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GDatagramBased

GDatagramBased — Low-level datagram communications interface

Types and Values

Object Hierarchy

    GInterface
    ╰── GDatagramBased

Prerequisites

GDatagramBased requires GObject.

Known Derived Interfaces

GDatagramBased is required by GDtlsClientConnection, GDtlsConnection and GDtlsServerConnection.

Known Implementations

GDatagramBased is implemented by GSocket.

Includes

#include <gio/gio.h>

Description

A GDatagramBased is a networking interface for representing datagram-based communications. It is a more or less direct mapping of the core parts of the BSD socket API in a portable GObject interface. It is implemented by GSocket, which wraps the UNIX socket API on UNIX and winsock2 on Windows.

GDatagramBased is entirely platform independent, and is intended to be used alongside higher-level networking APIs such as GIOStream.

It uses vectored scatter/gather I/O by default, allowing for many messages to be sent or received in a single call. Where possible, implementations of the interface should take advantage of vectored I/O to minimise processing or system calls. For example, GSocket uses recvmmsg() and sendmmsg() where possible. Callers should take advantage of scatter/gather I/O (the use of multiple buffers per message) to avoid unnecessary copying of data to assemble or disassemble a message.

Each GDatagramBased operation has a timeout parameter which may be negative for blocking behaviour, zero for non-blocking behaviour, or positive for timeout behaviour. A blocking operation blocks until finished or there is an error. A non-blocking operation will return immediately with a G_IO_ERROR_WOULD_BLOCK error if it cannot make progress. A timeout operation will block until the operation is complete or the timeout expires; if the timeout expires it will return what progress it made, or G_IO_ERROR_TIMED_OUT if no progress was made. To know when a call would successfully run you can call g_datagram_based_condition_check() or g_datagram_based_condition_wait(). You can also use g_datagram_based_create_source() and attach it to a GMainContext to get callbacks when I/O is possible.

When running a non-blocking operation 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.

As with GSocket, GDatagramBaseds can be either connection oriented (for example, SCTP) or connectionless (for example, UDP). GDatagramBaseds must be datagram-based, not stream-based. The interface does not cover connection establishment — use methods on the underlying type to establish a connection before sending and receiving data through the GDatagramBased API. For connectionless socket types the target/source address is specified or received in each I/O operation.

Like most other APIs in GLib, GDatagramBased is not inherently thread safe. To use a GDatagramBased concurrently from multiple threads, you must implement your own locking.

Functions

GDatagramBasedSourceFunc ()

gboolean
(*GDatagramBasedSourceFunc) (GDatagramBased *datagram_based,
                             GIOCondition condition,
                             gpointer user_data);

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

Parameters

datagram_based

the GDatagramBased

 

condition

the current condition at the source fired

 

user_data

data passed in by the user

 

Returns

G_SOURCE_REMOVE if the source should be removed, G_SOURCE_CONTINUE otherwise

Since: 2.48


g_datagram_based_receive_messages ()

gint
g_datagram_based_receive_messages (GDatagramBased *datagram_based,
                                   GInputMessage *messages,
                                   guint num_messages,
                                   gint flags,
                                   gint64 timeout,
                                   GCancellable *cancellable,
                                   GError **error);

Receive one or more data messages from datagram_based in one go.

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.

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 timeout is negative the call will block until num_messages have been received, the connection is closed remotely (EOS), cancellable is cancelled, or an error occurs.

If timeout is 0 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.

If timeout is positive the call will block on the same conditions as if timeout were negative. If the timeout is reached before any messages are received, G_IO_ERROR_TIMED_OUT is returned, otherwise it will return the number of messages received before timing out. (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_datagram_based_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 underlying receive buffer will be returned, and subsequent calls to g_datagram_based_receive_messages() will return 0 (with no error set).

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a GSocket, for example), all calls to this function will return G_IO_ERROR_CLOSED.

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. If cancellable is cancelled, G_IO_ERROR_CANCELLED is returned as with any other error.

