PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

RECVFROM(3P)              POSIX Programmer's Manual             RECVFROM(3P)

PROLOG         top

       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         top

       recvfrom — receive a message from a socket

SYNOPSIS         top

       #include <sys/socket.h>

       ssize_t recvfrom(int socket, void *restrict buffer, size_t length,
           int flags, struct sockaddr *restrict address,
           socklen_t *restrict address_len);

DESCRIPTION         top

       The recvfrom() function shall receive a message from a connection-
       mode or connectionless-mode socket. It is normally used with
       connectionless-mode sockets because it permits the application to
       retrieve the source address of received data.

       The recvfrom() function takes the following arguments:

       socket      Specifies the socket file descriptor.

       buffer      Points to the 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 recvfrom() 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.

       address     A null pointer, or points to a sockaddr structure in
                   which the sending address is to be stored. The length and
                   format of the address depend on the address family of the
                   socket.

       address_len Either a null pointer, if address is a null pointer, or a
                   pointer to a socklen_t object which on input specifies
                   the length of the supplied sockaddr structure, and on
                   output specifies the length of the stored address.

       The recvfrom() 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_RAW, 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.

       Not all protocols provide the source address for messages. If the
       address argument is not a null pointer and the protocol provides the
       source address of messages, the source address of the received
       message shall be stored in the sockaddr structure pointed to by the
       address argument, and the length of this address shall be stored in
       the object pointed to by the address_len argument.

       If the actual length of the address is greater than the length of the
       supplied sockaddr structure, the stored address shall be truncated.

       If the address argument is not a null pointer and the protocol does
       not provide the source address of messages, the value stored in the
       object pointed to by address is unspecified.

       If no messages are available at the socket and O_NONBLOCK is not set
       on the socket's file descriptor, recvfrom() 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, recvfrom() shall
       fail and set errno to [EAGAIN] or [EWOULDBLOCK].

RETURN VALUE         top

       Upon successful completion, recvfrom() 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, recvfrom() shall return 0.
       Otherwise, the function shall return −1 and set errno to indicate the
       error.

ERRORS         top

       The recvfrom() 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  A signal interrupted recvfrom() 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.

       ETIMEDOUT
              The connection timed out during connection establishment, or
              due to a transmission timeout on active connection.

       The recvfrom() 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         top

       None.

APPLICATION USAGE         top

       The select() and poll() functions can be used to determine when data
       is available to be received.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       poll(3p), pselect(3p), read(3p), recv(3p), recvmsg(3p), send(3p),
       sendmsg(3p), sendto(3p), shutdown(3p), socket(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_socket.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                        RECVFROM(3P)

Pages that refer to this page: sys_socket.h(0p)recv(3p)recvmsg(3p)send(3p)sendmsg(3p)sendto(3p)shutdown(3p)socket(3p)