_alias_or_id>_ with:

{}

Alternatively, a user can make a request to /rooms/<room_id>/join_ with the same request content. This is only provided for symmetry with the other membership APIs: /rooms/<room id>/invite and /rooms/<room id>/leave. If a room alias was specified, it will be automatically resolved to a room ID, which will then be joined. The room ID that was joined will be returned in response:

{
  "room_id": "!roomid:domain"
}

The membership state for the joining user can also be modified directly to be join by sending the following request to /rooms/<room id>/state/m.room.member/<url encoded user id>:

{
  "membership": "join"
}

See the Room events section for more information on m.room.member.

After the user has joined a room, they will receive subsequent events in that room. This room will now appear as an entry in the /initialSync_ API.

Some rooms enforce that a user is invited to a room before they can join that room. Other rooms will allow anyone to join the room even if they have not received an invite.

Inviting users

The purpose of inviting users to a room is to notify them that the room exists so they can choose to become a member of that room. Some rooms require that all users who join a room are previously invited to it (an "invite-only" room). Whether a given room is an "invite-only" room is determined by the room config key TODO. It can have one of the following values:

• TODO Room config invite only value explanation
• TODO Room config free-to-join value explanation

Only users who have a membership state of join in a room can invite new users to said room. The person being invited must not be in the join state in the room. The fully-qualified user ID must be specified when inviting a user, as the user may reside on a different home server. To invite a user, send the following request to /rooms/<room_id>/invite_, which will manage the entire invitation process:

{
  "user_id": "<user id to invite>"
}

Alternatively, the membership state for this user in this room can be modified directly by sending the following request to /rooms/<room id>/state/m.room.member/<url encoded user id>:

{
  "membership": "invite"
}

See the Room events section for more information on m.room.member.

Leaving rooms

A user can leave a room to stop receiving events for that room. A user must have joined the room before they are eligible to leave the room. If the room is an "invite-only" room, they will need to be re-invited before they can re-join the room. To leave a room, a request should be made to /rooms/<room_id>/leave_ with:

{}

Alternatively, the membership state for this user in this room can be modified directly by sending the following request to /rooms/<room id>/state/m.room.member/<url encoded user id>:

{
  "membership": "leave"
}

See the Room events section for more information on m.room.member.

Once a user has left a room, that room will no longer appear on the /initialSync_ API. Be aware that leaving a room is not equivalent to have never been in that room. A user who has previously left a room still maintains some residual state in that room. Their membership state will be marked as leave. This contrasts with a user who has never been invited or joined to that room who will not have any membership state for that room.

If all members in a room leave, that room becomes eligible for deletion.

Banning users in a room

A user may decide to ban another user in a room. 'Banning' forces the target user to leave the room and prevents them from re-joining the room. A banned user will not be treated as a joined user, and so will not be able to send or receive events in the room. In order to ban someone, the user performing the ban MUST have the required power level. To ban a user, a request should be made to /rooms/<room_id>/ban_ with:

{
  "user_id": "<user id to ban"
  "reason": "string: <reason for the ban>"
}

Banning a user adjusts the banned member's membership state to ban and adjusts the power level of this event to a level higher than the banned person. Like with other membership changes, a user can directly adjust the target member's state, by making a request to /rooms/<room id>/state/m.room.member/<user id>:

{
  "membership": "ban"
}

Events in a room

Room events can be split into two categories:

State Events

These are events which replace events that came before it, depending on a set of unique keys. These keys are the event type and a state_key. Events with the same set of keys will be overwritten. Typically, state events are used to store state, hence their name.

Non-state events

These are events which cannot be overwritten after sending. The list of events continues to grow as more events are sent. As this list grows, it becomes necessary to provide a mechanism for navigating this list. Pagination APIs are used to view the list of historical non-state events. Typically, non-state events are used to send messages.

This specification outlines several events, all with the event type prefix m.. However, applications may wish to add their own type of event, and this can be achieved using the REST API detailed in the following sections. If new events are added, the event type key SHOULD follow the Java package naming convention, e.g. com.example.myapp.event. This ensures event types are suitably namespaced for each application and reduces the risk of clashes.

State events

State events can be sent by PUT ing to /rooms/<room_id>/state/<event_type>/<state_key>_. These events will be overwritten if <room id>, <event type> and <state key> all match. If the state event has no state_key, it can be omitted from the path. These requests cannot use transaction IDs like other PUT paths because they cannot be differentiated from the state_key. Furthermore, POST is unsupported on state paths. Valid requests look like:

PUT /rooms/!roomid:domain/state/m.example.event
{ "key" : "without a state key" }

PUT /rooms/!roomid:domain/state/m.another.example.event/foo
{ "key" : "with 'foo' as the state key" }

In contrast, these requests are invalid:

POST /rooms/!roomid:domain/state/m.example.event/
{ "key" : "cannot use POST here" }

PUT /rooms/!roomid:domain/state/m.another.example.event/foo/11
{ "key" : "txnIds are not supported" }

Care should be taken to avoid setting the wrong state key:

PUT /rooms/!roomid:domain/state/m.another.example.event/11
{ "key" : "with '11' as the state key, but was probably intended to be a txnId" }

The state_key is often used to store state about individual users, by using the user ID as the state_key value. For example:

PUT /rooms/!roomid:domain/state/m.favorite.animal.event/%40my_user%3Adomain.com
{ "animal" : "cat", "reason": "fluffy" }

In some cases, there may be no need for a state_key, so it can be omitted:

PUT /rooms/!roomid:domain/state/m.room.bgd.color
{ "color": "red", "hex": "#ff0000" }

See Room Events for the m. event specification.

