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 (consult the correspond-
       ing 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  sock-
       ets 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 func-
			     tion 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 sock-
       ets, 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 descriptor, 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 null pointer address and address_len arguments, and to read() if the  socket  argument
       refers to a socket and the flags argument is 0.

       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(), pselect(), read(), recvmsg(), recvfrom(), send(), sendmsg(), sendto(), shutdown(), socket(), write()

       The Base Definitions volume of POSIX.1-2008, <sys_socket.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								  RECV(3P)