accept (BPX1ACP, BPX4ACP) — Accept a connection request from a client socket

Function

The accept callable service allows a server to accept a connection request from a client. It extracts the first connection on the queue of pending connections, creates a new socket with the same properties as the specified socket, and allocates a new descriptor for that socket. If there are no connections pending, the service either blocks until a connection request is received, or fails with an EWOULDBLOCK, depending on whether the specified socket is marked as blocking or nonblocking.

Requirements

Parameters

Socket_descriptor

Supplied parameter

Type:

Integer

Length:

Fullword

The name of a fullword that contains the socket file descriptor for which the accept is to be done.

Sockaddr_length

Supplied and returned parameter

Type:

Integer

Length:

Fullword

The name of a field that contains the length of Sockaddr. On return, this field specifies the size required to represent the address of the connecting socket. If this value is larger than the size supplied on input, the information contained in Sockaddr is truncated to the length supplied on input. The field can be zero if no value is passed for Sockaddr. The size of the field should be less than 4096 bytes (4KB) in length.

Sockaddr

Supplied and returned parameter

Type:

Structure

Length:

Length specified by Sockaddr_length

The name of a field that contains the socket address of the connecting client. The format of Sockaddr is determined by the domain in which the client resides. This field can be null if the caller is not interested in the client address. For more information about the format of this structure, see BPXYSOCK — Map SOCKADDR structure and constants.

Return_value

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the accept service returns one of the following:

• A socket descriptor, if the request is successful.
• -1, if the request is not successful.

Return_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword in which the accept service stores the return code. The accept service returns Return_code only if Return_value is -1. See z/OS UNIX System Services Messages and Codes for a complete list of possible return code values. The accept service can return one of the following values in the Return_code parameter:

Return_code	Explanation
EBADF	An incorrect file descriptor was specified. The following reason codes can accompany the return code: JRFileDesNotInUse, or JRFileNotOpen.
ECONNABORTED	Software-caused connection termination.
EINTR	A signal interrupted the accept service before any connections were available. The following reason code can accompany the return code: JRSignalReceived.
EINVAL	The socket is not accepting connections. A listen must be done prior to the accept. The following reason code can accompany the return code: JRListenNotDone.
EIO	There has been a network or transport failure. The following reason codes can accompany the return code: JRInetRecycled, JRPrevSockError.
ENFILE	Too many files are open in the system. The following reason code can accompany the return code: JRMaxSockets.
ENOBUFS	A buffer could not be obtained. The following reason code can accompany the return code: JROutofSocketCells.
ENOTSOCK	Socket_descriptor does not refer to a valid socket descriptor. The following reason code can accompany the return code: JRMustBeSocket.
EOPNOTSUPP	The referenced socket is not a type that supports the requested function.
EWOULDBLOCK	The socket file descriptor is marked nonblocking, and no connections are present to be accepted.

Reason_code

Returned parameter

Type:

Integer

Length:

Fullword

The name of a fullword where the accept service stores the reason code. The accept service returns Reason_code only if Return_value is -1. Reason_code further qualifies the Return_code value. For the reason codes, see z/OS UNIX System Services Messages and Codes.

Usage notes

1. The Socket_descriptor that is passed refers to the socket that was created with the socket callable service, was bound to an address with the bind callable service, and that has issued a successful call to the listen callable service.

   Before calling the accept service, you can find out if the socket is pending a connection by doing a read select with the select callable service.

2. In order for Sockaddr to be returned for a UNIX domain socket, the client application doing the connect must bind a unique local name to the socket using the bind service before running the connect service.
3. See Callable services available to SRB mode routines for more information about programming considerations for SRB mode.

Related services

• asyncio (BPX1AIO, BPX4AIO) — Asynchronous I/O for sockets
• bind (BPX1BND, BPX4BND) — Bind a unique local name to a socket descriptor
• listen (BPX1LSN, BPX4LSN) — Prepare a server socket to queue incoming connection requests from clients
• select/selectex (BPX1SEL, BPX4SEL) — Select on file descriptors and message queues
• socket or socketpair (BPX1SOC, BPX4SOC) — Create a socket or a pair of sockets

Characteristics and restrictions

There are no restrictions on the use of the accept service.