From c03625073165240684de4d59568d6157c50b22d2 Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Sat, 11 Mar 2023 16:24:18 +0200
Subject: [PATCH] Implement MSC2659

---
 appservice/http.go | 12 ++++++++++++
 bridge/bridge.go   | 41 ++++++++++++++++++++++++++++++++++-------
 client.go          | 11 +++++++++++
 error.go           |  5 +++++
 responses.go       |  4 ++++
 5 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/appservice/http.go b/appservice/http.go
index 21fc0961..85b2893a 100644
--- a/appservice/http.go
+++ b/appservice/http.go
@@ -31,6 +31,8 @@ func (as *AppService) Start() {
 	as.Router.HandleFunc("/_matrix/app/v1/transactions/{txnID}", as.PutTransaction).Methods(http.MethodPut)
 	as.Router.HandleFunc("/_matrix/app/v1/rooms/{roomAlias}", as.GetRoom).Methods(http.MethodGet)
 	as.Router.HandleFunc("/_matrix/app/v1/users/{userID}", as.GetUser).Methods(http.MethodGet)
+	as.Router.HandleFunc("/_matrix/app/v1/ping", as.PostPing).Methods(http.MethodPost)
+	as.Router.HandleFunc("/_matrix/app/unstable/fi.mau.msc2659/ping", as.PostPing).Methods(http.MethodPost)
 	as.Router.HandleFunc("/_matrix/mau/live", as.GetLive).Methods(http.MethodGet)
 	as.Router.HandleFunc("/_matrix/mau/ready", as.GetReady).Methods(http.MethodGet)
 
@@ -289,6 +291,16 @@ func (as *AppService) GetUser(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (as *AppService) PostPing(w http.ResponseWriter, r *http.Request) {
+	if !as.CheckServerToken(w, r) {
+		return
+	}
+
+	w.Header().Add("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	w.Write([]byte("{}"))
+}
+
 func (as *AppService) GetLive(w http.ResponseWriter, r *http.Request) {
 	w.Header().Add("Content-Type", "application/json")
 	if as.Live {
diff --git a/bridge/bridge.go b/bridge/bridge.go
index c3e60c1c..63f12e90 100644
--- a/bridge/bridge.go
+++ b/bridge/bridge.go
@@ -7,6 +7,7 @@
 package bridge
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/url"
@@ -291,15 +292,40 @@ func (br *Bridge) ensureConnection() {
 			}
 			br.ZLog.Err(err).Msg("Failed to connect to homeserver, retrying in 10 seconds...")
 			time.Sleep(10 * time.Second)
+			continue
 		} else if resp.UserID != br.Bot.UserID {
 			br.ZLog.WithLevel(zerolog.FatalLevel).
 				Stringer("got_user_id", resp.UserID).
 				Stringer("expected_user_id", br.Bot.UserID).
 				Msg("Unexpected user ID in whoami call")
 			os.Exit(17)
+		}
+
+		if br.SpecVersions.UnstableFeatures["fi.mau.msc2659"] && br.AS.Host.Port != 0 {
+			resp, err := br.Bot.AppservicePing()
+			if err != nil {
+				evt := br.ZLog.WithLevel(zerolog.FatalLevel).Err(err)
+				var httpErr mautrix.HTTPError
+				if errors.As(err, &httpErr) && httpErr.RespError != nil {
+					if val, ok := httpErr.RespError.ExtraData["body"].(string); ok {
+						val = strings.TrimSpace(val)
+						valBytes := []byte(val)
+						if json.Valid(valBytes) {
+							evt.RawJSON("body", valBytes)
+						} else {
+							evt.Str("body", val)
+						}
+					}
+				}
+				evt.Msg("Homeserver -> bridge connection is not working")
+				os.Exit(13)
+			}
+			br.ZLog.Debug().Int64("duration_ms", resp.DurationMS).Msg("Homeserver -> bridge connection works")
 		} else {
-			break
+			br.ZLog.Debug().Msg("Homeserver does not support checking status of homeserver -> bridge connection")
 		}
+
+		break
 	}
 }
 
