p2p/discover: fix Windows-specific issue for larger-than-buffer packets

On Windows, UDPConn.ReadFrom returns an error for packets larger
than the receive buffer. The error is not marked temporary, causing
our loop to exit when the first oversized packet arrived. The fix
is to treat this particular error as temporary.

Fixes: #1579, #2087
Updates: #2082

p2p/discover/udp.go

@@ -453,8 +453,11 @@ func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte,
 	return packet, nil
 }
 
-type tempError interface {
+func isTemporaryError(err error) bool {
+	tempErr, ok := err.(interface {
 		Temporary() bool
+	})
+	return ok && tempErr.Temporary() || isPacketTooBig(err)
 }
 
 // readLoop runs in its own goroutine. it handles incoming UDP packets.
@@ -466,7 +469,7 @@ func (t *udp) readLoop() {
 	buf := make([]byte, 1280)
 	for {
 		nbytes, from, err := t.conn.ReadFromUDP(buf)
-		if tempErr, ok := err.(tempError); ok && tempErr.Temporary() {
+		if isTemporaryError(err) {
 			// Ignore temporary read errors.
 			glog.V(logger.Debug).Infof("Temporary read error: %v", err)
 			continue

p2p/discover/udp_notwindows.go

@@ -0,0 +1,26 @@
+// Copyright 2016 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/>.
+
+//+build !windows
+
+package discover
+
+// reports whether err indicates that a UDP packet didn't
+// fit the receive buffer. There is no such error on
+// non-Windows platforms.
+func isPacketTooBig(err error) bool {
+	return false
+}

p2p/discover/udp_test.go

@@ -23,10 +23,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	logpkg "log"
 	"math/rand"
 	"net"
-	"os"
 	"path/filepath"
 	"reflect"
 	"runtime"
@@ -34,12 +32,62 @@ import (
 	"testing"
 	"time"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/ethereum/go-ethereum/crypto"
-	"github.com/ethereum/go-ethereum/logger"
 )
 
 func init() {
-	logger.AddLogSystem(logger.NewStdLogSystem(os.Stdout, logpkg.LstdFlags, logger.ErrorLevel))
+	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

p2p/discover/udp_windows.go

@@ -0,0 +1,40 @@
+// Copyright 2016 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/>.
+
+//+build windows
+
+package discover
+
+import (
+	"net"
+	"os"
+	"syscall"
+)
+
+const _WSAEMSGSIZE = syscall.Errno(10040)
+
+// reports whether err indicates that a UDP packet didn't
+// fit the receive buffer. On Windows, WSARecvFrom returns
+// code WSAEMSGSIZE and no data if this happens.
+func isPacketTooBig(err error) bool {
+	if opErr, ok := err.(*net.OpError); ok {
+		if scErr, ok := opErr.Err.(*os.SyscallError); ok {
+			return scErr.Err == _WSAEMSGSIZE
+		}
+		return opErr.Err == _WSAEMSGSIZE
+	}
+	return false
+}