// Copyright 2015 The go-ethereum Authors // This file is part of the go-ethereum library. // // The go-ethereum library is free software: you can redistribute it and/or modify // it under the terms of the GNU Lesser General Public License as published by // the Free Software Foundation, either version 3 of the License, or // (at your option) any later version. // // The go-ethereum library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU Lesser General Public License for more details. // // You should have received a copy of the GNU Lesser General Public License // along with the go-ethereum library. If not, see . package discover import ( "bytes" "crypto/ecdsa" "encoding/binary" "encoding/hex" "errors" "fmt" "io" "math/rand" "net" "path/filepath" "reflect" "runtime" "sync" "testing" "time" "github.com/davecgh/go-spew/spew" "github.com/ethereum/go-ethereum/common" "github.com/ethereum/go-ethereum/crypto" "github.com/ethereum/go-ethereum/rlp" ) func init() { spew.Config.DisableMethods = true } // This test checks that isPacketTooBig correctly identifies // errors that result from receiving a UDP packet larger // than the supplied receive buffer. func TestIsPacketTooBig(t *testing.T) { listener, err := net.ListenPacket("udp", "127.0.0.1:0") if err != nil { t.Fatal(err) } defer listener.Close() sender, err := net.Dial("udp", listener.LocalAddr().String()) if err != nil { t.Fatal(err) } defer sender.Close() sendN := 1800 recvN := 300 for i := 0; i < 20; i++ { go func() { buf := make([]byte, sendN) for i := range buf { buf[i] = byte(i) } sender.Write(buf) }() buf := make([]byte, recvN) listener.SetDeadline(time.Now().Add(1 * time.Second)) n, _, err := listener.ReadFrom(buf) if err != nil { if nerr, ok := err.(net.Error); ok && nerr.Timeout() { continue } if !isPacketTooBig(err) { t.Fatal("unexpected read error:", spew.Sdump(err)) } continue } if n != recvN { t.Fatalf("short read: %d, want %d", n, recvN) } for i := range buf { if buf[i] != byte(i) { t.Fatalf("error in pattern") break } } } } // shared test variables var ( futureExp = uint64(time.Now().Add(10 * time.Hour).Unix()) testTarget = NodeID{0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1} testRemote = rpcEndpoint{IP: net.ParseIP("1.1.1.1").To4(), UDP: 1, TCP: 2} testLocalAnnounced = rpcEndpoint{IP: net.ParseIP("2.2.2.2").To4(), UDP: 3, TCP: 4} testLocal = rpcEndpoint{IP: net.ParseIP("3.3.3.3").To4(), UDP: 5, TCP: 6} ) type udpTest struct { t *testing.T pipe *dgramPipe table *Table udp *udp sent [][]byte localkey, remotekey *ecdsa.PrivateKey remoteaddr *net.UDPAddr } func newUDPTest(t *testing.T) *udpTest { test := &udpTest{ t: t, pipe: newpipe(), localkey: newkey(), remotekey: newkey(), remoteaddr: &net.UDPAddr{IP: net.IP{1, 2, 3, 4}, Port: 30303}, } test.table, test.udp, _ = newUDP(test.localkey, test.pipe, nil, "") return test } // handles a packet as if it had been sent to the transport. func (test *udpTest) packetIn(wantError error, ptype byte, data packet) error { enc, err := encodePacket(test.remotekey, ptype, data) if err != nil { return test.errorf("packet (%d) encode error: %v", err) } test.sent = append(test.sent, enc) if err = test.udp.handlePacket(test.remoteaddr, enc); err != wantError { return test.errorf("error mismatch: got %q, want %q", err, wantError) } return nil } // waits for a packet to be sent by the transport. // validate should have type func(*udpTest, X) error, where X is a packet type. func (test *udpTest) waitPacketOut(validate interface{}) error { dgram := test.pipe.waitPacketOut() p, _, _, err := decodePacket(dgram) if err != nil { return test.errorf("sent packet decode error: %v", err) } fn := reflect.ValueOf(validate) exptype := fn.Type().In(0) if reflect.TypeOf(p) != exptype { return test.errorf("sent packet type mismatch, got: %v, want: %v", reflect.TypeOf(p), exptype) } fn.Call([]reflect.Value{reflect.ValueOf(p)}) return nil } func (test *udpTest) errorf(format string, args ...interface{}) error { _, file, line, ok := runtime.Caller(2) // errorf + waitPacketOut if ok { file = filepath.Base(file) } else { file = "???" line = 1 } err := fmt.Errorf(format, args...) fmt.Printf("\t%s:%d: %v\n", file, line, err) test.t.Fail() return err } func TestUDP_packetErrors(t *testing.T) { test := newUDPTest(t) defer test.table.Close() test.packetIn(errExpired, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: Version}) test.packetIn(errUnsolicitedReply, pongPacket, &pong{ReplyTok: []byte{}, Expiration: futureExp}) test.packetIn(errUnknownNode, findnodePacket, &findnode{Expiration: futureExp}) test.packetIn(errUnsolicitedReply, neighborsPacket, &neighbors{Expiration: futureExp}) } func TestUDP_pingTimeout(t *testing.T) { t.Parallel() test := newUDPTest(t) defer test.table.Close() toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222} toid := NodeID{1, 2, 3, 4} if err := test.udp.ping(toid, toaddr); err != errTimeout { t.Error("expected timeout error, got", err) } } func TestUDP_responseTimeouts(t *testing.T) { t.Parallel() test := newUDPTest(t) defer test.table.Close() rand.Seed(time.Now().UnixNano()) randomDuration := func(max time.Duration) time.Duration { return time.Duration(rand.Int63n(int64(max))) } var ( nReqs = 200 nTimeouts = 0 // number of requests with ptype > 128 nilErr = make(chan error, nReqs) // for requests that get a reply timeoutErr = make(chan error, nReqs) // for requests that time out ) for i := 0; i < nReqs; i++ { // Create a matcher for a random request in udp.loop. Requests // with ptype <= 128 will not get a reply and should time out. // For all other requests, a reply is scheduled to arrive // within the timeout window. p := &pending{ ptype: byte(rand.Intn(255)), callback: func(interface{}) bool { return true }, } binary.BigEndian.PutUint64(p.from[:], uint64(i)) if p.ptype <= 128 { p.errc = timeoutErr test.udp.addpending <- p nTimeouts++ } else { p.errc = nilErr test.udp.addpending <- p time.AfterFunc(randomDuration(60*time.Millisecond), func() { if !test.udp.handleReply(p.from, p.ptype, nil) { t.Logf("not matched: %v", p) } }) } time.Sleep(randomDuration(30 * time.Millisecond)) } // Check that all timeouts were delivered and that the rest got nil errors. // The replies must be delivered. var ( recvDeadline = time.After(20 * time.Second) nTimeoutsRecv, nNil = 0, 0 ) for i := 0; i < nReqs; i++ { select { case err := <-timeoutErr: if err != errTimeout { t.Fatalf("got non-timeout error on timeoutErr %d: %v", i, err) } nTimeoutsRecv++ case err := <-nilErr: if err != nil { t.Fatalf("got non-nil error on nilErr %d: %v", i, err) } nNil++ case <-recvDeadline: t.Fatalf("exceeded recv deadline") } } if nTimeoutsRecv != nTimeouts { t.Errorf("wrong number of timeout errors received: got %d, want %d", nTimeoutsRecv, nTimeouts) } if nNil != nReqs-nTimeouts { t.Errorf("wrong number of successful replies: got %d, want %d", nNil, nReqs-nTimeouts) } } func TestUDP_findnodeTimeout(t *testing.T) { t.Parallel() test := newUDPTest(t) defer test.table.Close() toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222} toid := NodeID{1, 2, 3, 4} target := NodeID{4, 5, 6, 7} result, err := test.udp.findnode(toid, toaddr, target) if err != errTimeout { t.Error("expected timeout error, got", err) } if len(result) > 0 { t.Error("expected empty result, got", result) } } func TestUDP_findnode(t *testing.T) { test := newUDPTest(t) defer test.table.Close() // put a few nodes