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Comment:Cache the JSON parse used by json_extract().
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SHA3-256:44ca6c2c4639f3c50ae9233ee299ff0fc4566462c31f28d8676f8de7ffdcd7f0
User & Date: drh 2017-05-11 16:49:59
Context
2017-05-11
18:42
Enhance the json_extract() function to reuse parses of the same JSON when the function appears multiple times in the same query. check-in: 3ba9e7ab user: drh tags: trunk
16:49
Cache the JSON parse used by json_extract(). Closed-Leaf check-in: 44ca6c2c user: drh tags: auxdata-cache
15:20
Negative N values in sqlite3_get_auxdata() and sqlite3_set_auxdata() can be used to access an auxiliary data cache over all functions in a single prepared statement. check-in: ff530675 user: drh tags: auxdata-cache
Changes
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Changes to ext/misc/json1.c.

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  u32 nAlloc;        /* Number of slots of aNode[] allocated */
  JsonNode *aNode;   /* Array of nodes containing the parse */
  const char *zJson; /* Original JSON string */
  u32 *aUp;          /* Index of parent of each node */
  u8 oom;            /* Set to true if out of memory */
  u8 nErr;           /* Number of errors seen */
  u16 iDepth;        /* Nesting depth */

};

/*
** Maximum nesting depth of JSON for this implementation.
**
** This limit is needed to avoid a stack overflow in the recursive
** descent parser.  A depth of 2000 is far deeper than any sane JSON
................................................................................
  sqlite3_free(pParse->aNode);
  pParse->aNode = 0;
  pParse->nNode = 0;
  pParse->nAlloc = 0;
  sqlite3_free(pParse->aUp);
  pParse->aUp = 0;
}









/*
** Convert the JsonNode pNode into a pure JSON string and
** append to pOut.  Subsubstructure is also included.  Return
** the number of JsonNode objects that are encoded.
*/
static void jsonRenderNode(
................................................................................
  if( aUp==0 ){
    pParse->oom = 1;
    return SQLITE_NOMEM;
  }
  jsonParseFillInParentage(pParse, 0, 0);
  return SQLITE_OK;
}












































/*
** Compare the OBJECT label at pNode against zKey,nKey.  Return true on
** a match.
*/
static int jsonLabelCompare(JsonNode *pNode, const char *zKey, u32 nKey){
  if( pNode->jnFlags & JNODE_RAW ){
................................................................................
** Return 0 if the input is not a well-formed JSON array.
*/
static void jsonArrayLengthFunc(
  sqlite3_context *ctx,
  int argc,
  sqlite3_value **argv
){
  JsonParse x;          /* The parse */
  sqlite3_int64 n = 0;
  u32 i;
  JsonNode *pNode;

  if( jsonParse(&x, ctx, (const char*)sqlite3_value_text(argv[0])) ) return;

  assert( x.nNode );
  if( argc==2 ){
    const char *zPath = (const char*)sqlite3_value_text(argv[1]);
    pNode = jsonLookup(&x, zPath, 0, ctx);
  }else{
    pNode = x.aNode;
  }
  if( pNode==0 ){
    x.nErr = 1;


  }else if( pNode->eType==JSON_ARRAY ){
    assert( (pNode->jnFlags & JNODE_APPEND)==0 );
    for(i=1; i<=pNode->n; n++){
      i += jsonNodeSize(&pNode[i]);
    }
  }
  if( x.nErr==0 ) sqlite3_result_int64(ctx, n);
  jsonParseReset(&x);
}

/*
** json_extract(JSON, PATH, ...)
**
** Return the element described by PATH.  Return NULL if there is no
** PATH element.  If there are multiple PATHs, then return a JSON array
................................................................................
** is malformed.
*/
static void jsonExtractFunc(
  sqlite3_context *ctx,
  int argc,
  sqlite3_value **argv
){
  JsonParse x;          /* The parse */
  JsonNode *pNode;
  const char *zPath;
  JsonString jx;
  int i;

  if( argc<2 ) return;
  if( jsonParse(&x, ctx, (const char*)sqlite3_value_text(argv[0])) ) return;

  jsonInit(&jx, ctx);
  jsonAppendChar(&jx, '[');
  for(i=1; i<argc; i++){
    zPath = (const char*)sqlite3_value_text(argv[i]);
    pNode = jsonLookup(&x, zPath, 0, ctx);
    if( x.nErr ) break;
    if( argc>2 ){
      jsonAppendSeparator(&jx);
      if( pNode ){
        jsonRenderNode(pNode, &jx, 0);
      }else{
        jsonAppendRaw(&jx, "null", 4);
      }
................................................................................
  }
  if( argc>2 && i==argc ){
    jsonAppendChar(&jx, ']');
    jsonResult(&jx);
    sqlite3_result_subtype(ctx, JSON_SUBTYPE);
  }
  jsonReset(&jx);
  jsonParseReset(&x);
}

/* This is the RFC 7396 MergePatch algorithm.
*/
static JsonNode *jsonMergePatch(
  JsonParse *pParse,   /* The JSON parser that contains the TARGET */
  u32 iTarget,         /* Node of the TARGET in pParse */







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  u32 nAlloc;        /* Number of slots of aNode[] allocated */
  JsonNode *aNode;   /* Array of nodes containing the parse */
  const char *zJson; /* Original JSON string */
  u32 *aUp;          /* Index of parent of each node */
  u8 oom;            /* Set to true if out of memory */
  u8 nErr;           /* Number of errors seen */
  u16 iDepth;        /* Nesting depth */
  int nJson;         /* Length of the zJson string in bytes */
};

