Tribblix: manual page: recv.3xnet

RECV(3XNET) X/Open Networking Services Library Functions RECV(3XNET)

NAME

recv - receive a message from a connected socket

SYNOPSIS

cc [ flag ... ] file ... -lxnet [ library ... ]
#include <sys/socket.h>

ssize_t recv(int socket, void *buffer, size_t length, int flags);

DESCRIPTION

The recv() function receives a message from a connection-mode or
connectionless-mode socket. It is normally used with connected
sockets because it does not permit the application to retrieve the
source address of received data. The function takes the following
arguments:

socket
Specifies the socket file descriptor.

buffer
Points to a 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 recv() or
similar function will 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
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 MSG_PEEK was
specified, or if an error is pending for the
socket.

The recv() function returns the length of the message written to the
buffer pointed to by the buffer argument. For message-based sockets
such as SOCK_DGRAM and SOCK_SEQPACKET, the entire message must 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 are discarded. For stream-based sockets such as
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.

If the MSG_WAITALL flag is not set, data will be returned only up to
the end of the first message.

If no messages are available at the socket and O_NONBLOCK is not set
on the socket's file descriptor, recv() blocks until a message
arrives. If no messages are available at the socket and O_NONBLOCK
is set on the socket's file descriptor, recv() fails and sets errno
to EAGAIN or EWOULDBLOCK.

USAGE

The recv() function is identical to recvfrom(3XNET) with a zero
address_len argument, and to read() if no flags are used.

The select(3C) and poll(2) functions can be used to determine when
data is available to be received.

RETURN VALUES

Upon successful completion, recv() returns the length of the message
in bytes. If no messages are available to be received and the peer
has performed an orderly shutdown, recv() returns 0. Otherwise, -1
is returned and errno is set to indicate the error.

ERRORS

In addition to the errors documented below, an asynchronous error
generated by the underlying socket protocol may be returned. For the
full list of errors, please see the corresponding socket protocol
manual page. For example, for a list of TCP errors, please see
tcp(4P).

The recv() function will fail if:

EAGAIN
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
The socket argument refers to a connection oriented
socket and the connection was forcibly closed by the
peer and is no longer valid. I/O can no longer be
performed to filedes.

EFAULT
The buffer parameter can not be accessed or written.

EINTR
The recv() function was interrupted by a signal that
was caught, 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 or protocol.

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

The recv() 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.

ENOSR
There were insufficient STREAMS resources available for
the operation to complete.

ATTRIBUTES