recvfrom(3p) — Linux manual page

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.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                      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)