Non-state events

Non-state events can be sent by sending a request to /rooms/<room_id>/send/<event_type>_. These requests can use transaction IDs and PUT/POST methods. Non-state events allow access to historical events and pagination, making it best suited for sending messages. For example:

POST /rooms/!roomid:domain/send/m.custom.example.message
{ "text": "Hello world!" }

PUT /rooms/!roomid:domain/send/m.custom.example.message/11
{ "text": "Goodbye world!" }

See Room Events for the m. event specification.

Syncing rooms

Note

This section is a work in progress.

When a client logs in, they may have a list of rooms which they have already joined. These rooms may also have a list of events associated with them. The purpose of 'syncing' is to present the current room and event information in a convenient, compact manner. The events returned are not limited to room events; presence events will also be returned. There are two APIs provided:

• /initialSync_ : A global sync which will present room and event information for all rooms the user has joined.
• /rooms/<room_id>/initialSync_ : A sync scoped to a single room. Presents room and event information for this room only.

Getting events for a room

There are several APIs provided to GET events for a room:

/rooms/<room id>/state/<event type>/<state key>

Description:

Get the state event identified.

Response format:

A JSON object representing the state event content.

Example:

/rooms/!room:domain.com/state/m.room.name returns { "name": "Room name" }

/rooms/<room_id>/state_

Description:

Get all state events for a room.

Response format:

[ { state event }, { state event }, ... ]

Example:

TODO-doc

/rooms/<room_id>/members_

Description:

Get all m.room.member state events.

Response format:

{ "start": "<token>", "end": "<token>", "chunk": [ { m.room.member event }, ... ] }

Example:

TODO-doc

/rooms/<room_id>/messages_

Description:

Get all m.room.message and m.room.member events. This API supports pagination using from and to query parameters, coupled with the start and end tokens from an /initialSync_ API.

Response format:

{ "start": "<token>", "end": "<token>" }

Example:

TODO-doc

/rooms/<room_id>/initialSync_

Description:

Get all relevant events for a room. This includes state events, paginated non-state events and presence events.

Response format:

{ TODO-doc }

Example:

TODO-doc

Redactions

Since events are extensible it is possible for malicious users and/or servers to add keys that are, for example offensive or illegal. Since some events cannot be simply deleted, e.g. membership events, we instead 'redact' events. This involves removing all keys from an event that are not required by the protocol. This stripped down event is thereafter returned anytime a client or remote server requests it.

Events that have been redacted include a redacted_because key whose value is the event that caused it to be redacted, which may include a reason.

Redacting an event cannot be undone, allowing server owners to delete the offending content from the databases.

Currently, only room admins can redact events by sending a m.room.redaction event, but server admins also need to be able to redact events by a similar mechanism.

Upon receipt of a redaction event, the server should strip off any keys not in the following list:

• event_id
• type
• room_id
• user_id
• state_key
• prev_state
• content

The content object should also be stripped of all keys, unless it is one of one of the following event types:

• m.room.member allows key membership
• m.room.create allows key creator
• m.room.join_rules allows key join_rule
• m.room.power_levels allows keys that are user ids or default
• m.room.add_state_level allows key level
• m.room.send_event_level allows key level
• m.room.ops_levels allows keys kick_level, ban_level and redact_level
• m.room.aliases allows key aliases

The redaction event should be added under the key redacted_because.

When a client receives a redaction event it should change the redacted event in the same way a server does.

Room Events

Note

This section is a work in progress.

This specification outlines several standard event types, all of which are prefixed with m.

m.room.name

Summary:

Set the human-readable name for the room.

Type:

State event

JSON format:

{ "name" : "string" }

Example:

{ "name" : "My Room" }

Description:

A room has an opaque room ID which is not human-friendly to read. A room alias is human-friendly, but not all rooms have room aliases. The room name is a human-friendly string designed to be displayed to the end-user. The room name is not unique, as multiple rooms can have the same room name set. The room name can also be set when creating a room using /createRoom_ with the name key.

m.room.topic

Summary:

Set a topic for the room.

Type:

State event

JSON format:

{ "topic" : "string" }

Example:

{ "topic" : "Welcome to the real world." }

Description:

A topic is a short message detailing what is currently being discussed in the room. It can also be used as a way to display extra information about the room, which may not be suitable for the room name. The room topic can also be set when creating a room using /createRoom_ with the topic key.

m.room.member

Summary:

The current membership state of a user in the room.

