recvfrom(2)							System Calls Manual						       recvfrom(2)

NAME

       recvfrom - Receives messages from sockets

SYNOPSIS

       #include <sys/socket.h>
       ssize_t	recvfrom(	int  socket,	   void *buffer,      size_t length,	  int flags,	  struct sockaddr *address,	 socklen_t
       *address_len) ;

       [XNS4.0]  The definition of the recvfrom() function in XNS4.0 uses a size_t data type for the address_len parameter instead of a  socklen_t
       data type as specified in XNS5.0 (the previous definition).

       [Tru64  UNIX]  The following definition of the recvfrom() function does not conform to current standards and is supported only for backward
       compatibility (see standards(5)):

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

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       recvfrom():  XNS5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS

       Specifies the socket file descriptor.  Specifies a pointer to the buffer to which the message should be written.  Specifies the length  (in
       bytes)  of the buffer pointed to by the buffer parameter.  Points to a value that controls message reception. The parameter to control mes-
       sage reception is formed by the logical OR of one or more of the following values: Peeks at the incoming  message.   Processes  out-of-band
       data.   Requests  that  the function block wait until the full amount of data requested can be returned.  The function may return a smaller
       amount of data if a signal is caught, the connection is terminated, MSG_PEEK was specified, or an error is pending for the socket.   Points
       to a sockaddr structure, the format of which is determined by the domain and by the behavior requested for the socket.  The sockaddr struc-
       ture is an overlay for a sockaddr_in or sockaddr_un structure, depending on which of the supported address families is active.

	      [Tru64 UNIX]   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 sock-
	      addr 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.  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 parameters 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 message to arrive, unless
       the socket is nonblocking. When the socket is nonblocking, errno is set to [EWOULDBLOCK].

       Use the select() and poll() functions to determine when more data arrives.

NOTES

       [Tru64  UNIX]  When compiled in the X/Open UNIX environment or the POSIX.1g socket environment, calls to the recvfrom() function are inter-
       nally renamed by prepending _E to the function name.  When you are debugging a module that includes the recvfrom() function and	for  which
       _XOPEN_SOURCE_EXTENDED or _POSIX_PII_SOCKET has been defined, use _Erecvfrom to refer to the recvfrom() call.  See standards(5) for further
       information.

RETURN VALUES

       Upon successful completion, the byte length of the written message is returned.	If no messages are available and the peer has  closed  the
       connection, the recv() function returns a value of 0.  Otherwise, the function returns a value of -1 and sets errno to indicate the error.

ERRORS

       If  the recvfrom() function fails, errno may be set to one of the following values: The socket parameter is not a valid file descriptor.  A
       connection was forcibly closed by a peer.  Nonexistent or protected address space is specified for the message buffer, sending address,	or
       address length.

	      [Tru64  UNIX]  A	valid message buffer was not specified.  A signal interrupted recvfrom before any data was available.  The MSG-OOB
	      flag is set and no out-of-band data is available.  An I/O error occurred while reading from or writing to the file system.  Insuffi-
	      cient resources are available in the system to complete the call.  The system did not have sufficient memory to fulfill the request.
	      The available STREAMS resources were insufficient for the operation to complete.	A receive is attempted	on  a  connection-oriented
	      socket  that  is	not  connected.   The socket parameter refers to a file, not a socket.	The specified flags are not supported this
	      socket type.  The connection timed out during connection establishment, or due to a transmission timeout on active connection.   The
	      socket is nonblocking; no data is ready to be received.

	      The  MSG_OOB  flag  is  set,  no out-of-band data is available, and either the socket is nonblocking or does not support blocking to
	      await out-of-band data.

RELATED INFORMATION

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

       Standards: standards(5).  delim off

																       recvfrom(2)