Parameters

datagram_based

a GDatagramBased

 

messages

an array of GInputMessage structs.

[array length=num_messages]

num_messages

the number of elements in messages

 

flags

an int containing GSocketMsgFlags flags for the overall operation

 

timeout

the maximum time (in microseconds) to wait, 0 to not block, or -1 to block indefinitely

 

cancellable

a GCancellable.

[nullable]

error

return location for a GError

 

Returns

number of messages received, or -1 on error. Note that the number of messages received may be smaller than num_messages if timeout is zero or positive, 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.

Since: 2.48


g_datagram_based_send_messages ()

gint
g_datagram_based_send_messages (GDatagramBased *datagram_based,
                                GOutputMessage *messages,
                                guint num_messages,
                                gint flags,
                                gint64 timeout,
                                GCancellable *cancellable,
                                GError **error);

Send one or more data messages from datagram_based in one go.

messages must point to an array of GOutputMessage structs and num_messages must be the length of this array. Each GOutputMessage contains an address to send the data to, and a pointer to an array of GOutputVector structs to describe the buffers that the data to be sent for each message will be gathered from.

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.

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

If timeout is negative the call will block until num_messages have been sent, cancellable is cancelled, or an error occurs.

If timeout is 0 the call will send up to num_messages without blocking, or will return G_IO_ERROR_WOULD_BLOCK if there is no space to send messages.

If timeout is positive the call will block on the same conditions as if timeout were negative. If the timeout is reached before any messages are sent, G_IO_ERROR_TIMED_OUT is returned, otherwise it will return the number of messages sent before timing out.

To be notified when messages can be sent, wait for the G_IO_OUT condition. Note though that you may still receive G_IO_ERROR_WOULD_BLOCK from g_datagram_based_send_messages() 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.)

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_write set, if it’s a GSocket, for example), all calls to this function will return G_IO_ERROR_CLOSED.

On error -1 is returned and error is set accordingly. An error will only be returned if zero messages could be sent; otherwise the number of messages successfully sent before the error will be returned. If cancellable is cancelled, G_IO_ERROR_CANCELLED is returned as with any other error.

Parameters

datagram_based

a GDatagramBased

 

messages

an array of GOutputMessage structs.

[array length=num_messages]

num_messages

the number of elements in messages

 

flags

an int containing GSocketMsgFlags flags

 

timeout

the maximum time (in microseconds) to wait, 0 to not block, or -1 to block indefinitely

 

cancellable

a GCancellable.

[nullable]

error

return location for a GError

 

Returns

number of messages sent, or -1 on error. Note that the number of messages sent may be smaller than num_messages if timeout is zero or positive, or if num_messages was larger than UIO_MAXIOV (1024), in which case the caller may re-try to send the remaining messages.

Since: 2.48


g_datagram_based_create_source ()

GSource *
g_datagram_based_create_source (GDatagramBased *datagram_based,
                                GIOCondition condition,
                                GCancellable *cancellable);

Creates a GSource that can be attached to a GMainContext to monitor for the availability of the specified condition on the GDatagramBased. The GSource keeps a reference to the datagram_based .

The callback on the source is of the GDatagramBasedSourceFunc type.

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

If non-NULL, cancellable 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().

Parameters

datagram_based

a GDatagramBased

 

condition

a GIOCondition mask to monitor

 

cancellable

a GCancellable.

[nullable]

Returns

a newly allocated GSource.

[transfer full]

Since: 2.48


g_datagram_based_condition_check ()

GIOCondition
g_datagram_based_condition_check (GDatagramBased *datagram_based,
                                  GIOCondition condition);

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

G_IO_IN will be set in the return value if data is available to read with g_datagram_based_receive_messages(), or if the connection is closed remotely (EOS); and if the datagram_based has not been closed locally using some implementation-specific method (such as g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a GSocket).