Type:

State event

JSON format:

{ "membership" : "enum[ invite|join|leave|ban ]" }

Example:

{ "membership" : "join" }

Description:

Adjusts the membership state for a user in a room. It is preferable to use the membership APIs (/rooms/<room id>/invite etc) when performing membership actions rather than adjusting the state directly as there are a restricted set of valid transformations. For example, user A cannot force user B to join a room, and trying to force this state change directly will fail. See the Rooms section for how to use the membership APIs.

m.room.create

Summary:

The first event in the room.

Type:

State event

JSON format:

{ "creator": "string"}

Example:

{ "creator": "@user:example.com" }

Description:

This is the first event in a room and cannot be changed. It acts as the root of all other events.

m.room.join_rules

Summary:

Descripes how/if people are allowed to join.

Type:

State event

JSON format:

{ "join_rule": "enum [ public|knock|invite|private ]" }

Example:

{ "join_rule": "public" }

Description:

TODO-doc : Use docs/models/rooms.rst

m.room.power_levels

Summary:

Defines the power levels of users in the room.

Type:

State event

JSON format:

{ "<user_id>": <int>, ..., "default": <int>}

Example:

{ "@user:example.com": 5, "@user2:example.com": 10, "default": 0 }

Description:

If a user is in the list, then they have the associated power level. Otherwise they have the default level. If not default key is supplied, it is assumed to be 0.

m.room.add_state_level

Summary:

Defines the minimum power level a user needs to add state.

Type:

State event

JSON format:

{ "level": <int> }

Example:

{ "level": 5 }

Description:

To add a new piece of state to the room a user must have the given power level. This does not apply to updating current state, which is goverened by the required_power_level event key.

m.room.send_event_level

Summary:

Defines the minimum power level a user needs to send an event.

Type:

State event

JSON format:

{ "level": <int> }

Example:

{ "level": 0 }

Description:

To send a new event into the room a user must have at least this power level. This allows ops to make the room read only by increasing this level, or muting individual users by lowering their power level below this threshold.

m.room.ops_levels

Summary:

Defines the minimum power levels that a user must have before they can kick and/or ban other users.

Type:

State event

JSON format:

{ "ban_level": <int>, "kick_level": <int> }

Example:

{ "ban_level": 5, "kick_level": 5 }

Description:

This defines who can ban and/or kick people in the room. Most of the time ban_level will be greater than or equal to kick_level since banning is more severe than kicking.

m.room.aliases

Summary:

These state events are used to inform the room about what room aliases it has.

Type:

State event

JSON format:

{ "aliases": ["string", ...] }

Example:

{ "aliases": ["#foo:example.com"] }

Description:

A server may inform the room that it has added or removed an alias for the room. This is purely for informational purposes and may become stale. Clients should check that the room alias is still valid before using it. The state_key of the event is the homeserver which owns the room alias.

m.room.message

Summary:

A message.

Type:

Non-state event

JSON format:

{ "msgtype": "string" }

Example:

{ "msgtype": "m.text", "body": "Testing" }

Description:

This event is used when sending messages in a room. Messages are not limited to be text. The msgtype key outlines the type of message, e.g. text, audio, image, video, etc. Whilst not required, the body key SHOULD be used with every kind of msgtype as a fallback mechanism when a client cannot render the message. For more information on the types of messages which can be sent, see m.room.message msgtypes.

m.room.message.feedback

Summary:

A receipt for a message.

Type:

Non-state event

JSON format:

{ "type": "enum [ delivered|read ]", "target_event_id": "string" }

Example:

{ "type": "delivered", "target_event_id": "e3b2icys" }

Description:

Feedback events are events sent to acknowledge a message in some way. There are two supported acknowledgements: delivered (sent when the event has been received) and read (sent when the event has been observed by the end-user). The target_event_id should reference the m.room.message event being acknowledged.

m.room.redaction

Summary:

Indicates a previous event has been redacted.

Type:

Non-state event

JSON format:

{ "reason": "string" }

Description:

Events can be redacted by either room or server admins. Redacting an event means that all keys not required by the protocol are stripped off, allowing admins to remove offensive or illegal content that may have been attached to any event. This cannot be undone, allowing server owners to physically delete the offending data. There is also a concept of a moderator hiding a non-state event, which can be undone, but cannot be applied to state events. The event that has been redacted is specified in the redacts event level key.

m.room.message msgtypes

Each m.room.message MUST have a msgtype key which identifies the type of message being sent. Each type has their own required and optional keys, as outlined below:

m.text

Required keys:

• body : "string" - The body of the message.

Optional keys:

None.

Example:

{ "msgtype": "m.text", "body": "I am a fish" }

m.emote

Required keys:

• body : "string" - The emote action to perform.

Optional keys:

None.

Example:

{ "msgtype": "m.emote", "body": "tries to come up with a witty explanation" }

m.image

Required keys:

• url : "string" - The URL to the image.

