RECV(3P)                                            POSIX Programmer's Manual                                           RECV(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       recv - receive a message from a connected socket

SYNOPSIS
       #include <sys/socket.h>

       ssize_t recv(int socket, void *buffer, size_t length, int flags);


DESCRIPTION
       The  recv()  function  shall  receive a message from a connection-mode or connectionless-mode socket. It is normally used
       with connected sockets because it does not permit the application to retrieve the source address of received data.

       The recv() function takes the following arguments:

       socket Specifies the socket file descriptor.

       buffer Points to a buffer where the message should be stored.

       length Specifies the length in bytes of the buffer pointed to by the buffer argument.

       flags  Specifies the type of message reception. Values of this argument are formed by logically OR'ing zero  or  more  of
              the following values:

       MSG_PEEK
              Peeks  at  an  incoming message. The data is treated as unread and the next recv() or similar function shall still
              return this data.

       MSG_OOB
              Requests out-of-band data. The significance and semantics of out-of-band data are protocol-specific.

       MSG_WAITALL
              On SOCK_STREAM sockets this requests that the function block until the full amount of data can  be  returned.  The
              function  may return the smaller amount of data if the socket is a message-based socket, if a signal is caught, if
              the connection is terminated, if MSG_PEEK was specified, or if an error is pending for the socket.



       The recv() function shall return the length of the message written to the buffer pointed to by the buffer  argument.  For
       message-based sockets, such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message shall be read in a single operation.  If
       a message is too long to fit in the supplied buffer, and MSG_PEEK is not set in the  flags  argument,  the  excess  bytes
       shall  be  discarded.  For  stream-based sockets, such as SOCK_STREAM, message boundaries shall be ignored. In this case,
       data shall be returned to the user as soon as it becomes available, and no data shall be discarded.

       If the MSG_WAITALL flag is not set, data shall be returned only up to the end of the first message.

       If no messages are available at the socket and O_NONBLOCK is not set on the socket's file descriptor, recv() shall  block
       until  a  message arrives. If no messages are available at the socket and O_NONBLOCK is set on the socket's file descrip-
       tor, recv() shall fail and set errno to [EAGAIN] or [EWOULDBLOCK].

RETURN VALUE
       Upon successful completion, recv() shall return the length of the message in bytes. If no messages are  available  to  be
       received and the peer has performed an orderly shutdown, recv() shall return 0. Otherwise, -1 shall be returned and errno
       set to indicate the error.

ERRORS
       The recv() function shall fail if:

       EAGAIN or EWOULDBLOCK

              The socket's file descriptor is marked O_NONBLOCK and no data is waiting to be received; or MSG_OOB is set and  no
              out-of-band  data is available and either the socket's file descriptor is marked O_NONBLOCK or the socket does not
              support blocking to await out-of-band data.

       EBADF  The socket argument is not a valid file descriptor.

       ECONNRESET
              A connection was forcibly closed by a peer.

       EINTR  The recv() function was interrupted by a signal that was caught, before any data was available.

       EINVAL The MSG_OOB flag is set and no out-of-band data is available.

       ENOTCONN
              A receive is attempted on a connection-mode socket that is not connected.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EOPNOTSUPP
              The specified flags are not supported for this socket type or protocol.

       ETIMEDOUT
              The connection timed out during connection establishment, or due to a transmission timeout on active connection.


       The recv() function may fail if:

       EIO    An I/O error occurred while reading from or writing to the file system.

       ENOBUFS
              Insufficient resources were available in the system to perform the operation.

       ENOMEM Insufficient memory was available to fulfill the request.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The recv() function is equivalent to recvfrom() with a zero address_len argument, and to read() if no flags are used.

       The select() and poll() functions can be used to determine when data is available to be received.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       poll(), read(), recvmsg(), recvfrom(), select(), send(), sendmsg(), sendto(), shutdown(),  socket(),  write(),  the  Base
       Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      RECV(3P)