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
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
poll(2),
select(3C),
recvfrom(3XNET),
recvmsg(3XNET),
send(3XNET),
sendmsg(3XNET),
sendto(3XNET),
shutdown(3XNET),
socket(3XNET),
tcp(4P),
attributes(7),
standards(7) September 10, 2018
RECV(3XNET)