PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       recv — receive a message from a connected socket

SYNOPSIS         top

       #include <sys/socket.h>

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

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       poll(3p), pselect(3p), read(3p), recvmsg(3p), recvfrom(3p), send(3p),
       sendmsg(3p), sendto(3p), shutdown(3p), socket(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_socket.h(0p)

COPYRIGHT         top

       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(3P)

Pages that refer to this page: sys_socket.h(0p)recvfrom(3p)recvmsg(3p)send(3p)sendmsg(3p)sendto(3p)shutdown(3p)sockatmark(3p)socket(3p)