NAME

recv, recvfrom – receive a message from a socket

SYNOPSIS

#include <sys/socket.h>

size_t recv(int s ,

void *buf ,

size_t len ,

int flags );

size_t recvfrom(int s ,

void *buf ,

size_t len ,

int flags ,

struct sockaddr *from ,

socklen_t *fromlen );

DESCRIPTION

recv() and recvfrom() are used to receive messages from another socket. recv() may be used only on a connected socket (see connect()), while recvfrom() can be used on any socket. s is a socket created with socket().

If from is not a NULL pointer, the source address of the message is filled in. fromlen is a value-result parameter, initialized to the size of the buffer associated with from , and modified on return to indicate the actual size of the address stored there. The length of the message is returned. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from (see socket()).

If no messages are available at the socket, the receive call waits for a message to arrive. Nonblocking sockets are not supported.

The flags parameter is formed by ORing one or more of the following:

MSG_OOB

Read any out-of-band data present on the socket rather than the regular in-band data. Only SOCK_STREAM sockets support out-of-band data.

MSG_PEEK

Peek at the data present on the socket; the data is returned, but not consumed, so that a subsequent receive operation will see the same data.

MSG_DONTWAIT

Tells the appropriate socket operation to work in a non-blocking way.

RETURN VALUES

These calls return the number of bytes received, or -1 if an error occurred.

ERRORS

This function is a member of Unison’s IOLIB family of functions. IOLIB is implemented as a message passing and generalized interface layer. Each Unison I/O server is responsible for its own error reporting.

For an exact list of error codes returned by a particular server, refer to that server’s documentation in the Unison Programmer’s Guide for each specific platform.

Servers may implement these errors codes in response to this function.

EBADF

s is an invalid file descriptor.

EIO

An I/O error occurred while reading from or writing to the file system.

ENOMEM

There was insufficient user memory available for the operation to complete.

ENOTSOCK

s is not a socket.

ESTALE

A stale NFS file handle exists.

EAGAIN or EWOULDBLOCK

The socket’s file descriptor is marked O_NONBLOCK and no data is waiting to be received.

SEE ALSO

ioctl(), read(), connect(), getsockopt(), send(), socket()