diff --git a/p2p/discover/udp.go b/p2p/discover/udp.go index 2b215b45c..539ccd460 100644 --- a/p2p/discover/udp.go +++ b/p2p/discover/udp.go @@ -363,7 +363,31 @@ const ( headSize = macSize + sigSize // space of packet frame data ) -var headSpace = make([]byte, headSize) +var ( + headSpace = make([]byte, headSize) + + // Neighbors responses are sent across multiple packets to + // stay below the 1280 byte limit. We compute the maximum number + // of entries by stuffing a packet until it grows too large. + maxNeighbors int +) + +func init() { + p := neighbors{Expiration: ^uint64(0)} + maxSizeNode := rpcNode{IP: make(net.IP, 16), UDP: ^uint16(0), TCP: ^uint16(0)} + for n := 0; ; n++ { + p.Nodes = append(p.Nodes, maxSizeNode) + size, _, err := rlp.EncodeToReader(p) + if err != nil { + // If this ever happens, it will be caught by the unit tests. + panic("cannot encode: " + err.Error()) + } + if headSize+size+1 >= 1280 { + maxNeighbors = n + break + } + } +} func (t *udp) send(toaddr *net.UDPAddr, ptype byte, req interface{}) error { packet, err := encodePacket(t.priv, ptype, req) @@ -402,6 +426,9 @@ func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte, // readLoop runs in its own goroutine. it handles incoming UDP packets. func (t *udp) readLoop() { defer t.conn.Close() + // Discovery packets are defined to be no larger than 1280 bytes. + // Packets larger than this size will be cut at the end and treated + // as invalid because their hash won't match. buf := make([]byte, 1280) for { nbytes, from, err := t.conn.ReadFromUDP(buf) @@ -504,20 +531,15 @@ func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte closest := t.closest(target, bucketSize).entries t.mutex.Unlock() - // TODO: this conversion could use a cached version of the slice - closestrpc := make([]rpcNode, len(closest)) + p := neighbors{Expiration: uint64(time.Now().Add(expiration).Unix())} + // Send neighbors in chunks with at most maxNeighbors per packet + // to stay below the 1280 byte limit. for i, n := range closest { - closestrpc[i] = nodeToRPC(n) - } - t.send(from, neighborsPacket, neighbors{ - Nodes: closestrpc[:13], - Expiration: uint64(time.Now().Add(expiration).Unix()), - }) - if len(closestrpc) > 13 { - t.send(from, neighborsPacket, neighbors{ - Nodes: closestrpc[13:], - Expiration: uint64(time.Now().Add(expiration).Unix()), - }) + p.Nodes = append(p.Nodes, nodeToRPC(n)) + if len(p.Nodes) == maxNeighbors || i == len(closest)-1 { + t.send(from, neighborsPacket, p) + p.Nodes = p.Nodes[:0] + } } return nil } diff --git a/p2p/discover/udp_test.go b/p2p/discover/udp_test.go index 7bf6df5ab..11fa31d7c 100644 --- a/p2p/discover/udp_test.go +++ b/p2p/discover/udp_test.go @@ -164,26 +164,21 @@ func TestUDP_findnode(t *testing.T) { // check that closest neighbors are returned. test.packetIn(nil, findnodePacket, &findnode{Target: testTarget, Expiration: futureExp}) expected := test.table.closest(targetHash, bucketSize) - test.waitPacketOut(func(p *neighbors) { - if len(p.Nodes) != 13 { - t.Errorf("wrong number of results: got %d, want %d", len(p.Nodes), bucketSize) - } - for i := range p.Nodes { - if p.Nodes[i].ID != expected.entries[i].ID { - t.Errorf("result mismatch at %d:\n got: %v\n want: %v", i, p.Nodes[i], expected.entries[i]) + + waitNeighbors := func(want []*Node) { + test.waitPacketOut(func(p *neighbors) { + if len(p.Nodes) != len(want) { + t.Errorf("wrong number of results: got %d, want %d", len(p.Nodes), bucketSize) } - } - }) - test.waitPacketOut(func(p *neighbors) { - if len(p.Nodes) != 3 { - t.Errorf("wrong number of results: got %d, want %d", len(p.Nodes), bucketSize) - } - for i := range p.Nodes { - if p.Nodes[i].ID != expected.entries[i + 13].ID { - t.Errorf("result mismatch at %d:\n got: %v\n want: %v", i, p.Nodes[i], expected.entries[i]) + for i := range p.Nodes { + if p.Nodes[i].ID != want[i].ID { + t.Errorf("result mismatch at %d:\n got: %v\n want: %v", i, p.Nodes[i], expected.entries[i]) + } } - } - }) + }) + } + waitNeighbors(expected.entries[:maxNeighbors]) + waitNeighbors(expected.entries[maxNeighbors:]) } func TestUDP_findnodeMultiReply(t *testing.T) {