mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-24 11:29:10 +00:00
7bdf80e571
in a bunch of man pages. Use the correct .Bx (BSD UNIX) or .At (AT&T UNIX) macros instead of explicitly specifying the version in the text in a bunch of man pages.
264 lines
7.9 KiB
Groff
264 lines
7.9 KiB
Groff
.\" Copyright (c) 1983, 1990, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)recv.2 8.3 (Berkeley) 2/21/94
|
|
.\"
|
|
.Dd February 21, 1994
|
|
.Dt RECV 2
|
|
.Os BSD 4.3r
|
|
.Sh NAME
|
|
.Nm recv ,
|
|
.Nm recvfrom ,
|
|
.Nm recvmsg
|
|
.Nd receive a message from a socket
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/types.h>
|
|
.Fd #include <sys/socket.h>
|
|
.Ft ssize_t
|
|
.Fn recv "int s" "void *buf" "size_t len" "int flags"
|
|
.Ft ssize_t
|
|
.Fn recvfrom "int s" "void *buf" "size_t len" "int flags" "struct sockaddr *from" "int *fromlen"
|
|
.Ft ssize_t
|
|
.Fn recvmsg "int s" "struct msghdr *msg" "int flags"
|
|
.Sh DESCRIPTION
|
|
.Fn Recvfrom
|
|
and
|
|
.Fn recvmsg
|
|
are used to receive messages from a socket,
|
|
and may be used to receive data on a socket whether or not
|
|
it is connection-oriented.
|
|
.Pp
|
|
If
|
|
.Fa from
|
|
is non-nil, and the socket is not connection-oriented,
|
|
the source address of the message is filled in.
|
|
.Fa Fromlen
|
|
is a value-result parameter, initialized to the size of
|
|
the buffer associated with
|
|
.Fa from ,
|
|
and modified on return to indicate the actual size of the
|
|
address stored there.
|
|
.Pp
|
|
The
|
|
.Fn recv
|
|
call is normally used only on a
|
|
.Em connected
|
|
socket (see
|
|
.Xr connect 2 )
|
|
and is identical to
|
|
.Fn recvfrom
|
|
with a nil
|
|
.Fa from
|
|
parameter.
|
|
As it is redundant, it may not be supported in future releases.
|
|
.Pp
|
|
All three routines return the length of the message on successful
|
|
completion.
|
|
If a message is too long to fit in the supplied buffer,
|
|
excess bytes may be discarded depending on the type of socket
|
|
the message is received from (see
|
|
.Xr socket 2 ) .
|
|
.Pp
|
|
If no messages are available at the socket, the
|
|
receive call waits for a message to arrive, unless
|
|
the socket is nonblocking (see
|
|
.Xr fcntl 2 )
|
|
in which case the value
|
|
-1 is returned and the external variable
|
|
.Va errno
|
|
set to
|
|
.Er EAGAIN .
|
|
The receive calls normally return any data available,
|
|
up to the requested amount,
|
|
rather than waiting for receipt of the full amount requested;
|
|
this behavior is affected by the socket-level options
|
|
.Dv SO_RCVLOWAT
|
|
and
|
|
.Dv SO_RCVTIMEO
|
|
described in
|
|
.Xr getsockopt 2 .
|
|
.Pp
|
|
The
|
|
.Xr select 2
|
|
call may be used to determine when more data arrive.
|
|
.Pp
|
|
The
|
|
.Fa flags
|
|
argument to a recv call is formed by
|
|
.Em or Ap ing
|
|
one or more of the values:
|
|
.Bl -column MSG_WAITALL -offset indent
|
|
.It Dv MSG_OOB Ta process out-of-band data
|
|
.It Dv MSG_PEEK Ta peek at incoming message
|
|
.It Dv MSG_WAITALL Ta wait for full request or error
|
|
.El
|
|
The
|
|
.Dv MSG_OOB
|
|
flag requests receipt of out-of-band data
|
|
that would not be received in the normal data stream.
|
|
Some protocols place expedited data at the head of the normal
|
|
data queue, and thus this flag cannot be used with such protocols.
|
|
The MSG_PEEK flag causes the receive operation to return data
|
|
from the beginning of the receive queue without removing that
|
|
data from the queue.
|
|
Thus, a subsequent receive call will return the same data.
|
|
The MSG_WAITALL flag requests that the operation block until
|
|
the full request is satisfied.
|
|
However, the call may still return less data than requested
|
|
if a signal is caught, an error or disconnect occurs,
|
|
or the next data to be received is of a different type than that returned.
