recvfrom() -- receive message from socket and capture address of sender

SYNOPSIS

#include <sys/socket.h>

int recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);

The recvfrom() system call receives a message from a socket and capture the address from which the data was sent. Unlike the recv() call, which can only be used on a connected stream socket or bound datagram socket, recvfrom() can be used to receive data on a socket whether or not it is connected. If no messages are available at the socket, the recvfrom() 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.

For a SOCK_STREAM socket, as much information is returned as is currently available, up to the size of the specified buffer. If the socket has been configured for inline 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 remain to be read.

For SOCK_DGRAM sockets, data is extracted from the first queued message, up to the size of the specified buffer. If the datagram or message is larger than the specified buffer, as much data are stored in the buffer as possible and recvfrom() generates an error message (EMSGSIZE). The remainder (or excess) of the message is lost if passed via an unreliable protocol.

If from is nonzero and the socket is not connection-oriented, the network address of the peer that sent the data is copied to the corresponding structure sockaddr. The value returned by fromlen is initialized to the size of this structure and is modified on return to indicate the actual size of the address stored there.

If the socket is connection-oriented and the remote side has shut down the connection gracefully, a recvfrom() call will complete immediately with 0 bytes received. If the connection has been reset, recvfrom() fails and returns the error message 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: Specifies the buffer in which to place the message.
len: Specifies the length of the buffer area.
flags: Allows the caller to control the reception by peeking at incoming data (MSG_PEEK)or by sending or receiving out-of-band data (MSG_OOB).
from: Specifies a socket address structure to record the address of the message sender.
fromlen: Specifies the length of the sender's address.

RETURN VALUES

If successful, recvfrom() 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 recvfrom() call
EINVAL: Socket has not been bound using bind(), or an invalid flag was specified, or len was 0 or negative.
EMSGSIZE: The message was too large to be stored in the specified buffer and was truncated.
ENETDOWN: The network subsystem has failed.
ENETRESET: The connection is broken; the remote host reset.
ENOTCONN: The socket was 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 recvfrom() would block

recvfrom()
receive message from socket and capture address of sender

Function

SYNOPSIS

DESCRIPTION

PARAMETERS

RETURN VALUES

CONFORMANCE

MULTITHREAD SAFETY LEVEL

PORTING ISSUES

AVAILABILITY

SEE ALSO

recvfrom() receive message from socket and capture address of sender

Function

recvfrom()
receive message from socket and capture address of sender