Initial Store & Forward Implementation (#2917)

This adds store & forward relays into dendrite for p2p.
A few things have changed:
- new relay api serves new http endpoints for s&f federation
- updated outbound federation queueing which will attempt to forward
using s&f if appropriate
- database entries to track s&f relays for other nodes

relayapi/routing/relaytxn.go

@@ -0,0 +1,74 @@
+// Copyright 2022 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 (
+	"encoding/json"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/relayapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
+)
+
+type RelayTransactionResponse struct {
+	Transaction   gomatrixserverlib.Transaction `json:"transaction"`
+	EntryID       int64                         `json:"entry_id,omitempty"`
+	EntriesQueued bool                          `json:"entries_queued"`
+}
+
+// GetTransactionFromRelay implements /_matrix/federation/v1/relay_txn/{userID}
+// This endpoint can be extracted into a separate relay server service.
+func GetTransactionFromRelay(
+	httpReq *http.Request,
+	fedReq *gomatrixserverlib.FederationRequest,
+	relayAPI api.RelayInternalAPI,
+	userID gomatrixserverlib.UserID,
+) util.JSONResponse {
+	logrus.Infof("Handling relay_txn for %s", userID.Raw())
+
+	previousEntry := gomatrixserverlib.RelayEntry{}
+	if err := json.Unmarshal(fedReq.Content(), &previousEntry); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: jsonerror.BadJSON("invalid json provided"),
+		}
+	}
+	if previousEntry.EntryID < 0 {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: jsonerror.BadJSON("Invalid entry id provided. Must be >= 0."),
+		}
+	}
+	logrus.Infof("Previous entry provided: %v", previousEntry.EntryID)
+
+	response, err := relayAPI.QueryTransactions(httpReq.Context(), userID, previousEntry)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+		}
+	}
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: RelayTransactionResponse{
+			Transaction:   response.Transaction,
+			EntryID:       response.EntryID,
+			EntriesQueued: response.EntriesQueued,
+		},
+	}
+}