matrix-spec-proposals/specification/application_service_api.rst

.. Copyright 2016 OpenMarket Ltd
.. Copyright 2018 New Vector Ltd
..
.. Licensed under the Apache License, Version 2.0 (the "License");
.. you may not use this file except in compliance with the License.
.. You may obtain a copy of the License at
..
..     http://www.apache.org/licenses/LICENSE-2.0
..
.. Unless required by applicable law or agreed to in writing, software
.. distributed under the License is distributed on an "AS IS" BASIS,
.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
.. See the License for the specific language governing permissions and
.. limitations under the License.

Application Service API
=======================

The Matrix client-server API and server-server APIs provide the means to
implement a consistent self-contained federated messaging fabric. However, they
provide limited means of implementing custom server-side behaviour in Matrix
(e.g. gateways, filters, extensible hooks etc). The Application Service API (AS API)
defines a standard API to allow such extensible functionality to be implemented
irrespective of the underlying homeserver implementation.

.. TODO-spec
  Add in Client-Server services? Overview of bots? Seems weird to be in the spec
  given it is VERY implementation specific.

.. contents:: Table of Contents
.. sectnum::

Specification version
---------------------

This version of the specification is generated from
`matrix-doc <https://github.com/matrix-org/matrix-doc>`_ as of Git commit
`{{git_version}} <https://github.com/matrix-org/matrix-doc/tree/{{git_rev}}>`_.

Application Services
--------------------
Application services are passive and can only observe events from a given
homeserver (HS). They can inject events into rooms they are participating in.
They cannot prevent events from being sent, nor can they modify the content of
the event being sent. In order to observe events from a homeserver, the
homeserver needs to be configured to pass certain types of traffic to the
application service.  This is achieved by manually configuring the homeserver
with information about the application service (AS).

