recv - receive a message from a connected socket
cc [ flag ... ] file ... -lxnet [ library ... ]
#include <sys/socket.h>
ssize_t recv(int socket, void *buffer, size_t length, int flags);
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.
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.
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.
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.
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
Standard |
| MT-Level |
MT-Safe |
poll(2), select(3C), recvfrom(3XNET),
recvmsg(3XNET), send(3XNET), sendmsg(3XNET),
sendto(3XNET), shutdown(3XNET), socket(3XNET),
tcp(4P), attributes(7), standards(7)