Implement client single event retrieval - #671

Spec: https://matrix.org/docs/spec/client_server/r0.4.0.html#get-matrix-client-r0-rooms-roomid-event-eventid

Signed-off-by: Alex Chen <minecnly@gmail.com>

clientapi/routing/routing.go

@@ -116,6 +116,12 @@ func Setup(
 				nil, cfg, queryAPI, producer, transactionsCache)
 		}),
 	).Methods(http.MethodPut, http.MethodOptions)
+	r0mux.Handle("/rooms/{roomID}/event/{eventID}",
+		common.MakeAuthAPI("room_get_event", authData, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
+			vars := mux.Vars(req)
+			return GetEvent(req, device, vars["roomID"], vars["eventID"], cfg, queryAPI, federation, keyRing)
+		}),
+	).Methods(http.MethodGet, http.MethodOptions)
 	r0mux.Handle("/rooms/{roomID}/state/{eventType:[^/]+/?}",
 		common.MakeAuthAPI("send_message", authData, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
 			vars := mux.Vars(req)

src/github.com/matrix-org/dendrite/clientapi/routing/getevent.go

@@ -0,0 +1,151 @@
+// Copyright 2017 Vector Creations 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 (
+	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
+	"github.com/matrix-org/dendrite/clientapi/httputil"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"net/http"
+)
+
+var (
+	unknownEventResponse = util.JSONResponse{
+		Code: http.StatusNotFound,
+		JSON: jsonerror.NotFound("The event was not found or you do not have permission to read this event."),
+	}
+)
+
+type getEventRequest struct {
+	req            *http.Request
+	device         *authtypes.Device
+	roomID         string
+	eventID        string
+	cfg            config.Dendrite
+	federation     *gomatrixserverlib.FederationClient
+	keyRing        gomatrixserverlib.KeyRing
+	requestedEvent gomatrixserverlib.Event
+}
+
+// GetEvent implements GET /_matrix/client/r0/rooms/{roomId}/event/{eventId}
+// https://matrix.org/docs/spec/client_server/r0.4.0.html#get-matrix-client-r0-rooms-roomid-event-eventid
+func GetEvent(
+	req *http.Request,
+	device *authtypes.Device,
+	roomID string,
+	eventID string,
+	cfg config.Dendrite,
+	queryAPI api.RoomserverQueryAPI,
+	federation *gomatrixserverlib.FederationClient,
+	keyRing gomatrixserverlib.KeyRing,
+) util.JSONResponse {
+	eventsReq := api.QueryEventsByIDRequest{
+		EventIDs: []string{eventID},
+	}
+	var eventsResp api.QueryEventsByIDResponse
+	err := queryAPI.QueryEventsByID(req.Context(), &eventsReq, &eventsResp)
+	if err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	if len(eventsResp.Events) == 0 {
+		// TODO: Event not found locally. May need a federation query here.
+		return unknownEventResponse
+	}
+
+	r := getEventRequest{
+		req:            req,
+		device:         device,
+		roomID:         roomID,
+		eventID:        eventID,
+		cfg:            cfg,
+		federation:     federation,
+		keyRing:        keyRing,
+		requestedEvent: eventsResp.Events[0],
+	}
+
+	stateNeeded := gomatrixserverlib.StateNeededForAuth([]gomatrixserverlib.Event{r.requestedEvent})
+	stateReq := api.QueryStateAfterEventsRequest{
+		RoomID:       r.requestedEvent.RoomID(),
+		PrevEventIDs: r.requestedEvent.PrevEventIDs(),
+		StateToFetch: stateNeeded.Tuples(),
+	}
+	var stateResp api.QueryStateAfterEventsResponse
+	if err := queryAPI.QueryStateAfterEvents(req.Context(), &stateReq, &stateResp); err != nil {
+		return httputil.LogThenError(req, err)
+	}
+
+	if !stateResp.RoomExists {
+		return unknownEventResponse
+	}
+
+	if !stateResp.PrevEventsExist {
+		// Missing some events locally so stateResp.StateEvents will be unavailable.
+		// Do a federation query in hope of getting the state events needed.
+		return r.proceedWithMissingState()
+	}
+
+	return r.proceedWithStateEvents(stateResp.StateEvents)
+}
+
+func (r *getEventRequest) proceedWithMissingState() util.JSONResponse {
+	// It's not guaranteed that the server we query has these events.
+	_, domain, err := gomatrixserverlib.SplitID('$', r.eventID)
+	if err != nil {
+		return httputil.LogThenError(r.req, err)
+	}
+
+	if domain == r.cfg.Matrix.ServerName {
+		// Don't send a federation query to self
+		return unknownEventResponse
+	}
+
+	state, err := r.federation.LookupState(r.req.Context(), domain, r.roomID, r.eventID)
+	if err != nil {
+		return httputil.LogThenError(r.req, err)
+	}
+
+	if err := state.Check(r.req.Context(), r.keyRing); err != nil {
+		return httputil.LogThenError(r.req, err)
+	}
+
+	return r.proceedWithStateEvents(state.StateEvents)
+}
+
+func (r *getEventRequest) proceedWithStateEvents(stateEvents []gomatrixserverlib.Event) util.JSONResponse {
+	allowed := false
+	for _, stateEvent := range stateEvents {
+		if stateEvent.StateKeyEquals(r.device.UserID) {
+			membership, err := stateEvent.Membership()
+			if err == nil && membership == "join" {
+				allowed = true
+				break
+			}
+		}
+	}
+
+	if allowed {
+		return util.JSONResponse{
+			Code: http.StatusOK,
+			JSON: r.requestedEvent,
+		}
+	}
+
+	return unknownEventResponse
+}