SQLite

void initStringBuffer(StringBuffer *sb){
  sb->len = 0;
  sb->alloced = 100;
  sb->s = malloc(100);
  sb->s[0] = '\0';
}

void nappend(StringBuffer *sb, const char *zFrom, int nFrom){

  if( sb->len + nFrom >= sb->alloced ){
    sb->alloced = sb->len + nFrom + 100;
    sb->s = realloc(sb->s, sb->alloced+1);
    if( sb->s==0 ){
      initStringBuffer(sb);
      return;
    }
  }
  memcpy(sb->s + sb->len, zFrom, nFrom);
  sb->len += nFrom;
  sb->s[sb->len] = 0;
}
void append(StringBuffer *sb, const char *zFrom){
  nappend(sb, zFrom, strlen(zFrom));
}

/* We encode variable-length integers in little-endian order using seven bits
 * per byte as follows:
**
** KEY:
**         A = 0xxxxxxx    7 bits of data and one flag bit

** An instance of the following structure keeps track of generated
** matching-word offset information and snippets.
*/
typedef struct Snippet {
  int nMatch;     /* Total number of matches */
  int nAlloc;     /* Space allocated for aMatch[] */
  struct snippetMatch { /* One entry for each matching term */
    char snStatus;       /* Status flag for use while constructing snippets */
    short int iCol;      /* The column that contains the match */
    short int iTerm;     /* The index in Query.pTerms[] of the matching term */
    short int nByte;     /* Number of bytes in the term */

    int iStart;          /* The offset to the first character of the term */

  } *aMatch;      /* Points to space obtained from malloc */
  char *zOffset;  /* Text rendering of aMatch[] */
  int nOffset;    /* strlen(zOffset) */
  char *zSnippet; /* Snippet text */
  int nSnippet;   /* strlen(zSnippet) */
} Snippet;


typedef enum QueryType {
  QUERY_GENERIC,   /* table scan */
  QUERY_ROWID,     /* lookup by rowid */
  QUERY_FULLTEXT   /* QUERY_FULLTEXT + [i] is a full-text search for column i*/

/* Free all of the dynamically allocated memory held by the
** Snippet
*/
static void snippetClear(Snippet *p){
  free(p->aMatch);
  free(p->zOffset);
  free(p->zSnippet);
  memset(p, 0, sizeof(*p));
}
/*
** Append a single entry to the p->aMatch[] log.
*/
static void snippetAppendMatch(
  Snippet *p,               /* Append the entry to this snippet */

      p->nMatch = 0;
      p->nAlloc = 0;
      return;
    }
  }
  i = p->nMatch++;
  pMatch = &p->aMatch[i];

  pMatch->iCol = iCol;
  pMatch->iTerm = iTerm;
  pMatch->iStart = iStart;
  pMatch->nByte = nByte;
}

/*

    cnt++;
  }
  p->zOffset = sb.s;
  p->nOffset = sb.len;
}

/*
** zDoc[0..nDoc-1] is phrase of text.  aMatch[0..nMatch-1] are a set
** of matching words some of which might be in zDoc.  zDoc is column
** number iCol.
**

** iBreak is suggested spot in zDoc where we could begin or end an
** excerpt.  Return a value similar to iBreak but possibly adjusted
** to be a little left or right so that the break point is better.
*/
static int wordBoundary(
  int iBreak,                   /* The suggested break point */
  const char *zDoc,             /* Document text */
  int nDoc,                     /* Number of bytes in zDoc[] */
  struct snippetMatch *aMatch,  /* Matching words */
  int nMatch,                   /* Number of entries in aMatch[] */
  int iCol                      /* The column number for zDoc[] */
){
  int i;
  if( iBreak<=10 ){
    return 0;
  }
  if( iBreak>=nDoc-10 ){
    return nDoc;
  }
  for(i=0; i<nMatch && aMatch[i].iCol<iCol; i++){}
  while( i<nMatch && aMatch[i].iStart+aMatch[i].nByte<iBreak ){ i++; }
  if( i<nMatch ){
    if( aMatch[i].iStart<iBreak+10 ){
      return aMatch[i].iStart;
    }
    if( i>0 && aMatch[i-1].iStart+aMatch[i-1].nByte>=iBreak ){
      return aMatch[i-1].iStart;
    }
  }
  for(i=1; i<=10; i++){
    if( isspace(zDoc[iBreak-i]) ){
      return iBreak - i + 1;
    }
    if( isspace(zDoc[iBreak+i]) ){
      return iBreak + i + 1;
    }
  }
  return iBreak;
}

