GSocket

GSocket — Low-level socket object

Synopsis

#include <gio/gio.h>

                    GSocket;
gboolean            (*GSocketSourceFunc)                (GSocket *socket,
                                                         GIOCondition condition,
                                                         gpointer user_data);
enum                GSocketType;
enum                GSocketProtocol;
enum                GSocketMsgFlags;
                    GInputVector;
                    GOutputVector;
GSocket *               g_socket_new                    (GSocketFamily family,
                                                         GSocketType type,
                                                         GSocketProtocol protocol,
                                                         GError **error);
GSocket *               g_socket_new_from_fd            (gint fd,
                                                         GError **error);
gboolean            g_socket_bind                       (GSocket *socket,
                                                         GSocketAddress *address,
                                                         gboolean allow_reuse,
                                                         GError **error);
gboolean            g_socket_listen                     (GSocket *socket,
                                                         GError **error);
GSocket *               g_socket_accept                 (GSocket *socket,
                                                         GCancellable *cancellable,
                                                         GError **error);
gboolean            g_socket_connect                    (GSocket *socket,
                                                         GSocketAddress *address,
                                                         GCancellable *cancellable,
                                                         GError **error);
gboolean            g_socket_check_connect_result       (GSocket *socket,
                                                         GError **error);
gssize              g_socket_receive                    (GSocket *socket,
                                                         gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_receive_from               (GSocket *socket,
                                                         GSocketAddress **address,
                                                         gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_receive_message            (GSocket *socket,
                                                         GSocketAddress **address,
                                                         GInputVector *vectors,
                                                         gint num_vectors,
                                                         GSocketControlMessage ***messages,
                                                         gint *num_messages,
                                                         gint *flags,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_receive_with_blocking      (GSocket *socket,
                                                         gchar *buffer,
                                                         gsize size,
                                                         gboolean blocking,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_send                       (GSocket *socket,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_send_to                    (GSocket *socket,
                                                         GSocketAddress *address,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_send_message               (GSocket *socket,
                                                         GSocketAddress *address,
                                                         GOutputVector *vectors,
                                                         gint num_vectors,
                                                         GSocketControlMessage **messages,
                                                         gint num_messages,
                                                         gint flags,
                                                         GCancellable *cancellable,
                                                         GError **error);
gssize              g_socket_send_with_blocking         (GSocket *socket,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         gboolean blocking,
                                                         GCancellable *cancellable,
                                                         GError **error);
gboolean            g_socket_close                      (GSocket *socket,
                                                         GError **error);
gboolean            g_socket_is_closed                  (GSocket *socket);
gboolean            g_socket_shutdown                   (GSocket *socket,
                                                         gboolean shutdown_read,
                                                         gboolean shutdown_write,
                                                         GError **error);
gboolean            g_socket_is_connected               (GSocket *socket);
GSource *               g_socket_create_source          (GSocket *socket,
                                                         GIOCondition condition,
                                                         GCancellable *cancellable);
GIOCondition        g_socket_condition_check            (GSocket *socket,
                                                         GIOCondition condition);
gboolean            g_socket_condition_wait             (GSocket *socket,
                                                         GIOCondition condition,
                                                         GCancellable *cancellable,
                                                         GError **error);
void                g_socket_set_listen_backlog         (GSocket *socket,
                                                         gint backlog);
gint                g_socket_get_listen_backlog         (GSocket *socket);
gboolean            g_socket_get_blocking               (GSocket *socket);
void                g_socket_set_blocking               (GSocket *socket,
                                                         gboolean blocking);
gboolean            g_socket_get_keepalive              (GSocket *socket);
void                g_socket_set_keepalive              (GSocket *socket,
                                                         gboolean keepalive);
guint               g_socket_get_timeout                (GSocket *socket);
void                g_socket_set_timeout                (GSocket *socket,
                                                         guint timeout);
GSocketFamily       g_socket_get_family                 (GSocket *socket);
int                 g_socket_get_fd                     (GSocket *socket);
GSocketAddress *        g_socket_get_local_address      (GSocket *socket,
                                                         GError **error);
GSocketProtocol     g_socket_get_protocol               (GSocket *socket);
GSocketAddress *        g_socket_get_remote_address     (GSocket *socket,
                                                         GError **error);
GSocketType         g_socket_get_socket_type            (GSocket *socket);
gboolean            g_socket_speaks_ipv4                (GSocket *socket);
GCredentials *      g_socket_get_credentials            (GSocket *socket,
                                                         GError **error);

Object Hierarchy

  GObject
   +----GSocket

Implemented Interfaces

GSocket implements GInitable.

Properties

  "blocking"                 gboolean              : Read / Write
  "family"                   GSocketFamily         : Read / Write / Construct Only
  "fd"                       gint                  : Read / Write / Construct Only
  "keepalive"                gboolean              : Read / Write
  "listen-backlog"           gint                  : Read / Write
  "local-address"            GSocketAddress*       : Read
  "protocol"                 GSocketProtocol       : Read / Write / Construct Only
  "remote-address"           GSocketAddress*       : Read
  "timeout"                  guint                 : Read / Write
  "type"                     GSocketType           : Read / Write / Construct Only

Description

A GSocket is a low-level networking primitive. It is a more or less direct mapping of the BSD socket API in a portable GObject based API. It supports both the UNIX socket implementations and winsock2 on Windows.