Registration
~~~~~~~~~~~~

.. NOTE::
  Previously, application services could register with a homeserver via HTTP
  APIs. This was removed as it was seen as a security risk. A compromised
  application service could re-register for a global ``*`` regex and sniff
  *all* traffic on the homeserver. To protect against this, application
  services now have to register via configuration files which are linked to
  the homeserver configuration file. The addition of configuration files
  allows homeserver admins to sanity check the registration for suspicious
  regex strings.

.. TODO
  Removing the API entirely is probably a mistake - having a standard cross-HS
  way of doing this stops ASes being coupled to particular HS implementations.
  A better solution would be to somehow mandate that the API done to avoid
  abuse.

Application services register "namespaces" of user IDs, room aliases and room IDs.
These namespaces are represented as regular expressions. An application service
is said to be "interested" in a given event if one of the IDs in the event match
the regular expression provided by the application service, such as the room having
an alias or ID in the relevant namespaces. Similarly, the application service is
said to be interested in a given event if one of the application service's namespaced
users is the target of the event, or is a joined member of the room where the event
occurred.

An application service can also state whether they should be the only ones who
can manage a specified namespace. This is referred to as an "exclusive"
namespace. An exclusive namespace prevents humans and other application
services from creating/deleting entities in that namespace. Typically,
exclusive namespaces are used when the rooms represent real rooms on
another service (e.g. IRC). Non-exclusive namespaces are used when the
application service is merely augmenting the room itself (e.g. providing
logging or searching facilities). Namespaces are represented by POSIX extended
regular expressions and look like:

.. code-block:: yaml

   users:
     - exclusive: true
       regex: "@_irc.freenode.net_.*"

Application services may define the following namespaces (with none being explicitly required):

+------------------+-----------------------------------------------------------+
| Name             | Description                                               |
+==================+===========================================================+
| users            | Events which are sent from certain users.                 |
+------------------+-----------------------------------------------------------+
| aliases          | Events which are sent in rooms with certain room aliases. |
+------------------+-----------------------------------------------------------+
| rooms            | Events which are sent in rooms with certain room IDs.     |
+------------------+-----------------------------------------------------------+

Each individual namespace MUST declare the following fields:

+------------------+-----------------------------------------------------------------------------------------------------------------------------------+
| Name             | Description                                                                                                                       |
+==================+===================================================================================================================================+
| exclusive        | **Required** A true or false value stating whether this application service has exclusive access to events within this namespace. |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------+
| regex            | **Required** A regular expression defining which values this namespace includes.                                                  |
+------------------+-----------------------------------------------------------------------------------------------------------------------------------+

Exclusive user and alias namespaces should begin with an underscore after the
sigil to avoid collisions with other users on the homeserver. Application
services should additionally attempt to identify the service they represent
in the reserved namespace. For example, ``@_irc_.*`` would be a good namespace
to register for an application service which deals with IRC.

The registration is represented by a series of key-value pairs, which this
specification will present as YAML. See below for the possible options along
with their explanation:

+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| Name             | Description                                                                                                                                        |
+==================+====================================================================================================================================================+
| id               | **Required.** A unique, user-defined ID of the application service which will never change.                                                        |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| url              | **Required.** The URL for the application service. May include a path after the domain name. Optionally set to ``null`` if no traffic is required. |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| as_token         | **Required.** A unique token for application services to use to authenticate requests to Homeservers.                                              |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| hs_token         | **Required.** A unique token for Homeservers to use to authenticate requests to application services.                                              |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| sender_localpart | **Required.** The localpart of the user associated with the application service.                                                                   |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| namespaces       | **Required.** A list of ``users``, ``aliases`` and ``rooms`` namespaces that the application service controls.                                     |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| rate_limited     | Whether requests from masqueraded users are rate-limited. The sender is excluded.                                                                  |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+
| protocols        | The external protocols which the application service provides (e.g. IRC).                                                                          |
+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------+

An example registration file for an IRC-bridging application service is below:

.. code-block:: yaml

    id: "IRC Bridge"
    url: "http://127.0.0.1:1234"
    as_token: "30c05ae90a248a4188e620216fa72e349803310ec83e2a77b34fe90be6081f46"
    hs_token: "312df522183efd404ec1cd22d2ffa4bbc76a8c1ccf541dd692eef281356bb74e"
    sender_localpart: "_irc_bot" # Will result in @_irc_bot:domain.com
    namespaces:
      users:
        - exclusive: true
          regex: "@_irc_bridge_.*"
      aliases:
        - exclusive: false 
          regex: "#_irc_bridge_.*"
      rooms: []

.. WARNING::
  If the homeserver in question has multiple application services, each
  ``as_token`` and ``id`` MUST be unique per application service as these are
  used to identify the application service. The homeserver MUST enforce this.

Homeserver -> Application Service API
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Pushing events
++++++++++++++

The application service API provides a transaction API for sending a list of
events. Each list of events includes a transaction ID, which works as follows:

::

 Typical
 HS ---> AS : Homeserver sends events with transaction ID T.
    <---    : AS sends back 200 OK.

 AS ACK Lost
 HS ---> AS : Homeserver sends events with transaction ID T.
    <-/-    : AS 200 OK is lost.
 HS ---> AS : Homeserver retries with the same transaction ID of T.
    <---    : AS sends back 200 OK. If the AS had processed these events