into the table. their exact // distribution shouldn't matter much, altough we need to // take care not to overflow any bucket. targetHash := crypto.Keccak256Hash(testTarget[:]) nodes := &nodesByDistance{target: targetHash} for i := 0; i < bucketSize; i++ { nodes.push(nodeAtDistance(test.table.self.sha, i+2), bucketSize) } test.table.stuff(nodes.entries) // ensure there's a bond with the test node, // findnode won't be accepted otherwise. test.table.db.updateNode(NewNode( PubkeyID(&test.remotekey.PublicKey), test.remoteaddr.IP, uint16(test.remoteaddr.Port), 99, )) // check that closest neighbors are returned. test.packetIn(nil, findnodePacket, &findnode{Target: testTarget, Expiration: futureExp}) expected := test.table.closest(targetHash, bucketSize) 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) } 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) { test := newUDPTest(t) defer test.table.Close() // queue a pending findnode request resultc, errc := make(chan []*Node), make(chan error) go func() { rid := PubkeyID(&test.remotekey.PublicKey) ns, err := test.udp.findnode(rid, test.remoteaddr, testTarget) if err != nil && len(ns) == 0 { errc <- err } else { resultc <- ns } }() // wait for the findnode to be sent. // after it is sent, the transport is waiting for a reply test.waitPacketOut(func(p *findnode) { if p.Target != testTarget { t.Errorf("wrong target: got %v, want %v", p.Target, testTarget) } }) // send the reply as two packets. list := []*Node{ MustParseNode("enode://ba85011c70bcc5c04d8607d3a0ed29aa6179c092cbdda10d5d32684fb33ed01bd94f588ca8f91ac48318087dcb02eaf36773a7a453f0eedd6742af668097b29c@10.0.1.16:30303?discport=30304"), MustParseNode("enode://81fa361d25f157cd421c60dcc28d8dac5ef6a89476633339c5df30287474520caca09627da18543d9079b5b288698b542d56167aa5c09111e55acdbbdf2ef799@10.0.1.16:30303"), MustParseNode("enode://9bffefd833d53fac8e652415f4973bee289e8b1a5c6c4cbe70abf817ce8a64cee11b823b66a987f51aaa9fba0d6a91b3e6bf0d5a5d1042de8e9eeea057b217f8@10.0.1.36:30301?discport=17"), MustParseNode("enode://1b5b4aa662d7cb44a7221bfba67302590b643028197a7d5214790f3bac7aaa4a3241be9e83c09cf1f6c69d007c634faae3dc1b1221793e8446c0b3a09de65960@10.0.1.16:30303"), } rpclist := make([]rpcNode, len(list)) for i := range list { rpclist[i] = nodeToRPC(list[i]) } test.packetIn(nil, neighborsPacket, &neighbors{Expiration: futureExp, Nodes: rpclist[:2]}) test.packetIn(nil, neighborsPacket, &neighbors{Expiration: futureExp, Nodes: rpclist[2:]}) // check that the sent neighbors are all returned by findnode select { case result := <-resultc: if !reflect.DeepEqual(result, list) { t.Errorf("neighbors mismatch:\n got: %v\n want: %v", result, list) } case err := <-errc: t.Errorf("findnode error: %v", err) case <-time.After(5 * time.Second): t.Error("findnode did not return within 5 seconds") } } func TestUDP_successfulPing(t *testing.T) { test := newUDPTest(t) added := make(chan *Node, 1) test.table.nodeAddedHook = func(n *Node) { added <- n } defer test.table.Close() // The remote side sends a ping packet to initiate the exchange. go test.packetIn(nil, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: Version, Expiration: futureExp}) // the ping is replied to. test.waitPacketOut(func(p *pong) { pinghash := test.sent[0][:macSize] if !bytes.Equal(p.ReplyTok, pinghash) { t.Errorf("got pong.ReplyTok %x, want %x", p.ReplyTok, pinghash) } wantTo := rpcEndpoint{ // The mirrored UDP address is the UDP packet sender IP: test.remoteaddr.IP, UDP: uint16(test.remoteaddr.Port), // The mirrored TCP port is the one from the ping packet TCP: testRemote.TCP, } if !reflect.DeepEqual(p.To, wantTo) { t.Errorf("got pong.To %v, want %v", p.To, wantTo) } }) // remote is