unix: implement uv_udp_set_ttl()

include/uv.h

@@ -658,6 +658,19 @@ UV_EXTERN int uv_udp_set_multicast_ttl(uv_udp_t* handle, int ttl);
  */
 UV_EXTERN int uv_udp_set_broadcast(uv_udp_t* handle, int on);
 
+/*
+ * Set the time to live
+ *
+ * Arguments:
+ *  handle              UDP handle. Should have been initialized with
+ *                      `uv_udp_init`.
+ *  ttl                 1 through 255
+ *
+ * Returns:
+ *  0 on success, -1 on error.
+ */
+UV_EXTERN int uv_udp_set_ttl(uv_udp_t* handle, int ttl);
+
 /*
  * Send data. If the socket has not previously been bound with `uv_udp_bind`
  * or `uv_udp_bind6`, it is bound to 0.0.0.0 (the "all interfaces" address)

src/unix/udp.c

@@ -528,6 +528,16 @@ int uv_udp_set_broadcast(uv_udp_t* handle, int on) {
 }
 
 
+int uv_udp_set_ttl(uv_udp_t* handle, int ttl) {
+  if (setsockopt(handle->fd, IPPROTO_IP, IP_TTL, &ttl, sizeof ttl)) {
+    uv__set_sys_error(handle->loop, errno);
+    return -1;
+  }
+
+  return 0;
+}
+
+
 int uv_udp_getsockname(uv_udp_t* handle, struct sockaddr* name,
     int* namelen) {
   socklen_t socklen;

src/win/udp.c

@@ -599,3 +599,9 @@ int uv_udp_set_broadcast(uv_udp_t* handle, int on) {
 
   return 0;
 }
+
+
+int uv_udp_set_ttl(uv_udp_t* handle, int ttl) {
+  uv__set_artificial_error(handle->loop, UV_ENOSYS);
+  return -1;
+}