corrected the TCP keepalive code for WinSock

src/anet.c

@@ -49,6 +49,7 @@
 #ifdef _WIN32
 #include "win32_Interop/win32fixes.h"
 #define ANET_NOTUSED(V) V
+#include <Mstcpip.h>
 #endif
 
 #include "anet.h"
@@ -81,20 +82,34 @@ int anetNonBlock(char *err, int fd)
     return ANET_OK;
 }
 
-/* Set TCP keep alive option to detect dead peers. The interval option
- * is only used for Linux as we are using Linux-specific APIs to set
- * the probe send time, interval, and count. */
-int anetKeepAlive(char *err, int fd, int interval)
-{
+/* Set TCP keep alive option to detect dead peers. */
+int anetKeepAlive(char *err, int fd, int interval) {
+#ifdef _WIN32    
     int val = 1;
 
-    if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) == -1)
-    {
+    if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof(val)) == -1) {
         anetSetError(err, "setsockopt SO_KEEPALIVE: %s", strerror(errno));
         return ANET_ERR;
     }
 
-#ifdef __linux__
+    struct tcp_keepalive alive; 
+    DWORD dwBytesRet = 0; 
+    alive.onoff = TRUE; 
+    alive.keepalivetime = interval * 1000; 
+    /* According to http://msdn.microsoft.com/en-us/library/windows/desktop/ee470551(v=vs.85).aspx 
+       On Windows Vista and later, the number of keep-alive probes (data retransmissions) is set to 10 and cannot be changed. 
+        So we set the keep alive interval as interval/10, as 10 probes will be send before 
+        detecting an error 
+    */ 
+    val = interval/10; 
+    if (val == 0) val = 1; 
+    alive.keepaliveinterval = val*1000; 
+    if(WSAIoctl(fd, SIO_KEEPALIVE_VALS, &alive, sizeof(alive), 
+       NULL, 0, &dwBytesRet, NULL, NULL) == SOCKET_ERROR) { 
+        anetSetError(err, "WSAIotcl(SIO_KEEPALIVE_VALS) failed with error code %d\n", WSAGetLastError()); 
+    	return ANET_ERR; 
+    } 
+#else
     /* Default settings are more or less garbage, with the keepalive time
      * set to 7200 by default on Linux. Modify settings to make the feature
      * actually useful. */