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/storage/interface.go

@@ -0,0 +1,47 @@
+// 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 storage
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/federationapi/storage/shared/receipt"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+type Database interface {
+	// Adds a new transaction to the queue json table.
+	// Adding a duplicate transaction will result in a new row being added and a new unique nid.
+	// return: unique nid representing this entry.
+	StoreTransaction(ctx context.Context, txn gomatrixserverlib.Transaction) (*receipt.Receipt, error)
+
+	// Adds a new transaction_id: server_name mapping with associated json table nid to the queue
+	// entry table for each provided destination.
+	AssociateTransactionWithDestinations(ctx context.Context, destinations map[gomatrixserverlib.UserID]struct{}, transactionID gomatrixserverlib.TransactionID, dbReceipt *receipt.Receipt) error
+
+	// Removes every server_name: receipt pair provided from the queue entries table.
+	// Will then remove every entry for each receipt provided from the queue json table.
+	// If any of the entries don't exist in either table, nothing will happen for that entry and
+	// an error will not be generated.
+	CleanTransactions(ctx context.Context, userID gomatrixserverlib.UserID, receipts []*receipt.Receipt) error
+
+	// Gets the oldest transaction for the provided server_name.
+	// If no transactions exist, returns nil and no error.
+	GetTransaction(ctx context.Context, userID gomatrixserverlib.UserID) (*gomatrixserverlib.Transaction, *receipt.Receipt, error)
+
+	// Gets the number of transactions being stored for the provided server_name.
+	// If the server doesn't exist in the database then 0 is returned with no error.
+	GetTransactionCount(ctx context.Context, userID gomatrixserverlib.UserID) (int64, error)
+}