Add MatrixRTC backend/services discovery endpoint (#18967)

Co-authored-by: Andrew Morgan <andrew@amorgan.xyz>

changelog.d/18967.feature

@@ -0,0 +1 @@
+Add experimental implementation for the latest draft of [MSC4143](https://github.com/matrix-org/matrix-spec-proposals/pull/4143).

docs/usage/configuration/config_documentation.md

@@ -2573,6 +2573,28 @@ Example configuration:
 turn_allow_guests: false
 ```
 ---
+### `matrix_rtc`
+
+*(object)* Options related to MatrixRTC. Defaults to `{}`.
+
+This setting has the following sub-options:
+
+* `transports` (array): A list of transport types and arguments to use for MatrixRTC connections. Defaults to `[]`.
+
+  Options for each entry include:
+
+  * `type` (string): The type of transport to use to connect to the selective forwarding unit (SFU).
+
+  * `livekit_service_url` (string): The base URL of the LiveKit service. Should only be used with LiveKit-based transports.
+
+Example configuration:
+```yaml
+matrix_rtc:
+  transports:
+  - type: livekit
+    livekit_service_url: https://matrix-rtc.example.com/livekit/jwt
+```
+---
 ## Registration
 
 Registration can be rate-limited using the parameters in the [Ratelimiting](#ratelimiting) section of this manual.

schema/synapse-config.schema.yaml

@@ -2884,6 +2884,35 @@ properties:
     default: true
     examples:
       - false
+  matrix_rtc:
+    type: object 
+    description: >-
+      Options related to MatrixRTC.
+    properties:
+      transports:
+        type: array
+        items:
+          type: object
+          required:
+            - type
+          properties:
+            type:
+              type: string
+              description: The type of transport to use to connect to the selective forwarding unit (SFU).
+              example: livekit
+            livekit_service_url:
+              type: string
+              description: >-
+                The base URL of the LiveKit service. Should only be used with LiveKit-based transports.
+              example: https://matrix-rtc.example.com/livekit/jwt
+        description:
+          A list of transport types and arguments to use for MatrixRTC connections.
+        default: []
+    default: {}
+    examples:
+      - transports:
+        - type: livekit
+          livekit_service_url: https://matrix-rtc.example.com/livekit/jwt
   enable_registration:
     type: boolean
     description: >-

synapse/config/_base.pyi

@@ -37,6 +37,7 @@ from synapse.config import (  # noqa: F401
     key,
     logger,
     mas,
+    matrixrtc,
     metrics,
     modules,
     oembed,
@@ -126,6 +127,7 @@ class RootConfig:
     auto_accept_invites: auto_accept_invites.AutoAcceptInvitesConfig
     user_types: user_types.UserTypesConfig
     mas: mas.MasConfig
+    matrix_rtc: matrixrtc.MatrixRtcConfig
 
     config_classes: List[Type["Config"]] = ...
     config_files: List[str]

synapse/config/experimental.py

@@ -556,6 +556,9 @@ class ExperimentalConfig(Config):
         # MSC4133: Custom profile fields
         self.msc4133_enabled: bool = experimental.get("msc4133_enabled", False)
 
+        # MSC4143: Matrix RTC Transport using Livekit Backend
+        self.msc4143_enabled: bool = experimental.get("msc4143_enabled", False)
+
         # MSC4169: Backwards-compatible redaction sending using `/send`
         self.msc4169_enabled: bool = experimental.get("msc4169_enabled", False)
 

synapse/config/homeserver.py

@@ -37,6 +37,7 @@ from .jwt import JWTConfig
 from .key import KeyConfig
 from .logger import LoggingConfig
 from .mas import MasConfig
+from .matrixrtc import MatrixRtcConfig
 from .metrics import MetricsConfig
 from .modules import ModulesConfig
 from .oembed import OembedConfig
@@ -80,6 +81,7 @@ class HomeServerConfig(RootConfig):
         OembedConfig,
         CaptchaConfig,
         VoipConfig,
+        MatrixRtcConfig,
         RegistrationConfig,
         AccountValidityConfig,
         MetricsConfig,

synapse/config/matrixrtc.py

@@ -0,0 +1,67 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+
+from typing import Any, Optional
+
+from pydantic import ValidationError
+
+from synapse._pydantic_compat import Field, StrictStr, validator
+from synapse.types import JsonDict
+from synapse.util.pydantic_models import ParseModel
+
+from ._base import Config, ConfigError
+
+
+class TransportConfigModel(ParseModel):
+    type: StrictStr
+
+    livekit_service_url: Optional[StrictStr] = Field(default=None)
+    """An optional livekit service URL. Only required if type is "livekit"."""
+
+    @validator("livekit_service_url", always=True)
+    def validate_livekit_service_url(cls, v: Any, values: dict) -> Any:
+        if values.get("type") == "livekit" and not v:
+            raise ValueError(
+                "You must set a `livekit_service_url` when using the 'livekit' transport."
+            )
+
+        return v
+
+
+class MatrixRtcConfigModel(ParseModel):
+    transports: list = []
+
+
+class MatrixRtcConfig(Config):
+    section = "matrix_rtc"
+
+    def read_config(
+        self, config: JsonDict, allow_secrets_in_config: bool, **kwargs: Any
+    ) -> None:
+        matrix_rtc = config.get("matrix_rtc", {})
+        if matrix_rtc is None:
+            matrix_rtc = {}
+
+        try:
+            parsed = MatrixRtcConfigModel(**matrix_rtc)
