[rrd-developers] "rrdtool restore" error handling and implementation
link at pobox.com
Thu Feb 21 18:42:27 CET 2008
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Hi, cf. the thread on rrdtool-users at
(«Segfault on rrdtool restore...»).
The summary is: while attempting to add a DS to a RRD I'd
flubbed my editing of the XML dump file and "rrdtool restore"
segfaulted as a result.
Now segfaulting on bad input — particularly on input that is
well formed but logically wrong — is not an optimal failure
mode. It suggests to me that the code there needs more
sanitizing of input and saner error handling (so it'll bail with
a descriptive error message).
But rooting around in the code I notice that rrdtool seems to
have implemented its own XML parser. I'm quite surprised at
this given the ubiquity of XML parsing libraries (expat and
libxml, to name two), the usefulness of enabling processing with
general XML tools, and the pitfalls inherent in “rolling one's
own” when dealing with XML.
At first I speculated that this was a kind of optimization, but
the “restore” code doesn't seem particularly performance
critical. And in terms of dependencies, real XML parsers are
much more widely available than some of rrdtool's other
dependencies (and expat is even quite embedable, if that's a concern).
Perhaps it would be prudent to reevaluate how the dump/restore
functions implement their parsing and serialization?
 — “Faux XML Parser” I should probably say; it doesn't
seem to try to
be an “XML Processor” as defined in the spec, just
simple XML-like syntax.
>Did you notice the three words "hurricane relief work" in there?
I think we've just discovered a new corollary to Godwin's Law.
- Rich Siegel <siegel at barebones.com>
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