Symbian XML parsing plugins

Comments

Hamishwillee - Minor subedit for wiki style

Hi

Thanks for this. I've given it a minor subedit for wiki style (e.g. used Icode for inline code objects), added some version categories and Known Issue category etc. Not a complete job.

Questions:

1. Is this finished? ie should we remove the "Draft" category?
2. Is there anywhere easy to get the PDK source for those who didn't pick one up when Symbian Foundation was around?

Regards

Hamish

hamishwillee 09:08, 28 January 2013 (EET)

Hamishwillee - Thanks for the updates

All good I think. I'll delete this and the above comment next time I come back here.

Regards

Hamish

hamishwillee 03:27, 29 January 2013 (EET)

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CParser default plugin - Expat

CParser class is using by default Expat parser. It is stream based let's say SAX-like parser. Symbian implementation of the Expat XML parser plugin is a little bit old (S^3 has version 1.95.5 from 2002 year) and it has one known problem - it wrongly parses XML attributes of size larger tham 12kB. Elements with such large attributes are notified to the application as a content of the parent element and also they missing first ~12kB of data.

Source code of the Expat parser plugin can be found in Symbian Foundation source code: \PDK_4.0.a\src_oss_os.zip\src_oss_os_xmlsrv.zip\sf\os\xmlsrv\xml\xmlexpatparser\
Symbian Foundation source code is available on SourceForge prtal: http://sourceforge.net/projects/symbiandump/files/PDK_4.0.a/

CParser Libxml2 plugin

To resolve problem with large attributes and parse XML by CParse class, we can change XML parsing plugin from Expat to Libxml2. It is available at least from S^3 (tested on Nokia E7). To select parsing plugin we are passing it during construction of CParse class:

_LIT8(KMimeType, "text/xml");
_LIT8(KParser, "libxml2");
iParserPlugin = CMatchData::NewL();
iParserPlugin->SetMimeTypeL( KMimeType() );
iParserPlugin->SetVariantL( KParser() );
iParser = CParser::NewL( *iParserPlugin, *this ); // assuming the this class implements MContentHandler interface

This will resolve large attribute problem without need of moving to DOM parser and with only little code change.
Remember to destroy CMatchData in your class destructor.

Source code of the Libxml2 parser plugin can be found also in Symbian Foundation source code: \PDK_4.0.a\src_oss_os.zip\src_oss_os_xmlsrv.zip\sf\os\xmlsrv\xml\xmllibxml2parser\

CParser optimization using string table

Using SAX parsing element and attributes resolve requires comparison of the element and attributes names. To minimize string comparisons count we can pass predefined string table to the CParser object and get elements and attributes indexes in our table.

Firstly we need to declare our string table:

#include <stringpool.h> 
 
_LIT8(KParserStr_1, "element1");
_LIT8(KParserStr_2, "element2");
_LIT8(KParserStr_3, "attr1");
_LIT8(KParserStr_4, "attr2");
 
const void * const KParserStringPointers[] =
{
    (const void*)&KParserStr_1,
    (const void*)&KParserStr_2,
    (const void*)&KParserStr_3,
    (const void*)&KParserStr_4
};
 
const TStringTable KParserStringTable = { 4, KParserStringPointers, ETrue };    // to use it with CParser case sensitive must be set to ETrue
 
enum TParserStringTable
    {
    EParserString_element1,
    EParserString_element2,
    EParserString_attr1,
    EParserString_attr2
    };

Now we need to load the table to the parser. We can do it just before starting of parsing:

iParser->StringPool().OpenL( KParserStringTable );
iParser->ParseBeginL();
...

Now in callbacks we can resolve element and attribute string names just by enumeration:

void CMyParser::OnStartElementL(const RTagInfo& aElement, const RAttributeArray& aAttributes,TInt aErrorCode)
    {
    TInt idx = aElement.LocalName().Index( KParserStringTable );
    switch ( idx )
        {
        case EParserString_element1:
                ParseElement( aAttributes );
            break;
        case EParserString_element1:
                ParseElement( aAttributes );
            break;
        default:
            break;
        }
    }
 
void CMyParser::ParseElement(const RAttributeArray& aAttributes)
    {
    for ( TInt i = 0; i < aAttributes.Count(); i++ )
        {
        TInt idx = aAttributes[ i ].Attribute().LocalName().Index( KParserStringTable );
        switch ( idx )
            {
            case EParserString_attr1:
                break;
            case EParserString_attr2:
                break;
            default:
                break;
            }
        }
    }

Article Metadata

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Compatibility

Platform(s): Symbian^1 and later

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Article

Keywords: XML, SAX, Expat, libxml2, DOM

Created: mstrug (24 Jan 2013)

Last edited: mstrug (28 Jan 2013)