The READ macro reads data on a socket and stores it in a buffer. The READ macro applies only to connected sockets.

For datagram sockets, the READ call returns the entire datagram that was sent. If a datagram packet is too long to fit in the supplied buffer, datagram sockets discard extra bytes.

Keyword

Description

S

Input parameter. A value or the address of a halfword binary number specifying the socket that is going to read the data.

NBYTE

Input parameter. A fullword binary number set to the size of BUF. READ does not return more than the number of bytes of data in NBYTE even if more data is available.

BUF

On input, a buffer to be filled by completion of the call. The length of BUF must be at least as long as the value of NBYTE.

ALET

Optional input parameter. A fullword binary field containing the ALET or BUF. The default is 0 (primary address space).

If a nonzero ALET is specified, the ALET must represent a valid entry in the dispatchable unit access list (DU-AL) for the task issuing this call. Note that ALETs can be specified only for synchronous socket calls (for example, ECB/REQAREA cannot be specified). An exception to this is an ALET representing a SCOPE=COMMON data space.

ERRNO

Output parameter. A fullword binary field. If RETCODE is negative, ERRNO contains a valid error number. Otherwise, ignore the ERRNO field.

See Socket call error return codes for information about ERRNO return codes.

RETCODE

A fullword binary field that returns one of the following values:

Value

Description

0

A 0 return code indicates that the connection is closed and no data is available.

>0

A positive value indicates the number of bytes copied into the buffer.

-1

Check ERRNO for an error code.

ECB or REQAREA

Input parameter. This parameter is required if you are using APITYPE=3. It points to a 104-byte field containing the following information:

For ECB

A 4-byte ECB posted by TCP/IP when the macro completes.

For REQAREA

A 4-byte user token (set by you) that is presented to your exit when the response to this function request is complete.

For ECB/REQAREA

The last 100 bytes is a storage field used by the interface to save the state information.

Note: This storage must not be modified until the macro function has completed and the ECB has been posted or the asynchronous exit has been driven.

ERROR

Input parameter. The location in your program to receive control when the application programming interface (API) processing module cannot be loaded.

TASK

Input parameter. The location of the task storage area in your program.

READ returns up to the number of bytes specified by NBYTE. If less than the number of bytes requested is available, the READ macro returns the number currently available.

If data is not available for the socket and the socket is in blocking mode, the READ macro blocks the caller until data arrives. If data is not available and the socket is in nonblocking mode, READ returns a -1 and sets ERRNO to 35 (EWOULDBLOCK). See IOCTL or FCNTL for a description of how to set the nonblocking mode.