Optional keys:

• info : "string" - info : JSON object (ImageInfo) - The image info for image referred to in url.
• thumbnail_url : "string" - The URL to the thumbnail.
• thumbnail_info : JSON object (ImageInfo) - The image info for the image referred to in thumbnail_url.
• body : "string" - The alt text of the image, or some kind of content description for accessibility e.g. "image attachment".

ImageInfo:

Information about an image:

{ 
  "size" : integer (size of image in bytes),
  "w" : integer (width of image in pixels),
  "h" : integer (height of image in pixels),
  "mimetype" : "string (e.g. image/jpeg)",
}

m.audio

Required keys:

• url : "string" - The URL to the audio.

Optional keys:

• info : JSON object (AudioInfo) - The audio info for the audio referred to in url.
• body : "string" - A description of the audio e.g. "Bee Gees - Stayin' Alive", or some kind of content description for accessibility e.g. "audio attachment".

AudioInfo:

Information about a piece of audio:

{
  "mimetype" : "string (e.g. audio/aac)",
  "size" : integer (size of audio in bytes),
  "duration" : integer (duration of audio in milliseconds),
}

m.video

Required keys:

• url : "string" - The URL to the video.

Optional keys:

• info : JSON object (VideoInfo) - The video info for the video referred to in url.
• body : "string" - A description of the video e.g. "Gangnam style", or some kind of content description for accessibility e.g. "video attachment".

VideoInfo:

Information about a video:

{
  "mimetype" : "string (e.g. video/mp4)",
  "size" : integer (size of video in bytes),
  "duration" : integer (duration of video in milliseconds),
  "w" : integer (width of video in pixels),
  "h" : integer (height of video in pixels),
  "thumbnail_url" : "string (URL to image)",
  "thumbanil_info" : JSON object (ImageInfo)
}

m.location

Required keys:

• geo_uri : "string" - The geo URI representing the location.

Optional keys:

• thumbnail_url : "string" - The URL to a thumnail of the location being represented.
• thumbnail_info : JSON object (ImageInfo) - The image info for the image referred to in thumbnail_url.
• body : "string" - A description of the location e.g. "Big Ben, London, UK", or some kind of content description for accessibility e.g. "location attachment".

The following keys can be attached to any m.room.message:

Optional keys:

• sender_ts : integer - A timestamp (ms resolution) representing the wall-clock time when the message was sent from the client.

Presence

Note

This section is a work in progress.

Each user has the concept of presence information. This encodes the "availability" of that user, suitable for display on other user's clients. This is transmitted as an m.presence event and is one of the few events which are sent outside the context of a room. The basic piece of presence information is represented by the presence key, which is an enum of one of the following:

• online : The default state when the user is connected to an event stream.
• unavailable : The user is not reachable at this time.
• offline : The user is not connected to an event stream.
• free_for_chat : The user is generally willing to receive messages moreso than default.
• hidden : Behaves as offline, but allows the user to see the client state anyway and generally interact with client features. (Not yet implemented in synapse).

This basic presence field applies to the user as a whole, regardless of how many client devices they have connected. The home server should synchronise this status choice among multiple devices to ensure the user gets a consistent experience.

In addition, the server maintains a timestamp of the last time it saw an active action from the user; either sending a message to a room, or changing presence state from a lower to a higher level of availability (thus: changing state from unavailable to online will count as an action for being active, whereas in the other direction will not). This timestamp is presented via a key called last_active_ago, which gives the relative number of miliseconds since the message is generated/emitted, that the user was last seen active.

Home servers can also use the user's choice of presence state as a signal for how to handle new private one-to-one chat message requests. For example, it might decide:

• free_for_chat : accept anything
• online : accept from anyone in my addres book list
• busy : accept from anyone in this "important people" group in my address book list

Presence List

Each user's home server stores a "presence list" for that user. This stores a list of other user IDs the user has chosen to add to it. To be added to this list, the user being added must receive permission from the list owner. Once granted, both user's HS(es) store this information. Since such subscriptions are likely to be bidirectional, HSes may wish to automatically accept requests when a reverse subscription already exists.

As a convenience, presence lists should support the ability to collect users into groups, which could allow things like inviting the entire group to a new ("ad-hoc") chat room, or easy interaction with the profile information ACL implementation of the HS.

Presence and Permissions

For a viewing user to be allowed to see the presence information of a target user, either:

• The target user has allowed the viewing user to add them to their presence list, or
• The two users share at least one room in common

In the latter case, this allows for clients to display some minimal sense of presence information in a user list for a room.

Client API

The client API for presence is on the following set of REST calls.

Fetching basic status:

GET $PREFIX/presence/:user_id/status

Returned content: JSON object containing the following keys:
  presence: "offline"|"unavailable"|"online"|"free_for_chat"
  status_msg: (optional) string of freeform text
  last_active_ago: miliseconds since the last activity by the user

Setting basic status:

PUT $PREFIX/presence/:user_id/status

Content: JSON object containing the following keys:
  presence and status_msg: as above

When setting the status, the activity time is updated to reflect that activity; the client does not need to specify the last_active_ago field.