GSocket is the platform independent base upon which the higher level network primitives are based. Applications are not typically meant to use it directly, but rather through classes like GSocketClient, GSocketService and GSocketConnection. However there may be cases where direct use of GSocket is useful.

GSocket implements the GInitable interface, so if it is manually constructed by e.g. g_object_new() you must call g_initable_init() and check the results before using the object. This is done automatically in g_socket_new() and g_socket_new_from_fd(), so these functions can return NULL.

Sockets operate in two general modes, blocking or non-blocking. When in blocking mode all operations block until the requested operation is finished or there is an error. In non-blocking mode all calls that would block return immediately with a G_IO_ERROR_WOULD_BLOCK error. To know when a call would successfully run you can call g_socket_condition_check(), or g_socket_condition_wait(). You can also use g_socket_create_source() and attach it to a GMainContext to get callbacks when I/O is possible. Note that all sockets are always set to non blocking mode in the system, and blocking mode is emulated in GSocket.

When working in non-blocking mode applications should always be able to handle getting a G_IO_ERROR_WOULD_BLOCK error even when some other function said that I/O was possible. This can easily happen in case of a race condition in the application, but it can also happen for other reasons. For instance, on Windows a socket is always seen as writable until a write returns G_IO_ERROR_WOULD_BLOCK.

GSockets can be either connection oriented or datagram based. For connection oriented types you must first establish a connection by either connecting to an address or accepting a connection from another address. For connectionless socket types the target/source address is specified or received in each I/O operation.

All socket file descriptors are set to be close-on-exec.

Note that creating a GSocket causes the signal SIGPIPE to be ignored for the remainder of the program. If you are writing a command-line utility that uses GSocket, you may need to take into account the fact that your program will not automatically be killed if it tries to write to stdout after it has been closed.

Details

GSocket

typedef struct _GSocket GSocket;

A lowlevel network socket object.

Since 2.22


GSocketSourceFunc ()

gboolean            (*GSocketSourceFunc)                (GSocket *socket,
                                                         GIOCondition condition,
                                                         gpointer user_data);

This is the function type of the callback used for the GSource returned by g_socket_create_source().

socket :

the GSocket

condition :

the current condition at the source fired.

user_data :

data passed in by the user.

Returns :

it should return FALSE if the source should be removed.

Since 2.22


enum GSocketType

typedef enum
{
  G_SOCKET_TYPE_INVALID,
  G_SOCKET_TYPE_STREAM,
  G_SOCKET_TYPE_DATAGRAM,
  G_SOCKET_TYPE_SEQPACKET
} GSocketType;

Flags used when creating a GSocket. Some protocols may not implement all the socket types.

G_SOCKET_TYPE_INVALID

Type unknown or wrong

G_SOCKET_TYPE_STREAM

Reliable connection-based byte streams (e.g. TCP).

G_SOCKET_TYPE_DATAGRAM

Connectionless, unreliable datagram passing. (e.g. UDP)

G_SOCKET_TYPE_SEQPACKET

Reliable connection-based passing of datagrams of fixed maximum length (e.g. SCTP).

Since 2.22


enum GSocketProtocol

typedef enum {
  G_SOCKET_PROTOCOL_UNKNOWN = -1,
  G_SOCKET_PROTOCOL_DEFAULT = 0,
  G_SOCKET_PROTOCOL_TCP     = 6,
  G_SOCKET_PROTOCOL_UDP     = 17,
  G_SOCKET_PROTOCOL_SCTP    = 132
} GSocketProtocol;

A protocol identifier is specified when creating a GSocket, which is a family/type specific identifier, where 0 means the default protocol for the particular family/type.

This enum contains a set of commonly available and used protocols. You can also pass any other identifiers handled by the platform in order to use protocols not listed here.

G_SOCKET_PROTOCOL_UNKNOWN

The protocol type is unknown

G_SOCKET_PROTOCOL_DEFAULT

The default protocol for the family/type

G_SOCKET_PROTOCOL_TCP

TCP over IP

G_SOCKET_PROTOCOL_UDP

UDP over IP

G_SOCKET_PROTOCOL_SCTP

SCTP over IP

Since 2.22


enum GSocketMsgFlags

typedef enum
{
  G_SOCKET_MSG_NONE,
  G_SOCKET_MSG_OOB = GLIB_SYSDEF_MSG_OOB,
  G_SOCKET_MSG_PEEK = GLIB_SYSDEF_MSG_PEEK,
  G_SOCKET_MSG_DONTROUTE = GLIB_SYSDEF_MSG_DONTROUTE
} GSocketMsgFlags;

Flags used in g_socket_receive_message() and g_socket_send_message(). The flags listed in the enum are some commonly available flags, but the values used for them are the same as on the platform, and any other flags are passed in/out as is. So to use a platform specific flag, just include the right system header and pass in the flag.

