fts2_tokenizer.h

/*
** 2006 July 10
**
** The author disclaims copyright to this source code.
**
*************************************************************************
** Defines the interface to tokenizers used by fulltext-search.  There
** are three basic components:
**
** sqlite3_tokenizer_module is a singleton defining the tokenizer
** interface functions.  This is essentially the class structure for
** tokenizers.
**
** sqlite3_tokenizer is used to define a particular tokenizer, perhaps
** including customization information defined at creation time.
**
** sqlite3_tokenizer_cursor is generated by a tokenizer to generate
** tokens from a particular input.
*/
#ifndef _FTS2_TOKENIZER_H_
#define _FTS2_TOKENIZER_H_

/* TODO(shess) Only used for SQLITE_OK and SQLITE_DONE at this time.
** If tokenizers are to be allowed to call sqlite3_*() functions, then
** we will need a way to register the API consistently.
*/
#include "sqlite3.h"

/*
** Structures used by the tokenizer interface. When a new tokenizer
** implementation is registered, the caller provides a pointer to
** an sqlite3_tokenizer_module containing pointers to the callback
** functions that make up an implementation.
**
** When an fts2 table is created, it passes any arguments passed to
** the tokenizer clause of the CREATE VIRTUAL TABLE statement to the
** sqlite3_tokenizer_module.xCreate() function of the requested tokenizer
** implementation. The xCreate() function in turn returns an 
** sqlite3_tokenizer structure representing the specific tokenizer to
** be used for the fts2 table (customized by the tokenizer clause arguments).
**
** To tokenize an input buffer, the sqlite3_tokenizer_module.xOpen()
** method is called. It returns an sqlite3_tokenizer_cursor object
** that may be used to tokenize a specific input buffer based on
** the tokenization rules supplied by a specific sqlite3_tokenizer
** object.
*/
typedef struct sqlite3_tokenizer_module sqlite3_tokenizer_module;
typedef struct sqlite3_tokenizer sqlite3_tokenizer;
typedef struct sqlite3_tokenizer_cursor sqlite3_tokenizer_cursor;

struct sqlite3_tokenizer_module {

  /*
  ** Structure version. Should always be set to 0.
  */
  int iVersion;

  /*
  ** Create a new tokenizer. The values in the argv[] array are the
  ** arguments passed to the "tokenizer" clause of the CREATE VIRTUAL
  ** TABLE statement that created the fts2 table. For example, if
  ** the following SQL is executed:
  **
  **   CREATE .. USING fts2( ... , tokenizer <tokenizer-name> arg1 arg2)
  **
  ** then argc is set to 2, and the argv[] array contains pointers
  ** to the strings "arg1" and "arg2".
  **
  ** This method should return either SQLITE_OK (0), or an SQLite error 
  ** code. If SQLITE_OK is returned, then *ppTokenizer should be set
  ** to point at the newly created tokenizer structure. The generic
  ** sqlite3_tokenizer.pModule variable should not be initialized by
  ** this callback. The caller will do so.
  */
  int (*xCreate)(
    int argc,                           /* Size of argv array */
    const char *const*argv,             /* Tokenizer argument strings */
    sqlite3_tokenizer **ppTokenizer     /* OUT: Created tokenizer */
  );

  /*
  ** Destroy an existing tokenizer. The fts2 module calls this method
  ** exactly once for each successful call to xCreate().
  */
  int (*xDestroy)(sqlite3_tokenizer *pTokenizer);

  /*
  ** Create a tokenizer cursor to tokenize an input buffer. The caller
  ** is responsible for ensuring that the input buffer remains valid
  ** until the cursor is closed (using the xClose() method). 
  */
  int (*xOpen)(
    sqlite3_tokenizer *pTokenizer,       /* Tokenizer object */
    const char *pInput, int nBytes,      /* Input buffer */
    sqlite3_tokenizer_cursor **ppCursor  /* OUT: Created tokenizer cursor */
  );

  /*
  ** Destroy an existing tokenizer cursor. The fts2 module calls this 
  ** method exactly once for each successful call to xOpen().
  */
  int (*xClose)(sqlite3_tokenizer_cursor *pCursor);

  /*
  ** Retrieve the next token from the tokenizer cursor pCursor. This
  ** method should either return SQLITE_OK and set the values of the
  ** "OUT" variables identified below, or SQLITE_DONE to indicate that
  ** the end of the buffer has been reached, or an SQLite error code.
  **
  ** *ppToken should be set to point at a buffer containing the 
  ** normalized version of the token (i.e. after any case-folding and/or
  ** stemming has been performed). *pnBytes should be set to the length
  ** of this buffer in bytes. The input text that generated the token is
  ** identified by the byte offsets returned in *piStartOffset and
  ** *piEndOffset.
  **
  ** The buffer *ppToken is set to point at is managed by the tokenizer
  ** implementation. It is only required to be valid until the next call
  ** to xNext() or xClose(). 
  */
  /* TODO(shess) current implementation requires pInput to be
  ** nul-terminated.  This should either be fixed, or pInput/nBytes
  ** should be converted to zInput.
  */
  int (*xNext)(
    sqlite3_tokenizer_cursor *pCursor,   /* Tokenizer cursor */
    const char **ppToken, int *pnBytes,  /* OUT: Normalized text for token */
    int *piStartOffset,  /* OUT: Byte offset of token in input buffer */
    int *piEndOffset,    /* OUT: Byte offset of end of token in input buffer */
    int *piPosition      /* OUT: Number of tokens returned before this one */
  );
};

struct sqlite3_tokenizer {
  const sqlite3_tokenizer_module *pModule;  /* The module for this tokenizer */
  /* Tokenizer implementations will typically add additional fields */
};

struct sqlite3_tokenizer_cursor {
  sqlite3_tokenizer *pTokenizer;       /* Tokenizer for this cursor. */
  /* Tokenizer implementations will typically add additional fields */
};

#endif /* _FTS2_TOKENIZER_H_ */