Fetching the presence list:

GET $PREFIX/presence/list

Returned content: JSON array containing objects; each object containing the
  following keys:
  user_id: observed user ID
  presence: "offline"|"unavailable"|"online"|"free_for_chat"
  status_msg: (optional) string of freeform text
  last_active_ago: miliseconds since the last activity by the user

Maintaining the presence list:

POST $PREFIX/presence/list

Content: JSON object containing either or both of the following keys:
  invite: JSON array of strings giving user IDs to send invites to
  drop: JSON array of strings giving user IDs to remove from the list

Server API

The server API for presence is based entirely on exchange of the following EDUs. There are no PDUs or Federation Queries involved.

Performing a presence update and poll subscription request:

EDU type: m.presence

Content keys:
  push: (optional): list of push operations.
    Each should be an object with the following keys:
      user_id: string containing a User ID
      presence: "offline"|"unavailable"|"online"|"free_for_chat"
      status_msg: (optional) string of freeform text
      last_active_ago: miliseconds since the last activity by the user

  poll: (optional): list of strings giving User IDs

  unpoll: (optional): list of strings giving User IDs

The presence of this combined message is two-fold: it informs the recipient server of the current status of one or more users on the sending server (by the push key), and it maintains the list of users on the recipient server that the sending server is interested in receiving updates for, by adding (by the poll key) or removing them (by the unpoll key). The poll and unpoll lists apply changes to the implied list of users; any existing IDs that the server sent as poll operations in a previous message are not removed until explicitly requested by a later unpoll.

On receipt of a message containing a non-empty poll list, the receiving server should immediately send the sending server a presence update EDU of its own, containing in a push list the current state of every user that was in the orginal EDU's poll list.

Sending a presence invite:

EDU type: m.presence_invite

Content keys:
  observed_user: string giving the User ID of the user whose presence is
    requested (i.e. the recipient of the invite)
  observer_user: string giving the User ID of the user who is requesting to
    observe the presence (i.e. the sender of the invite)

Accepting a presence invite:

EDU type: m.presence_accept

Content keys - as for m.presence_invite

Rejecting a presence invite:

EDU type: m.presence_deny

Content keys - as for m.presence_invite

Voice over IP

Matrix can also be used to set up VoIP calls. This is part of the core specification, although is still in a very early stage. Voice (and video) over Matrix is based on the WebRTC standards.

Call events are sent to a room, like any other event. This means that clients must only send call events to rooms with exactly two participants as currently the WebRTC standard is based around two-party communication.

Events

m.call.invite This event is sent by the caller when they wish to establish a call.

Required keys:

• call_id : "string" - A unique identifier for the call
• offer : "offer object" - The session description
• version : "integer" - The version of the VoIP specification this message adheres to. This specification is version 0.
• lifetime : "integer" - The time in milliseconds that the invite is valid for. Once the invite age exceeds this value, clients should discard it. They should also no longer show the call as awaiting an answer in the UI.

Optional keys:

None.

Example:

{ "version" : 0, "call_id": "12345", "offer": { "type" : "offer", "sdp" : "v=0\r\no=- 6584580628695956864 2 IN IP4 127.0.0.1[...]" } }

Offer Object

Required keys:

• type : "string" - The type of session description, in this case 'offer'
• sdp : "string" - The SDP text of the session description

m.call.candidates This event is sent by callers after sending an invite and by the callee after answering. Its purpose is to give the other party additional ICE candidates to try using to communicate.

Required keys:

• call_id : "string" - The ID of the call this event relates to
• version : "integer" - The version of the VoIP specification this messages adheres to. his specification is version 0.
• candidates : "array of candidate objects" - Array of object describing the candidates.

Candidate Object

Required Keys:

• sdpMid : "string" - The SDP media type this candidate is intended for.
• sdpMLineIndex : "integer" - The index of the SDP 'm' line this candidate is intended for
• candidate : "string" - The SDP 'a' line of the candidate

m.call.answer

Required keys:

• call_id : "string" - The ID of the call this event relates to
• version : "integer" - The version of the VoIP specification this messages
• answer : "answer object" - Object giving the SDK answer

Answer Object

Required keys:

• type : "string" - The type of session description. 'answer' in this case.
• sdp : "string" - The SDP text of the session description

m.call.hangup Sent by either party to signal their termination of the call. This can be sent either once the call has has been established or before to abort the call.

Required keys:

• call_id : "string" - The ID of the call this event relates to
• version : "integer" - The version of the VoIP specification this messages

Message Exchange

A call is set up with messages exchanged as follows:

Caller                   Callee
m.call.invite ----------->
m.call.candidate -------->
[more candidates events]
                      User answers call
               <------ m.call.answer
            [...]
               <------ m.call.hangup

Or a rejected call:

Caller                   Callee
m.call.invite ----------->
m.call.candidate -------->
[more candidates events]
                     User rejects call
              <------- m.call.hangup

Calls are negotiated according to the WebRTC specification.