/*
** Allowed values for Snippet.aMatch[].snStatus
*/
#define SNIPPET_IGNORE  0   /* It is ok to omit this match from the snippet */
#define SNIPPET_DESIRED 1   /* We want to include this match in the snippet */  

/*
** Generate the text of a snippet.
*/
static void snippetText(
  fulltext_cursor *pCursor,   /* The cursor we need the snippet for */
  const char *zStartMark,     /* Markup to appear before each match */
  const char *zEndMark,       /* Markup to appear after each match */
  const char *zEllipsis       /* Ellipsis mark */
){
  int i, j;
  struct snippetMatch *aMatch;
  int nMatch;
  int nDesired;
  StringBuffer sb;
  int tailCol = -1;
  int tailOffset = -1;
  int iCol;
  int nDoc;
  const char *zDoc;
  int iStart, iEnd;
  int wantEllipsis;
  int tailEllipsis = 0;
  int iMatch;
  

  free(pCursor->snippet.zSnippet);
  pCursor->snippet.zSnippet = 0;
  aMatch = pCursor->snippet.aMatch;
  nMatch = pCursor->snippet.nMatch;
  initStringBuffer(&sb);

  for(i=0; i<nMatch; i++){
    aMatch[i].snStatus = SNIPPET_IGNORE;
  }
  nDesired = 0;
  for(i=0; i<pCursor->q.nTerms; i++){
    for(j=0; j<nMatch; j++){
      if( aMatch[j].iTerm==i ){
        aMatch[j].snStatus = SNIPPET_DESIRED;
        nDesired++;
        break;
      }
    }
  }

  iMatch = 0;
  for(i=0; i<nMatch && nDesired>0; i++){
    if( aMatch[i].snStatus!=SNIPPET_DESIRED ) continue;
    nDesired--;
    iCol = aMatch[i].iCol;
    zDoc = (const char*)sqlite3_column_text(pCursor->pStmt, iCol+1);
    nDoc = sqlite3_column_bytes(pCursor->pStmt, iCol+1);
    iStart = aMatch[i].iStart - 40;
    iStart = wordBoundary(iStart, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iStart<=10 ){
      iStart = 0;
      wantEllipsis = 0;
    }else{
      wantEllipsis = 1;
    }

    if( iCol==tailCol && iStart<=tailOffset+20 ){
      iStart = tailOffset;
      wantEllipsis = 0;
      tailEllipsis = 0;
    }
    if( wantEllipsis || tailEllipsis ){
      append(&sb, zEllipsis);
    }
    iEnd = aMatch[i].iStart + aMatch[i].nByte + 40;
    iEnd = wordBoundary(iEnd, zDoc, nDoc, aMatch, nMatch, iCol);
    if( iEnd>=nDoc-10 ){
      iEnd = nDoc;
      tailEllipsis = 0;
    }else{
      tailEllipsis = 1;
    }
    while( iMatch<nMatch && aMatch[iMatch].iCol<iCol ){ iMatch++; }
    while( iStart<iEnd ){
      while( iMatch<nMatch && aMatch[iMatch].iStart<iStart ){ iMatch++; }
      if( iMatch<nMatch && aMatch[iMatch].iStart<iEnd ){
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].iStart - iStart);
        iStart = aMatch[iMatch].iStart;
        append(&sb, zStartMark);
        nappend(&sb, &zDoc[iStart], aMatch[iMatch].nByte);
        append(&sb, zEndMark);
        iStart += aMatch[iMatch].nByte;
        for(j=iMatch+1; j<nMatch; j++){
          if( aMatch[j].iTerm==aMatch[iMatch].iTerm
              && aMatch[j].snStatus==SNIPPET_DESIRED ){
            nDesired--;
            aMatch[j].snStatus = SNIPPET_IGNORE;
          }
        }
      }else{
        nappend(&sb, &zDoc[iStart], iEnd - iStart);
        iStart = iEnd;
      }
    }
    tailCol = iCol;
    tailOffset = iEnd;
  }
  if( tailEllipsis ){
    append(&sb, zEllipsis);
  }
  pCursor->snippet.zSnippet = sb.s;
  pCursor->snippet.nSnippet = sb.len;  
}


/*
** Close the cursor.  For additional information see the documentation
** on the xClose method of the virtual table interface.
*/

){
  fulltext_cursor *pCursor;
  if( argc<1 ) return;
  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
    sqlite3_result_error(pContext, "illegal first argument to html_snippet",-1);
  }else{
    const char *zStart = "<b>";
    const char *zEnd = "</b>";
    const char *zEllipsis = "<b>...</b>";
    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
    if( argc>=2 ){
      zStart = (const char*)sqlite3_value_text(argv[1]);
      if( argc>=3 ){
        zEnd = (const char*)sqlite3_value_text(argv[2]);
        if( argc>=4 ){
          zEllipsis = (const char*)sqlite3_value_text(argv[3]);
        }
      }
    }
    snippetAllOffsets(pCursor);
    snippetText(pCursor, zStart, zEnd, zEllipsis);
    sqlite3_result_text(pContext, pCursor->snippet.zSnippet,
                        pCursor->snippet.nSnippet, SQLITE_STATIC);
  }
}

/*
** Implementation of the offsets() function for FTS1
*/
static void snippetOffsetsFunc(

# 2006 September 14
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#*************************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this script is testing the FTS1 module.
#
# $Id: fts1c.test,v 1.7 2006/09/21 02:03:11 drh Exp $
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# If SQLITE_ENABLE_FTS1 is defined, omit this file.
ifcapable !fts1 {

} {32 {3 0 94 5 3 0 114 5 3 0 207 5 3 1 213 7 3 0 245 5 3 1 251 7 3 0 409 5 3 1 415 7 3 1 493 7}}
do_test fts1c-3.2 {
  execsql {
    SELECT rowid, offsets(email) FROM email
     WHERE body MATCH '"child product"'
  }
} {32 {3 0 207 5 3 1 213 7 3 0 245 5 3 1 251 7 3 0 409 5 3 1 415 7}}

# Snippet generator tests
#
do_test fts1c-4.1 {
  execsql {
    SELECT snippet(email) FROM email
     WHERE email MATCH 'subject:gas reminder'
  }
} {{Alert Posted 10:00 AM November 20,2000: E-<b>GAS</b> Request <b>Reminder</b>}}
do_test fts1c-4.2 {
  execsql {
    SELECT snippet(email) FROM email
     WHERE email MATCH 'christmas candlelight'
  }
} {{<b>...</b>place.? What do you think about going here <b>Christmas</b> 
eve?? They have an 11:00 a.m. service and a <b>candlelight</b> service at 5:00 p.m., 
among others.

<b>...</b>}}

do_test fts1c-4.3 {
  execsql {
    SELECT snippet(email) FROM email
     WHERE email MATCH 'deal sheet potential reuse'
  }
} {{EOL-Accenture <b>Deal</b> <b>Sheet</b><b>...</b>intent
     Review Enron asset base for <b>potential</b> <b>reuse</b>/ licensing
     Contract negotiations

<b>...</b>}}
do_test fts1c-4.4 {
  execsql {
    SELECT snippet(email,'<<<','>>>',' ') FROM email
     WHERE email MATCH 'deal sheet potential reuse'
  }
} {{EOL-Accenture <<<Deal>>> <<<Sheet>>> intent
     Review Enron asset base for <<<potential>>> <<<reuse>>>/ licensing
     Contract negotiations

 }}

finish_test