@@ -518,6 +544,13 @@ func (br *Bridge) start() {
 		br.LogDBUpgradeErrorAndExit("matrix_state", err)
 	}
 
+	if br.AS.Host.Port != 0 {
+		br.ZLog.Debug().Msg("Starting application service HTTP server")
+		go br.AS.Start()
+	} else {
+		br.ZLog.Debug().Msg("Appservice port not configured, not starting HTTP server")
+	}
+
 	br.ZLog.Debug().Msg("Checking connection to homeserver")
 	br.ensureConnection()
 	go br.fetchMediaConfig()
@@ -530,12 +563,6 @@ func (br *Bridge) start() {
 		}
 	}
 
-	if br.AS.Host.Port != 0 {
-		br.ZLog.Debug().Msg("Starting application service HTTP server")
-		go br.AS.Start()
-	} else {
-		br.ZLog.Debug().Msg("Appservice port not configured, not starting HTTP server")
-	}
 	br.ZLog.Debug().Msg("Starting event processor")
 	br.EventProcessor.Start()
 
diff --git a/client.go b/client.go
index 27a299dc..ed94b802 100644
--- a/client.go
+++ b/client.go
@@ -1963,6 +1963,17 @@ func (cli *Client) BatchSend(roomID id.RoomID, req *ReqBatchSend) (resp *RespBat
 	return
 }
 
+func (cli *Client) AppservicePing() (resp *RespAppservicePing, err error) {
+	_, err = cli.MakeFullRequest(FullRequest{
+		Method:       http.MethodPost,
+		URL:          cli.BuildClientURL("unstable", "fi.mau.msc2659", "appservice", "ping"),
+		ResponseJSON: &resp,
+		// This endpoint intentionally returns 50x, so don't retry
+		MaxAttempts: 1,
+	})
+	return
+}
+
 func (cli *Client) BeeperMergeRooms(req *ReqBeeperMergeRoom) (resp *RespBeeperMergeRoom, err error) {
 	urlPath := cli.BuildClientURL("unstable", "com.beeper.chatmerging", "merge")
 	_, err = cli.MakeRequest(http.MethodPost, urlPath, req, &resp)
diff --git a/error.go b/error.go
index 36fa74f5..9c5e8a0e 100644
--- a/error.go
+++ b/error.go
@@ -60,6 +60,11 @@ var (
 	MIncompatibleRoomVersion = RespError{ErrCode: "M_INCOMPATIBLE_ROOM_VERSION"}
 	// The client specified a parameter that has the wrong value.
 	MInvalidParam = RespError{ErrCode: "M_INVALID_PARAM"}
+
+	MSC2659URLNotSet         = RespError{ErrCode: "FI.MAU.MSC2659_URL_NOT_SET"}
+	MSC2659BadStatus         = RespError{ErrCode: "FI.MAU.MSC2659_BAD_STATUS"}
+	MSC2659ConnectionTimeout = RespError{ErrCode: "FI.MAU.MSC2659_CONNECTION_TIMEOUT"}
+	MSC2659ConnectionFailed  = RespError{ErrCode: "FI.MAU.MSC2659_CONNECTION_FAILED"}
 )
 
 // HTTPError An HTTP Error response, which may wrap an underlying native Go Error.
diff --git a/responses.go b/responses.go
index e6b7b61e..ac6bbfe7 100644
--- a/responses.go
+++ b/responses.go
@@ -552,6 +552,10 @@ type StrippedStateWithTime struct {
 	Timestamp jsontime.UnixMilli `json:"origin_server_ts"`
 }
 
+type RespAppservicePing struct {
+	DurationMS int64 `json:"duration"`
+}
+
 type RespBeeperMergeRoom RespCreateRoom
 
 type RespBeeperSplitRoom struct {