/*
** Maximum nesting depth of JSON for this implementation.
**
** This limit is needed to avoid a stack overflow in the recursive
** descent parser.  A depth of 2000 is far deeper than any sane JSON
................................................................................
  sqlite3_free(pParse->aNode);
  pParse->aNode = 0;
  pParse->nNode = 0;
  pParse->nAlloc = 0;
  sqlite3_free(pParse->aUp);
  pParse->aUp = 0;
}

/*
** Free a JsonParse object that was obtained from sqlite3_malloc().
*/
static void jsonParseFree(JsonParse *pParse){
  jsonParseReset(pParse);
  sqlite3_free(pParse);
}

/*
** Convert the JsonNode pNode into a pure JSON string and
** append to pOut.  Subsubstructure is also included.  Return
** the number of JsonNode objects that are encoded.
*/
static void jsonRenderNode(
................................................................................
  if( aUp==0 ){
    pParse->oom = 1;
    return SQLITE_NOMEM;
  }
  jsonParseFillInParentage(pParse, 0, 0);
  return SQLITE_OK;
}

/*
** Magic number used for the JSON parse cache in sqlite3_get_auxdata()
*/
#define JSON_CACHE_ID  (-429938)

/*
** Obtain a complete parse of the JSON found in the first argument
** of the argv array.  Use the sqlite3_get_auxdata() cache for this
** parse if it is available.  If the cache is not available or if it
** is no longer valid, parse the JSON again and return the new parse,
** and also register the new parse so that it will be available for
** future sqlite3_get_auxdata() calls.
*/
static JsonParse *jsonParseCached(
  sqlite3_context *pCtx,
  sqlite3_value **argv
){
  const char *zJson = (const char*)sqlite3_value_text(argv[0]);
  int nJson = sqlite3_value_bytes(argv[0]);
  JsonParse *p;
  if( zJson==0 ) return 0;
  p = (JsonParse*)sqlite3_get_auxdata(pCtx, JSON_CACHE_ID);
  if( p && p->nJson==nJson && memcmp(p->zJson,zJson,nJson)==0 ){
    p->nErr = 0;
    return p; /* The cached entry matches, so return it */
  }
  p = sqlite3_malloc( sizeof(*p) + nJson + 1 );
  if( p==0 ){
    sqlite3_result_error_nomem(pCtx);
    return 0;
  }
  memset(p, 0, sizeof(*p));
  p->zJson = (char*)&p[1];
  memcpy((char*)p->zJson, zJson, nJson+1);
  if( jsonParse(p, pCtx, p->zJson) ){
    sqlite3_free(p);
    return 0;
  }
  p->nJson = nJson;
  sqlite3_set_auxdata(pCtx, JSON_CACHE_ID, p, (void(*)(void*))jsonParseFree);
  return (JsonParse*)sqlite3_get_auxdata(pCtx, JSON_CACHE_ID);
}

/*
** Compare the OBJECT label at pNode against zKey,nKey.  Return true on
** a match.
*/
static int jsonLabelCompare(JsonNode *pNode, const char *zKey, u32 nKey){
  if( pNode->jnFlags & JNODE_RAW ){
................................................................................
** Return 0 if the input is not a well-formed JSON array.
*/
static void jsonArrayLengthFunc(
  sqlite3_context *ctx,
  int argc,
  sqlite3_value **argv
){
  JsonParse *p;          /* The parse */
  sqlite3_int64 n = 0;
  u32 i;
  JsonNode *pNode;

  p = jsonParseCached(ctx, argv);
  if( p==0 ) return;
  assert( p->nNode );
  if( argc==2 ){
    const char *zPath = (const char*)sqlite3_value_text(argv[1]);
    pNode = jsonLookup(p, zPath, 0, ctx);
  }else{
    pNode = p->aNode;
  }
  if( pNode==0 ){

    return;
  }
  if( pNode->eType==JSON_ARRAY ){
    assert( (pNode->jnFlags & JNODE_APPEND)==0 );
    for(i=1; i<=pNode->n; n++){
      i += jsonNodeSize(&pNode[i]);
    }
  }
  sqlite3_result_int64(ctx, n);

}

/*
** json_extract(JSON, PATH, ...)
**
** Return the element described by PATH.  Return NULL if there is no
** PATH element.  If there are multiple PATHs, then return a JSON array
................................................................................
** is malformed.
*/
static void jsonExtractFunc(
  sqlite3_context *ctx,
  int argc,
  sqlite3_value **argv
){
  JsonParse *p;          /* The parse */
  JsonNode *pNode;
  const char *zPath;
  JsonString jx;
  int i;

  if( argc<2 ) return;
  p = jsonParseCached(ctx, argv);
  if( p==0 ) return;
  jsonInit(&jx, ctx);
  jsonAppendChar(&jx, '[');
  for(i=1; i<argc; i++){
    zPath = (const char*)sqlite3_value_text(argv[i]);
    pNode = jsonLookup(p, zPath, 0, ctx);
    if( p->nErr ) break;
    if( argc>2 ){
      jsonAppendSeparator(&jx);
      if( pNode ){
        jsonRenderNode(pNode, &jx, 0);
      }else{
        jsonAppendRaw(&jx, "null", 4);
      }
................................................................................
  }
  if( argc>2 && i==argc ){
    jsonAppendChar(&jx, ']');
    jsonResult(&jx);
    sqlite3_result_subtype(ctx, JSON_SUBTYPE);
  }
  jsonReset(&jx);

}

/* This is the RFC 7396 MergePatch algorithm.
*/
static JsonNode *jsonMergePatch(
  JsonParse *pParse,   /* The JSON parser that contains the TARGET */
  u32 iTarget,         /* Node of the TARGET in pParse */