/_synapse/admin/v1/send_server_notice 500s on use.

[TruncatedDinoSour]

Background information

• Dendrite version or git SHA: 0.14.1+40bef6a
• SQLite3 or Postgres?: Postgres
• Running in Docker?: Unprivileged user
• go version: go version go1.23.4 linux/amd64
• Client used (if applicable): Python requests

Description

• What is the problem: When making a standard request to the send_server_notice admin API endpoint, when server notices are enabled as well as profile picture is set (unsure if the profile picture one is related), the API returns an internal error.
• Who is affected: The administrator.
• How is this bug manifesting: By returning error responses as well as putting errors in logs.
• When did this first appear: When I first used this API, in v0.14.1.

Steps to reproduce

• Enable server notices:

  server_notices:
    enabled: true
    # The local part, display name and avatar URL (as a mxc:// URL) for the user that
    # will send the server notices. These are visible to all users on the deployment.
    local_part: "_server"
    display_name: "Ari-web -> Matrix (notifications)"
    avatar_url: "https://matrix.ari.lt/_matrix/media/r0/download/ari.lt/3c37dc4c292330bb27f05794190cf87b10715473c73c0d8d582babad22d44f9f"
    # The room name to be used when sending server notices. This room name will
    # appear in user clients.
    room_name: "Ari-web -> Matrix (notifications)"

Note: I notice I made it an https:// URL for the avatar. But this might still be a problem regardless. Fixing this does not fix the problem (tested with mxc://ari.lt/3c37dc4c292330bb27f05794190cf87b10715473c73c0d8d582babad22d44f9f).

• Make a standard request:

    pprint(
        requests.post(
            f"http://127.0.0.1:8008/_synapse/admin/v1/send_server_notice",
            json={
                "user_id": "@ari:ari.lt",
                "content": {
                    "msgtype": "m.text",
                    "body": msg,
                    "format": "org.matrix.custom.html",
                    "formatted_body": markdown.markdown(msg),
                },
            },
            headers={"Authorization": f"Bearer {token}"},
        ).json()
    )

• Get an error response ({'message': 'Internal Server Error'}) as well as the following log:

goroutine 372895 [running]:
runtime/debug.Stack()
        /usr/lib/go/src/runtime/debug/stack.go:26 +0x5e
github.com/element-hq/dendrite/internal/httputil.MakeExternalAPI.MakeJSONAPI.Protect.func3.1()
        /home/ari/go/pkg/mod/github.com/matrix-org/util@v0.0.0-20221111132719-399730281e66/json.go:98 +0x13c
panic({0x16ffbe0?, 0x26cf940?})
        /usr/lib/go/src/runtime/panic.go:785 +0x132
github.com/element-hq/dendrite/internal/httputil.MakeAuthAPI.func1.1()
        /home/ari/Src/dendrite/internal/httputil/httpapi.go:94 +0x4a
panic({0x16ffbe0?, 0x26cf940?})
        /usr/lib/go/src/runtime/panic.go:785 +0x132
github.com/matrix-org/util.ErrorResponse(...)
        /home/ari/go/pkg/mod/github.com/matrix-org/util@v0.0.0-20221111132719-399730281e66/json.go:52
github.com/element-hq/dendrite/clientapi/routing.SendServerNotice(0xc0252eaf00, 0xc0001909c8, 0xc000190a68, {0x7f106167a6f8, 0xc0004ee090}, {0x7f106167a580, 0xc00664cc60}, {0x1c02180, 0xc00a37a3a8}, 0xc00c0c2510, ...)
        /home/ari/Src/dendrite/clientapi/routing/server_notices.go:103 +0x600
github.com/element-hq/dendrite/clientapi/routing.Setup.func15(0xc0252eaf00, 0xc00c0c2510)
        /home/ari/Src/dendrite/clientapi/routing/routing.go:281 +0x138
github.com/element-hq/dendrite/internal/httputil.MakeAuthAPI.func1(0xc022d91b80)
        /home/ari/Src/dendrite/internal/httputil/httpapi.go:111 +0x58d
github.com/matrix-org/util.(*jsonRequestHandlerWrapper).OnIncomingRequest(0xc022d91a40?, 0x47335d?)
        /home/ari/go/pkg/mod/github.com/matrix-org/util@v0.0.0-20221111132719-399730281e66/json.go:79 +0x19
github.com/element-hq/dendrite/internal/httputil.MakeExternalAPI.MakeJSONAPI.func2({0x1bfd4f8, 0xc01c5c2d20}, 0x0?)
        /home/ari/go/pkg/mod/github.com/matrix-org/util@v0.0.0-20221111132719-399730281e66/json.go:141 +0xaa
github.com/element-hq/dendrite/internal/httputil.MakeExternalAPI.MakeJSONAPI.Protect.func3({0x1bfd4f8?, 0xc01c5c2d20?}, 0x192fee4?)
        /home/ari/go/pkg/mod/github.com/matrix-org/util@v0.0.0-20221111132719-399730281e66/json.go:103 +0x57
net/http.HandlerFunc.ServeHTTP(...)
        /usr/lib/go/src/net/http/server.go:2220
github.com/element-hq/dendrite/internal/httputil.MakeExternalAPI.func1({0x1bfd4f8?, 0xc01c5c2d20?}, 0xc022d91900)
        /home/ari/Src/dendrite/internal/httputil/httpapi.go:194 +0x3b2
net/http.HandlerFunc.ServeHTTP(0xc022d917c0?, {0x1bfd4f8?, 0xc01c5c2d20?}, 0x0?)
        /usr/lib/go/src/net/http/server.go:2220 +0x29
github.com/gorilla/mux.(*Router).ServeHTTP(0xc0000ed5c0, {0x1bfd4f8, 0xc01c5c2d20}, 0xc022d91680)
        /home/ari/go/pkg/mod/github.com/gorilla/mux@v1.8.0/mux.go:210 +0x1e2
github.com/gorilla/mux.(*Router).ServeHTTP(0xc00bd5e9c0, {0x1bfd4f8, 0xc01c5c2d20}, 0xc022d91400)
        /home/ari/go/pkg/mod/github.com/gorilla/mux@v1.8.0/mux.go:210 +0x1e2
net/http.serverHandler.ServeHTTP({0x1bf9860?}, {0x1bfd4f8?, 0xc01c5c2d20?}, 0x6?)
        /usr/lib/go/src/net/http/server.go:3210 +0x8e
net/http.(*conn).serve(0xc00c0c2360, {0x1c00160, 0xc00bfb7470})
        /usr/lib/go/src/net/http/server.go:2092 +0x5d0
created by net/http.(*Server).Serve in goroutine 2383
        /usr/lib/go/src/net/http/server.go:3360 +0x485

I.e. runtime error: invalid memory address or nil pointer dereference

Note: Dendrite is built on a separate machine it is running on.