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+'\" et
+.TH RECVMSG "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.SH PROLOG
+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.
+
+.SH NAME
+recvmsg
+\(em receive a message from a socket
+.SH SYNOPSIS
+.LP
+.nf
+#include <sys/socket.h>
+.P
+ssize_t recvmsg(int \fIsocket\fP, struct msghdr *\fImessage\fP, int \fIflags\fP);
+.fi
+.SH DESCRIPTION
+The
+\fIrecvmsg\fR()
+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.
+.P
+The
+\fIrecvmsg\fR()
+function takes the following arguments:
+.IP "\fIsocket\fR" 12
+Specifies the socket file descriptor.
+.IP "\fImessage\fR" 12
+Points to a
+.BR msghdr
+structure, containing both the buffer to store the source address and
+the buffers for the incoming message. The length and format of the
+address depend on the address family of the socket. The
+.IR msg_flags
+member is ignored on input, but may contain meaningful values on
+output.
+.IP "\fIflags\fR" 12
+Specifies the type of message reception. Values of this argument are
+formed by logically OR'ing zero or more of the following values:
+.RS 12 
+.IP MSG_OOB 12
+Requests out-of-band data. The significance and semantics of
+out-of-band data are protocol-specific.
+.IP MSG_PEEK 12
+Peeks at the incoming message.
+.IP MSG_WAITALL 12
+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.
+.RE
+.P
+The
+\fIrecvmsg\fR()
+function shall receive messages from unconnected or connected
+sockets and shall return the length of the message.
+.P
+The
+\fIrecvmsg\fR()
+function shall return the total length of the message. 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 buffers, and MSG_PEEK is not set in the
+.IR flags
+argument, the excess bytes shall be discarded, and MSG_TRUNC shall be
+set in the
+.IR msg_flags
+member of the
+.BR msghdr
+structure. 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.
+.P
+If the MSG_WAITALL flag is not set, data shall be returned only up to
+the end of the first message.
+.P
+If no messages are available at the socket and O_NONBLOCK is not set on
+the socket's file descriptor,
+\fIrecvmsg\fR()
+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, the
+\fIrecvmsg\fR()
+function shall fail and set
+.IR errno
+to
+.BR [EAGAIN] 
+or
+.BR [EWOULDBLOCK] .
+.P
+In the
+.BR msghdr
+structure, the
+.IR msg_name
+member may be a null pointer if the source address is not required.
+Otherwise, if the socket is unconnected, the
+.IR msg_name
+member points to a
+.BR sockaddr
+structure in which the source address is to be stored, and the
+.IR msg_namelen
+member on input specifies the length of the supplied
+.BR sockaddr
+structure and on output specifies the length of the stored address.
+If the actual length of the address is greater than the length of the
+supplied
+.BR sockaddr
+structure, the stored address shall be truncated. If the socket is
+connected, the
+.IR msg_name
+and
+.IR msg_namelen
+members shall be ignored. The
+.IR msg_iov
+and
+.IR msg_iovlen
+fields are used to specify where the received data shall be stored.
+The
+.IR msg_iov
+member points to an array of
+.BR iovec
+structures; the
+.IR msg_iovlen
+member shall be set to the dimension of this array. In each
+.BR iovec
+structure, the
+.IR iov_base
+field specifies a storage area and the
+.IR iov_len
+field gives its size in bytes. Each storage area indicated by
+.IR msg_iov
+is filled with received data in turn until all of the received data is
+stored or all of the areas have been filled.
+.P
+Upon successful completion, the
+.IR msg_flags
+member of the message header shall be the bitwise-inclusive OR of all
+of the following flags that indicate conditions detected for the
+received message:
+.IP MSG_EOR 12
+End-of-record was received (if supported by the protocol).
+.IP MSG_OOB 12
+Out-of-band data was received.
+.IP MSG_TRUNC 12
+Normal data was truncated.
+.IP MSG_CTRUNC 12
+Control data was truncated.
+.SH "RETURN VALUE"
+Upon successful completion,
+\fIrecvmsg\fR()
+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,
+\fIrecvmsg\fR()
+shall return 0. Otherwise, \(mi1 shall be returned and
+.IR errno
+set to indicate the error.
+.SH ERRORS
+The
+\fIrecvmsg\fR()
+function shall fail if:
+.TP
+.BR EAGAIN " or " EWOULDBLOCK
+.br
+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.
+.TP
+.BR EBADF
+The
+.IR socket
+argument is not a valid open file descriptor.
+.TP
+.BR ECONNRESET
+A connection was forcibly closed by a peer.
+.TP
+.BR EINTR
+This function was interrupted by a signal before any data was
+available.
+.TP
+.BR EINVAL
+The sum of the
+.IR iov_len
+values overflows a
+.BR ssize_t ,
+or the MSG_OOB flag is set and no out-of-band data is available.
+.TP
+.BR EMSGSIZE
+The
+.IR msg_iovlen
+member of the
+.BR msghdr
+structure pointed to by
+.IR message
+is less than or equal to 0, or is greater than
+{IOV_MAX}.
+.TP
+.BR ENOTCONN
+A receive is attempted on a connection-mode socket that is not
+connected.
+.TP
+.BR ENOTSOCK
+The
+.IR socket
+argument does not refer to a socket.
+.TP
+.BR EOPNOTSUPP
+The specified flags are not supported for this socket type.
+.TP
+.BR ETIMEDOUT
+The connection timed out during connection establishment, or due to a
+transmission timeout on active connection.
+.P
+The
+\fIrecvmsg\fR()
+function may fail if:
+.TP
+.BR EIO
+An I/O error occurred while reading from or writing to the file
+system.
+.TP
+.BR ENOBUFS
+Insufficient resources were available in the system to perform the
+operation.
+.TP
+.BR ENOMEM
+Insufficient memory was available to fulfill the request.
+.LP
+.IR "The following sections are informative."
+.SH "EXAMPLES"
+None.
+.SH "APPLICATION USAGE"
+The
+\fIselect\fR()
+and
+\fIpoll\fR()
+functions can be used to determine when data is available to be
+received.
+.SH "RATIONALE"
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "\fIpoll\fR\^(\|)",
+.IR "\fIpselect\fR\^(\|)",
+.IR "\fIrecv\fR\^(\|)",
+.IR "\fIrecvfrom\fR\^(\|)",
+.IR "\fIsend\fR\^(\|)",
+.IR "\fIsendmsg\fR\^(\|)",
+.IR "\fIsendto\fR\^(\|)",
+.IR "\fIshutdown\fR\^(\|)",
+.IR "\fIsocket\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2008,
+.IR "\fB<sys_socket.h>\fP"
+.SH COPYRIGHT
+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 .