Glare

This specification aims to address the problem of two users calling each other at roughly the same time and their invites crossing on the wire. It is a far better experience for the users if their calls are connected if it is clear that their intention is to set up a call with one another.

In Matrix, calls are to rooms rather than users (even if those rooms may only contain one other user) so we consider calls which are to the same room.

The rules for dealing with such a situation are as follows:

• If an invite to a room is received whilst the client is preparing to send an invite to the same room, the client should cancel its outgoing call and instead automatically accept the incoming call on behalf of the user.
• If an invite to a room is received after the client has sent an invite to the same room and is waiting for a response, the client should perform a lexicographical comparison of the call IDs of the two calls and use the lesser of the two calls, aborting the greater. If the incoming call is the lesser, the client should accept this call on behalf of the user.

The call setup should appear seamless to the user as if they had simply placed a call and the other party had accepted. Thusly, any media stream that had been setup for use on a call should be transferred and used for the call that replaces it.

Profiles

Note

This section is a work in progress.

Internally within Matrix users are referred to by their user ID, which is typically a compact unique identifier. Profiles grant users the ability to see human-readable names for other users that are in some way meaningful to them. Additionally, profiles can publish additional information, such as the user's age or location.

A Profile consists of a display name, an avatar picture, and a set of other metadata fields that the user may wish to publish (email address, phone numbers, website URLs, etc...). This specification puts no requirements on the display name other than it being a valid unicode string.

Identity

Note

This section is a work in progress.

Federation

Federation is the term used to describe how to communicate between Matrix home servers. Federation is a mechanism by which two home servers can exchange Matrix event messages, both as a real-time push of current events, and as a historic fetching mechanism to synchronise past history for clients to view. It uses HTTPS connections between each pair of servers involved as the underlying transport. Messages are exchanged between servers in real-time by active pushing from each server's HTTP client into the server of the other. Queries to fetch historic data for the purpose of back-filling scrollback buffers and the like can also be performed. Currently routing of messages between homeservers is full mesh (like email) - however, fan-out refinements to this design are currently under consideration.

There are three main kinds of communication that occur between home servers:

Queries

These are single request/response interactions between a given pair of servers, initiated by one side sending an HTTPS GET request to obtain some information, and responded by the other. They are not persisted and contain no long-term significant history. They simply request a snapshot state at the instant the query is made.

Ephemeral Data Units (EDUs)

These are notifications of events that are pushed from one home server to another. They are not persisted and contain no long-term significant history, nor does the receiving home server have to reply to them.

Persisted Data Units (PDUs)

These are notifications of events that are broadcast from one home server to any others that are interested in the same "context" (namely, a Room ID). They are persisted to long-term storage and form the record of history for that context.

EDUs and PDUs are further wrapped in an envelope called a Transaction, which is transferred from the origin to the destination home server using an HTTP PUT request.

Transactions

Warning

This section may be misleading or inaccurate.

The transfer of EDUs and PDUs between home servers is performed by an exchange of Transaction messages, which are encoded as JSON objects, passed over an HTTP PUT request. A Transaction is meaningful only to the pair of home servers that exchanged it; they are not globally-meaningful.

Each transaction has:

• An opaque transaction ID.
• A timestamp (UNIX epoch time in milliseconds) generated by its origin server.
• An origin and destination server name.
• A list of "previous IDs".
• A list of PDUs and EDUs - the actual message payload that the Transaction carries.

origin

Type:

String

Description:

DNS name of homeserver making this transaction.

ts

Type:

Integer

Description:

Timestamp in milliseconds on originating homeserver when this transaction started.

previous_ids

Type:

List of strings

Description:

List of transactions that were sent immediately prior to this transaction.

pdus

Type:

List of Objects.

Description:

List of updates contained in this transaction.

{
 "transaction_id":"916d630ea616342b42e98a3be0b74113",
 "ts":1404835423000,
 "origin":"red",
 "destination":"blue",
 "prev_ids":["e1da392e61898be4d2009b9fecce5325"],
 "pdus":[...],
 "edus":[...]
}

The prev_ids field contains a list of previous transaction IDs that the origin server has sent to this destination. Its purpose is to act as a sequence checking mechanism - the destination server can check whether it has successfully received that Transaction, or ask for a retransmission if not.

The pdus field of a transaction is a list, containing zero or more PDUs.[*] Each PDU is itself a JSON object containing a number of keys, the exact details of which will vary depending on the type of PDU. Similarly, the edus field is another list containing the EDUs. This key may be entirely absent if there are no EDUs to transfer.

(* Normally the PDU list will be non-empty, but the server should cope with receiving an "empty" transaction, as this is useful for informing peers of other transaction IDs they should be aware of. This effectively acts as a push mechanism to encourage peers to continue to replicate content.)

PDUs and EDUs

Warning

This section may be misleading or inaccurate.