              already, it can NO-OP this request (and it knows if it is the same
              events based on the transaction ID).

The events sent to the application service should be linearised, as if they were
from the event stream. The homeserver MUST maintain a queue of transactions to
send to the AS. If the application service cannot be reached, the homeserver
SHOULD backoff exponentially until the application service is reachable again.
As application services cannot *modify* the events in any way, these requests can
be made without blocking other aspects of the homeserver. Homeservers MUST NOT
alter (e.g. add more) events they were going to send within that transaction ID
on retries, as the AS may have already processed the events.

{{transactions_as_http_api}}

Querying
++++++++

The application service API includes two querying APIs: for room aliases and for
user IDs. The application service SHOULD create the queried entity if it desires.
During this process, the application service is blocking the homeserver until the
entity is created and configured. If the homeserver does not receive a response
to this request, the homeserver should retry several times before timing out. This
should result in an HTTP status 408 "Request Timeout" on the client which initiated
this request (e.g. to join a room alias).

.. admonition:: Rationale

  Blocking the homeserver and expecting the application service to create the entity
  using the client-server API is simpler and more flexible than alternative methods
  such as returning an initial sync style JSON blob and get the HS to provision
  the room/user. This also meant that there didn't need to be a "backchannel" to inform
  the application service about information about the entity such as room ID to
  room alias mappings.

{{query_user_as_http_api}}

{{query_room_as_http_api}}


Third party networks
++++++++++++++++++++

Application services may declare which protocols they support via their registration
configuration for the homeserver. These networks are generally for third party services
such as IRC that the application service is managing. Application services may populate
a Matrix room directory for their registered protocols, as defined in the Client-Server
API Extensions.

Each protocol may have several "locations" (also known as "third party locations" or "3PLs").
A location within a protocol is a place in the third party network, such as an IRC channel.
Users of the third party network may also be represented by the application service.

Locations and users can be searched by fields defined by the application service, such
as by display name or other attribute. When clients request the homeserver to search
in a particular "network" (protocol), the search fields will be passed along to the
application service for filtering.

{{protocols_as_http_api}}


.. _create the user: `sect:asapi-permissions`_

Client-Server API Extensions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Application services can use a more powerful version of the
client-server API by identifying itself as an application service to the
homeserver.

Endpoints defined in this section MUST be supported by homeservers in the
client-server API as accessible only by application services.

Identity assertion
++++++++++++++++++
The client-server API infers the user ID from the ``access_token`` provided in
every request. To avoid the application service from having to keep track of each
user's access token, the application service should identify itself to the Client-Server
API by providing its ``as_token`` for the ``access_token`` alongside the user the
application service would like to masquerade as.

Inputs:
 - Application service token (``as_token``)
 - User ID in the AS namespace to act as.

Notes:
 - This applies to all aspects of the Client-Server API, except for Account Management.
 - The ``as_token`` is inserted into ``access_token`` which is usually where the
   client token is, such as via the query string or ``Authorization`` header. This 
   is done on purpose to allow application services to reuse client SDKs.
 - The ``access_token`` should be supplied through the ``Authorization`` header where
   possible to prevent the token appearing in HTTP request logs by accident.

The application service may specify the virtual user to act as through use of a
``user_id`` query string parameter on the request. The user specified in the query
string must be covered by one of the application service's ``user`` namespaces. If
the parameter is missing, the homeserver is to assume the application service intends
to act as the user implied by the ``sender_localpart`` property of the registration.

An example request would be::

 GET /_matrix/client/%CLIENT_MAJOR_VERSION%/account/whoami?user_id=@_irc_user:example.org
 Authorization: Bearer YourApplicationServiceTokenHere


Timestamp massaging
+++++++++++++++++++
The application service may want to inject events at a certain time (reflecting
the time on the network they are tracking e.g. irc, xmpp). Application services
need to be able to adjust the ``origin_server_ts`` value to do this.

Inputs:
 - Application service token (``as_token``)
 - Desired timestamp (in milliseconds since the unix epoch)

Notes:
 - This will only apply when sending events.

::

 PUT /_matrix/client/r0/rooms/!somewhere:domain.com/send/m.room.message/txnId?ts=1534535223283
  Authorization: Bearer YourApplicationServiceTokenHere

 Content: The event to send, as per the Client-Server API.

Server admin style permissions
++++++++++++++++++++++++++++++

.. _sect:asapi-permissions:

The homeserver needs to give the application service *full control* over its
namespace, both for users and for room aliases. This means that the AS should
be able to create/edit/delete any room alias in its namespace, as well as
create/delete any user in its namespace. No additional API changes need to be
made in order for control of room aliases to be granted to the AS. Creation of
users needs API changes in order to:

- Work around captchas.
- Have a 'passwordless' user.

This involves bypassing the registration flows entirely. This is achieved by
including the AS token on a ``/register`` request, along with a login type of
``m.login.application_service`` to set the desired user ID without a password.

::

  POST /_matrix/client/%CLIENT_MAJOR_VERSION%/register
  Authorization: Bearer YourApplicationServiceTokenHere

  Content:
  {
    type: "m.login.application_service",
    username: "_irc_example"
  }

Application services which attempt to create users or aliases *outside* of
their defined namespaces will receive an error code ``M_EXCLUSIVE``. Similarly,
normal users who attempt to create users or aliases *inside* an application
service-defined namespace will receive the same ``M_EXCLUSIVE`` error code,
but only if the application service has defined the namespace as ``exclusive``.

Using ``/sync`` and ``/events``
+++++++++++++++++++++++++++++++

Application services wishing to use ``/sync`` or ``/events`` from the Client-Server
API MUST do so with a virtual user (provide a ``user_id`` via the query string). It
is expected that the application service use the transactions pushed to it to
handle events rather than syncing with the user implied by ``sender_localpart``.

Application service room directories
++++++++++++++++++++++++++++++++++++

Application services can maintain their own room directories for their defined
third party protocols. These room directories may be accessed by clients through
additional parameters on the ``/publicRooms`` client-server endpoint.

{{appservice_room_directory_cs_http_api}}

Event fields
~~~~~~~~~~~~

.. TODO-TravisR: Fix this section to be a general "3rd party networks" section

We recommend that any events that originated from a remote network should
include an ``external_url`` field in their content to provide a way for Matrix
clients to link into the 'native' client from which the event originated.
For instance, this could contain the message-ID for emails/nntp posts, or a link
to a blog comment when bridging blog comment traffic in & out of Matrix.