Review Request 125762: External extractor plugin support for KFileMetaData

[Boudhayan Gupta]

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This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/125762/
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(Updated Oct. 24, 2015, 5:49 p.m.)


Review request for Baloo, KDE Frameworks, Pinak Ahuja, and Vishesh Handa.


Changes
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Update diff based on offline comments from pinakahuja.

* Comment explaining methods in cpp above ctor/dtor are static
* Look at cwd, KFILEMETADATA_EXTRACTOR_PATH and PATH, in that order, for extractors.
* Fail on malformed JSON input


Repository: kfilemetadata


Description
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This patch introduces support for external metadata extractors in KFileMetaData

The external extractors themselves can be written in any language, provided that it can be executed as a standalone executable (compiled or script with a hashbang), with command line arguments, and can output data to stdout.

The extractors are executed like so:

* `extractor --mimetypes` - outputs a list of mimetypes supported by the extractor, one per line.
* `extractor filename` - outputs a json document with the metadata. The keys are such that they can be directly used with PropertyInfo::fromName().

At the KFileMetaData end, an additional internal plugin (ExternalExtractor) is provided that forms a conduit between external extractors and the internal API. This plugin looks for executables called kfilemetadata_extractor_<something> in /usr/bin to find external extractors, and executes them with the --mimetypes arg to find the list of mimetypes each extractor supports. ExternalExtractor then claims to support all of these mimetypes, and then delegates to the extractor executable when doing the actual extraction.


Diffs (updated)
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  README.md 19b1a26 
  src/extractors/CMakeLists.txt 5dd223e 
  src/extractors/externalextractor.h PRE-CREATION 
  src/extractors/externalextractor.cpp PRE-CREATION 

Diff: https://git.reviewboard.kde.org/r/125762/diff/


Testing
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Tested with the sample executable file extractor (as attched, written in python) with the dump manual test in KFileMetaData. Works.


File Attachments
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kfilemetadata_extractor_executable
  https://git.reviewboard.kde.org/media/uploaded/files/2015/10/23/146b657f-31d9-4117-a82f-ef966a6339d4__kfilemetadata_extractor_executable


Thanks,

Boudhayan Gupta

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