unknown, the table pings back. test.waitPacketOut(func(p *ping) error { if !reflect.DeepEqual(p.From, test.udp.ourEndpoint) { t.Errorf("got ping.From %v, want %v", p.From, test.udp.ourEndpoint) } wantTo := rpcEndpoint{ // The mirrored UDP address is the UDP packet sender. IP: test.remoteaddr.IP, UDP: uint16(test.remoteaddr.Port), TCP: 0, } if !reflect.DeepEqual(p.To, wantTo) { t.Errorf("got ping.To %v, want %v", p.To, wantTo) } return nil }) test.packetIn(nil, pongPacket, &pong{Expiration: futureExp}) // the node should be added to the table shortly after getting the // pong packet. select { case n := <-added: rid := PubkeyID(&test.remotekey.PublicKey) if n.ID != rid { t.Errorf("node has wrong ID: got %v, want %v", n.ID, rid) } if !bytes.Equal(n.IP, test.remoteaddr.IP) { t.Errorf("node has wrong IP: got %v, want: %v", n.IP, test.remoteaddr.IP) } if int(n.UDP) != test.remoteaddr.Port { t.Errorf("node has wrong UDP port: got %v, want: %v", n.UDP, test.remoteaddr.Port) } if n.TCP != testRemote.TCP { t.Errorf("node has wrong TCP port: got %v, want: %v", n.TCP, testRemote.TCP) } case <-time.After(2 * time.Second): t.Errorf("node was not added within 2 seconds") } } var testPackets = []struct { input string wantPacket interface{} }{ { input: "71dbda3a79554728d4f94411e42ee1f8b0d561c10e1e5f5893367948c6a7d70bb87b235fa28a77070271b6c164a2dce8c7e13a5739b53b5e96f2e5acb0e458a02902f5965d55ecbeb2ebb6cabb8b2b232896a36b737666c55265ad0a68412f250001ea04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a355", wantPacket: &ping{ Version: 4, From: rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544}, To: rpcEndpoint{net.ParseIP("::1"), 2222, 3333}, Expiration: 1136239445, Rest: []rlp.RawValue{}, }, }, { input: "e9614ccfd9fc3e74360018522d30e1419a143407ffcce748de3e22116b7e8dc92ff74788c0b6663aaa3d67d641936511c8f8d6ad8698b820a7cf9e1be7155e9a241f556658c55428ec0563514365799a4be2be5a685a80971ddcfa80cb422cdd0101ec04cb847f000001820cfa8215a8d790000000000000000000000000000000018208ae820d058443b9a3550102", wantPacket: &ping{ Version: 4, From: rpcEndpoint{net.ParseIP("127.0.0.1").To4(), 3322, 5544}, To: rpcEndpoint{net.ParseIP("::1"), 2222, 3333}, Expiration: 1136239445, Rest: []rlp.RawValue{{0x01}, {0x02}}, }, }, { input: "577be4349c4dd26768081f58de4c6f375a7a22f3f7adda654d1428637412c3d7fe917cadc56d4e5e7ffae1dbe3efffb9849feb71b262de37977e7c7a44e677295680e9e38ab26bee2fcbae207fba3ff3d74069a50b902a82c9903ed37cc993c50001f83e82022bd79020010db83c4d001500000000abcdef12820cfa8215a8d79020010db885a308d313198a2e037073488208ae82823a8443b9a355c5010203040531b9019afde696e582a78fa8d95ea13ce3297d4afb8ba6433e4154caa5ac6431af1b80ba76023fa4090c408f6b4bc3701562c031041d4702971d102c9ab7fa5eed4cd6bab8f7af956f7d565ee1917084a95398b6a21eac920fe3dd1345ec0a7ef39367ee69ddf092cbfe5b93e5e568ebc491983c09c76d922dc3", wantPacket: &ping{ Version: 555, From: rpcEndpoint{net.ParseIP("2001:db8:3c4d:15::abcd:ef12"), 3322, 5544}, To: rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338}, Expiration: 1136239445, Rest: []rlp.RawValue{{0xC5, 0x01, 0x02, 0x03, 0x04, 0x05}}, }, }, { input: "09b2428d83348d27cdf7064ad9024f526cebc19e4958f0fdad87c15eb598dd61d08423e0bf66b2069869e1724125f820d851c136684082774f870e614d95a2855d000f05d1648b2d5945470bc187c2d2216fbe870f43ed0909009882e176a46b0102f846d79020010db885a308d313198a2e037073488208ae82823aa0fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c9548443b9a355c6010203c2040506a0c969a58f6f9095004c0177a6b47f451530cab38966a25cca5cb58f055542124e", wantPacket: &pong{ To: rpcEndpoint{net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), 2222, 33338}, ReplyTok: common.Hex2Bytes("fbc914b16819237dcd8801d7e53f69e9719adecb3cc0e790c57e91ca4461c954"), Expiration: 