recv

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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult 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 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 Technology
       -- 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 Standard
       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(3POSIX)