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Resumen del manual
4 SPI Programming
Considerations
The Communications Management Programming Manual discusses general programming
considerations for writing applications that use the Subsystem Programmatic Interface
(SPI) to communicate with data communications subsystems such as the TELNET
subsystem. This section discusses SPI programming considerations that are specific to
the TELNET subsystem.
Building the Command
The following programming considerations apply when an application builds the
Buffer
command buffer for a TELNET command.
The recommended buffer length (in bytes) for a command is a predefined value with
the symbolic name ZTNT-VAL-BUFLEN.
The subsystem does not support multiple commands in a single request message.
However, many of the commands can contain an object-name template; therefore, one
command can affect multiple objects. All of the objects whose names appear in a
command must be of the same object type.
The subsystem does not support the continuation of a command across multiple
command messages, but it does support the special case of multiple reply messages
using the context token, as described in the Distributed Systems Management (DSM)
Programming Manual.
The command buffers for all commands can contain extensible structured tokens. An
extensible structured token that is to appear in a command should always be
initialized by the SPI procedure SSNULL to ensure that every field of the token is set
to its null value. This action is important because a command is performed if a field
contains a value other than its null value. For example, in the ALTER WINDOW
command, if a field of the extensible structured token that describes the window
attributes contains a value other than its null value, that value is assigned to the
attribute corresponding to that field. Using SSNULL is important even when every
field of an extensible structured token has a value assigned to it; if SSNULL is used,
the application can still function even when it is compiled with new definition files
that add new fields to the token.
The only tokens that can appear more than once in a command are ZSPI-TKN-
COMMENT and ZCOM-TKN-TRACE-OPT. ZSPI-TKN-COMMENT, the comment
token, is described in the Distributed Systems Management (DSM) Programming Manual.
ZCOM-TKN-TRACE-OPT, a token used in the TRACE command, is described under
“TRACE Command” in Section 6, “Commands and Responses.” If any of the other
tokens in a command appear more than once, an error is returned.
Discontinuing a
General programming considerations for discontinuing a command in progress are
Command in Progress
discussed in the Communications Management Programming Manual.
Although the subsystem supports the use of the token ZSPI-TKN-ALLOW-TYPE
(which allows an application to specify in a command operating on multiple objects
whether the subsystem should continue immediately to the next object if the operation
failed on the previous object), the only value supported for this token is ZSPI-VAL-
NORM-ONLY. The ZSPI-VAL-NORM-ONLY value indicates that the TELNET
53474 Tandem Computers Incorporated
4–1
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