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.

roomserver/internal/api.go

@@ -22,6 +22,7 @@ type RoomserverInternalAPI struct {
 	*query.Queryer
 	*perform.Inviter
 	*perform.Joiner
+	*perform.Peeker
 	*perform.Leaver
 	*perform.Publisher
 	*perform.Backfiller
@@ -83,6 +84,13 @@ func (r *RoomserverInternalAPI) SetFederationSenderAPI(fsAPI fsAPI.FederationSen
 		FSAPI:      r.fsAPI,
 		Inputer:    r.Inputer,
 	}
+	r.Peeker = &perform.Peeker{
+		ServerName: r.Cfg.Matrix.ServerName,
+		Cfg:        r.Cfg,
+		DB:         r.DB,
+		FSAPI:      r.fsAPI,
+		Inputer:    r.Inputer,
+	}
 	r.Leaver = &perform.Leaver{
 		Cfg:     r.Cfg,
 		DB:      r.DB,

roomserver/internal/perform/perform_peek.go

@@ -0,0 +1,206 @@
+// 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 perform
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	fsAPI "github.com/matrix-org/dendrite/federationsender/api"
+	"github.com/matrix-org/dendrite/internal/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/internal/input"
+	"github.com/matrix-org/dendrite/roomserver/storage"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
+)
+
+type Peeker struct {
+	ServerName gomatrixserverlib.ServerName
+	Cfg        *config.RoomServer
+	FSAPI      fsAPI.FederationSenderInternalAPI
+	DB         storage.Database
+
+	Inputer *input.Inputer
+}
+
+// PerformPeek handles peeking into matrix rooms, including over federation by talking to the federationsender.
+func (r *Peeker) PerformPeek(
+	ctx context.Context,
+	req *api.PerformPeekRequest,
+	res *api.PerformPeekResponse,
+) {
+	roomID, err := r.performPeek(ctx, req)
+	if err != nil {
+		perr, ok := err.(*api.PerformError)
+		if ok {
+			res.Error = perr
+		} else {
+			res.Error = &api.PerformError{
+				Msg: err.Error(),
+			}
+		}
+	}
+	res.RoomID = roomID
+}
+
+func (r *Peeker) performPeek(
+	ctx context.Context,
+	req *api.PerformPeekRequest,
+) (string, error) {
+	// FIXME: there's way too much duplication with performJoin
+	_, domain, err := gomatrixserverlib.SplitID('@', req.UserID)
+	if err != nil {
+		return "", &api.PerformError{
+			Code: api.PerformErrorBadRequest,
+			Msg:  fmt.Sprintf("Supplied user ID %q in incorrect format", req.UserID),
+		}
+	}
+	if domain != r.Cfg.Matrix.ServerName {
+		return "", &api.PerformError{
+			Code: api.PerformErrorBadRequest,
+			Msg:  fmt.Sprintf("User %q does not belong to this homeserver", req.UserID),
+		}
+	}
+	if strings.HasPrefix(req.RoomIDOrAlias, "!") {
+		return r.performPeekRoomByID(ctx, req)
+	}
+	if strings.HasPrefix(req.RoomIDOrAlias, "#") {
+		return r.performPeekRoomByAlias(ctx, req)
+	}
+	return "", &api.PerformError{
+		Code: api.PerformErrorBadRequest,
+		Msg:  fmt.Sprintf("Room ID or alias %q is invalid", req.RoomIDOrAlias),
+	}
+}
+
+func (r *Peeker) performPeekRoomByAlias(
+	ctx context.Context,
+	req *api.PerformPeekRequest,
+) (string, error) {
+	// Get the domain part of the room alias.
+	_, domain, err := gomatrixserverlib.SplitID('#', req.RoomIDOrAlias)
+	if err != nil {
+		return "", fmt.Errorf("Alias %q is not in the correct format", req.RoomIDOrAlias)
+	}
+	req.ServerNames = append(req.ServerNames, domain)
+
+	// Check if this alias matches our own server configuration. If it
+	// doesn't then we'll need to try a federated peek.
+	var roomID string
+	if domain != r.Cfg.Matrix.ServerName {
