NAME
	  recvfrom - Receives messages from sockets

     SYNOPSIS
	  #include <sys/types.h>

	  #include <sys/socket.h>

	  int recvfrom(
	       int socket,
	       char *buffer,
	       int length,
	       int flags,
	       struct sockaddr *address,
	       int *address_len) ;

     PARAMETERS
	  socket
	       Specifies the socket file descriptor.

	  buffer
	       Specifies a pointer to the buffer to which the message
	       should be written.

	  length
	       Specifies the length in bytes of	the buffer pointed to
	       by the buffer parameter.

	  flags
	       Points to a value that controls message reception. The
	       parameter to control message reception is formed	by the
	       logical OR of one or more of the	following values:

	       MSG_PEEK	 Peeks at the incoming message.

	       MSG_OOB	 Processes out-of-band data.

	  address
	       Points to a sockaddr structure, the format of which is
	       determined by the domain	and by the behavior requested
	       for the socket.	The sockaddr structure is an overlay
	       for a sockaddr_in, sockaddr_un, or sockaddr_ns struc-
	       ture, depending on which	of the supported address fami-
	       lies is active.	If the compile-time option
	       _SOCKADDR_LEN is	defined	before the sys/socket.h	header
	       file is included, the sockaddr structure	takes 4.4BSD
	       behavior, with a	field for specifying the length	of the
	       socket address.	Otherwise, the default 4.3BSD sockaddr
	       structure is used, with the length of the socket
	       address assumed to be 14	bytes or less.

	       If _SOCKADDR_LEN	is defined, the	4.3BSD sockaddr
	       structure is defined with the name osockaddr.

	  address_len
	       Specifies the length of the sockaddr structure pointed
	       to by the address parameter.

     DESCRIPTION
	  The recvfrom() function permits an application program to
	  receive messages from	unconnected sockets.  It is normally
	  applied to unconnected sockets because it includes parame-
	  ters that permit a calling program to	retrieve the source
	  endpoint of received data.

	  To obtain the	source address of the message, specify a
	  nonzero value	for the	address	parameter.  The	recvfrom()
	  function is called with the address_len parameter set	to the
	  size of the buffer specified by the address parameter. On
	  return, this function	modifies the address_len parameter to
	  the actual size in bytes of the address specified by the
	  address parameter. The recvfrom() function returns the
	  length of the	message	written	to the buffer pointed to by
	  the buffer parameter.	When a message is too long for the
	  specified buffer, excess bytes may be	truncated depending on
	  the type of socket that issued the message, and depending on
	  which	flags are set with the flags parameter.

	  When no message is available at the socket specified by the
	  socket parameter, the	recvfrom() function waits for a	mes-
	  sage to arrive, unless the socket is nonblocking. When the
	  socket is nonblocking, errno is set to [EWOULDBLOCK].

     RETURN VALUES
	  Upon successful completion, the byte length of the written
	  message is returned.	Otherwise, a value of -1 is returned
	  and errno is set to indicate the error.

     ERRORS
	  If the recvfrom() function fails, errno may be set to	one of
	  the following	values:

	  [EBADF]   The	socket parameter is not	a valid	file descrip-
		    tor.

	  [ENOTSOCK]
		    The	socket parameter refers	to a file, not a
		    socket.

	  [EWOULDBLOCK]
		    The	socket is nonblocking; no data is ready	to be
		    received.

	  [EFAULT]  A valid message buffer was not specified.
		    Nonexistent	or protected address space is speci-
		    fied for the message buffer.

     RELATED INFORMATION
	  Functions: recv(2), recvmsg(2), send(2), sendmsg(2),
	  sendto(2), select(2),	shutdown(2), socket(2),	read(2),
	  write(2)