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


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(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO


poll(2), recvmsg(3XNET), recvfrom(3XNET), select(3C), send(3XNET),
sendmsg(3XNET), sendto(3XNET), shutdown(3XNET), socket(3XNET),
attributes(5), standards(5)


December 3, 2014 RECV(3XNET)