+		// The alias isn't owned by us, so we will need to try peeking using
+		// a remote server.
+		dirReq := fsAPI.PerformDirectoryLookupRequest{
+			RoomAlias:  req.RoomIDOrAlias, // the room alias to lookup
+			ServerName: domain,            // the server to ask
+		}
+		dirRes := fsAPI.PerformDirectoryLookupResponse{}
+		err = r.FSAPI.PerformDirectoryLookup(ctx, &dirReq, &dirRes)
+		if err != nil {
+			logrus.WithError(err).Errorf("error looking up alias %q", req.RoomIDOrAlias)
+			return "", fmt.Errorf("Looking up alias %q over federation failed: %w", req.RoomIDOrAlias, err)
+		}
+		roomID = dirRes.RoomID
+		req.ServerNames = append(req.ServerNames, dirRes.ServerNames...)
+	} else {
+		// Otherwise, look up if we know this room alias locally.
+		roomID, err = r.DB.GetRoomIDForAlias(ctx, req.RoomIDOrAlias)
+		if err != nil {
+			return "", fmt.Errorf("Lookup room alias %q failed: %w", req.RoomIDOrAlias, err)
+		}
+	}
+
+	// If the room ID is empty then we failed to look up the alias.
+	if roomID == "" {
+		return "", fmt.Errorf("Alias %q not found", req.RoomIDOrAlias)
+	}
+
+	// If we do, then pluck out the room ID and continue the peek.
+	req.RoomIDOrAlias = roomID
+	return r.performPeekRoomByID(ctx, req)
+}
+
+func (r *Peeker) performPeekRoomByID(
+	ctx context.Context,
+	req *api.PerformPeekRequest,
+) (roomID string, err error) {
+	roomID = req.RoomIDOrAlias
+
+	// Get the domain part of the room ID.
+	_, domain, err := gomatrixserverlib.SplitID('!', roomID)
+	if err != nil {
+		return "", &api.PerformError{
+			Code: api.PerformErrorBadRequest,
+			Msg:  fmt.Sprintf("Room ID %q is invalid: %s", roomID, err),
+		}
+	}
+
+	// If the server name in the room ID isn't ours then it's a
+	// possible candidate for finding the room via federation. Add
+	// it to the list of servers to try.
+	if domain != r.Cfg.Matrix.ServerName {
+		req.ServerNames = append(req.ServerNames, domain)
+	}
+
+	// If this room isn't world_readable, we reject.
+	// XXX: would be nicer to call this with NIDs
+	// XXX: we should probably factor out history_visibility checks into a common utility method somewhere
+	// which handles the default value etc.
+	var worldReadable = false
+	ev, _ := r.DB.GetStateEvent(ctx, roomID, "m.room.history_visibility", "")
+	if ev != nil {
+		content := map[string]string{}
+		if err = json.Unmarshal(ev.Content(), &content); err != nil {
+			util.GetLogger(ctx).WithError(err).Error("json.Unmarshal for history visibility failed")
+			return
+		}
+		if visibility, ok := content["history_visibility"]; ok {
+			worldReadable = visibility == "world_readable"
+		}
+	}
+
+	if !worldReadable {
+		return "", &api.PerformError{
+			Code: api.PerformErrorNotAllowed,
+			Msg:  "Room is not world-readable",
+		}
+	}
+
+	// TODO: handle federated peeks
+
+	err = r.Inputer.WriteOutputEvents(roomID, []api.OutputEvent{
+		{
+			Type: api.OutputTypeNewPeek,
+			NewPeek: &api.OutputNewPeek{
+				RoomID:   roomID,
+				UserID:   req.UserID,
+				DeviceID: req.DeviceID,
+			},
+		},
+	})
+	if err != nil {
+		return
+	}
+
+	// By this point, if req.RoomIDOrAlias contained an alias, then
+	// it will have been overwritten with a room ID by performPeekRoomByAlias.
+	// We should now include this in the response so that the CS API can
+	// return the right room ID.
+	return roomID, nil
+}