1136239445, Rest: []rlp.RawValue{{0xC6, 0x01, 0x02, 0x03, 0xC2, 0x04, 0x05}, {0x06}}, }, }, { input: "c7c44041b9f7c7e41934417ebac9a8e1a4c6298f74553f2fcfdcae6ed6fe53163eb3d2b52e39fe91831b8a927bf4fc222c3902202027e5e9eb812195f95d20061ef5cd31d502e47ecb61183f74a504fe04c51e73df81f25c4d506b26db4517490103f84eb840ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f8443b9a35582999983999999280dc62cc8255c73471e0a61da0c89acdc0e035e260add7fc0c04ad9ebf3919644c91cb247affc82b69bd2ca235c71eab8e49737c937a2c396", wantPacket: &findnode{ Target: MustHexID("ca634cae0d49acb401d8a4c6b6fe8c55b70d115bf400769cc1400f3258cd31387574077f301b421bc84df7266c44e9e6d569fc56be00812904767bf5ccd1fc7f"), Expiration: 1136239445, Rest: []rlp.RawValue{{0x82, 0x99, 0x99}, {0x83, 0x99, 0x99, 0x99}}, }, }, { input: "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", wantPacket: &neighbors{ Nodes: []rpcNode{ { ID: MustHexID("3155e1427f85f10a5c9a7755877748041af1bcd8d474ec065eb33df57a97babf54bfd2103575fa829115d224c523596b401065a97f74010610fce76382c0bf32"), IP: net.ParseIP("99.33.22.55").To4(), UDP: 4444, TCP: 4445, }, { ID: MustHexID("312c55512422cf9b8a4097e9a6ad79402e87a15ae909a4bfefa22398f03d20951933beea1e4dfa6f968212385e829f04c2d314fc2d4e255e0d3bc08792b069db"), IP: net.ParseIP("1.2.3.4").To4(), UDP: 1, TCP: 1, }, { ID: MustHexID("38643200b172dcfef857492156971f0e6aa2c538d8b74010f8e140811d53b98c765dd2d96126051913f44582e8c199ad7c6d6819e9a56483f637feaac9448aac"), IP: net.ParseIP("2001:db8:3c4d:15::abcd:ef12"), UDP: 3333, TCP: 3333, }, { ID: MustHexID("8dcab8618c3253b558d459da53bd8fa68935a719aff8b811197101a4b2b47dd2d47295286fc00cc081bb542d760717d1bdd6bec2c37cd72eca367d6dd3b9df73"), IP: net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:7348"), UDP: 999, TCP: 1000, }, }, Expiration: 1136239445, Rest: []rlp.RawValue{{0x01}, {0x02}, {0x03}}, }, }, } func TestForwardCompatibility(t *testing.T) { testkey, _ := crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291") wantNodeID := PubkeyID(&testkey.PublicKey) for _, test := range testPackets { input, err := hex.DecodeString(test.input) if err != nil { t.Fatalf("invalid hex: %s", test.input) } packet, nodeid, _, err := decodePacket(input) if err != nil { t.Errorf("did not accept packet %s\n%v", test.input, err) continue } if !reflect.DeepEqual(packet, test.wantPacket) { t.Errorf("got %s\nwant %s", spew.Sdump(packet), spew.Sdump(test.wantPacket)) } if nodeid != wantNodeID { t.Errorf("got id %v\nwant id %v", nodeid, wantNodeID) } } } // dgramPipe is a fake UDP socket. It queues all sent datagrams. type dgramPipe struct { mu *sync.Mutex cond *sync.Cond closing chan struct{} closed bool queue [][]byte } func newpipe() *dgramPipe { mu := new(sync.Mutex) return &dgramPipe{ closing: make(chan struct{}), cond: &sync.Cond{L: mu}, mu: mu, } } // WriteToUDP queues a datagram. func (c *dgramPipe) WriteToUDP(b []byte, to *net.UDPAddr) (n int, err error) { msg := make([]byte, len(b)) copy(msg, b) c.mu.Lock() defer c.mu.Unlock() if c.closed { return 0, errors.New("closed") } c.queue = append(c.queue, msg) c.cond.Signal() return len(b), nil } // ReadFromUDP just hangs until the pipe is closed. func (c *dgramPipe) ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error) { <-c.closing return 0, nil, io.EOF } func (c *dgramPipe) Close() error { c.mu.Lock() defer c.mu.Unlock() if !c.closed { close(c.closing) c.closed = true } return nil } func (c *dgramPipe) LocalAddr() net.Addr { return &net.UDPAddr{IP: testLocal.IP, Port: int(testLocal.UDP)} } func (c *dgramPipe) waitPacketOut() []byte { c.mu.Lock() defer c.mu.Unlock() for len(c.queue) == 0 { c.cond.Wait() } p := c.queue[0] copy(c.queue, c.queue[1:]) c.queue = c.queue[:len(c.queue)-1] return p }