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 .

IEEE/The Open Group                                   2003                                               RECV(P)