since: 2.48


g_socket_receive_messages (
  GSocket* socket,
  GInputMessage* messages,
  guint num_messages,
  gint flags,
  GCancellable* cancellable,
  GError** error


Receive multiple data messages from socket in one go. This is the most complicated and fully-featured version of this call. For easier use, see g_socket_receive(), g_socket_receive_from(), and g_socket_receive_message().

messages must point to an array of GInputMessage structs and num_messages must be the length of this array. Each GInputMessage contains a pointer to an array of GInputVector structs describing the buffers that the data received in each message will be written to. Using multiple GInputVectors is more memory-efficient than manually copying data out of a single buffer to multiple sources, and more system-call-efficient than making multiple calls to g_socket_receive(), such as in scenarios where a lot of data packets need to be received (e.g. high-bandwidth video streaming over RTP/UDP).

flags modify how all messages are received. The commonly available arguments for this are available in the GSocketMsgFlags enum, but the values there are the same as the system values, and the flags are passed in as-is, so you can pass in system-specific flags too. These flags affect the overall receive operation. Flags affecting individual messages are returned in GInputMessage.flags.

The other members of GInputMessage are treated as described in its documentation.

If GSocket:blocking is TRUE the call will block until num_messages have been received, or the end of the stream is reached.

If GSocket:blocking is FALSE the call will return up to num_messages without blocking, or G_IO_ERROR_WOULD_BLOCK if no messages are queued in the operating system to be received.

In blocking mode, if GSocket:timeout is positive and is reached before any messages are received, G_IO_ERROR_TIMED_OUT is returned, otherwise up to num_messages are returned. (Note: This is effectively the behaviour of MSG_WAITFORONE with recvmmsg().)

To be notified when messages are available, wait for the G_IO_IN condition. Note though that you may still receive G_IO_ERROR_WOULD_BLOCK from g_socket_receive_messages() even if you were previously notified of a G_IO_IN condition.

If the remote peer closes the connection, any messages queued in the operating system will be returned, and subsequent calls to g_socket_receive_messages() will return 0 (with no error set).

On error -1 is returned and error is set accordingly. An error will only be returned if zero messages could be received; otherwise the number of messages successfully received before the error will be returned.

Available since: 2.48



Type: An array of GInputMessage

An array of GInputMessage structs.

The length of the array is specified in the num_messages argument.
The data is owned by the caller of the function.

Type: guint

The number of elements in messages.


Type: gint

An int containing GSocketMsgFlags flags for the overall operation, which may additionally contain other platform specific flags


Type: GCancellable

A %GCancellable or NULL.

The argument can be NULL.
The data is owned by the caller of the function.

Type: GError **

The return location for a recoverable error.

The argument can be NULL.
If the return location is not NULL, then you must initialize it to a NULL GError*.
The argument will left initialized to NULL by the method if there are no errors.
In case of error, the argument will be set to a newly allocated GError; the caller will take ownership of the data, and be responsible for freeing it.

Return value

Type: gint

Number of messages received, or -1 on error. Note that the number of messages received may be smaller than num_messages if in non-blocking mode, if the peer closed the connection, or if num_messages was larger than UIO_MAXIOV (1024), in which case the caller may re-try to receive the remaining messages.