+        except ValidationError as e:
+            raise ConfigError(
+                "Could not validate matrix_rtc config",
+                ("matrix_rtc",),
+            ) from e
+
+        self.transports = parsed.transports

synapse/rest/__init__.py

@@ -42,6 +42,7 @@ from synapse.rest.client import (
     login,
     login_token_request,
     logout,
+    matrixrtc,
     mutual_rooms,
     notifications,
     openid,
@@ -89,6 +90,7 @@ CLIENT_SERVLET_FUNCTIONS: Tuple[RegisterServletsFunc, ...] = (
     presence.register_servlets,
     directory.register_servlets,
     voip.register_servlets,
+    matrixrtc.register_servlets,
     pusher.register_servlets,
     push_rule.register_servlets,
     logout.register_servlets,

synapse/rest/client/matrixrtc.py

@@ -0,0 +1,52 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+
+from typing import TYPE_CHECKING, Tuple
+
+from synapse.http.server import HttpServer
+from synapse.http.servlet import RestServlet
+from synapse.http.site import SynapseRequest
+from synapse.rest.client._base import client_patterns
+from synapse.types import JsonDict
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+
+class MatrixRTCRestServlet(RestServlet):
+    PATTERNS = client_patterns(r"/org\.matrix\.msc4143/rtc/transports$", releases=())
+    CATEGORY = "Client API requests"
+
+    def __init__(self, hs: "HomeServer"):
+        super().__init__()
+        self._hs = hs
+        self._auth = hs.get_auth()
+        self._transports = hs.config.matrix_rtc.transports
+
+    async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        # Require authentication for this endpoint.
+        await self._auth.get_user_by_req(request)
+
+        if self._transports:
+            return 200, {"rtc_transports": self._transports}
+
+        return 200, {}
+
+
+def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
+    if hs.config.experimental.msc4143_enabled:
+        MatrixRTCRestServlet(hs).register(http_server)

tests/rest/client/test_matrixrtc.py

@@ -0,0 +1,105 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+
+"""Tests REST events for /rtc/endpoints path."""
+
+from twisted.internet.testing import MemoryReactor
+
+from synapse.rest import admin
+from synapse.rest.client import login, matrixrtc, register, room
+from synapse.server import HomeServer
+from synapse.util.clock import Clock
+
+from tests.unittest import HomeserverTestCase, override_config
+
+PATH_PREFIX = "/_matrix/client/unstable/org.matrix.msc4143"
+RTC_ENDPOINT = {"type": "focusA", "required_field": "theField"}
+LIVEKIT_ENDPOINT = {
+    "type": "livekit",
+    "livekit_service_url": "https://livekit.example.com",
+}
+
+
+class MatrixRtcTestCase(HomeserverTestCase):
+    """Tests /rtc/transports Client-Server REST API."""
+
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+        register.register_servlets,
+        matrixrtc.register_servlets,
+    ]
+
+    def prepare(
+        self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer
+    ) -> None:
+        self.register_user("alice", "password")
+        self._alice_tok = self.login("alice", "password")
+
+    def test_matrixrtc_endpoint_not_enabled(self) -> None:
+        channel = self.make_request(
+            "GET", f"{PATH_PREFIX}/rtc/transports", access_token=self._alice_tok
+        )
+        self.assertEqual(404, channel.code, channel.json_body)
+        self.assertEqual(
+            "M_UNRECOGNIZED", channel.json_body["errcode"], channel.json_body
+        )
+
+    @override_config({"experimental_features": {"msc4143_enabled": True}})
+    def test_matrixrtc_endpoint_requires_authentication(self) -> None:
+        channel = self.make_request("GET", f"{PATH_PREFIX}/rtc/transports")
+        self.assertEqual(401, channel.code, channel.json_body)
+
+    @override_config(
+        {
+            "experimental_features": {"msc4143_enabled": True},
+            "matrix_rtc": {"transports": [RTC_ENDPOINT]},
+        }
+    )
+    def test_matrixrtc_endpoint_contains_expected_transport(self) -> None:
+        channel = self.make_request(
+            "GET", f"{PATH_PREFIX}/rtc/transports", access_token=self._alice_tok
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        self.assert_dict({"rtc_transports": [RTC_ENDPOINT]}, channel.json_body)
+
+    @override_config(
+        {
+            "experimental_features": {"msc4143_enabled": True},
+            "matrix_rtc": {"transports": []},
+        }
+    )
+    def test_matrixrtc_endpoint_no_transports_configured(self) -> None:
+        channel = self.make_request(
+            "GET", f"{PATH_PREFIX}/rtc/transports", access_token=self._alice_tok
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        self.assert_dict({}, channel.json_body)
+
+    @override_config(
+        {
+            "experimental_features": {"msc4143_enabled": True},
+            "matrix_rtc": {"transports": [LIVEKIT_ENDPOINT]},
+        }
+    )
+    def test_matrixrtc_endpoint_livekit_transport(self) -> None:
+        channel = self.make_request(
+            "GET", f"{PATH_PREFIX}/rtc/transports", access_token=self._alice_tok
+        )
+        self.assertEqual(200, channel.code, channel.json_body)
+        self.assert_dict({"rtc_transports": [LIVEKIT_ENDPOINT]}, channel.json_body)