p2p/netutil: new package for network utilities

The new package contains three things for now:

- IP network list parsing and matching
- The WSAEMSGSIZE workaround, which is duplicated in p2p/discover and
  p2p/discv5.

p2p/netutil/error_test.go

@@ -0,0 +1,73 @@
+// 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/>.
+
+package netutil
+
+import (
+	"net"
+	"testing"
+	"time"
+)
+
+// 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.Fatalf("unexpected read error: %v", 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
+			}
+		}
+	}
+}