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How Messages Are Passed from BEA TOP END Clients to BEA Tuxedo Servers
BEA TOP END clients communicate with BEA Tuxedo servers through the TEDG. If, in the DM_LOCAL_SERVICES section of the DMCONFIG file, the SERVICE entry for a TEDG service contains the setting CONV=N, then BEA TOP END 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.)
Relative to a BEA TOP END client, the TEDG functions as a BEA TOP END server on a remote BEA TOP END node. The TEDG receives a BEA TOP END client request and maps it to a corresponding BEA Tuxedo request. Note that the BEA Tuxedo system may route the request to a BEA Tuxedo server anywhere within the BEA Tuxedo configuration.
The process for passing messages in request/response mode from a BEA TOP END client to a BEA Tuxedo server is as follows:
How the TEDG Works with BEA TOP END Clients
Client operations are programmed with the same functions used for any BEA TOP END client.
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Use this API . . . |
For . . . |
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tp_client_send |
Making asynchronous requests |
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tp_client_signon |
Making asynchronous requests |
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tp_client_receive |
Receiving responses |
These functions are used in the normal manner when making a service request to a BEA Tuxedo server through the TEDG.
As a BEA TOP END client programmer, you need to know the following information:
If a BEA Tuxedo service supports FML32 input, the BEA TOP END client must use the FML32 message 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 Tuxedo service may support one or more of these buffer types.
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 TOP END client flags are mapped. By processing these flags, the TEDG accomplishes tasks that are normally done in the BEA TOP END system. Do not use the input_format and attach_info parameters on requests to the TEDG; they are not supported.
The status and extended status values returned to the BEA TOP END client are standard values. Additional information on the mapping of error values is provided later in this topic.
The TEDG maps the response from the BEA Tuxedo system/server to a response that the BEA TOP END client accesses through the tp_client_receive(3T) call. A BEA Tuxedo server may deliver a response in a CARRAY, X_OCTET, or FML32 buffer. A CARRAY or X_OCTET buffer is mapped by the TEDG to a raw message; an FML32 buffer, to a BEA TOP END FML32 message. Additionally, the administrator may constrain the response buffer to one of the following types: CARRAY, X_OCTET, or FML32. If the BEA Tuxedo service returns an incompatible buffer, the TEDG returns a TP_RESET status.
How the TEDG Works with BEA Tuxedo Servers
Relative to a BEA Tuxedo server, the TEDG functions as a BEA Tuxedo client: it receives mapped BEA TOP END client requests in the normal manner. The type of the buffer it receives (CARRAY, X_OCTET, or FML32) depends on the message sent by the client. The BEA Tuxedo server processes the request in the normal manner. The request may be transactional or non-transactional. It may be a "no-reply" request.
A BEA Tuxedo server responds to a client request using tpreturn(3c). TPSUCCESS is mapped to a TP_OK BEA TOP END status. TPFAIL and TPEXIT, along with a number of other error conditions, are mapped to a TP_RESET BEA TOP END status. A reply message is supported only with TPSUCCESS.
Note: The application-defined return code, rcode, is not supported by the TEDG.
The BEA Tuxedo server may deliver a reply in a CARRAY, X_OCTET, or FML32 buffer, depending on which buffer types are supported by the BEA TOP END system, the TEDG configuration, and the BEA TOP END client. The reply buffer is mapped to a BEA TOP END message. The server may indicate an error by sending a TPFAIL error or by responding with an application-defined field value in the reply buffer. The BEA TOP END client must be programmed to handle that error reporting interface of the server.
Because BEA TOP END messages are limited to 30K bytes, the BEA Tuxedo server reply may not exceed that limit. For an FML32 message, the limit applies after the FML index is stripped from the message.
Error Values
In addition to regular BEA TOP END error status messages, a number of other status messages may be returned to a BEA TOP END client as a result of problems in the TEDG, the BEA Tuxedo system, or the BEA Tuxedo server. Keep in mind that a single error status 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 Tuxedo services, a message may be routed to a BEA Tuxedo node where the services actually are unavailable, resulting in a TP_SERVICE error, 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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