DatagramBased

Interface for socket-like objects with datagram semantics.

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 [class@Gio.Socket], 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 [ class@Gio.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, `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 [method@Gio.DatagramBased.condition_check] or [method@Gio.DatagramBased.condition_wait]. You can also use [method@Gio.DatagramBased.create_source] and attach it to a [struct@GLib.MainContext] 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`, `GDatagramBased`s can be either connection oriented (for example, SCTP) or connectionless (for example, UDP). `GDatagramBased`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 `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.