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 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 .