If the connection is shut down or closed (by calling g_socket_close() or g_socket_shutdown() with shutdown_read set, if it’s a GSocket, for example), all calls to this function will return G_IO_ERROR_CLOSED.

G_IO_OUT will be set if it is expected that at least one byte can be sent using g_datagram_based_send_messages() without blocking. It will not be set if the datagram_based has been closed locally.

G_IO_HUP will be set if the connection has been closed locally.

G_IO_ERR will be set if there was an asynchronous error in transmitting data previously enqueued using g_datagram_based_send_messages().

Note that on Windows, it is possible for an operation to return G_IO_ERROR_WOULD_BLOCK even immediately after g_datagram_based_condition_check() has claimed that the GDatagramBased is ready for writing. Rather than calling g_datagram_based_condition_check() and then writing to the GDatagramBased if it succeeds, it is generally better to simply try writing 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. Apart from these flags, the output is guaranteed to be masked by condition .

This call never blocks.

Parameters

datagram_based

a GDatagramBased

 

condition

a GIOCondition mask to check

 

Returns

the GIOCondition mask of the current state

Since: 2.48


g_datagram_based_condition_wait ()

gboolean
g_datagram_based_condition_wait (GDatagramBased *datagram_based,
                                 GIOCondition condition,
                                 gint64 timeout,
                                 GCancellable *cancellable,
                                 GError **error);

Waits for up to timeout microseconds for condition to become true on datagram_based . If the condition is met, TRUE is returned.

If cancellable is cancelled before the condition is met, or if timeout is reached before the condition is met, then FALSE is returned and error is set appropriately (G_IO_ERROR_CANCELLED or G_IO_ERROR_TIMED_OUT).

Parameters

datagram_based

a GDatagramBased

 

condition

a GIOCondition mask to wait for

 

timeout

the maximum time (in microseconds) to wait, 0 to not block, or -1 to block indefinitely

 

cancellable

a GCancellable.

[nullable]

error

return location for a GError

 

Returns

TRUE if the condition was met, FALSE otherwise

Since: 2.48

Types and Values

GDatagramBased

typedef struct _GDatagramBased GDatagramBased;

Interface for socket-like objects with datagram semantics.

Since: 2.48


struct GDatagramBasedInterface

struct GDatagramBasedInterface {
  GTypeInterface g_iface;

  /* Virtual table */
  gint          (*receive_messages)     (GDatagramBased       *datagram_based,
                                         GInputMessage        *messages,
                                         guint                 num_messages,
                                         gint                  flags,
                                         gint64                timeout,
                                         GCancellable         *cancellable,
                                         GError              **error);
  gint          (*send_messages)        (GDatagramBased       *datagram_based,
                                         GOutputMessage       *messages,
                                         guint                 num_messages,
                                         gint                  flags,
                                         gint64                timeout,
                                         GCancellable         *cancellable,
                                         GError              **error);

  GSource      *(*create_source)        (GDatagramBased       *datagram_based,
                                         GIOCondition          condition,
                                         GCancellable         *cancellable);
  GIOCondition  (*condition_check)      (GDatagramBased       *datagram_based,
                                         GIOCondition          condition);
  gboolean      (*condition_wait)       (GDatagramBased       *datagram_based,
                                         GIOCondition          condition,
                                         gint64                timeout,
                                         GCancellable         *cancellable,
                                         GError              **error);
};

Provides an interface for socket-like objects which have datagram semantics, following the Berkeley sockets API. The interface methods are thin wrappers around the corresponding virtual methods, and no pre-processing of inputs is implemented — so implementations of this API must handle all functionality documented in the interface methods.

Members

receive_messages ()

Virtual method for g_datagram_based_receive_messages().

 

send_messages ()

Virtual method for g_datagram_based_send_messages().

 

create_source ()

Virtual method for g_datagram_based_create_source().

 

condition_check ()

Virtual method for g_datagram_based_condition_check().

 

condition_wait ()

Virtual method for g_datagram_based_condition_wait().

 

Since: 2.48

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