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.. _udp:

:c:type:`uv_udp_t` --- UDP handle
=================================

UDP handles encapsulate UDP communication for both clients and servers.


Data types
----------

.. c:type:: uv_udp_t

    UDP handle type.

.. c:type:: uv_udp_send_t

    UDP send request type.

.. c:type:: uv_udp_flags

    Flags used in :c:func:`uv_udp_bind` and :c:type:`uv_udp_recv_cb`..

    ::

        enum uv_udp_flags {
            /* Disables dual stack mode. */
            UV_UDP_IPV6ONLY = 1,
            /*
            * Indicates message was truncated because read buffer was too small. The
            * remainder was discarded by the OS. Used in uv_udp_recv_cb.
            */
            UV_UDP_PARTIAL = 2,
            /*
            * Indicates if SO_REUSEADDR will be set when binding the handle in
            * uv_udp_bind.
            * This sets the SO_REUSEPORT socket flag on the BSDs and OS X. On other
            * Unix platforms, it sets the SO_REUSEADDR flag. What that means is that
            * multiple threads or processes can bind to the same address without error
            * (provided they all set the flag) but only the last one to bind will receive
            * any traffic, in effect "stealing" the port from the previous listener.
            */
            UV_UDP_REUSEADDR = 4
        };

.. c:type:: void (*uv_udp_send_cb)(uv_udp_send_t* req, int status)

    Type definition for callback passed to :c:func:`uv_udp_send`, which is
    called after the data was sent.

.. c:type:: void (*uv_udp_recv_cb)(uv_udp_t* handle, ssize_t nread, const uv_buf_t* buf, const struct sockaddr* addr, unsigned flags)

    Type definition for callback passed to :c:func:`uv_udp_recv_start`, which
    is called when the endpoint receives data.

    * `handle`: UDP handle
    * `nread`:  Number of bytes that have been received.
      0 if there is no more data to read. You may discard or repurpose
      the read buffer. Note that 0 may also mean that an empty datagram
      was received (in this case `addr` is not NULL). < 0 if a transmission
      error was detected.
    * `buf`: :c:type:`uv_buf_t` with the received data.
    * `addr`: ``struct sockaddr*`` containing the address of the sender.
      Can be NULL. Valid for the duration of the callback only.
    * `flags`: One or more or'ed UV_UDP_* constants. Right now only
      ``UV_UDP_PARTIAL`` is used.

    .. note::
        The receive callback will be called with `nread` == 0 and `addr` == NULL when there is
        nothing to read, and with `nread` == 0 and `addr` != NULL when an empty UDP packet is
        received.

.. c:type:: uv_membership

    Membership type for a multicast address.

    ::

        typedef enum {
            UV_LEAVE_GROUP = 0,
            UV_JOIN_GROUP
        } uv_membership;


Public members
^^^^^^^^^^^^^^

.. c:member:: size_t uv_udp_t.send_queue_size

    Number of bytes queued for sending. This field strictly shows how much
    information is currently queued.

.. c:member:: size_t uv_udp_t.send_queue_count

    Number of send requests currently in the queue awaiting to be processed.

.. c:member:: uv_udp_t* uv_udp_send_t.handle

    UDP handle where this send request is taking place.

.. seealso:: The :c:type:`uv_handle_t` members also apply.


API
---

.. c:function:: int uv_udp_init(uv_loop_t* loop, uv_udp_t* handle)

    Initialize a new UDP handle. The actual socket is created lazily.
    Returns 0 on success.

.. c:function:: int uv_udp_init_ex(uv_loop_t* loop, uv_udp_t* handle, unsigned int flags)

    Initialize the handle with the specified flags. At the moment the lower 8 bits