plugeth/p2p/discover/v4_udp_test.go
jwasinger 28e7371701
all: replace log15 with slog (#28187)
This PR replaces Geth's logger package (a fork of [log15](https://github.com/inconshreveable/log15)) with an implementation using slog, a logging library included as part of the Go standard library as of Go1.21.

Main changes are as follows:
* removes any log handlers that were unused in the Geth codebase.
* Json, logfmt, and terminal formatters are now slog handlers.
* Verbosity level constants are changed to match slog constant values.  Internal translation is done to make this opaque to the user and backwards compatible with existing `--verbosity` and `--vmodule` options.
* `--log.backtraceat` and `--log.debug` are removed.

The external-facing API is largely the same as the existing Geth logger.  Logger method signatures remain unchanged.

A small semantic difference is that a `Handler` can only be set once per `Logger` and not changed dynamically.  This just means that a new logger must be instantiated every time the handler of the root logger is changed.

----
For users of the `go-ethereum/log` module. If you were using this module for your own project, you will need to change the initialization. If you previously did 
```golang
log.Root().SetHandler(log.LvlFilterHandler(log.LvlInfo, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
```
You now instead need to do 
```golang
log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelInfo, true)))
```
See more about reasoning here: https://github.com/ethereum/go-ethereum/issues/28558#issuecomment-1820606613
2023-11-29 08:33:50 +01:00

662 lines
20 KiB
Go

// 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 <http://www.gnu.org/licenses/>.
package discover
import (
"bytes"
"crypto/ecdsa"
crand "crypto/rand"
"encoding/binary"
"errors"
"fmt"
"io"
"math/rand"
"net"
"reflect"
"sync"
"testing"
"time"
"github.com/ethereum/go-ethereum/internal/testlog"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/p2p/discover/v4wire"
"github.com/ethereum/go-ethereum/p2p/enode"
"github.com/ethereum/go-ethereum/p2p/enr"
)
// shared test variables
var (
futureExp = uint64(time.Now().Add(10 * time.Hour).Unix())
testTarget = v4wire.Pubkey{0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1}
testRemote = v4wire.Endpoint{IP: net.ParseIP("1.1.1.1").To4(), UDP: 1, TCP: 2}
testLocalAnnounced = v4wire.Endpoint{IP: net.ParseIP("2.2.2.2").To4(), UDP: 3, TCP: 4}
testLocal = v4wire.Endpoint{IP: net.ParseIP("3.3.3.3").To4(), UDP: 5, TCP: 6}
)
type udpTest struct {
t *testing.T
pipe *dgramPipe
table *Table
db *enode.DB
udp *UDPv4
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{10, 0, 1, 99}, Port: 30303},
}
test.db, _ = enode.OpenDB("")
ln := enode.NewLocalNode(test.db, test.localkey)
test.udp, _ = ListenV4(test.pipe, ln, Config{
PrivateKey: test.localkey,
Log: testlog.Logger(t, log.LvlTrace),
})
test.table = test.udp.tab
// Wait for initial refresh so the table doesn't send unexpected findnode.
<-test.table.initDone
return test
}
func (test *udpTest) close() {
test.udp.Close()
test.db.Close()
}
// handles a packet as if it had been sent to the transport.
func (test *udpTest) packetIn(wantError error, data v4wire.Packet) {
test.t.Helper()
test.packetInFrom(wantError, test.remotekey, test.remoteaddr, data)
}
// handles a packet as if it had been sent to the transport by the key/endpoint.
func (test *udpTest) packetInFrom(wantError error, key *ecdsa.PrivateKey, addr *net.UDPAddr, data v4wire.Packet) {
test.t.Helper()
enc, _, err := v4wire.Encode(key, data)
if err != nil {
test.t.Errorf("%s encode error: %v", data.Name(), err)
}
test.sent = append(test.sent, enc)
if err = test.udp.handlePacket(addr, enc); err != wantError {
test.t.Errorf("error mismatch: got %q, want %q", err, wantError)
}
}
// waits for a packet to be sent by the transport.