|
|
.Pp
|
|
The
|
|
.Fn recvmsg
|
|
call uses a
|
|
.Fa msghdr
|
|
structure to minimize the number of directly supplied parameters.
|
|
This structure has the following form, as defined in
|
|
.Ao Pa sys/socket.h Ac :
|
|
.Pp
|
|
.Bd -literal
|
|
struct msghdr {
|
|
caddr_t msg_name; /* optional address */
|
|
u_int msg_namelen; /* size of address */
|
|
struct iovec *msg_iov; /* scatter/gather array */
|
|
u_int msg_iovlen; /* # elements in msg_iov */
|
|
caddr_t msg_control; /* ancillary data, see below */
|
|
u_int msg_controllen; /* ancillary data buffer len */
|
|
int msg_flags; /* flags on received message */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
Here
|
|
.Fa msg_name
|
|
and
|
|
.Fa msg_namelen
|
|
specify the destination address if the socket is unconnected;
|
|
.Fa msg_name
|
|
may be given as a null pointer if no names are desired or required.
|
|
.Fa Msg_iov
|
|
and
|
|
.Fa msg_iovlen
|
|
describe scatter gather locations, as discussed in
|
|
.Xr read 2 .
|
|
.Fa Msg_control ,
|
|
which has length
|
|
.Fa msg_controllen ,
|
|
points to a buffer for other protocol control related messages
|
|
or other miscellaneous ancillary data.
|
|
The messages are of the form:
|
|
.Bd -literal
|
|
struct cmsghdr {
|
|
u_int cmsg_len; /* data byte count, including hdr */
|
|
int cmsg_level; /* originating protocol */
|
|
int cmsg_type; /* protocol-specific type */
|
|
/* followed by
|
|
u_char cmsg_data[]; */
|
|
};
|
|
.Ed
|
|
As an example, one could use this to learn of changes in the data-stream
|
|
in XNS/SPP, or in ISO, to obtain user-connection-request data by requesting
|
|
a recvmsg with no data buffer provided immediately after an
|
|
.Fn accept
|
|
call.
|
|
.Pp
|
|
Open file descriptors are now passed as ancillary data for
|
|
.Dv AF_UNIX
|
|
domain sockets, with
|
|
.Fa cmsg_level
|
|
set to
|
|
.Dv SOL_SOCKET
|
|
and
|
|
.Fa cmsg_type
|
|
set to
|
|
.Dv SCM_RIGHTS .
|
|
.Pp
|
|
The
|
|
.Fa msg_flags
|
|
field is set on return according to the message received.
|
|
.Dv MSG_EOR
|
|
indicates end-of-record;
|
|
the data returned completed a record (generally used with sockets of type
|
|
.Dv SOCK_SEQPACKET ) .
|
|
.Dv MSG_TRUNC
|
|
indicates that
|
|
the trailing portion of a datagram was discarded because the datagram
|
|
was larger than the buffer supplied.
|
|
.Dv MSG_CTRUNC
|
|
indicates that some
|
|
control data were discarded due to lack of space in the buffer
|
|
for ancillary data.
|
|
.Dv MSG_OOB
|
|
is returned to indicate that expedited or out-of-band data were received.
|
|
.Pp
|
|
.Sh RETURN VALUES
|
|
These calls return the number of bytes received, or -1
|
|
if an error occurred.
|
|
.Sh ERRORS
|
|
The calls fail if:
|
|
.Bl -tag -width ENOTCONNAA
|
|
.It Bq Er EBADF
|
|
The argument
|
|
.Fa s
|
|
is an invalid descriptor.
|
|
.It Bq Er ENOTCONN
|
|
The socket is associated with a connection-oriented protocol
|
|
and has not been connected (see
|
|
.Xr connect 2
|
|
and
|
|
.Xr accept 2 ).
|
|
.It Bq Er ENOTSOCK
|
|
The argument
|
|
.Fa s
|
|
does not refer to a socket.
|
|
.It Bq Er EAGAIN
|
|
The socket is marked non-blocking, and the receive operation
|
|
would block, or
|
|
a receive timeout had been set,
|
|
and the timeout expired before data were received.
|
|
.It Bq Er EINTR
|
|
The receive was interrupted by delivery of a signal before
|
|
any data were available.
|
|
.It Bq Er EFAULT
|
|
The receive buffer pointer(s) point outside the process's
|
|
address space.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr fcntl 2 ,
|
|
.Xr read 2 ,
|
|
.Xr select 2 ,
|
|
.Xr getsockopt 2 ,
|
|
.Xr socket 2
|
|
.Sh HISTORY
|
|
The
|
|
.Fn recv
|
|
function call appeared in
|
|
.Bx 4.2 .
|