accept(2) accept(2) NAME accept - accept a connection on a socket SYNOPSIS #include <sys/socket.h> AF_CCITT only #include <x25/x25addrstr.h> int accept(int s, void *addr, int *addrlen); _XOPEN_SOURCE_EXTENDED only int accept(int s, struct sockaddr *addr, size_t *addrlen); DESCRIPTION The accept() system call is used with connection-based socket types, such as SOCK_STREAM. The argument, s, is a socket descriptor created with socket(), bound to a local address by bind(), and listening for connections after a listen(). accept() extracts the first connection on the queue of pending connections, creates a new socket with the same properties as s, and returns a new file descriptor, ns, for the socket. If no pending connections are present on the queue and nonblocking mode has not been enabled with the fcntl() O_NONBLOCK or O_NDELAY flags or the ioctl() FIOSNBIO request, accept() blocks the caller until a connection is present. O_NONBLOCK and O_NDELAY are defined in <sys/fcntl.h> (see fcntl(2) fcntl(5), and socket(7)). FIOSNBIO and the equivalent request FIONBIO are defined in <sys/ioctl.h>, although use of FIONBIO is not recommended (see ioctl(2), ioctl(5), and socket(7)). If the socket has nonblocking mode enabled and no pending connections are present on the queue, accept() returns an error as described below. The accepted socket, ns, cannot be used to accept more connections. The original socket s remains open for incoming connection requests. To determine whether a listening socket has pending connection requests ready for an accept() call, use select() for reading. The argument addr should point to a socket address structure. The accept() call fills in this structure with the address of the connecting entity, as known to the underlying protocol. In the case of AF_UNIX sockets, the peer's address is filled in only if the peer had done an explicit bind() before doing a connect(). Therefore, for AF_UNIX sockets, in the common case, when the peer had not done an explicit bind() before doing a connect(), the structure is filled with a string of nulls for the address. The format of the address depends upon the protocol and the address-family of the socket s. addrlen is a pointer to an int; it should initially contain the size of the structure pointed to by addr. On return, it contains the actual Hewlett-Packard Company - 1 - HP-UX Release 10.20: July 1996 accept(2) accept(2) length (in bytes) of the address returned. If the memory pointed to by addr is not large enough to contain the entire address, only the first addrlen bytes of the address are returned. If addr is NULL or addrlen contains 0, then the connecting entity's address will not be returned. The fcntl() O_NONBLOCK and O_NDELAY flags and ioctl() FIOSNBIO request are all supported. These features interact as follows: o If the O_NONBLOCK or O_NDELAY flag has been set, accept() requests behave accordingly, regardless of any FIOSNBIO requests. o If neither the O_NONBLOCK flag nor the O_NDELAY flag has been set, FIOSNBIO requests control the behavior of accept(). AF_CCITT only The addr parameter to accept() returns addressing information for the connecting entity, except for the x25ifname[] field of addr which contains the name of the local X.25 interface through which the connection request arrived. Call-acceptance can be controlled with the ioctl() X25_CALL_ACPT_APPROVAL request (see socketx25(7)). RETURN VALUE Upon successful completion, accept() returns a nonnegative integer which is a descriptor for the accepted socket. If an error occurs, accept() returns -1 and sets errno to indicate the cause. ERRORS If accept() fails, errno is set to one of the following values: [EAGAIN] Nonblocking I/O is enabled using O_NONBLOCK and no connections are present to be accepted. [EBADF] The argument, s, is not a valid file descriptor. [EFAULT] The addr parameter is not a valid pointer. [EINTR] The call was interrupted by a signal before a valid connection arrived. [EINVAL] The socket referenced by s is not currently a listen socket or has been shut down with shutdown(). A listen() must be done before an accept() is allowed. [EMFILE] The maximum number of file descriptors for this process are currently open. Hewlett-Packard Company - 2 - HP-UX Release 10.20: July 1996 accept(2) accept(2) [ENFILE] The system's table of open files is full and no more accept() calls can be processed at this time. [ENOBUFS] No buffer space is available. The accept() cannot complete. The queued socket connect request is aborted. [ENOTSOCK] The argument, s, is a valid file descriptor, but it is not a socket. [EOPNOTSUPP] The socket referenced by s does not suppport accept(). [EWOULDBLOCK] Nonblocking I/O is enabled using O_NDELAY or FIOSNBIO and no connections are present to be accepted. AUTHOR accept() was developed by the University of California, Berkeley. FUTURE DIRECTION The default behavior in this release is still the classic HP-UX BSD Sockets, however it will be changed to X/Open Sockets in some future release. At that time, any HP-UX BSD Sockets behavior which is incompatible with X/Open Sockets may be obsoleted. HP customers are advised to migrate their applications to conform to X/Open specification( see xopen_networking(7) ). SEE ALSO bind(2), connect(2), listen(2), select(2), socket(2) socketx25(7), xopen_networking(7). STANDARDS CONFORMANCE accept(): XPG4 Hewlett-Packard Company - 3 - HP-UX Release 10.20: July 1996