// validate should have type func(X, *net.UDPAddr, []byte), where X is a packet type.
func (test *udpTest) waitPacketOut(validate interface{}) (closed bool) {
test.t.Helper()
dgram, err := test.pipe.receive()
if err == errClosed {
return true
} else if err != nil {
test.t.Error("packet receive error:", err)
return false
}
p, _, hash, err := v4wire.Decode(dgram.data)
if err != nil {
test.t.Errorf("sent packet decode error: %v", err)
return false
}
fn := reflect.ValueOf(validate)
exptype := fn.Type().In(0)
if !reflect.TypeOf(p).AssignableTo(exptype) {
test.t.Errorf("sent packet type mismatch, got: %v, want: %v", reflect.TypeOf(p), exptype)
return false
}
fn.Call([]reflect.Value{reflect.ValueOf(p), reflect.ValueOf(&dgram.to), reflect.ValueOf(hash)})
return false
}
func TestUDPv4_packetErrors(t *testing.T) {
test := newUDPTest(t)
defer test.close()
test.packetIn(errExpired, &v4wire.Ping{From: testRemote, To: testLocalAnnounced, Version: 4})
test.packetIn(errUnsolicitedReply, &v4wire.Pong{ReplyTok: []byte{}, Expiration: futureExp})
test.packetIn(errUnknownNode, &v4wire.Findnode{Expiration: futureExp})
test.packetIn(errUnsolicitedReply, &v4wire.Neighbors{Expiration: futureExp})
}
func TestUDPv4_pingTimeout(t *testing.T) {
t.Parallel()
test := newUDPTest(t)
defer test.close()
key := newkey()
toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222}
node := enode.NewV4(&key.PublicKey, toaddr.IP, 0, toaddr.Port)
if _, err := test.udp.ping(node); err != errTimeout {
t.Error("expected timeout error, got", err)
}
}
type testPacket byte
func (req testPacket) Kind() byte { return byte(req) }
func (req testPacket) Name() string { return "" }
func TestUDPv4_responseTimeouts(t *testing.T) {
t.Parallel()
test := newUDPTest(t)
defer test.close()
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 := &replyMatcher{
ptype: byte(rand.Intn(255)),
callback: func(v4wire.Packet) (bool, bool) { return true, true },
}
binary.BigEndian.PutUint64(p.from[:], uint64(i))
if p.ptype <= 128 {
p.errc = timeoutErr
test.udp.addReplyMatcher <- p
nTimeouts++
} else {
p.errc = nilErr
test.udp.addReplyMatcher <- p
time.AfterFunc(randomDuration(60*time.Millisecond), func() {
if !test.udp.handleReply(p.from, p.ip, testPacket(p.ptype)) {
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 TestUDPv4_findnodeTimeout(t *testing.T) {
t.Parallel()
test := newUDPTest(t)
defer test.close()
toaddr := &net.UDPAddr{IP: net.ParseIP("1.2.3.4"), Port: 2222}
toid := enode.ID{1, 2, 3, 4}
target := v4wire.Pubkey{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 TestUDPv4_findnode(t *testing.T) {
test := newUDPTest(t)
defer test.close()
// put a few nodes into the table. their exact
// distribution shouldn't matter much, although we need to
// take care not to overflow any bucket.
nodes := &nodesByDistance{target: testTarget.ID()}
live := make(map[enode.ID]bool)
numCandidates := 2 * bucketSize
for i := 0; i < numCandidates; i++ {
key := newkey()
ip := net.IP{10, 13, 0, byte(i)}
n := wrapNode(enode.NewV4(&key.PublicKey, ip, 0, 2000))
// Ensure half of table content isn't verified live yet.
if i > numCandidates/2 {
n.livenessChecks = 1
live[n.ID()] = true
}
nodes.push(n, numCandidates)
}
fillTable(test.table, nodes.entries)
// ensure there's a bond with the test node,
// findnode won't be accepted otherwise.
remoteID := v4wire.EncodePubkey(&test.remotekey.PublicKey).ID()
test.table.db.UpdateLastPongReceived(remoteID, test.remoteaddr.IP, time.Now())
// check that closest neighbors are returned.
