Implement local redaction (#1182)

* Create redaction events and apply checks (but do not send them)

* Send redactions to the roomserver

* Linting

* Slightly better wording

clientapi/routing/redaction.go

@@ -0,0 +1,136 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// 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 (
+	"context"
+	"net/http"
+	"time"
+
+	"github.com/matrix-org/dendrite/clientapi/httputil"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	currentstateAPI "github.com/matrix-org/dendrite/currentstateserver/api"
+	"github.com/matrix-org/dendrite/internal/config"
+	"github.com/matrix-org/dendrite/internal/eventutil"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+)
+
+type redactionContent struct {
+	Reason string `json:"reason"`
+}
+
+type redactionResponse struct {
+	EventID string `json:"event_id"`
+}
+
+func SendRedaction(
+	req *http.Request, device *userapi.Device, roomID, eventID string, cfg *config.Dendrite,
+	rsAPI roomserverAPI.RoomserverInternalAPI, stateAPI currentstateAPI.CurrentStateInternalAPI,
+) util.JSONResponse {
+	resErr := checkMemberInRoom(req.Context(), stateAPI, device.UserID, roomID)
+	if resErr != nil {
+		return *resErr
+	}
+
+	ev := roomserverAPI.GetEvent(req.Context(), rsAPI, eventID)
+	if ev == nil {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.NotFound("unknown event ID"), // TODO: is it ok to leak existence?
+		}
+	}
+	if ev.RoomID() != roomID {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.NotFound("cannot redact event in another room"),
+		}
+	}
+
+	// "Users may redact their own events, and any user with a power level greater than or equal
+	// to the redact power level of the room may redact events there"
+	// https://matrix.org/docs/spec/client_server/r0.6.1#put-matrix-client-r0-rooms-roomid-redact-eventid-txnid
+	allowedToRedact := ev.Sender() == device.UserID
+	if !allowedToRedact {
+		plEvent := currentstateAPI.GetEvent(req.Context(), stateAPI, roomID, gomatrixserverlib.StateKeyTuple{
+			EventType: gomatrixserverlib.MRoomPowerLevels,
+			StateKey:  "",
+		})
+		if plEvent == nil {
+			return util.JSONResponse{
+				Code: 403,
+				JSON: jsonerror.Forbidden("You don't have permission to redact this event, no power_levels event in this room."),
+			}
+		}
+		pl, err := plEvent.PowerLevels()
+		if err != nil {
+			return util.JSONResponse{
+				Code: 403,
+				JSON: jsonerror.Forbidden(
+					"You don't have permission to redact this event, the power_levels event for this room is malformed so auth checks cannot be performed.",
+				),
+			}
+		}
+		allowedToRedact = pl.UserLevel(device.UserID) >= pl.Redact
+	}
+	if !allowedToRedact {
+		return util.JSONResponse{
+			Code: 403,
+			JSON: jsonerror.Forbidden("You don't have permission to redact this event, power level too low."),
+		}
+	}
+
+	var r redactionContent
+	resErr = httputil.UnmarshalJSONRequest(req, &r)
+	if resErr != nil {
+		return *resErr
+	}
+
+	// create the new event and set all the fields we can
+	builder := gomatrixserverlib.EventBuilder{
+		Sender:  device.UserID,
+		RoomID:  roomID,
+		Type:    gomatrixserverlib.MRoomRedaction,
+		Redacts: eventID,
+	}
+	err := builder.SetContent(r)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Error("builder.SetContent failed")
+		return jsonerror.InternalServerError()
+	}
+
+	var queryRes api.QueryLatestEventsAndStateResponse
+	e, err := eventutil.BuildEvent(req.Context(), &builder, cfg, time.Now(), rsAPI, &queryRes)
+	if err == eventutil.ErrRoomNoExists {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: jsonerror.NotFound("Room does not exist"),
+		}
+	}
+	_, err = roomserverAPI.SendEvents(context.Background(), rsAPI, []gomatrixserverlib.HeaderedEvent{*e}, cfg.Matrix.ServerName, nil)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Errorf("failed to SendEvents")
+		return jsonerror.InternalServerError()
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: redactionResponse{
+			EventID: e.EventID(),
+		},
+	}
+}