SNAX/HLS Application Programming Manual

Procedure Specifications

Customization

104707 Tandem Computers Incorporated 7–21

snu

points to the SNALU buffer using extended addressing.

vlen

defines the length (in bytes) of the messages about to be sent to the SNALU

interface. In case of requests, you can only reduce this value although it should not

be reduced to below 9 bytes. For responses, the value can be increased to a

maximum of 265 bytes. No attempt should be made to reduce it below 9 bytes.

The USEREXIT^SNAX^OUT routine can be used as part of response-time statistics

collection. You can examine the message, verify that it is the pertinent SNA message,

and record a value in the session-specific storage.

You might also use this routine to change the text of an SNA message. However, you

must be very careful in doing this, since a wrong modification can cause unpredictable

results in the protocol handling.

Although the customization routine can change the text of the SNA RU being sent,

certain types of changes can cause unwanted side effects. For example, clearing the

Exception Response Indicator (ERI) in an attempt to solicit a definite response can

cause problems because the SNAX/HLS server built the request as an exception-

response chain and treats any definite response as a violation of protocol. Similar care

should be taken with other indicators in the Request/Response Header.

The following points should be noted when modifying outbound SNA messages:

Changing the length of messages other than FMD RUs is almost always invalid.

Changing the bits in the RH almost always produces undesirable side effects—the

two half-sessions might end up in incompatible states.

Changing the request code of DFC or SC messages is almost always wrong.

Enlarging the size of any request is invalid. Enlarging the size of any response

beyond 265 bytes is invalid. Reducing the size of any request or response below 9

bytes is invalid. A log message is produced and the SNAX/HLS server abends if

any attempt is made to violate this restriction.