RECV

RECV returns the length of the incoming message or data. If a datagram packet is too long to fit in the supplied buffer, datagram sockets discard extra bytes.

For stream sockets, the data is processed like streams of information with no boundaries separating data. For example, if applications A and B are connected with a stream socket and Application A sends 1000 bytes, each call to RECV can return 1 byte, or 10 bytes, or the entire 1000 bytes. Therefore, applications using stream sockets should place RECV in a loop that repeats the call until all data has been received.

Keyword

Description

S

Input parameter. A value or the address of a halfword binary number specifying the socket descriptor.

NBYTE

Input parameter. A fullword binary number set to the size of BUF. RECV does not receive 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 of 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, this field contains an error number. 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.

FLAGS

Input parameter. FLAGS can be a literal value or a fullword binary field.

Literal Value	Binary Value	Description
'MSG_OOB'	X'00000001'	Receive out-of-band data (stream sockets only). Out-of-band data can be read if the SO_OOBINLINE option is set for the socket regardless of whether the MSG_OOB flag is set.
'MSG_PEEK'	X'00000002'	Peek at the data, but do not destroy the data. If the peek flag is set, the next receive operation reads the same data.
'MSG_WAITALL'	X'00000040'	Requests that the function block until the full amount of requested data can be returned (stream sockets only). The function might return a smaller amount of data if the connection is terminated, if an error is pending, or if the SO_RCVTIMEO field is set and the timer expired for the socket.

ECB or REQAREA

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

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.

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