G_SOCKET_MSG_NONE

No flags.

G_SOCKET_MSG_OOB

Request to send/receive out of band data.

G_SOCKET_MSG_PEEK

Read data from the socket without removing it from the queue.

G_SOCKET_MSG_DONTROUTE

Don't use a gateway to send out the packet, only send to hosts on directly connected networks.

Since 2.22


GInputVector

typedef struct {
  gpointer buffer;
  gsize size;
} GInputVector;

Structure used for scatter/gather data input. You generally pass in an array of GInputVectors and the operation will store the read data starting in the first buffer, switching to the next as needed.

gpointer buffer;

Pointer to a buffer where data will be written.

gsize size;

the available size in buffer.

Since 2.22


GOutputVector

typedef struct {
  gconstpointer buffer;
  gsize size;
} GOutputVector;

Structure used for scatter/gather data output. You generally pass in an array of GOutputVectors and the operation will use all the buffers as if they were one buffer.

gconstpointer buffer;

Pointer to a buffer of data to read.

gsize size;

the size of buffer.

Since 2.22


g_socket_new ()

GSocket *               g_socket_new                    (GSocketFamily family,
                                                         GSocketType type,
                                                         GSocketProtocol protocol,
                                                         GError **error);

Creates a new GSocket with the defined family, type and protocol. If protocol is 0 (G_SOCKET_PROTOCOL_DEFAULT) the default protocol type for the family and type is used.

The protocol is a family and type specific int that specifies what kind of protocol to use. GSocketProtocol lists several common ones. Many families only support one protocol, and use 0 for this, others support several and using 0 means to use the default protocol for the family and type.

The protocol id is passed directly to the operating system, so you can use protocols not listed in GSocketProtocol if you know the protocol number used for it.

family :

the socket family to use, e.g. G_SOCKET_FAMILY_IPV4.

type :

the socket type to use.

protocol :

the id of the protocol to use, or 0 for default.

error :

GError for error reporting, or NULL to ignore.

Returns :

a GSocket or NULL on error. Free the returned object with g_object_unref().

Since 2.22


g_socket_new_from_fd ()

GSocket *               g_socket_new_from_fd            (gint fd,
                                                         GError **error);

Creates a new GSocket from a native file descriptor or winsock SOCKET handle.

This reads all the settings from the file descriptor so that all properties should work. Note that the file descriptor will be set to non-blocking mode, independent on the blocking mode of the GSocket.

fd :

a native socket file descriptor.

error :

GError for error reporting, or NULL to ignore.

Returns :

a GSocket or NULL on error. Free the returned object with g_object_unref().

Since 2.22


g_socket_bind ()

gboolean            g_socket_bind                       (GSocket *socket,
                                                         GSocketAddress *address,
                                                         gboolean allow_reuse,
                                                         GError **error);

When a socket is created it is attached to an address family, but it doesn't have an address in this family. g_socket_bind() assigns the address (sometimes called name) of the socket.

It is generally required to bind to a local address before you can receive connections. (See g_socket_listen() and g_socket_accept() ). In certain situations, you may also want to bind a socket that will be used to initiate connections, though this is not normally required.

allow_reuse should be TRUE for server sockets (sockets that you will eventually call g_socket_accept() on), and FALSE for client sockets. (Specifically, if it is TRUE, then g_socket_bind() will set the SO_REUSEADDR flag on the socket, allowing it to bind address even if that address was previously used by another socket that has not yet been fully cleaned-up by the kernel. Failing to set this flag on a server socket may cause the bind call to return G_IO_ERROR_ADDRESS_IN_USE if the server program is stopped and then immediately restarted.)

socket :

a GSocket.

address :

a GSocketAddress specifying the local address.

allow_reuse :

whether to allow reusing this address

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE on success, FALSE on error.

Since 2.22


g_socket_listen ()

gboolean            g_socket_listen                     (GSocket *socket,
                                                         GError **error);

Marks the socket as a server socket, i.e. a socket that is used to accept incoming requests using g_socket_accept().

Before calling this the socket must be bound to a local address using g_socket_bind().

To set the maximum amount of outstanding clients, use g_socket_set_listen_backlog().

socket :

a GSocket.

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE on success, FALSE on error.

Since 2.22


g_socket_accept ()

GSocket *               g_socket_accept                 (GSocket *socket,
                                                         GCancellable *cancellable,
                                                         GError **error);

Accept incoming connections on a connection-based socket. This removes the first outstanding connection request from the listening socket and creates a GSocket object for it.

The socket must be bound to a local address with g_socket_bind() and must be listening for incoming connections (g_socket_listen()).

If there are no outstanding connections then the operation will block or return G_IO_ERROR_WOULD_BLOCK if non-blocking I/O is enabled. To be notified of an incoming connection, wait for the G_IO_IN condition.

socket :

a GSocket.

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

a new GSocket, or NULL on error. Free the returned object with g_object_unref().

