net: enable SO_REUSEPORT on BSD variants

Fixes #1694.

R=golang-dev, rsc1, rsc
CC=golang-dev
https://golang.org/cl/4445067

src/pkg/net/Makefile

@@ -29,6 +29,7 @@ GOFILES_freebsd=\
 	dnsconfig.go\
 	dnsclient.go\
 	port.go\
+	sock_bsd.go\
 
 CGOFILES_freebsd=\
 	cgo_bsd.go\
@@ -41,6 +42,7 @@ GOFILES_darwin=\
 	dnsconfig.go\
 	dnsclient.go\
 	port.go\
+	sock_bsd.go\
 
 CGOFILES_darwin=\
 	cgo_bsd.go\
@@ -53,6 +55,7 @@ GOFILES_linux=\
 	dnsconfig.go\
 	dnsclient.go\
 	port.go\
+	sock_linux.go\
 
 ifeq ($(GOARCH),arm)
 # ARM has no cgo, so use the stubs.
@@ -67,6 +70,7 @@ GOFILES_windows=\
 	cgo_stub.go\
 	resolv_windows.go\
 	file_windows.go\
+	sock_windows.go\
 
 GOFILES+=$(GOFILES_$(GOOS))
 ifneq ($(CGOFILES_$(GOOS)),)

src/pkg/net/sock.go

@@ -32,17 +32,7 @@ func socket(net string, f, p, t int, la, ra syscall.Sockaddr, toAddr func(syscal
 	syscall.CloseOnExec(s)
 	syscall.ForkLock.RUnlock()
 
-	// Allow reuse of recently-used addresses.
-	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
-
-	// Allow broadcast.
-	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
-
-	if f == syscall.AF_INET6 {
-		// using ip, tcp, udp, etc.
-		// allow both protocols even if the OS default is otherwise.
-		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
-	}
+	setKernelSpecificSockopt(s, f)
 
 	if la != nil {
 		e = syscall.Bind(s, la)

src/pkg/net/sock_bsd.go

@@ -0,0 +1,31 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Sockets for BSD variants
+
+package net
+
+import (
+	"syscall"
+)
+
+func setKernelSpecificSockopt(s, f int) {
+	// Allow reuse of recently-used addresses.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+
+	// Allow reuse of recently-used ports.
+	// This option is supported only in descendants of 4.4BSD,
+	// to make an effective multicast application and an application
+	// that requires quick draw possible.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEPORT, 1)
+
+	// Allow broadcast.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
+
+	if f == syscall.AF_INET6 {
+		// using ip, tcp, udp, etc.
+		// allow both protocols even if the OS default is otherwise.
+		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+	}
+}

src/pkg/net/sock_linux.go

@@ -0,0 +1,25 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Sockets for Linux
+
+package net
+
+import (
+	"syscall"
+)
+
+func setKernelSpecificSockopt(s, f int) {
+	// Allow reuse of recently-used addresses.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+
+	// Allow broadcast.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
+
+	if f == syscall.AF_INET6 {
+		// using ip, tcp, udp, etc.
+		// allow both protocols even if the OS default is otherwise.
+		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+	}
+}

src/pkg/net/sock_windows.go

@@ -0,0 +1,25 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Sockets for Windows
+
+package net
+
+import (
+	"syscall"
+)
+
+func setKernelSpecificSockopt(s, f int) {
+	// Allow reuse of recently-used addresses and ports.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+
+	// Allow broadcast.
+	syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
+
+	if f == syscall.AF_INET6 {
+		// using ip, tcp, udp, etc.
+		// allow both protocols even if the OS default is otherwise.
+		syscall.SetsockoptInt(s, syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY, 0)
+	}
+}