accept.2freebsd

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Version: 338509 (ubuntu - 24/10/10)

Section: 2 (Appels système)


BSD mandoc

NAME

accept - accept a connection on a socket

LIBRARY

Lb libc

SYNOPSIS

In sys/types.h In sys/socket.h Ft int Fn accept int s struct sockaddr * restrict addr socklen_t * restrict 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 system call extracts the first connection request on the queue of pending connections, creates a new socket, and allocates a new file descriptor for the socket which inherits the state of the O_NONBLOCK property from the original socket Fa s .

If no pending connections are present on the queue, and the original socket is not marked as non-blocking, Fn accept blocks the caller until a connection is present. If the original 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 argument that is filled-in with the address of the connecting entity, as known to the communications layer. The exact format of the Fa addr argument is determined by the domain in which the communication is occurring. A null pointer may be specified for Fa addr if the address information is not desired; in this case, Fa addrlen is not used and should also be null. Otherwise, the Fa addrlen argument is a value-result argument; 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 dequeueing 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.

For some applications, performance may be enhanced by using an accept_filter9 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 Fn accept system call will fail if:
Bq Er EBADF
The descriptor is invalid.
Bq Er EINTR
The Fn accept operation was interrupted.
Bq Er EMFILE
The per-process descriptor table is full.
Bq Er ENFILE
The system file table is full.
Bq Er ENOTSOCK
The descriptor references a file, not a socket.
Bq Er EINVAL
listen(2) has not been called on the socket descriptor.
Bq Er EINVAL
The Fa addrlen argument is negative.
Bq Er EFAULT
The Fa addr argument 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.
Bq Er ECONNABORTED
A connection arrived, but it was closed while waiting on the listen queue.

SEE ALSO

bind(2), connect(2), getpeername(2), getsockname(2), listen(2), select(2), socket(2), accept_filter9

HISTORY

The Fn accept system call appeared in BSD 4.2