DragonFly On-Line Manual Pages


ACCEPT(2)		 DragonFly System Calls Manual		     ACCEPT(2)

NAME

accept -- accept a connection on a socket

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h> #include <sys/socket.h> int accept(int s, struct sockaddr *addr, socklen_t *addrlen);

DESCRIPTION

The argument s is a socket that has been created with socket(2), bound to an address with bind(2), and is listening for connections after a listen(2). The accept() call extracts the first connection request on the queue of pending connections, creates a new socket with the same properties as s, and allocates a new file descriptor for the socket. If no pending connections are present on the queue, and the socket is not marked as non-blocking, accept() blocks the caller until a connection is present. If the socket is marked non-blocking and no pending connections are present on the queue, accept() returns an error as described below. The accepted socket may not be used to accept more connections. The original socket s remains open. The argument addr is a result parameter that is filled-in with the address of the connecting entity, as known to the communications layer. The exact format of the addr parameter is determined by the domain in which the communication is occurring. To ensure that the returned address fits, *addr should have a size of at least sizeof(struct sockaddr_storage). The addrlen is a value-result parameter; it should initially contain the amount of space pointed to by addr; on return it will contain the actual length (in bytes) of the address returned. This call is used with connection-based socket types, currently with SOCK_STREAM. It is possible to select(2) a socket for the purposes of doing an accept() by selecting it for read. For certain protocols which require an explicit confirmation, such as ISO or DATAKIT, accept() can be thought of as merely dequeueing the next con- nection request and not implying confirmation. Confirmation can be implied by a normal read or write on the new file descriptor, and rejec- tion can be implied by closing the new socket. For some applications, performance may be enhanced by using an accept_filter(9) to pre-process incoming connections.

RETURN VALUES

The call returns -1 on error. If it succeeds, it returns a non-negative integer that is a descriptor for the accepted socket.

ERRORS

The accept() will fail if: [EBADF] The descriptor is invalid. [EINTR] The accept() operation was interrupted. [EMFILE] The per-process descriptor table is full. [ENFILE] The system file table is full. [ENOTSOCK] The descriptor references a file, not a socket. [EINVAL] listen(2) has not been called on the socket descrip- tor. [EFAULT] The addr parameter is not in a writable part of the user address space. [EWOULDBLOCK] The socket is marked non-blocking and no connections are present to be accepted. [ECONNABORTED] A connection arrived, but it was closed while waiting on the listen queue.

SEE ALSO

bind(2), connect(2), getpeername(2), listen(2), select(2), socket(2), accept_filter(9)

HISTORY

The accept() function appeared in 4.2BSD. DragonFly 3.9 December 11, 1993 DragonFly 3.9