Since 2.22


g_socket_connect ()

gboolean            g_socket_connect                    (GSocket *socket,
                                                         GSocketAddress *address,
                                                         GCancellable *cancellable,
                                                         GError **error);

Connect the socket to the specified remote address.

For connection oriented socket this generally means we attempt to make a connection to the address. For a connection-less socket it sets the default address for g_socket_send() and discards all incoming datagrams from other sources.

Generally connection oriented sockets can only connect once, but connection-less sockets can connect multiple times to change the default address.

If the connect call needs to do network I/O it will block, unless non-blocking I/O is enabled. Then G_IO_ERROR_PENDING is returned and the user can be notified of the connection finishing by waiting for the G_IO_OUT condition. The result of the connection can then be checked with g_socket_check_connect_result().

socket :

a GSocket.

address :

a GSocketAddress specifying the remote address.

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE if connected, FALSE on error.

Since 2.22


g_socket_check_connect_result ()

gboolean            g_socket_check_connect_result       (GSocket *socket,
                                                         GError **error);

Checks and resets the pending connect error for the socket. This is used to check for errors when g_socket_connect() is used in non-blocking mode.

socket :

a GSocket

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE if no error, FALSE otherwise, setting error to the error

Since 2.22


g_socket_receive ()

gssize              g_socket_receive                    (GSocket *socket,
                                                         gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

Receive data (up to size bytes) from a socket. This is mainly used by connection-oriented sockets; it is identical to g_socket_receive_from() with address set to NULL.

For G_SOCKET_TYPE_DATAGRAM and G_SOCKET_TYPE_SEQPACKET sockets, g_socket_receive() will always read either 0 or 1 complete messages from the socket. If the received message is too large to fit in buffer, then the data beyond size bytes will be discarded, without any explicit indication that this has occurred.

For G_SOCKET_TYPE_STREAM sockets, g_socket_receive() can return any number of bytes, up to size. If more than size bytes have been received, the additional data will be returned in future calls to g_socket_receive().

If the socket is in blocking mode the call will block until there is some data to receive or there is an error. If there is no data available and the socket is in non-blocking mode, a G_IO_ERROR_WOULD_BLOCK error will be returned. To be notified when data is available, wait for the G_IO_IN condition.

On error -1 is returned and error is set accordingly.

socket :

a GSocket

buffer :

a buffer to read data into (which should be at least size bytes long).

size :

the number of bytes you want to read from the socket

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes read, or -1 on error

Since 2.22


g_socket_receive_from ()

gssize              g_socket_receive_from               (GSocket *socket,
                                                         GSocketAddress **address,
                                                         gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

Receive data (up to size bytes) from a socket.

If address is non-NULL then address will be set equal to the source address of the received packet. address is owned by the caller.

See g_socket_receive() for additional information.

socket :

a GSocket

address :

a pointer to a GSocketAddress pointer, or NULL

buffer :

a buffer to read data into (which should be at least size bytes long).

size :

the number of bytes you want to read from the socket

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes read, or -1 on error

Since 2.22


g_socket_receive_message ()

gssize              g_socket_receive_message            (GSocket *socket,
                                                         GSocketAddress **address,
                                                         GInputVector *vectors,
                                                         gint num_vectors,
                                                         GSocketControlMessage ***messages,
                                                         gint *num_messages,
                                                         gint *flags,
                                                         GCancellable *cancellable,
                                                         GError **error);

Receive data from a socket. This is the most complicated and fully-featured version of this call. For easier use, see g_socket_receive() and g_socket_receive_from().

If address is non-NULL then address will be set equal to the source address of the received packet. address is owned by the caller.

vector must point to an array of GInputVector structs and num_vectors must be the length of this array. These structs describe the buffers that received data will be scattered into. If num_vectors is -1, then vectors is assumed to be terminated by a GInputVector with a NULL buffer pointer.

As a special case, if num_vectors is 0 (in which case, vectors may of course be NULL), then a single byte is received and discarded. This is to facilitate the common practice of sending a single '\0' byte for the purposes of transferring ancillary data.

messages, if non-NULL, will be set to point to a newly-allocated array of GSocketControlMessage instances or NULL if no such messages was received. These correspond to the control messages received from the kernel, one GSocketControlMessage per message from the kernel. This array is NULL-terminated and must be freed by the caller using g_free() after calling g_object_unref() on each element. If messages is NULL, any control messages received will be discarded.

num_messages, if non-NULL, will be set to the number of control messages received.

If both messages and num_messages are non-NULL, then num_messages gives the number of GSocketControlMessage instances in messages (ie: not including the NULL terminator).

flags is an in/out parameter. 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 (and g_socket_receive_message() may pass system-specific flags out).

As with g_socket_receive(), data may be discarded if socket is G_SOCKET_TYPE_DATAGRAM or G_SOCKET_TYPE_SEQPACKET and you do not provide enough buffer space to read a complete message. You can pass G_SOCKET_MSG_PEEK in flags to peek at the current message without removing it from the receive queue, but there is no portable way to find out the length of the message other than by reading it into a sufficiently-large buffer.

