LIBEXTRACTOR(3)

NAME
libextractor - meta-information extraction library 0.5.2

SYNOPSIS
#include <extractor.h>
 typedef struct EXTRACTOR_Keywords {
   char * keyword;
   EXTRACTOR_KeywordType keywordType;
   struct EXTRACTOR_Keywords * next;
 } EXTRACTOR_KeywordList;
 EXTRACTOR_ExtractorList * EXTRACTOR_loadDefaultLibraries ();
 const char * EXTRACTOR_getKeywordTypeAsString (const EXTRACTOR_KeywordType type);
 EXTRACTOR_ExtractorList * EXTRACTOR_loadConfigLibraries (EXTRACTOR_ExtractorList * prev, const char * config);
 EXTRACTOR_ExtractorList * EXTRACTOR_addLibrary (EXTRACTOR_ExtractorList * prev, const char * library);
 EXTRACTOR_ExtractorList * EXTRACTOR_addLibraryLast (EXTRACTOR_ExtractorList * prev, const char * library);
 EXTRACTOR_ExtractorList * EXTRACTOR_removeLibrary (EXTRACTOR_ExtractorList * prev, const char * library);
 void EXTRACTOR_removeAll (EXTRACTOR_ExtractorList * prev);
 EXTRACTOR_KeywordList * EXTRACTOR_getKeywords (EXTRACTOR_ExtractorList * extractor, const char * filename);
 EXTRACTOR_KeywordList * EXTRACTOR_getKeywords (EXTRACTOR_ExtractorList * extractor, const char * data, size_t size);
 EXTRACTOR_KeywordList * EXTRACTOR_removeEmptyKeywords (EXTRACTOR_KeywordList * list);
 EXTRACTOR_KeywordList * EXTRACTOR_removeDuplicateKeywords (EXTRACTOR_KeywordList * list, const unsigned int options);
 void EXTRACTOR_printKeywords (FILE * handle, EXTRACTOR_KeywordList * keywords);
 void EXTRACTOR_freeKeywords (EXTRACTOR_KeywordList * keywords);
 const char * EXTRACTOR_extractLast (const EXTRACTOR_KeywordType * type, EXTRACTOR_KeywordList * keywords);
 const char * EXTRACTOR_extractLastByString (const char * type, EXTRACTOR_KeywordList * keywords);
 unsigned int EXTRACTOR_countKeywords (EXTRACTOR_KeywordList * keywords);
 EXTRACTOR_DEFAULT_LIBRARIES
 EXTRACTOR_VERSION

DESCRIPTION

libextractor is a simple library for keyword extraction. libExtractor does not support all formats but supports a simple plugging mechanism such that you can quickly add extractors for additional formats, even without recompiling libExtractor. libExtractor typically ships with one or more helper-libraries that can be used to obtain keywords from common file-types. If you want to write your own extractor for some filetype, all you need to do is write a little library that implements a single method with this signature:
 EXTRACTOR_KeywordList * LIBRARYNAME_extract(const char * filename,
                        char * data,
                        size_t size,
                        EXTRACTOR_KeywordList * prev);

The filename is the name of the file, data is a pointer to the contents of the file and size is the size of the file. The extract method must prepend keywords that it finds to the linked list 'prev' and return the new head. The library must allocate (malloc) the entry in the keyword list and the memory for the filename since both will be free'ed by libExtractor once the application calls freeKeywords. An example implementation can be found in mp3extractor.c. The application extract gives an example how to use libExtractor.

The basic use of libextractor is to load the plugins (for example with EXTRACTOR_loadDefaultLibraries), then to extract the keyword list using EXTRACTOR_getKeywords, processing the list (using application specific code and possibly some of the postprocessing convenience functions like EXTRACTOR_removeDuplicateKeywords), freeing the keyword list (using EXTRACTOR_freeKeywords) and finally unloading the plugins (with EXTRACTOR_removeAll).

The keywords obtained from libextractor are supposed to be UTF-8 encoded. The EXTRACTOR_printKeywords function converts the UTF-8 keywords to the character set from the current locale before printing them. Plugins are supposed to convert meta-data to UTF-8 if necessary.

SEE ALSO
extract(1)

LEGAL NOTICE
libextractor is released under the GPL and a GNU project (http://www.gnu.org/).

BUGS
A couple of file-formats (on the order of 10^3) are not recognized...

AUTHORS
extract was originally written by Christian Grothoff <christian@grothoff.org> and Vidyut Samanta <vids@cs.ucla.edu>. Use <libextractor@gnu.org> to contact the current maintainer(s).

AVAILABILITY
You can obtain the original author's latest version from http://gnunet.org/libextractor/.