recv() -- receive message from socket

SYNOPSIS

#include <sys/socket.h>

int recv(int s, void *buf, size_t len, int flags);

The recv() function receives a message from a socket. The recv() call can be used on a connection mode socket or a bound, connectionless socket. If no messages are available at the socket, the recv() call waits for a message to arrive unless the socket is nonblocking. If a socket is nonblocking, -1 is returned and the external variable errno is set to EWOULDBLOCK. select() can be used to wait for incoming messages.

A recv() on a SOCK_STREAM socket returns as much available information as the size of the buffer supplied can hold. If the socket has been configured for in-line reception of out-of-band data (socket option SO_OOBINLINE) and out-of-band data is unread, only out-of-band data is returned. The application may use the ioctl() SIOCATMARK to determine whether any more out-of-band data remains to be read.

For SOCK_DGRAM sockets, data is extracted from the first queued datagram for the destination address specified in the connect call. If unconnected, the socket must be bound and have no source address restrictions on the datagrams received. If the datagram is larger than the buffer supplied, the buffer is filled with the first part of the datagram and recv() generates the error EMSGSIZE. For unreliable protocols (such as UDP), excess data is lost. For reliable protocols, data is successfully read by calling recv() with a large enough buffer.

If the socket is connection-oriented and the remote side has shut down the connection gracefully, a recv() call completes with 0 bytes received. If the connection has been reset, recv() fails and sets errno to ECONNRESET.

flags may be used to influence the behavior of the function invocation beyond the options specified for the associated socket. That is, the semantics of this function are determined by the socket options and the flags parameter. The latter is constructed by or-ing any of the following values:

MSG_PEEK: Peek at the incoming data. The data is copied into the buffer but is not removed from the input queue.
MSG_OOB: Process out-of-band data

PARAMETERS

s: Specifies a socket descriptor from which data should be received.
buf: Points to the buffer in which to place the message.
len: Specifies the length of the buffer.
flags: Lets the caller control the reception by peeking at incoming data (MSG_PEEK) or receive out-of-band data (MSG_OOB).

RETURN VALUES

If successful, recv() returns the number of bytes received. On failure, it returns a value of -1 and sets errno to one of the following values:

EBADF: s is an invalid descriptor.
ECONNABORTED: The virtual circuit was aborted because of a timeout or other failure.
ECONNRESET: The virtual circuit was reset by the remote host executing a hard or abortive close.
EFAULT: buf is an invalid pointer.
EINTR: A signal interrupted the recv() call.
EINVAL: The socket was not bound using bind(), or an invalid flag was specified, or len was 0 or negative.
EMSGSIZE: The message was too large to fit the specified buffer.
ENETDOWN: The network subsystem has failed.
ENETRESET: The connection is broken; the remote host reset.
ENOTCONN: The socket is not connected.
ENOTSOCK: s is not a socket descriptor.
EOPNOTSUPP: MSG_OOB was specified on socket that does not support out of band data.
ESHUTDOWN: The socket has been shut down.
ETIMEDOUT: The connection has been dropped because of a network failure.
EWOULDBLOCK: s is nonblocking and recv() would block.

recv()
receive message from socket

Function

SYNOPSIS

DESCRIPTION

PARAMETERS

RETURN VALUES

CONFORMANCE

MULTITHREAD SAFETY LEVEL

PORTING ISSUES

AVAILABILITY

SEE ALSO

recv() receive message from socket

Function

recv()
receive message from socket