If the socket is in blocking mode the call will block until there is some data to receive or there is an error. If there is no data available and the socket is in non-blocking mode, a G_IO_ERROR_WOULD_BLOCK error will be returned. To be notified when data is available, wait for the G_IO_IN condition.

On error -1 is returned and error is set accordingly.

socket :

a GSocket

address :

a pointer to a GSocketAddress pointer, or NULL

vectors :

an array of GInputVector structs

num_vectors :

the number of elements in vectors, or -1

messages :

a pointer which may be filled with an array of GSocketControlMessages, or NULL

num_messages :

a pointer which will be filled with the number of elements in messages, or NULL

flags :

a pointer to an int containing GSocketMsgFlags flags

cancellable :

a GCancellable or NULL

error :

a GError pointer, or NULL

Returns :

Number of bytes read, or -1 on error

Since 2.22


g_socket_receive_with_blocking ()

gssize              g_socket_receive_with_blocking      (GSocket *socket,
                                                         gchar *buffer,
                                                         gsize size,
                                                         gboolean blocking,
                                                         GCancellable *cancellable,
                                                         GError **error);

This behaves exactly the same as g_socket_receive(), except that the choice of blocking or non-blocking behavior is determined by the blocking argument rather than by socket's properties.

socket :

a GSocket

buffer :

a buffer to read data into (which should be at least size bytes long).

size :

the number of bytes you want to read from the socket

blocking :

whether to do blocking or non-blocking I/O

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes read, or -1 on error

Since 2.26


g_socket_send ()

gssize              g_socket_send                       (GSocket *socket,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

Tries to send size bytes from buffer on the socket. This is mainly used by connection-oriented sockets; it is identical to g_socket_send_to() with address set to NULL.

If the socket is in blocking mode the call will block until there is space for the data in the socket queue. If there is no space available and the socket is in non-blocking mode a G_IO_ERROR_WOULD_BLOCK error will be returned. To be notified when space is available, wait for the G_IO_OUT condition. Note though that you may still receive G_IO_ERROR_WOULD_BLOCK from g_socket_send() even if you were previously notified of a G_IO_OUT condition. (On Windows in particular, this is very common due to the way the underlying APIs work.)

On error -1 is returned and error is set accordingly.

socket :

a GSocket

buffer :

the buffer containing the data to send.

size :

the number of bytes to send

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes written (which may be less than size), or -1 on error

Since 2.22


g_socket_send_to ()

gssize              g_socket_send_to                    (GSocket *socket,
                                                         GSocketAddress *address,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

Tries to send size bytes from buffer to address. If address is NULL then the message is sent to the default receiver (set by g_socket_connect()).

See g_socket_send() for additional information.

socket :

a GSocket

address :

a GSocketAddress, or NULL

buffer :

the buffer containing the data to send.

size :

the number of bytes to send

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes written (which may be less than size), or -1 on error

Since 2.22


g_socket_send_message ()

gssize              g_socket_send_message               (GSocket *socket,
                                                         GSocketAddress *address,
                                                         GOutputVector *vectors,
                                                         gint num_vectors,
                                                         GSocketControlMessage **messages,
                                                         gint num_messages,
                                                         gint flags,
                                                         GCancellable *cancellable,
                                                         GError **error);

Send data to address on socket. This is the most complicated and fully-featured version of this call. For easier use, see g_socket_send() and g_socket_send_to().

If address is NULL then the message is sent to the default receiver (set by g_socket_connect()).

vectors must point to an array of GOutputVector structs and num_vectors must be the length of this array. (If num_vectors is -1, then vectors is assumed to be terminated by a GOutputVector with a NULL buffer pointer.) The GOutputVector structs describe the buffers that the sent data will be gathered from. Using multiple GOutputVectors is more memory-efficient than manually copying data from multiple sources into a single buffer, and more network-efficient than making multiple calls to g_socket_send().

messages, if non-NULL, is taken to point to an array of num_messages GSocketControlMessage instances. These correspond to the control messages to be sent on the socket. If num_messages is -1 then messages is treated as a NULL-terminated array.

flags modify how the message is sent. 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.

If the socket is in blocking mode the call will block until there is space for the data in the socket queue. If there is no space available and the socket is in non-blocking mode a G_IO_ERROR_WOULD_BLOCK error will be returned. To be notified when space is available, wait for the G_IO_OUT condition. Note though that you may still receive G_IO_ERROR_WOULD_BLOCK from g_socket_send() even if you were previously notified of a G_IO_OUT condition. (On Windows in particular, this is very common due to the way the underlying APIs work.)