expected := test.table.findnodeByID(testTarget.ID(), bucketSize, true)
test.packetIn(nil, &v4wire.Findnode{Target: testTarget, Expiration: futureExp})
waitNeighbors := func(want []*node) {
test.waitPacketOut(func(p *v4wire.Neighbors, to *net.UDPAddr, hash []byte) {
if len(p.Nodes) != len(want) {
t.Errorf("wrong number of results: got %d, want %d", len(p.Nodes), bucketSize)
return
}
for i, n := range p.Nodes {
if n.ID.ID() != want[i].ID() {
t.Errorf("result mismatch at %d:\n got: %v\n want: %v", i, n, expected.entries[i])
}
if !live[n.ID.ID()] {
t.Errorf("result includes dead node %v", n.ID.ID())
}
}
})
}
// Receive replies.
want := expected.entries
if len(want) > v4wire.MaxNeighbors {
waitNeighbors(want[:v4wire.MaxNeighbors])
want = want[v4wire.MaxNeighbors:]
}
waitNeighbors(want)
}
func TestUDPv4_findnodeMultiReply(t *testing.T) {
test := newUDPTest(t)
defer test.close()
rid := enode.PubkeyToIDV4(&test.remotekey.PublicKey)
test.table.db.UpdateLastPingReceived(rid, test.remoteaddr.IP, time.Now())
// queue a pending findnode request
resultc, errc := make(chan []*node, 1), make(chan error, 1)
go func() {
rid := encodePubkey(&test.remotekey.PublicKey).id()
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 *v4wire.Findnode, to *net.UDPAddr, hash []byte) {
if p.Target != testTarget {
t.Errorf("wrong target: got %v, want %v", p.Target, testTarget)
}
})
// send the reply as two packets.
list := []*node{
wrapNode(enode.MustParse("enode://ba85011c70bcc5c04d8607d3a0ed29aa6179c092cbdda10d5d32684fb33ed01bd94f588ca8f91ac48318087dcb02eaf36773a7a453f0eedd6742af668097b29c@10.0.1.16:30303?discport=30304")),
wrapNode(enode.MustParse("enode://81fa361d25f157cd421c60dcc28d8dac5ef6a89476633339c5df30287474520caca09627da18543d9079b5b288698b542d56167aa5c09111e55acdbbdf2ef799@10.0.1.16:30303")),
wrapNode(enode.MustParse("enode://9bffefd833d53fac8e652415f4973bee289e8b1a5c6c4cbe70abf817ce8a64cee11b823b66a987f51aaa9fba0d6a91b3e6bf0d5a5d1042de8e9eeea057b217f8@10.0.1.36:30301?discport=17")),
wrapNode(enode.MustParse("enode://1b5b4aa662d7cb44a7221bfba67302590b643028197a7d5214790f3bac7aaa4a3241be9e83c09cf1f6c69d007c634faae3dc1b1221793e8446c0b3a09de65960@10.0.1.16:30303")),
}
rpclist := make([]v4wire.Node, len(list))
for i := range list {
rpclist[i] = nodeToRPC(list[i])
}
test.packetIn(nil, &v4wire.Neighbors{Expiration: futureExp, Nodes: rpclist[:2]})
test.packetIn(nil, &v4wire.Neighbors{Expiration: futureExp, Nodes: rpclist[2:]})
// check that the sent neighbors are all returned by findnode
select {
case result := <-resultc:
want := append(list[:2], list[3:]...)
if !reflect.DeepEqual(result, want) {
t.Errorf("neighbors mismatch:\n got: %v\n want: %v", result, want)
}
case err := <-errc:
t.Errorf("findnode error: %v", err)
case <-time.After(5 * time.Second):
t.Error("findnode did not return within 5 seconds")
}
}
// This test checks that reply matching of pong verifies the ping hash.
