recvmsg.3.man

This a separate release of the OpenSS7 X/Open XTI/TLI library, TLI modules (timod, tirdwr) and the I

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.TH RECVMSG 3 "2004/05/16 02:35:35" "strxnet-0_9_2-4" "Linux Fast-STREAMS Sockets Library"
.SH NAME
.B recvmsg
\- receive a message from a socket
.SH SYNOPSIS
.PP
.B #include <sys/socket.h>
.HP
.BI "ssize_t recvmsg(int " socket ", struct msghdr *" message ", int " flags );
.SH DESCRIPTION
.PP
The
.BR recvmsg ()
function receives 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.
.PP
The function takes the following arguments:
.TP
.I socket
Specifies the socket file descriptor.
.TP
.I message
Points to a
.B 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
.I msg_flags
member is
ignored on input, but may contain meaningful values on output.
.TP
.I flags
Specifies the type of message reception. Values of this argument are formed by
logically OR'ing zero or more of the following values:
.RS
.TP
.B MSG_OOB
Requests out-of-band data. The significance and semantics of out-of-band data
are protocol-specific.
.TP
.B MSG_PEEK
Peeks at the incoming message.
.TP
.B MSG_WAITALL
Requests that the function block until the full amount of data requested can
be returned. The function may return a smaller amount of data if a signal is
caught, if the connection is terminated, if
.B MSG_PEEK
was specified, or if an
error is pending for the socket.
.RE
.PP
The
.BR recvmsg ()
function receives messages from unconnected or connected sockets
and returns the length of the message.
.PP
The
.BR recvmsg ()
function returns the total length of the message. For
message-based sockets such as
.B SOCK_DGRAM
and
.BR SOCK_SEQPACKET ,
the entire
message must be read in a single operation. If a message is too long to fit in
the supplied buffers, and
.B MSG_PEEK
is not set in the
.I flags
argument, the
excess bytes are discarded, and
.B MSG_TRUNC
is set in the
.I msg_flags
member of
the
.B msghdr
structure. For stream-based sockets such as
.BR SOCK_STREAM ,
message
boundaries are ignored. In this case, data is returned to the user as soon as
it becomes available, and no data is discarded.
.PP
If the
.B MSG_WAITALL
flag is not set, data will be returned only up to the end
of the first message.
.PP
If no messages are available at the socket and
.B O_NONBLOCK
is not set on the
socket's file descriptor,
.BR recvfrom (3)
blocks until a message arrives. If no
messages are available at the socket and
.B O_NONBLOCK
is set on the socket's
file descriptor,
.BR recvfrom (3)
function fails and sets errno to
.RB [ EAGAIN ]
or
.RB [ EWOULDBLOCK ].
.PP
In the
.B msghdr
structure, the
.I msg_name
and
.I msg_namelen
members specify the
source address if the socket is unconnected. If the socket is connected, the
.I msg_name
and
.I msg_namelen
members are ignored. The
.I msg_name
member may be a
null pointer if no names are desired or required. The
.I msg_iov
and
.I msg_iovlen
fields are used to specify where the received data will be stored.
.I msg_iov
points to an array of
.B iovec
structures;
.I msg_iovlen
must be set to the
dimension of this array. In each
.B iovec
structure, the iov_base field specifies
a storage area and the iov_len field gives its size in bytes. Each storage
area indicated by
.I 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.
.PP
On successful completion, the
.I msg_flags
member of the message header is the
bitwise-inclusive OR of all of the following flags that indicate conditions
detected for the received message:.
.TP
.B MSG_EOR
End of record was received (if supported by the protocol).
.TP
.B MSG_OOB
Out-of-band data was received.
.TP
.B MSG_TRUNC
Normal data was truncated.
.TP
.B MSG_CTRUNC
Control data was truncated.
.SH NOTES
.PP
The
.BR select (2)
and
.BR poll (2)
functions can be used to determine when data is
available to be received.
.SH CAVEATS
.PP
This system call is implemented as a
.B SIOCSOCKSYS
IOCTL.  See
.BR socksys (4)
for more information.
.SH CAVEATS
.PP
This system call is implemented as a
.B SIOCSOCKSYS
IOCTL.  See
.BR socksys (4)
for more information.
.SH "RETURN VALUE"
.PP
Upon successful completion,
.BR recvmsg ()
returns the length of the message in
bytes. If no messages are available to be received and the peer has performed
an orderly shutdown,
.BR recvmsg ()
returns 0.  Otherwise, -1 is returned and errno
is set to indicate the error.
.SH ERRORS
.PP
The
.BR recvmsg ()
function will fail if:
.TP
.RB [ EAGAIN "] or [" EWOULDBLOCK ]
The socket's file descriptor is marked
.B O_NONBLOCK
and no data is waiting to be
received; or
.B MSG_OOB
is set and no out-of-band data is available and either
the socket's file descriptor is marked
.B O_NONBLOCK
or the socket does not
support blocking to await out-of-band data.
.TP
.RB [ EBADF ]
The
.I socket
argument is not a valid open file descriptor.
.TP
.RB [ ECONNRESET ]
A connection was forcibly closed by a peer.
.TP
.RB [ EFAULT ]
The
.I message
parameter, or storage pointed to by the
.IR msg_name ,
.I msg_control
or
.I msg_iov
fields of the
.I message
parameter, or storage pointed to by the
.B iovec
structures pointed to by the
.I msg_iov
field can not be accessed or written.
.TP
.RB [ EINTR ]
This function was interrupted by a signal before any data was available.
.TP
.RB [ EINVAL ]
The sum of the iov_len values overflows an
.BR ssize_t .
or the
.B MSG_OOB
flag is set
and no out-of-band data is available.
.TP
.RB [ EMSGSIZE ]
The
.I msg_iovlen
member of the
.B msghdr
structure pointed to by
.I message
is less
than or equal to 0, or is greater than
.RB { IOV_MAX }.
.TP
.RB [ ENOTCONN ]
A receive is attempted on a connection-mode socket that is not connected.
.TP
.RB [ ENOTSOCK ]
The
.I socket
argument does not refer to a socket.
.TP
.RB [ EOPNOTSUPP ]
The specified
.I flags
are not supported for this socket type.
.TP
.RB [ ETIMEDOUT ]
The connection timed out during connection establishment, or due to a
transmission timeout on active connection.
.PP
The
.BR recvmsg ()
function may fail if:
.TP
.RB [ EIO ]
An I/O error occurred while reading from or writing to the file system.
.TP
.RB [ ENOBUFS ]
Insufficient resources were available in the system to perform the operation.
.TP
.RB [ ENOMEM ]
Insufficient memory was available to fulfill the request.
.TP
.RB [ ENOSR ]
There were insufficient
.IR STREAMS (4)
resources available for the operation to
complete.
.SH "SEE ALSO"
.PP
.BR poll (2),
.BR recv (3),
.BR recvfrom (3),
.BR select (2),
.BR send (3),
.BR sendmsg (3),
.BR sendto (3),
.BR shutdown (3),
.BR socket (3),
.BR <sys/socket.h> (5).
.SH "CONFORMING TO"
.PP
The Open Group XNS Issue 5.2.
.[
xns
.]
.\"
.\"
.[
$LIST$
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.TI