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How Messages Are Passed from BEA Tuxedo Clients to BEA TOP END Servers
BEA Tuxedo clients communicate with BEA TOP END services through the TEDG. Relative to a BEA Tuxedo client, the TEDG functions as a local server. The TEDG advertises services specified in the SERVICE entries in the DM_REMOTE_SERVICES section of the DMCONFIG file. Client programs make requests and receive responses using tpcall(3c) in the same way they use tpcall() to interact with local services. Asynchronous requests and responses are supported through the tpacall(3c) and tpgetrply(3c) functions. If, in the DM_REMOTE_SERVICES section of the DMCONFIG file, the SERVICE entry for a TEDG service contains the setting CONV=N, then BEA Tuxedo clients may communicate with that service in only one mode: request/response. (CONV=N is the default value and does not need to be set.)
The TEDG uses the requested service name to locate the SERVICE entry in the DM_REMOTE_SERVICES section to determine the corresponding BEA TOP END product, function, Message Sensitive Routing (MSR) target, and function qualifier for the mapped BEA TOP END request. Data marshalling is performed by the TEDG, as required, before the message is sent to the BEA TOP END system. The BEA TOP END system then routes the request to a server on a BEA TOP END node that has received the message. The BEA TOP END server response is unmarshalled, if necessary. The TEDG maps the status of the request and prepares the buffer for delivering the response to the BEA Tuxedo client.
How the TEDG Works with BEA Tuxedo Clients
Client operations are programmed with the same functions used for any BEA Tuxedo client.
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Use this function . . . |
For . . . |
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tpcall() |
Synchronous requests and responses |
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tpacall() |
Asynchronous requests and responses |
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tpgetreply() |
Asynchronous requests and responses |
These functions are programmed in the normal manner.
As a BEA Tuxedo client programmer, you need to know the following information:
If a BEA TOP END service supports FML32 input, the BEA Tuxedo client uses the BEA Tuxedo FML32 buffer type. FML32 is beneficial because the TEDG and the BEA TOP END system support data marshalling of these buffers when the buffers are transmitted between the TEDG and a BEA TOP END node of a different type. A BEA TOP END service may support one or more of these buffer types.
Because BEA TOP END messages are limited to 30K bytes, the size of the client request may not exceed that limit. For an FML32 message, the limit applies after the FML index is stripped from the message.
How the TEDG Maps Client Requests
A client request may be transactional or non-transactional and it may or may not require a response. The following table shows how BEA Tuxedo client flags are mapped to a BEA TOP END request. All other flags (TPNOCHANGE, TPNOBLOCK, TPNOTIME, TPSIGRSTRT) and the service priority (see tpsprio()) either are local to the application or affect only client-TEDG interactions in the BEA Tuxedo system. By processing the following flags, the TEDG accomplishes tasks that are normally done in the BEA Tuxedo system.
The tperrno values returned to the BEA Tuxedo client are standard values. Because the TEDG acts as a BEA Tuxedo server, it also returns TPESVCERR and TPESVCFAIL for certain conditions. The BEA Tuxedo client cannot interpret these messages as "application defined errors" exclusively:
For additional information, see Error Values.
Note: tpurcode is not supported by the TEDG.
The TEDG maps the response from the BEA TOP END system/server to a response that the BEA Tuxedo client accesses through the tpcall parameters or the tpgetrply function. A BEA TOP END server may deliver a response in either a raw buffer or an FML32 buffer. A raw buffer is normally mapped by the TEDG to a CARRAY buffer unless the administrator configures it to map to an X_OCTET buffer. Additionally, the administrator may constrain the response buffer to one of the following types: CARRAY, X_OCTET or FML32. If the BEA TOP END service returns an incompatible buffer, the TEDG returns a tperrno of TPEOTYPE.
How the TEDG Works with BEA TOP END Servers
Relative to a BEA TOP END server, the TEDG functions as a BEA TOP END client: it receives mapped BEA Tuxedo client requests in the normal manner through tp_server_receive(3T). The buffer received is either a raw buffer or an FML32 buffer, depending on the message sent by the BEA Tuxedo client. The BEA TOP END server receives one of the following types of requests:
The BEA TOP END server handles both types of requests according to standard BEA TOP END programming requirements. The client request may be transactional or non-transactional.
How the TEDG Maps BEA TOP END Server Send Flags
The BEA TOP END server responds to a client request using tp_server_send(3T). The response buffer may be either a raw buffer or an FML32 buffer, depending on what is supported by the BEA TOP END application, the TEDG configuration, and the BEA Tuxedo client. This buffer is mapped to a BEA Tuxedo client buffer as described in How the TEDG Maps Client Requests.
The following table shows how BEA TOP END tp_server_send(3T) flags are mapped. The server may indicate an error by resetting the dialog or by responding with an application-defined field value in the response buffer. The BEA Tuxedo client must be programmed to respond appropriately. Do not use the output_format and attach_info parameters on responses to the TEDG; they are not supported.
The following error values may be returned to a BEA Tuxedo client because problems exist in the TEDG, the BEA TOP END system, or the BEA TOP END server. Keep in mind that a single tperrno value may be used to report any one of many possible causes of the error being reported.
Because the TEDG does not advertise services based upon the actual availability of BEA TOP END services, a message may be routed to a BEA TOP END node where the services actually are unavailable, resulting in a tperrno of TPENOENT, while other routing decisions may result in successful requests. If a service is to be available on multiple nodes, the design of the BEA Tuxedo application, the BEA TOP END application, and the TEDG must take into account the possibility that this type of failure may occur. A well-designed application, that ensures that there are multiple, restartable copies of the servers, reduces the possibility of such errors occurring.
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Copyright © 2000 BEA Systems, Inc. All rights reserved.
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