func TestUDPv4_pingMatch(t *testing.T) {
test := newUDPTest(t)
defer test.close()
randToken := make([]byte, 32)
crand.Read(randToken)
test.packetIn(nil, &v4wire.Ping{From: testRemote, To: testLocalAnnounced, Version: 4, Expiration: futureExp})
test.waitPacketOut(func(*v4wire.Pong, *net.UDPAddr, []byte) {})
test.waitPacketOut(func(*v4wire.Ping, *net.UDPAddr, []byte) {})
test.packetIn(errUnsolicitedReply, &v4wire.Pong{ReplyTok: randToken, To: testLocalAnnounced, Expiration: futureExp})
}
// This test checks that reply matching of pong verifies the sender IP address.
func TestUDPv4_pingMatchIP(t *testing.T) {
test := newUDPTest(t)
defer test.close()
test.packetIn(nil, &v4wire.Ping{From: testRemote, To: testLocalAnnounced, Version: 4, Expiration: futureExp})
test.waitPacketOut(func(*v4wire.Pong, *net.UDPAddr, []byte) {})
test.waitPacketOut(func(p *v4wire.Ping, to *net.UDPAddr, hash []byte) {
wrongAddr := &net.UDPAddr{IP: net.IP{33, 44, 1, 2}, Port: 30000}
test.packetInFrom(errUnsolicitedReply, test.remotekey, wrongAddr, &v4wire.Pong{
ReplyTok: hash,
To: testLocalAnnounced,
Expiration: futureExp,
})
})
}
func TestUDPv4_successfulPing(t *testing.T) {
test := newUDPTest(t)
added := make(chan *node, 1)
test.table.nodeAddedHook = func(b *bucket, n *node) { added <- n }
defer test.close()
// The remote side sends a ping packet to initiate the exchange.
go test.packetIn(nil, &v4wire.Ping{From: testRemote, To: testLocalAnnounced, Version: 4, Expiration: futureExp})
// The ping is replied to.
test.waitPacketOut(func(p *v4wire.Pong, to *net.UDPAddr, hash []byte) {
pinghash := test.sent[0][:32]
if !bytes.Equal(p.ReplyTok, pinghash) {
t.Errorf("got pong.ReplyTok %x, want %x", p.ReplyTok, pinghash)
}
wantTo := v4wire.Endpoint{
// 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 *v4wire.Ping, to *net.UDPAddr, hash []byte) {
if !reflect.DeepEqual(p.From, test.udp.ourEndpoint()) {
t.Errorf("got ping.From %#v, want %#v", p.From, test.udp.ourEndpoint())
}
wantTo := v4wire.Endpoint{
// 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)
}
test.packetIn(nil, &v4wire.Pong{ReplyTok: hash, Expiration: futureExp})
})
// The node should be added to the table shortly after getting the
// pong packet.
select {
case n := <-added:
rid := encodePubkey(&test.remotekey.PublicKey).id()
if n.ID() != rid {
t.Errorf("node has wrong ID: got %v, want %v", n.ID(), rid)
}
if !n.IP().Equal(test.remoteaddr.IP) {
t.Errorf("node has wrong IP: got %v, want: %v", n.IP(), test.remoteaddr.IP)
}
if n.UDP() != test.remoteaddr.Port {
t.Errorf("node has wrong UDP port: got %v, want: %v", n.UDP(), test.remoteaddr.Port)
}
if n.TCP() != int(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")
}
}
// This test checks that EIP-868 requests work.
func TestUDPv4_EIP868(t *testing.T) {
test := newUDPTest(t)
defer test.close()
test.udp.localNode.Set(enr.WithEntry("foo", "bar"))
wantNode := test.udp.localNode.Node()
// ENR requests aren't allowed before endpoint proof.
test.packetIn(errUnknownNode, &v4wire.ENRRequest{Expiration: futureExp})
// Perform endpoint proof and check for sequence number in packet tail.