On error -1 is returned and error is set accordingly.

socket :

a GSocket

address :

a GSocketAddress, or NULL

vectors :

an array of GOutputVector structs

num_vectors :

the number of elements in vectors, or -1

messages :

a pointer to an array of GSocketControlMessages, or NULL.

num_messages :

number of elements in messages, or -1.

flags :

an int containing GSocketMsgFlags flags

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes written (which may be less than size), or -1 on error

Since 2.22


g_socket_send_with_blocking ()

gssize              g_socket_send_with_blocking         (GSocket *socket,
                                                         const gchar *buffer,
                                                         gsize size,
                                                         gboolean blocking,
                                                         GCancellable *cancellable,
                                                         GError **error);

This behaves exactly the same as g_socket_send(), except that the choice of blocking or non-blocking behavior is determined by the blocking argument rather than by socket's properties.

socket :

a GSocket

buffer :

the buffer containing the data to send.

size :

the number of bytes to send

blocking :

whether to do blocking or non-blocking I/O

cancellable :

a GCancellable or NULL

error :

GError for error reporting, or NULL to ignore.

Returns :

Number of bytes written (which may be less than size), or -1 on error

Since 2.26


g_socket_close ()

gboolean            g_socket_close                      (GSocket *socket,
                                                         GError **error);

Closes the socket, shutting down any active connection.

Closing a socket does not wait for all outstanding I/O operations to finish, so the caller should not rely on them to be guaranteed to complete even if the close returns with no error.

Once the socket is closed, all other operations will return G_IO_ERROR_CLOSED. Closing a socket multiple times will not return an error.

Sockets will be automatically closed when the last reference is dropped, but you might want to call this function to make sure resources are released as early as possible.

Beware that due to the way that TCP works, it is possible for recently-sent data to be lost if either you close a socket while the G_IO_IN condition is set, or else if the remote connection tries to send something to you after you close the socket but before it has finished reading all of the data you sent. There is no easy generic way to avoid this problem; the easiest fix is to design the network protocol such that the client will never send data "out of turn". Another solution is for the server to half-close the connection by calling g_socket_shutdown() with only the shutdown_write flag set, and then wait for the client to notice this and close its side of the connection, after which the server can safely call g_socket_close(). (This is what GTcpConnection does if you call g_tcp_connection_set_graceful_disconnect(). But of course, this only works if the client will close its connection after the server does.)

socket :

a GSocket

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE on success, FALSE on error

Since 2.22


g_socket_is_closed ()

gboolean            g_socket_is_closed                  (GSocket *socket);

Checks whether a socket is closed.

socket :

a GSocket

Returns :

TRUE if socket is closed, FALSE otherwise

Since 2.22


g_socket_shutdown ()

gboolean            g_socket_shutdown                   (GSocket *socket,
                                                         gboolean shutdown_read,
                                                         gboolean shutdown_write,
                                                         GError **error);

Shut down part of a full-duplex connection.

If shutdown_read is TRUE then the recieving side of the connection is shut down, and further reading is disallowed.

If shutdown_write is TRUE then the sending side of the connection is shut down, and further writing is disallowed.

It is allowed for both shutdown_read and shutdown_write to be TRUE.

One example where this is used is graceful disconnect for TCP connections where you close the sending side, then wait for the other side to close the connection, thus ensuring that the other side saw all sent data.

socket :

a GSocket

shutdown_read :

whether to shut down the read side

shutdown_write :

whether to shut down the write side

error :

GError for error reporting, or NULL to ignore.

Returns :

TRUE on success, FALSE on error

Since 2.22


g_socket_is_connected ()

gboolean            g_socket_is_connected               (GSocket *socket);

Check whether the socket is connected. This is only useful for connection-oriented sockets.

socket :

a GSocket.

Returns :

TRUE if socket is connected, FALSE otherwise.

Since 2.22


g_socket_create_source ()

GSource *               g_socket_create_source          (GSocket *socket,
                                                         GIOCondition condition,
                                                         GCancellable *cancellable);

Creates a GSource that can be attached to a GMainContext to monitor for the availibility of the specified condition on the socket.

The callback on the source is of the GSocketSourceFunc type.

It is meaningless to specify G_IO_ERR or G_IO_HUP in condition; these conditions will always be reported output if they are true.

cancellable if not NULL can be used to cancel the source, which will cause the source to trigger, reporting the current condition (which is likely 0 unless cancellation happened at the same time as a condition change). You can check for this in the callback using g_cancellable_is_cancelled().

If socket has a timeout set, and it is reached before condition occurs, the source will then trigger anyway, reporting G_IO_IN or G_IO_OUT depending on condition. However, socket will have been marked as having had a timeout, and so the next GSocket I/O method you call will then fail with a G_IO_ERROR_TIMED_OUT.

socket :

a GSocket

condition :

a GIOCondition mask to monitor

cancellable :

a GCancellable or NULL

Returns :

a newly allocated GSource, free with g_source_unref().

Since 2.22


g_socket_condition_check ()

GIOCondition        g_socket_condition_check            (GSocket *socket,
                                                         GIOCondition condition);

Checks on the readiness of socket to perform operations. The operations specified in condition are checked for and masked against the currently-satisfied conditions on socket. The result is returned.