All PDUs have:

• An ID
• A context
• A declaration of their type
• A list of other PDU IDs that have been seen recently on that context (regardless of which origin sent them)

context

Type:

String

Description:

Event context identifier

origin

Type:

String

Description:

DNS name of homeserver that created this PDU.

pdu_id

Type:

String

Description:

Unique identifier for PDU within the context for the originating homeserver

ts

Type:

Integer

Description:

Timestamp in milliseconds on originating homeserver when this PDU was created.

pdu_type

Type:

String

Description:

PDU event type.

prev_pdus

Type:

List of pairs of strings

Description:

The originating homeserver and PDU ids of the most recent PDUs the homeserver was aware of for this context when it made this PDU.

depth

Type:

Integer

Description:

The maximum depth of the previous PDUs plus one.

For state updates:

is_state

Type:

Boolean

Description:

True if this PDU is updating state.

state_key

Type:

String

Description:

Optional key identifying the updated state within the context.

power_level

Type:

Integer

Description:

The asserted power level of the user performing the update.

min_update

Type:

Integer

Description:

The required power level needed to replace this update.

prev_state_id

Type:

String

Description:

PDU event type.

prev_state_origin

Type:

String

Description:

The PDU id of the update this replaces.

user

Type:

String

Description:

The user updating the state.

{
 "pdu_id":"a4ecee13e2accdadf56c1025af232176",
 "context":"#example.green",
 "origin":"green",
 "ts":1404838188000,
 "pdu_type":"m.text",
 "prev_pdus":[["blue","99d16afbc857975916f1d73e49e52b65"]],
 "content":...
 "is_state":false
}

In contrast to Transactions, it is important to note that the prev_pdus field of a PDU refers to PDUs that any origin server has sent, rather than previous IDs that this origin has sent. This list may refer to other PDUs sent by the same origin as the current one, or other origins.

Because of the distributed nature of participants in a Matrix conversation, it is impossible to establish a globally-consistent total ordering on the events. However, by annotating each outbound PDU at its origin with IDs of other PDUs it has received, a partial ordering can be constructed allowing causality relationships to be preserved. A client can then display these messages to the end-user in some order consistent with their content and ensure that no message that is semantically in reply of an earlier one is ever displayed before it.

PDUs fall into two main categories: those that deliver Events, and those that synchronise State. For PDUs that relate to State synchronisation, additional keys exist to support this:

{...,
 "is_state":true,
 "state_key":TODO-doc
 "power_level":TODO-doc
 "prev_state_id":TODO-doc
 "prev_state_origin":TODO-doc}

EDUs, by comparison to PDUs, do not have an ID, a context, or a list of "previous" IDs. The only mandatory fields for these are the type, origin and destination home server names, and the actual nested content.

{"edu_type":"m.presence",
 "origin":"blue",
 "destination":"orange",
 "content":...}

Protocol URLs

Warning

This section may be misleading or inaccurate.

All these URLs are namespaced within a prefix of:

/_matrix/federation/v1/...

For active pushing of messages representing live activity "as it happens":

PUT .../send/:transaction_id/
  Body: JSON encoding of a single Transaction
  Response: TODO-doc

The transaction_id path argument will override any ID given in the JSON body. The destination name will be set to that of the receiving server itself. Each embedded PDU in the transaction body will be processed.

To fetch a particular PDU:

GET .../pdu/:origin/:pdu_id/
  Response: JSON encoding of a single Transaction containing one PDU

Retrieves a given PDU from the server. The response will contain a single new Transaction, inside which will be the requested PDU.

To fetch all the state of a given context:

GET .../state/:context/
  Response: JSON encoding of a single Transaction containing multiple PDUs

Retrieves a snapshot of the entire current state of the given context. The response will contain a single Transaction, inside which will be a list of PDUs that encode the state.

To backfill events on a given context:

GET .../backfill/:context/
  Query args: v, limit
  Response: JSON encoding of a single Transaction containing multiple PDUs

Retrieves a sliding-window history of previous PDUs that occurred on the given context. Starting from the PDU ID(s) given in the "v" argument, the PDUs that preceeded it are retrieved, up to a total number given by the "limit" argument. These are then returned in a new Transaction containing all of the PDUs.

To stream events all the events:

GET .../pull/
  Query args: origin, v
  Response: JSON encoding of a single Transaction consisting of multiple PDUs

Retrieves all of the transactions later than any version given by the "v" arguments.

To make a query:

GET .../query/:query_type
  Query args: as specified by the individual query types
  Response: JSON encoding of a response object

Performs a single query request on the receiving home server. The Query Type part of the path specifies the kind of query being made, and its query arguments have a meaning specific to that kind of query. The response is a JSON-encoded object whose meaning also depends on the kind of query.

Backfilling

Note

This section is a work in progress.

SRV Records

Note

This section is a work in progress.

Security

Note

This section is a work in progress.

Threat Model

Denial of Service

The attacker could attempt to prevent delivery of messages to or from the victim in order to:

• Disrupt service or marketing campaign of a commercial competitor.
• Censor a discussion or censor a participant in a discussion.
• Perform general vandalism.

