ACCEPT

Section: System Calls (2)
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BSD mandoc
BSD 4.2

NAME

accept - accept a connection on a socket

SYNOPSIS

Fd #include <sys/types.h> Fd #include <sys/socket.h> Ft int Fn accept int s struct sockaddr *addr int *addrlen

DESCRIPTION

The argument Fa 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 Fn accept argument extracts the first connection request on the queue of pending connections, creates a new socket with the same properties of Fa 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, Fn 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, Fn accept returns an error as described below. The accepted socket may not be used to accept more connections. The original socket Fa s remains open.

The argument Fa 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 Fa addr parameter is determined by the domain in which the communication is occurring. The Fa addrlen is a value-result parameter; it should initially contain the amount of space pointed to by Fa 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 Fn accept by selecting it for read.

For certain protocols which require an explicit confirmation, such as ISO or DATAKIT Fn accept can be thought of as merely dequeuing the next connection request and not implying confirmation. Confirmation can be implied by a normal read or write on the new file descriptor, and rejection can be implied by closing the new socket.

One can obtain user connection request data without confirming the connection by issuing a recvmsg(2) call with an Fa msg_iovlen of 0 and a non-zero Fa msg_controllen , or by issuing a getsockopt(2) request. Similarly, one can provide user connection rejection information by issuing a sendmsg(2) call with providing only the control information, or by calling setsockopt(2).

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 Fn accept will fail if:

Bq Er EBADF: The descriptor is invalid.
Bq Er ENOTSOCK: The descriptor references a file, not a socket.
Bq Er EOPNOTSUPP: The referenced socket is not of type SOCK_STREAM .
Bq Er EFAULT: The Fa addr parameter is not in a writable part of the user address space.
Bq Er EWOULDBLOCK: The socket is marked non-blocking and no connections are present to be accepted.

HISTORY

The Fn accept function appeared in BSD 4.2

This document was created by man2html, using the manual pages.
Time: 16:29:00 GMT, April 18, 2022