net: add SetKeepAlivePeriod for windows

R=golang-codereviews, alex.brainman, bradfitz, mikioh.mikioh
CC=golang-codereviews
https://golang.org/cl/11393043

src/pkg/net/tcpsockopt_windows.go

@@ -7,7 +7,10 @@
 package net
 
 import (
+	"os"
+	"syscall"
 	"time"
+	"unsafe"
 )
 
 func setKeepAlivePeriod(fd *netFD, d time.Duration) error {
@@ -16,6 +19,16 @@ func setKeepAlivePeriod(fd *netFD, d time.Duration) error {
 	}
 	defer fd.decref()
 
-	// We can't actually set this per connection.  Act as a noop rather than an error.
-	return nil
+	// Windows expects milliseconds so round to next highest millisecond.
+	d += (time.Millisecond - time.Nanosecond)
+	millis := uint32(d / time.Millisecond)
+	ka := syscall.TCPKeepalive{
+		OnOff:    1,
+		Time:     millis,
+		Interval: millis,
+	}
+	ret := uint32(0)
+	size := uint32(unsafe.Sizeof(ka))
+	err := syscall.WSAIoctl(fd.sysfd, syscall.SIO_KEEPALIVE_VALS, (*byte)(unsafe.Pointer(&ka)), size, nil, 0, &ret, nil, 0)
+	return os.NewSyscallError("WSAIoctl", err)
 }

src/pkg/syscall/ztypes_windows.go

@@ -512,9 +512,11 @@ const (
 
 	IOC_OUT                            = 0x40000000
 	IOC_IN                             = 0x80000000
+	IOC_VENDOR                         = 0x18000000
 	IOC_INOUT                          = IOC_IN | IOC_OUT
 	IOC_WS2                            = 0x08000000
 	SIO_GET_EXTENSION_FUNCTION_POINTER = IOC_INOUT | IOC_WS2 | 6
+	SIO_KEEPALIVE_VALS                 = IOC_IN | IOC_VENDOR | 4
 
 	// cf. http://support.microsoft.com/default.aspx?scid=kb;en-us;257460
 
@@ -1031,3 +1033,9 @@ type WSAProtocolChain struct {
 	ChainLen     int32
 	ChainEntries [MAX_PROTOCOL_CHAIN]uint32
 }
+
+type TCPKeepalive struct {
+	OnOff    uint32
+	Time     uint32
+	Interval uint32
+}