gio.datagram_based

Interface for socket-like objects with datagram semantics.

A [gio.datagram_based.DatagramBased] 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 [gio.socket.Socket], which wraps the UNIX socket API on UNIX and winsock2 on Windows.

[gio.datagram_based.DatagramBased] is entirely platform independent, and is intended to be used alongside higher-level networking APIs such as [gio.iostream.IOStream].

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, [gio.socket.Socket] 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 [gio.datagram_based.DatagramBased] 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 [gio.types.IOErrorEnum.WouldBlock] 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 [gio.types.IOErrorEnum.TimedOut] if no progress was made. To know when a call would successfully run you can call [gio.datagram_based.DatagramBased.conditionCheck] or [gio.datagram_based.DatagramBased.conditionWait]. You can also use [gio.datagram_based.DatagramBased.createSource] and attach it to a [glib.main_context.MainContext] to get callbacks when I/O is possible.

When running a non-blocking operation applications should always be able to handle getting a [gio.types.IOErrorEnum.WouldBlock] 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 [gio.types.IOErrorEnum.WouldBlock].

As with [gio.socket.Socket], [gio.datagram_based.DatagramBased]s can be either connection oriented (for example, SCTP) or connectionless (for example, UDP). [gio.datagram_based.DatagramBased]s 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 [gio.datagram_based.DatagramBased] API. For connectionless socket types the target/source address is specified or received in each I/O operation.

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