--- title: "Application Service API" weight: 30 type: docs --- 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. ## Application Services Application services are passive and can only observe events from homeserver. 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. ### Registration {{% boxes/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. {{% /boxes/note %}} 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: users: - exclusive: true regex: "@_irc_bridge_.*" 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: 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:example.org namespaces: users: - exclusive: true regex: "@_irc_bridge_.*" aliases: - exclusive: false regex: "#_irc_bridge_.*" rooms: [] {{% boxes/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. {{% /boxes/warning %}} ### Homeserver -> Application Service API #### Authorization Homeservers MUST include a query parameter named `access_token` containing the `hs_token` from the application service's registration when making requests to the application service. Application services MUST verify the provided `access_token` matches their known `hs_token`, failing the request with an `M_FORBIDDEN` error if it does not match. #### Legacy routes Previous drafts of the application service specification had a mix of endpoints that have been used in the wild for a significant amount of time. The application service specification now defines a version on all endpoints to be more compatible with the rest of the Matrix specification and the future. Homeservers should attempt to use the specified endpoints first when communicating with application services. However, if the application service receives an HTTP status code that does not indicate success (i.e.: 404, 500, 501, etc) then the homeserver should fall back to the older endpoints for the application service. The older endpoints have the exact same request body and response format, they just belong at a different path. The equivalent path for each is as follows: - `/_matrix/app/v1/transactions/{txnId}` should fall back to `/transactions/{txnId}` - `/_matrix/app/v1/users/{userId}` should fall back to `/users/{userId}` - `/_matrix/app/v1/rooms/{roomAlias}` should fall back to `/rooms/{roomAlias}` - `/_matrix/app/v1/thirdparty/protocol/{protocol}` should fall back to `/_matrix/app/unstable/thirdparty/protocol/{protocol}` - `/_matrix/app/v1/thirdparty/user/{user}` should fall back to `/_matrix/app/unstable/thirdparty/user/{user}` - `/_matrix/app/v1/thirdparty/location/{location}` should fall back to `/_matrix/app/unstable/thirdparty/location/{location}` - `/_matrix/app/v1/thirdparty/user` should fall back to `/_matrix/app/unstable/thirdparty/user` - `/_matrix/app/v1/thirdparty/location` should fall back to `/_matrix/app/unstable/thirdparty/location` Homeservers should periodically try again for the newer endpoints because the application service may have been updated. #### 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. <--- : Application Service 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. <--- : Application Service 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 application service. 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 application service may have already processed the events. {{% http-api spec="application-service" api="transactions" %}} #### 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). {{% boxes/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. {{% /boxes/rationale %}} {{% http-api spec="application-service" api="query_user" %}} {{% http-api spec="application-service" api="query_room" %}} #### 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. {{% http-api spec="application-service" api="protocols" %}} ### 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 Previous drafts of the Application Service API permitted application services to alter the timestamp of their sent events by providing a `ts` query parameter when sending an event. This API has been excluded from the first release due to design concerns, however some servers may still support the feature. Please visit [issue \#1585](https://github.com/matrix-org/matrix-doc/issues/1585) for more information. #### Server admin style 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. {{% http-api spec="client-server" api="appservice_room_directory" %}} ### Referencing messages from a third party network Application services should include an `external_url` in the `content` of events it emits to indicate where the message came from. This typically applies to application services that bridge other networks into Matrix, such as IRC, where an HTTP URL may be available to reference. Clients should provide users with a way to access the `external_url` if it is present. Clients should additionally ensure the URL has a scheme of `https` or `http` before making use of it. The presence of an `external_url` on an event does not necessarily mean the event was sent from an application service. Clients should be wary of the URL contained within, as it may not be a legitimate reference to the event's source.