recv(2)                                                         recv(2)

  recv()

  NAME

    recv(), recvfrom() - receive a message from a socket

  SYNOPSIS

    #include 
    #include 

    ssize_t recv (int s, void *buf, size_t len, int flags)
    ssize_t recvfrom (int s, void *buf, size_t len, int flags,
                      struct sockaddr *from, int *fromlen)

  DESCRIPTION

    The recvfrom(2) function is used to receive messages from a socket, and
    may be used to receive data on a socket whether or not it is connection-
    oriented.

    If from is non-nil, and the socket is not connection-oriented, the source
    address of the message is filled in. Fromlen is a value-result parameter,
    initialized to the size of the buffer associated with from, and modified
    on return to indicate the actual size of the address stored there.

    The recv(2) call is normally used only on a connected socket (see
    connect(2)) and is identical to recvfrom(2) with a nil from parameter. As
    it is redundant, it may not be supported in future releases.

    Both routines return the length of the message on successful completion.
    If a message is too long to fit in the supplied buffer, excess bytes may
    be discarded depending on the type of socket the message is received from
    (see socket(2)).

    If no messages are available at the socket, the receive call waits for a
    message to arrive, unless the socket is nonblocking (see fcntl(2)) in
    which case the value -1 is returned and the external variable errno set to
    [EAGAIN]. The receive calls normally return any data available, up to the
    requested amount, rather than waiting for receipt of the full amount
    requested; this behavior is affected by the socket-level options
    SO_RCVLOWAT and SO_RCVTIMEO described in getsockopt(2).

    The select(2) call may be used to determine when more data arrive.

    The flags argument to a recv call is formed by OR'ing one or more of the
    values:
    *     process out-of-band data
    *     peek at incoming message

    The MSG_OOB flag requests receipt of out-of-band data that would not be
    received in the normal data stream. Some protocols place expedited data at
    the head of the normal data queue, and thus this flag cannot be used with
    such protocols. The MSG_PEEK flag causes the receive operation to return
    data from the beginning of the receive queue without removing that data
    from the queue. Thus, a subsequent receive call will return the same data.

  RETURN VALUES

    These calls return the number of bytes received, or -1 if an error
    occurred.

  ERRORS

    The calls fail if:

    [EBADF]
        The argument s is an invalid descriptor.

    [ENOTCONN]
        The socket is associated with a connection-oriented protocol and has
        not been connected (see connect(2) and accept(2)).

    [ENOTSOCK]
        The argument s does not refer to a socket.

    [EAGAIN]
        The socket is marked non-blocking, and the receive operation would
        block, or a receive time-out had been set, and the time-out expired
        before data were received.

    [EINTR]
        The receive was interrupted by delivery of a signal before any data
        were available.

    [EFAULT]
        The receive buffer pointer(s) point outside the process's address
        space.

  SEE ALSO

    fcntl(2)

    read(2)

    select(2)

    getsockopt(2)

    socket(2)

  USAGE NOTES

    All of these functions are thread safe.

    All of these functions are async-signal safe.