Threat: Resource Exhaustion

An attacker could cause the victims server to exhaust a particular resource (e.g. open TCP connections, CPU, memory, disk storage)

Threat: Unrecoverable Consistency Violations

An attacker could send messages which created an unrecoverable "split-brain" state in the cluster such that the victim's servers could no longer dervive a consistent view of the chatroom state.

Threat: Bad History

An attacker could convince the victim to accept invalid messages which the victim would then include in their view of the chatroom history. Other servers in the chatroom would reject the invalid messages and potentially reject the victims messages as well since they depended on the invalid messages.

Threat: Block Network Traffic

An attacker could try to firewall traffic between the victim's server and some or all of the other servers in the chatroom.

Threat: High Volume of Messages

An attacker could send large volumes of messages to a chatroom with the victim making the chatroom unusable.

Threat: Banning users without necessary authorisation

An attacker could attempt to ban a user from a chatroom with the necessary authorisation.

Spoofing

An attacker could try to send a message claiming to be from the victim without the victim having sent the message in order to:

• Impersonate the victim while performing illict activity.
• Obtain privileges of the victim.

Threat: Altering Message Contents

An attacker could try to alter the contents of an existing message from the victim.

Threat: Fake Message "origin" Field

An attacker could try to send a new message purporting to be from the victim with a phony "origin" field.

Spamming

The attacker could try to send a high volume of solicicted or unsolicted messages to the victim in order to:

• Find victims for scams.
• Market unwanted products.

Threat: Unsoliticted Messages

An attacker could try to send messages to victims who do not wish to receive them.

Threat: Abusive Messages

An attacker could send abusive or threatening messages to the victim

Spying

The attacker could try to access message contents or metadata for messages sent by the victim or to the victim that were not intended to reach the attacker in order to:

• Gain sensitive personal or commercial information.
• Impersonate the victim using credentials contained in the messages. (e.g. password reset messages)
• Discover who the victim was talking to and when.

Threat: Disclosure during Transmission

An attacker could try to expose the message contents or metadata during transmission between the servers.

Threat: Disclosure to Servers Outside Chatroom

An attacker could try to convince servers within a chatroom to send messages to a server it controls that was not authorised to be within the chatroom.

Threat: Disclosure to Servers Within Chatroom

An attacker could take control of a server within a chatroom to expose message contents or metadata for messages in that room.

Rate limiting

Home servers SHOULD implement rate limiting to reduce the risk of being overloaded. If a request is refused due to rate limiting, it should return a standard error response of the form:

{
  "errcode": "M_LIMIT_EXCEEDED",
  "error": "string",
  "retry_after_ms": integer (optional)
}

The retry_after_ms key SHOULD be included to tell the client how long they have to wait in milliseconds before they can try again.

Policy Servers

Note

This section is a work in progress.

Content repository

Note

This section is a work in progress.

Address book repository

Note

This section is a work in progress.

Glossary

Note

This section is a work in progress.

Backfilling:

The process of synchronising historic state from one home server to another, to backfill the event storage so that scrollback can be presented to the client(s). Not to be confused with pagination.

Context:

A single human-level entity of interest (currently, a chat room)

EDU (Ephemeral Data Unit):

A message that relates directly to a given pair of home servers that are exchanging it. EDUs are short-lived messages that related only to one single pair of servers; they are not persisted for a long time and are not forwarded on to other servers. Because of this, they have no internal ID nor previous EDUs reference chain.

Event:

A record of activity that records a single thing that happened on to a context (currently, a chat room). These are the "chat messages" that Synapse makes available.

PDU (Persistent Data Unit):

A message that relates to a single context, irrespective of the server that is communicating it. PDUs either encode a single Event, or a single State change. A PDU is referred to by its PDU ID; the pair of its origin server and local reference from that server.

PDU ID:

The pair of PDU Origin and PDU Reference, that together globally uniquely refers to a specific PDU.

PDU Origin:

The name of the origin server that generated a given PDU. This may not be the server from which it has been received, due to the way they are copied around from server to server. The origin always records the original server that created it.

PDU Reference:

A local ID used to refer to a specific PDU from a given origin server. These references are opaque at the protocol level, but may optionally have some structured meaning within a given origin server or implementation.

Presence:

The concept of whether a user is currently online, how available they declare they are, and so on. See also: doc/model/presence

Profile:

A set of metadata about a user, such as a display name, provided for the benefit of other users. See also: doc/model/profiles

Room ID:

An opaque string (of as-yet undecided format) that identifies a particular room and used in PDUs referring to it.

Room Alias:

A human-readable string of the form #name:some.domain that users can use as a pointer to identify a room; a Directory Server will map this to its Room ID

State:

A set of metadata maintained about a Context, which is replicated among the servers in addition to the history of Events.

User ID:

A string of the form @localpart:domain.name that identifies a user for wire-protocol purposes. The localpart is meaningless outside of a particular home server. This takes a human-readable form that end-users can use directly if they so wish, avoiding the 3PIDs.

Transaction:

A message which relates to the communication between a given pair of servers. A transaction contains possibly-empty lists of PDUs and EDUs.