code review 6482044: go.net/ipv4: new package

ipv4/helper_windows.go

Index: ipv4/helper_windows.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/ipv4/helper_windows.go
@@ -0,0 +1,49 @@
+// Copyright 2012 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.
+
+package ipv4
+
+import (
+	"net"
+	"reflect"
+	"syscall"
+)
+
+func (c *genericOpt) sysfd() (syscall.Handle, error) {
+	switch p := c.c.(type) {
+	case *net.TCPConn, *net.UDPConn, *net.IPConn:
+		return sysfd(p)
+	}
+	return syscall.InvalidHandle, errInvalidConnType
+}
+
+func (c *dgramOpt) sysfd() (syscall.Handle, error) {
+	switch p := c.c.(type) {
+	case *net.UDPConn, *net.IPConn:
+		return sysfd(p.(net.Conn))
+	}
+	return syscall.InvalidHandle, errInvalidConnType
+}
+
+func (c *payloadHandler) sysfd() (syscall.Handle, error) {
+	return sysfd(c.c.(net.Conn))
+}
+
+func (c *packetHandler) sysfd() (syscall.Handle, error) {
+	return sysfd(c.c)
+}
+
+func sysfd(c net.Conn) (syscall.Handle, error) {
+	cv := reflect.ValueOf(c)
+	switch ce := cv.Elem(); ce.Kind() {
+	case reflect.Struct:
+		fd := ce.FieldByName("conn").FieldByName("fd")
+		switch fe := fd.Elem(); fe.Kind() {
+		case reflect.Struct:
+			sysfd := fe.FieldByName("sysfd")
+			return syscall.Handle(sysfd.Uint()), nil
+		}
+	}
+	return syscall.InvalidHandle, errInvalidConnType
+}