Posted on 13/10/2015 by Philip Withnall
For those who like their I/O packetised, GLib now has a companion for its GIOStream class — the GDatagramBasedinterface, which we’ve implemented as part of R&D work at Collabora. This is designed to be implemented by any class which does datagram-based I/O. GSocket implements it, essentially as an interface to recvmmsg() and sendmmsg(). The upcoming DTLS support in glib-networking will use it.
How is it shaped? Basically as a GLib-shaped version of recvmmsg() and sendmmsg(), where GInputMessage and GOutputMessage are effectively equivalent to struct mmsghdr, and GInputVector and GOutputVector are equivalent to struct msghdr.
The interface is designed around polling, potentially-blocking I/O. What’s ‘potentially-blocking’ about it? The timeout parameter. Set it to zero for non-blocking behaviour, where the functions will return G_IO_ERROR_WOULD_BLOCK if they would block. Set it negative for blocking behaviour, where the functions will not return until they can do at least some I/O. Set it positive for timeout behaviour, where the functions will block for the given number of microseconds, then return G_IO_ERROR_TIMED_OUT if they managed to perform no I/O.
gint g_datagram_based_receive_messages (GDatagramBased *datagram_based, GInputMessage *messages, guint num_messages, gint flags, gint64 timeout, GCancellable *cancellable, GError **error); gint g_datagram_based_send_messages (GDatagramBased *datagram_based, GOutputMessage *messages, guint num_messages, gint flags, gint64 timeout, GCancellable *cancellable, GError **error); GSource * g_datagram_based_create_source (GDatagramBased *datagram_based, GIOCondition condition, GCancellable *cancellable); GIOCondition g_datagram_based_condition_check (GDatagramBased *datagram_based, GIOCondition condition); gboolean g_datagram_based_condition_wait (GDatagramBased *datagram_based, GIOCondition condition, gint64 timeout, GCancellable *cancellable, GError **error);
Currently, the API (particularly GInputMessage and GOutputMessage, due to the way they are used as in-out parameters) doesn’t support introspection. This can be added in future if needed by creating some convenience API for allocating and freeing the message structures as boxed types.
The grand, overarching plan is for this to appear in a libnice version near you, some time soon, exposing the whole of an ICE connection as a GDatagramBased.
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