The HP PEXlib client, when emitting PEX protocol, does no
parameter error checking. The standard PEX method is for the server
to detect parameter errors in incoming protocol requests and report
them to the client.
If DHA rendering is being used, or the X protocol method is
in effect, parameter error checking will be done in the client process.
Error reporting is handled differently when in the DHA and client
process methods versus the PEX protocol method. In DHA and X methods,
errors are synchronous so that special PEX sequence numbers are
not reported.
The standard PEX error types and messages documented in the
PEX Protocol Specification are generated by HP PEXlib. When running
remotely to an HP PEX server or when running DHA, additional error
data is included with the standard PEX error messages to help users
better under stand the sources of the errors. An NLS-compatible
error catalog, 〈nls〉/PEX.cat[10], contains the additional error messages
for DHA PEXlib or when communicating with an HP PEX server. Some
of these error messages cannot be adequately explained in 80 characters,
the limit on error messages, so the file 〈err-help〉/PEXErrorHelp provides the
additional HP-specific information to which users are referred.
The NLS error catalog resides in the directories 〈nls〉/msg/C and 〈nls〉/american. This additional
information is handled by special functions installed in the Xlib
extension hooks that enable the default X error handler to detect
and print the values. The default X error handler, as of X11R6,
is able to call these value-printing functions.
The basic and standard PEX error messages reside in the usual
X11 error message catalog, 〈x11〉/XErrorDB, which is not NLS-compatible.
Certain errors, such as those related to calling a PEXlib
routine before PEXlib itself has been initialized, and some graphics
pipeline errors, cannot be handled as regular PEX errors. These
types of errors are printed to stderr
with PEX context information to aid troubleshooting.
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