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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  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 termi-
              nated,  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 mes-
       sage 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,  Copyright  (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                             RECV(3P)