Note that on Windows, it is possible for an operation to return G_IO_ERROR_WOULD_BLOCK even immediately after g_socket_condition_check() has claimed that the socket is ready for writing. Rather than calling g_socket_condition_check() and then writing to the socket if it succeeds, it is generally better to simply try writing to the socket right away, and try again later if the initial attempt returns G_IO_ERROR_WOULD_BLOCK.

It is meaningless to specify G_IO_ERR or G_IO_HUP in condition; these conditions will always be set in the output if they are true.

This call never blocks.

socket :

a GSocket

condition :

a GIOCondition mask to check

Returns :

the GIOCondition mask of the current state

Since 2.22


g_socket_condition_wait ()

gboolean            g_socket_condition_wait             (GSocket *socket,
                                                         GIOCondition condition,
                                                         GCancellable *cancellable,
                                                         GError **error);

Waits for condition to become true on socket. When the condition is met, TRUE is returned.

If cancellable is cancelled before the condition is met, or if the socket has a timeout set and it is reached before the condition is met, then FALSE is returned and error, if non-NULL, is set to the appropriate value (G_IO_ERROR_CANCELLED or G_IO_ERROR_TIMED_OUT).

socket :

a GSocket

condition :

a GIOCondition mask to wait for

cancellable :

a GCancellable, or NULL

error :

a GError pointer, or NULL

Returns :

TRUE if the condition was met, FALSE otherwise

Since 2.22


g_socket_set_listen_backlog ()

void                g_socket_set_listen_backlog         (GSocket *socket,
                                                         gint backlog);

Sets the maximum number of outstanding connections allowed when listening on this socket. If more clients than this are connecting to the socket and the application is not handling them on time then the new connections will be refused.

Note that this must be called before g_socket_listen() and has no effect if called after that.

socket :

a GSocket.

backlog :

the maximum number of pending connections.

Since 2.22


g_socket_get_listen_backlog ()

gint                g_socket_get_listen_backlog         (GSocket *socket);

Gets the listen backlog setting of the socket. For details on this, see g_socket_set_listen_backlog().

socket :

a GSocket.

Returns :

the maximum number of pending connections.

Since 2.22


g_socket_get_blocking ()

gboolean            g_socket_get_blocking               (GSocket *socket);

Gets the blocking mode of the socket. For details on blocking I/O, see g_socket_set_blocking().

socket :

a GSocket.

Returns :

TRUE if blocking I/O is used, FALSE otherwise.

Since 2.22


g_socket_set_blocking ()

void                g_socket_set_blocking               (GSocket *socket,
                                                         gboolean blocking);

Sets the blocking mode of the socket. In blocking mode all operations block until they succeed or there is an error. In non-blocking mode all functions return results immediately or with a G_IO_ERROR_WOULD_BLOCK error.

All sockets are created in blocking mode. However, note that the platform level socket is always non-blocking, and blocking mode is a GSocket level feature.

socket :

a GSocket.

blocking :

Whether to use blocking I/O or not.

Since 2.22


g_socket_get_keepalive ()

gboolean            g_socket_get_keepalive              (GSocket *socket);

Gets the keepalive mode of the socket. For details on this, see g_socket_set_keepalive().

socket :

a GSocket.

Returns :

TRUE if keepalive is active, FALSE otherwise.

Since 2.22


g_socket_set_keepalive ()

void                g_socket_set_keepalive              (GSocket *socket,
                                                         gboolean keepalive);

Sets or unsets the SO_KEEPALIVE flag on the underlying socket. When this flag is set on a socket, the system will attempt to verify that the remote socket endpoint is still present if a sufficiently long period of time passes with no data being exchanged. If the system is unable to verify the presence of the remote endpoint, it will automatically close the connection.

This option is only functional on certain kinds of sockets. (Notably, G_SOCKET_PROTOCOL_TCP sockets.)

The exact time between pings is system- and protocol-dependent, but will normally be at least two hours. Most commonly, you would set this flag on a server socket if you want to allow clients to remain idle for long periods of time, but also want to ensure that connections are eventually garbage-collected if clients crash or become unreachable.

socket :

a GSocket.

keepalive :

Value for the keepalive flag

Since 2.22


g_socket_get_timeout ()

guint               g_socket_get_timeout                (GSocket *socket);

Gets the timeout setting of the socket. For details on this, see g_socket_set_timeout().

socket :

a GSocket.

Returns :

the timeout in seconds

Since 2.26


g_socket_set_timeout ()

void                g_socket_set_timeout                (GSocket *socket,
                                                         guint timeout);

Sets the time in seconds after which I/O operations on socket will time out if they have not yet completed.

On a blocking socket, this means that any blocking GSocket operation will time out after timeout seconds of inactivity, returning G_IO_ERROR_TIMED_OUT.

On a non-blocking socket, calls to g_socket_condition_wait() will also fail with G_IO_ERROR_TIMED_OUT after the given time. Sources created with g_socket_create_source() will trigger after timeout seconds of inactivity, with the requested condition set, at which point calling g_socket_receive(), g_socket_send(), g_socket_check_connect_result(), etc, will fail with G_IO_ERROR_TIMED_OUT.

