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How to debug Writer file format issues?

Miklos V
February 03, 2013
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How to debug Writer file format issues?

Miklos V

February 03, 2013
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  1. How to debug Writer file
    format issues?
    We won't give you fish, but we'll teach you how to fish.
    Miklos Vajna
    3 February 2013

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  2. 2
    A good and a bad news for you
    • Good news: file filters is one area which can be
    easily unit-tested in most cases
    ‒ Compared to layout or UI
    ‒ So it's not an endless fixing wrt a particular problem
    • Bad news: in most cases it's about modifying the
    source code
    ‒ In rare cases you can work around by modifying the input
    file

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  3. 3
    What is a file format issue?
    • It is the situation when your problem is caused by an
    import or export filter
    • Good examples:
    ‒ Stroke weight of the line inside a group shape is too large,
    when importing from DOCX
    ‒ This document is supposed to be of a single page, not two
    • Bad examples:
    ‒ The imported document causes a layout loop
    ‒ Writer doesn't support a particular feature, which is
    supported by the given format

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  4. 4
    More terminology
    • Technically, we only do import and export
    • “Open” on the UI: Import to an empty document,
    then reset the undo stack
    • “Copy and paste” on the UI: partial export, followed
    by an import to an existing document
    • “Save” on the UI: exporting to an already existing
    path
    • Explains:
    ‒ Why a single character modification totally rewrites the file
    ‒ Why it's not possible to extract the “conversion machine”
    from LibreOffice (but: we have a headless mode)

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  5. 5
    How to check the document model?
    • Basic building block: paragraphs
    • XML dump:
    ‒ SW_DEBUG=1 ./soffice.bin –writer
    ‒ Shift-F12 creates nodes.xml
    • GDB:
    ‒ print pDoc->GetNodes()
    • UNO:
    ‒ Iterating over ThisCompoment → paragraphs
    ‒ Iterating over a paragraph → runs

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  6. Writer file formats:
    ODF, Word formats and the rest

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  7. 7
    ODF filter
    • The only “own” filter, both import and export
    supposed to be loss-less
    • ODF semantics are very close to Writer document
    model:
    ‒ Example for paragraphs: UNO properties ↔ XML attributes
    • Most of the implementation is an UNO filter
    ‒ Can serve as a good example for other filters
    • Code under xmloff/ and sw/source/filter/xml/
    • ODF validator:
    ‒ http://odf-validator2.rhcloud.com/odf-validator2/

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  8. 8
    RTF filter
    • About the format
    ‒ Motivation: easily-readable like HTML, but supports all word
    processing features (page size, columns, etc.)
    ‒ Can be hard to read
    • Export
    ‒ New in LibreOffice 3.3
    ‒ Internal filter, core shared with DOC/DOCX
    • Import
    ‒ New in LibreOffice 3.5
    ‒ UNO filter, domain mapper shared with DOCX
    • Mostly my fault

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  9. 9
    DOC filter
    • Probably the oldest filter in Writer
    ‒ Not counting binfilter
    • Both import and export are internal filters
    • Specification is available as [MS-DOC]
    • Tokenizer and domain mapper is not separated
    • For tokenizer problems, mso-dumper can help:
    ‒ http://cgit.freedesktop.org/libreoffice/contrib/mso-dumper/
    • Import/export somewhat shared

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  10. 10
    DOCX filter
    • Two variants: ECMA and Microsoft
    ‒ Example: left/right or start/end for paragraph margins
    • Import is older
    ‒ Over-engineered in writerfilter/
    ‒ XSLT generates the tokenizer code, challenging to debug
    ‒ Inherited from OpenOffice.org, UNO-based
    ‒ Domain mapper shared with RTF
    • Export is LibreOffice-only
    ‒ Internal
    ‒ Shared with DOC/RTF

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  11. Testcases:
    core, document model and layout tests

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  12. 12
    Unit tests
    • We only care if the filter can handle the file
    ‒ CVE tests
    ‒ If the filter provides the expected return value, we're good
    • Internal tests
    ‒ Provide access to private Writer symbols
    ‒ Handy to test methods used by the UI
    ‒ In most cases not needed by filter tests

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  13. 13
    Document model tests
    • The most commonly used one
    • Import
    ‒ Load the file, then assert the accessed UNO document
    model
    • Export
    ‒ Import → export → import
    ‒ This way the same API can be used for tests, and export is
    tested as well
    ‒ Alternative: building the document from code, then somehow check
    the result (XPath for XML-based formats, but what about the rest?)
    ‒ Drawback: import should be fine
    ‒ Not a bad thing anyway

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  14. 14
    Layout tests
    • Testing the layout
    ‒ Not: contents of the header in page style “Default”
    ‒ But: text in the header on page 3
    • Sometimes handy, but be careful
    ‒ Writer layout is partly counted in the idle, tests won't wait
    for that
    ‒ Layout may be OK to differ
    ‒ E.g. missing fonts

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  15. Thanks for listening!
    15
    Slides:
    http://vmiklos.hu/odp/
    All text and image content in this document, unless otherwise specified, is licensed under
    the Creative Commons Attribution-Share Alike 3.0 License . This does not include the
    LibreOffice name, logo, or icon. All SUSE marks referenced in this presentation are trademarks
    or registered trademarks of Novell, Inc. in the United States.

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