Peeking via MSC2753 (#1370)

Initial implementation of MSC2753, as tested by https://github.com/matrix-org/sytest/pull/944.
Doesn't yet handle unpeeks, peeked EDUs, or history viz changing during a peek - these will follow.
https://github.com/matrix-org/dendrite/pull/1370 has full details.

clientapi/routing/joinroom.go

@@ -52,7 +52,7 @@ func JoinRoomByIDOrAlias(
 		}
 	}
 
-	// If content was provided in the request then incude that
+	// If content was provided in the request then include that
 	// in the request. It'll get used as a part of the membership
 	// event content.
 	_ = httputil.UnmarshalJSONRequest(req, &joinReq.Content)

clientapi/routing/peekroom.go

@@ -0,0 +1,79 @@
+// Copyright 2020 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.
+
+package routing
+
+import (
+	"net/http"
+
+	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/accounts"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+)
+
+func PeekRoomByIDOrAlias(
+	req *http.Request,
+	device *api.Device,
+	rsAPI roomserverAPI.RoomserverInternalAPI,
+	accountDB accounts.Database,
+	roomIDOrAlias string,
+) util.JSONResponse {
+	// if this is a remote roomIDOrAlias, we have to ask the roomserver (or federation sender?) to
+	// to call /peek and /state on the remote server.
+	// TODO: in future we could skip this if we know we're already participating in the room,
+	// but this is fiddly in case we stop participating in the room.
+
+	// then we create a local peek.
+	peekReq := roomserverAPI.PerformPeekRequest{
+		RoomIDOrAlias: roomIDOrAlias,
+		UserID:        device.UserID,
+		DeviceID:      device.ID,
+	}
+	peekRes := roomserverAPI.PerformPeekResponse{}
+
+	// Check to see if any ?server_name= query parameters were
+	// given in the request.
+	if serverNames, ok := req.URL.Query()["server_name"]; ok {
+		for _, serverName := range serverNames {
+			peekReq.ServerNames = append(
+				peekReq.ServerNames,
+				gomatrixserverlib.ServerName(serverName),
+			)
+		}
+	}
+
+	// Ask the roomserver to perform the peek.
+	rsAPI.PerformPeek(req.Context(), &peekReq, &peekRes)
+	if peekRes.Error != nil {
+		return peekRes.Error.JSONResponse()
+	}
+
+	// if this user is already joined to the room, we let them peek anyway
+	// (given they might be about to part the room, and it makes things less fiddly)
+
+	// Peeking stops if none of the devices who started peeking have been
+	// /syncing for a while, or if everyone who was peeking calls /leave
+	// (or /unpeek with a server_name param? or DELETE /peek?)
+	// on the peeked room.
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		// TODO: Put the response struct somewhere internal.
+		JSON: struct {
+			RoomID string `json:"room_id"`
+		}{peekRes.RoomID},
+	}
+}

clientapi/routing/routing.go

@@ -103,6 +103,17 @@ func Setup(
 			)
 		}),
 	).Methods(http.MethodPost, http.MethodOptions)
+	r0mux.Handle("/peek/{roomIDOrAlias}",
+		httputil.MakeAuthAPI(gomatrixserverlib.Peek, userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+			if err != nil {
+				return util.ErrorResponse(err)
+			}
+			return PeekRoomByIDOrAlias(
+				req, device, rsAPI, accountDB, vars["roomIDOrAlias"],
+			)
+		}),
+	).Methods(http.MethodPost, http.MethodOptions)
 	r0mux.Handle("/joined_rooms",
 		httputil.MakeAuthAPI("joined_rooms", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
 			return GetJoinedRooms(req, device, rsAPI)