accept, accept4 - accept a new connection on a socket
#include <sys/socket.h> int accept(int socket, struct sockaddr *restrict address, socklen_t *restrict address_len); int accept4(int socket, struct sockaddr *restrict address, socklen_t *restrict address_len, int flags);
The accept() function extracts the first connection on the queue of pending connections, creates a new socket with the same socket type protocol and address family as the specified socket, and allocates a new file descriptor for that socket.
The function takes the following arguments:
Either a null pointer, or a pointer to a sockaddr structure where the address of the connecting socket will be returned.
Points to a socklen_t which on input specifies the length of the supplied sockaddr structure, and on output specifies the length of the stored address.
If address is not a null pointer, the address of the peer for the accepted connection is stored in the sockaddr structure pointed to by address, and the length of this address is stored in the object pointed to by address_len.
If the actual length of the address is greater than the length of the supplied sockaddr structure, the stored address will be truncated.
If the protocol permits connections by unbound clients, and the peer is not bound, then the value stored in the object pointed to by address is unspecified.
If the listen queue is empty of connection requests and O_NONBLOCK is not set on the file descriptor for the socket, accept() and accept4() will block until a connection is present. If the listen(3C) queue is empty of connection requests and O_NONBLOCK is set on the file descriptor for the socket, accept() and accept4() will fail and set errno to EAGAIN or EWOULDBLOCK.
The accepted socket cannot itself accept more connections. The original socket remains open and can accept more connections.
The accept4() function behaves like accept() but the accepting socket does not inherit NDELAY and NONBLOCKING from the original socket, instead it will take the settings from the flags argument:
As if O_NDELAY is set for the socket.
As if O_NONBLOCK is set for the socket.
No SIGPIPE will be sent on write when the remote connection was closed; instead EPIPE is returned.
The socket will be closed on exec() or spawn().
The socket will not be inherited by the child on fork() or spawn().
If both SOCK_NDELAY and SOCK_NONBLOCK are set, the socket will behave as if only SOCK_NONBLOCK is set.
When a connection is available, select(3C) will indicate that the file descriptor for the socket is ready for reading.
Upon successful completion, accept() and accept4() return the nonnegative file descriptor of the accepted socket. Otherwise, −1 is returned and errno is set to indicate the error.
The accept() and accept4() functions will fail if:
O_NONBLOCK is set for the socket file descriptor and no connections are present to be accepted.
The socket argument is not a valid file descriptor.
A connection has been aborted.
The address or address_len parameter can not be accessed or written.
The accept() function was interrupted by a signal that was caught before a valid connection arrived.
The socket is not accepting connections.
OPEN_MAX file descriptors are currently open in the calling process.
The maximum number of file descriptors in the system are already open.
The socket argument does not refer to a socket.
The socket type of the specified socket does not support accepting connections.
The accept() and accept4() functions may fail if:
No buffer space is available.
There was insufficient memory available to complete the operation.
There was insufficient STREAMS resources available to complete the operation.
A protocol error has occurred; for example, the STREAMS protocol stack has not been initialized.
See attributes(7) for descriptions of the following attributes: