WIP: Add libp2p-go (#956)

* Add libp2p-go

* Some tweaks, tidying up

(cherry picked from commit 1a5bb121f8121c4f68a27abbf25a9a35a1b7c63e)

* Move p2p dockerfile

(cherry picked from commit 8d3bf44ea1bf37f950034e73bcdc315afdabe79a)

* Remove containsBackwardsExtremity

* Fix some linter errors, update some libp2p packages/calls, other tidying up

* Add -port for dendrite-p2p-demo

* Use instance name as key ID

* Remove P2P demo docker stuff, no longer needed now that we have SQLite

* Remove Dockerfile-p2p too

* Remove p2p logic from dendrite-monolith-server

* Inject publicRoomsDB in publicroomsapi

Inject publicRoomsDB instead of switching on base.libP2P.
See: https://github.com/matrix-org/dendrite/pull/956/files?file-filters%5B%5D=.go#r406276914

* Fix lint warning

* Extract mDNSListener from base.go

* Extract CreateFederationClient into demo

* Create P2PDendrite from BaseDendrite

Extract logic specific to P2PDendrite from base.go

* Set base.go to upstream/master

* Move pubsub to demo cmd

* Move PostgreswithDHT to cmd

* Remove unstable features

* Add copyrights

* Move libp2pvalidator into p2pdendrite

* Rename dendrite-p2p-demo -> dendrite-demo-libp2p

* Update copyrights

* go mod tidy

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

cmd/dendrite-demo-libp2p/mdnslistener.go

@@ -0,0 +1,63 @@
+// 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 main
+
+import (
+	"context"
+	"fmt"
+	"math"
+
+	"github.com/libp2p/go-libp2p-core/host"
+	"github.com/libp2p/go-libp2p-core/peer"
+	"github.com/matrix-org/dendrite/common/keydb"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+type mDNSListener struct {
+	keydb keydb.Database
+	host  host.Host
+}
+
+func (n *mDNSListener) HandlePeerFound(p peer.AddrInfo) {
+	if err := n.host.Connect(context.Background(), p); err != nil {
+		fmt.Println("Error adding peer", p.ID.String(), "via mDNS:", err)
+	}
+	if pubkey, err := p.ID.ExtractPublicKey(); err == nil {
+		raw, _ := pubkey.Raw()
+		if err := n.keydb.StoreKeys(
+			context.Background(),
+			map[gomatrixserverlib.PublicKeyLookupRequest]gomatrixserverlib.PublicKeyLookupResult{
+				{
+					ServerName: gomatrixserverlib.ServerName(p.ID.String()),
+					KeyID:      "ed25519:p2pdemo",
+				}: {
+					VerifyKey: gomatrixserverlib.VerifyKey{
+						Key: gomatrixserverlib.Base64String(raw),
+					},
+					ValidUntilTS: math.MaxUint64 >> 1,
+					ExpiredTS:    gomatrixserverlib.PublicKeyNotExpired,
+				},
+			},
+		); err != nil {
+			fmt.Println("Failed to store keys:", err)
+		}
+	}
+	fmt.Println("Discovered", len(n.host.Peerstore().Peers())-1, "other libp2p peer(s):")
+	for _, peer := range n.host.Peerstore().Peers() {
+		if peer != n.host.ID() {
+			fmt.Println("-", peer)
+		}
+	}
+}