Re: [xml] Need help understanding customer error handlers

["John J. Boyer" <john boyer abilitiessoft com>]

On Mon, Aug 13, 2012 at 09:43:25PM -0400, John Schember wrote:
> I'm having trouble getting custom error functions working properly. I
> want to be able to get the error information from parsing errors so I
> can store it for use later. Specifically with Relax-NG
I would like to know this also. In fact, I already inquired about it on 
this list.

John

> I've attached a sample application which demonstrates how I'm setting
> up error handlers. I'm using 2.8.0 on OS X 10.8.0. I'm compiling and
> running with:
>
> $ gcc -I /usr/local/Cellar/libxml2/2.8.0/include/libxml2/ -lxml2 test.c
> $ /a.out 1 b.xml c.xml schema.xml
> $ /a.out 2 b.xml c.xml schema.xml
> $ /a.out 3 b.xml c.xml schema.xml
> $ /a.out 4 b.xml c.xml schema.xml
> $ /a.out 5 b.xml c.xml schema.xml
>
> The numbers on the command line represent different functions I'm
> setting for the error handler and different types of errors generated
> by the parser.
>
> 1: error function is fprintf and a validation error occurs
> 2: error function is err_func (a varg function that passes input to
> fprintf) and a validation error occurs.
> 3. error function is fprintf and a structural error occurs.
> 4. error function is err_func and a structural error occurs.
>
> I'm seeing strange output when comparing the various tests.
>
> A) Test 1 gives, "b.xml:5: element note: Relax-NG validity error : Did
> not expect element note there" as the output but test 2 gives, "Did
> not expect element note there". Test 2 just passes the vargs on to
> fprintf which test 1 is calling directly. Yet as far as I can tell the
> varg list that err_func receives "%s" as the message and the last part
> of the error message as the output. So, why is fprintf getting extra
> error text?
>
> B) Test 3 and Test 4 gives the same output and my marker for err_func
> is never displayed. Test 4 thus isn't every calling err_func but must
> be using the internal error handler. I've tried multiple ways to set
> structural error handlers (comments in test.c) but none seem to work.
> There are 5 different error handler setting functions in test.c I'm
> not sure which if any of the 5 are correct.
>
> xmlRelaxNGSetParserErrors and xmlRelaxNGSetParserStructuredErrors
> don't appear to do anything.
>
> Setting xmlRelaxNGSetValidStructuredErrors causes no error messages to
> be relayed to the error handling functions. fprintf (as far as I can
> tell) and err_func (marker is displayed) do not have any message text
> and display not error output.
>
> xmlSetGenericErrorFunc and xmlSetStructuredErrorFunc both end up with
> strange output when they are set. When 5 is used for the test number
> (5 runs all 4 tests in a row) fprintf test 3 calls err_func multiple
> times. It's the full error message just each part is sent to err_func
> separately. That in itself is strange but what is more strange is
> error fprintf is the error handler for that test. However, this could
> be due to some kind of misuse due to the test function calling this on
> each test. But I don't see how redefining a general error function
> would cause error handling to use a function other than what was
> defined...
>
> How do I properly define an error handler for both validation and
> malformed xml errors? How do I get the full error message from the
> error function? Basically, I'm confused and I'm hoping someone can
> point me in the right direction as to what I'm missing.
>
> John Schember





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-- 
John J. Boyer; President, Chief Software Developer
Abilitiessoft, Inc.
http://www.abilitiessoft.com
Madison, Wisconsin USA
Developing software for people with disabilities