GSocket: Add function to get the currently available bytes for reading

https://bugzilla.gnome.org/show_bug.cgi?id=668009

docs/reference/gio/gio-sections.txt

@@ -1806,6 +1806,7 @@ g_socket_is_connected
 g_socket_create_source
 g_socket_condition_check
 g_socket_condition_wait
+g_socket_get_available_bytes
 g_socket_set_listen_backlog
 g_socket_get_listen_backlog
 g_socket_get_blocking

gio/gio.symbols

@@ -949,6 +949,7 @@ g_socket_condition_check
 g_socket_condition_wait
 g_socket_connect
 g_socket_create_source
+g_socket_get_available_bytes
 g_socket_get_blocking
 g_socket_get_broadcast
 g_socket_get_family

gio/gsocket.c

@@ -41,6 +41,7 @@
 #ifndef G_OS_WIN32
 # include <fcntl.h>
 # include <unistd.h>
+# include <sys/ioctl.h>
 #endif
 
 #ifdef HAVE_SYS_UIO_H
@@ -2335,6 +2336,39 @@ g_socket_check_connect_result (GSocket  *socket,
   return TRUE;
 }
 
+/**
+ * g_socket_get_available_bytes:
+ * @socket: a #GSocket
+ *
+ * Get the amount of data pending in the OS input buffer.
+ *
+ * Returns: the number of bytes that can be read from the socket
+ * without blocking or -1 on error.
+ *
+ * Since: 2.32
+ */
+gssize
+g_socket_get_available_bytes (GSocket *socket)
+{
+#ifndef G_OS_WIN32
+  gulong avail = 0;
+#else
+  gint avail = 0;
+#endif
+
+  g_return_val_if_fail (G_IS_SOCKET (socket), -1);
+
+#ifndef G_OS_WIN32
+  if (ioctl (socket->priv->fd, FIONREAD, &avail) < 0)
+    return -1;
+#else
+  if (ioctlsocket (socket->priv->fd, FIONREAD, &avail) == SOCKET_ERROR)
+    return -1;
+#endif
+
+  return avail;
+}
+
 /**
  * g_socket_receive:
  * @socket: a #GSocket

gio/gsocket.h

@@ -137,6 +137,8 @@ gboolean               g_socket_connect                 (GSocket
 gboolean               g_socket_check_connect_result    (GSocket                 *socket,
 							 GError                 **error);
 
+gssize                 g_socket_get_available_bytes     (GSocket                 *socket);
+
 GIOCondition           g_socket_condition_check         (GSocket                 *socket,
 							 GIOCondition             condition);
 gboolean               g_socket_condition_wait          (GSocket                 *socket,