If timeout is 0 (the default), operations will never time out on their own.

Note that if an I/O operation is interrupted by a signal, this may cause the timeout to be reset.

socket :

a GSocket.

timeout :

the timeout for socket, in seconds, or 0 for none

Since 2.26


g_socket_get_family ()

GSocketFamily       g_socket_get_family                 (GSocket *socket);

Gets the socket family of the socket.

socket :

a GSocket.

Returns :

a GSocketFamily

Since 2.22


g_socket_get_fd ()

int                 g_socket_get_fd                     (GSocket *socket);

Returns the underlying OS socket object. On unix this is a socket file descriptor, and on windows this is a Winsock2 SOCKET handle. This may be useful for doing platform specific or otherwise unusual operations on the socket.

socket :

a GSocket.

Returns :

the file descriptor of the socket.

Since 2.22


g_socket_get_local_address ()

GSocketAddress *        g_socket_get_local_address      (GSocket *socket,
                                                         GError **error);

Try to get the local address of a bound socket. This is only useful if the socket has been bound to a local address, either explicitly or implicitly when connecting.

socket :

a GSocket.

error :

GError for error reporting, or NULL to ignore.

Returns :

a GSocketAddress or NULL on error. Free the returned object with g_object_unref().

Since 2.22


g_socket_get_protocol ()

GSocketProtocol     g_socket_get_protocol               (GSocket *socket);

Gets the socket protocol id the socket was created with. In case the protocol is unknown, -1 is returned.

socket :

a GSocket.

Returns :

a protocol id, or -1 if unknown

Since 2.22


g_socket_get_remote_address ()

GSocketAddress *        g_socket_get_remote_address     (GSocket *socket,
                                                         GError **error);

Try to get the remove address of a connected socket. This is only useful for connection oriented sockets that have been connected.

socket :

a GSocket.

error :

GError for error reporting, or NULL to ignore.

Returns :

a GSocketAddress or NULL on error. Free the returned object with g_object_unref().

Since 2.22


g_socket_get_socket_type ()

GSocketType         g_socket_get_socket_type            (GSocket *socket);

Gets the socket type of the socket.

socket :

a GSocket.

Returns :

a GSocketType

Since 2.22


g_socket_speaks_ipv4 ()

gboolean            g_socket_speaks_ipv4                (GSocket *socket);

Checks if a socket is capable of speaking IPv4.

IPv4 sockets are capable of speaking IPv4. On some operating systems and under some combinations of circumstances IPv6 sockets are also capable of speaking IPv4. See RFC 3493 section 3.7 for more information.

No other types of sockets are currently considered as being capable of speaking IPv4.

socket :

a GSocket

Returns :

TRUE if this socket can be used with IPv4.

Since 2.22


g_socket_get_credentials ()

GCredentials *      g_socket_get_credentials            (GSocket *socket,
                                                         GError **error);

Returns the credentials of the foreign process connected to this socket, if any (e.g. it is only supported for G_SOCKET_FAMILY_UNIX sockets).

If this operation isn't supported on the OS, the method fails with the G_IO_ERROR_NOT_SUPPORTED error. On Linux this is implemented by reading the SO_PEERCRED option on the underlying socket.

Other ways to obtain credentials from a foreign peer includes the GUnixCredentialsMessage type and g_unix_connection_send_credentials() / g_unix_connection_receive_credentials() functions.

socket :

a GSocket.

error :

GError for error reporting, or NULL to ignore.

Returns :

NULL if error is set, otherwise a GCredentials object that must be freed with g_object_unref().

Since 2.26

Property Details

The "blocking" property

  "blocking"                 gboolean              : Read / Write

Whether or not I/O on this socket is blocking.

Default value: TRUE


The "family" property

  "family"                   GSocketFamily         : Read / Write / Construct Only

The sockets address family.

Default value: G_SOCKET_FAMILY_INVALID


The "fd" property

  "fd"                       gint                  : Read / Write / Construct Only

The sockets file descriptor.

Default value: -1


The "keepalive" property

  "keepalive"                gboolean              : Read / Write

Keep connection alive by sending periodic pings.

Default value: FALSE


The "listen-backlog" property

  "listen-backlog"           gint                  : Read / Write

Outstanding connections in the listen queue.

Allowed values: [0,128]

Default value: 10


The "local-address" property

  "local-address"            GSocketAddress*       : Read

The local address the socket is bound to.


The "protocol" property

  "protocol"                 GSocketProtocol       : Read / Write / Construct Only

The id of the protocol to use, or -1 for unknown.

Default value: G_SOCKET_PROTOCOL_UNKNOWN


The "remote-address" property

  "remote-address"           GSocketAddress*       : Read

The remote address the socket is connected to.


The "timeout" property

  "timeout"                  guint                 : Read / Write

The timeout in seconds on socket I/O

Default value: 0

Since 2.26


The "type" property

  "type"                     GSocketType           : Read / Write / Construct Only

The sockets type.

Default value: G_SOCKET_TYPE_STREAM

See Also

GInitable