test.packetIn(nil, &v4wire.Ping{Expiration: futureExp})
test.waitPacketOut(func(p *v4wire.Pong, addr *net.UDPAddr, hash []byte) {
if p.ENRSeq != wantNode.Seq() {
t.Errorf("wrong sequence number in pong: %d, want %d", p.ENRSeq, wantNode.Seq())
}
})
test.waitPacketOut(func(p *v4wire.Ping, addr *net.UDPAddr, hash []byte) {
if p.ENRSeq != wantNode.Seq() {
t.Errorf("wrong sequence number in ping: %d, want %d", p.ENRSeq, wantNode.Seq())
}
test.packetIn(nil, &v4wire.Pong{Expiration: futureExp, ReplyTok: hash})
})
// Request should work now.
test.packetIn(nil, &v4wire.ENRRequest{Expiration: futureExp})
test.waitPacketOut(func(p *v4wire.ENRResponse, addr *net.UDPAddr, hash []byte) {
n, err := enode.New(enode.ValidSchemes, &p.Record)
if err != nil {
t.Fatalf("invalid record: %v", err)
}
if !reflect.DeepEqual(n, wantNode) {
t.Fatalf("wrong node in ENRResponse: %v", n)
}
})
}
// This test verifies that a small network of nodes can boot up into a healthy state.
func TestUDPv4_smallNetConvergence(t *testing.T) {
t.Parallel()
// Start the network.
nodes := make([]*UDPv4, 4)
for i := range nodes {
var cfg Config
if i > 0 {
bn := nodes[0].Self()
cfg.Bootnodes = []*enode.Node{bn}
}
nodes[i] = startLocalhostV4(t, cfg)
defer nodes[i].Close()
}
// Run through the iterator on all nodes until
// they have all found each other.
status := make(chan error, len(nodes))
for i := range nodes {
node := nodes[i]
go func() {
found := make(map[enode.ID]bool, len(nodes))
it := node.RandomNodes()
for it.Next() {
found[it.Node().ID()] = true
if len(found) == len(nodes) {
status <- nil
return
}
}
status <- fmt.Errorf("node %s didn't find all nodes", node.Self().ID().TerminalString())
}()
}
// Wait for all status reports.
timeout := time.NewTimer(30 * time.Second)
defer timeout.Stop()
for received := 0; received < len(nodes); {
select {
case <-timeout.C:
for _, node := range nodes {
node.Close()
}
case err := <-status:
received++
if err != nil {
t.Error("ERROR:", err)
return
}
}
}
}
func startLocalhostV4(t *testing.T, cfg Config) *UDPv4 {
t.Helper()
cfg.PrivateKey = newkey()
db, _ := enode.OpenDB("")
ln := enode.NewLocalNode(db, cfg.PrivateKey)
// Prefix logs with node ID.
lprefix := fmt.Sprintf("(%s)", ln.ID().TerminalString())
cfg.Log = testlog.Logger(t, log.LevelTrace).With("node-id", lprefix)
// Listen.
socket, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IP{127, 0, 0, 1}})
if err != nil {
t.Fatal(err)
}
realaddr := socket.LocalAddr().(*net.UDPAddr)
ln.SetStaticIP(realaddr.IP)
ln.SetFallbackUDP(realaddr.Port)
udp, err := ListenV4(socket, ln, cfg)
if err != nil {
t.Fatal(err)
}
return udp
}
// 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 []dgram
}
type dgram struct {
to net.UDPAddr
data []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, dgram{*to, b})
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
}
c.cond.Broadcast()
return nil
}
func (c *dgramPipe) LocalAddr() net.Addr {
return &net.UDPAddr{IP: testLocal.IP, Port: int(testLocal.UDP)}
}
func (c *dgramPipe) receive() (dgram, error) {
c.mu.Lock()
defer c.mu.Unlock()
var timedOut bool
timer := time.AfterFunc(3*time.Second, func() {
c.mu.Lock()
timedOut = true
c.mu.Unlock()
c.cond.Broadcast()
})
defer timer.Stop()
for len(c.queue) == 0 && !c.closed && !timedOut {
c.cond.Wait()
}
if c.closed {
return dgram{}, errClosed
}
if timedOut {
return dgram{}, errTimeout
}
p := c.queue[0]
copy(c.queue, c.queue[1:])
c.queue = c.queue[:len(c.queue)-1]
return p, nil
}