Method GetJsonObjectImpl

be/src/exprs/string-functions.cc:307–408

TODO(IMPALA-7610): parse the JSON path and cache it so we don't need to parse it everytime

/// TODO(IMPALA-7610): parse the JSON path and cache it so we don't need to parse it
/// everytime
StringVal StringFunctions::GetJsonObjectImpl(FunctionContext* ctx,
    const StringVal& json_str, const StringVal& path_str) {
  if (UNLIKELY(json_str.is_null || json_str.len == 0)) return StringVal::null();
  if (UNLIKELY(path_str.is_null || path_str.len == 0)) {
    ctx->SetError("Empty json path");
    return StringVal::null();
  }
  int beg = 0;
  // Strip off preceding whitespace.
  while (beg < path_str.len && path_str.ptr[beg] == ' ') beg++;
  if (UNLIKELY(beg == path_str.len || path_str.ptr[beg] != '$')) {
    // Here we use '$$' to escape '$' in Substitute
    string msg = Substitute("Failed to parse json path '$0': Should start with '$$'",
        AnyValUtil::ToString(path_str));
    ctx->SetError(msg.c_str());
    return StringVal::null();
  }

  JsonUdfAllocator allocator(ctx);
  JsonUdfDocument document(&allocator);
  if (!ParseStringVal(ctx, json_str, &document)) return StringVal::null();

  // BFS to extract selected values. We use array of RapidJson instead of std::vector to
  // track its memory.
  JsonUdfValue queue(kArrayType);
  RETURN_NULL_IF_OOM(queue.Reserve(INITIAL_QUEUE_CAPACITY, allocator));
  RETURN_NULL_IF_OOM(queue.PushBack(document, allocator));
  const uint8_t* path = path_str.ptr;
  const uint8_t* path_end = path + path_str.len;
  for (int i = beg + 1; i < path_str.len;) {
    // Each round we extract new items into the queue. Old items will be removed.
    switch (path[i]) {
      case '$': {
        string msg = Substitute("Failed to parse json path '$0':"
            " $$ should only be placed at start", AnyValUtil::ToString(path_str));
        ctx->SetError(msg.c_str());
        return StringVal::null();
      }
      case '.': {
        // Hive does not skip the heading and trailing whitespaces since it simply splits
        // the json path by '.'. We should keep the same behavior with MySQL. See
        // JSON_EXTRACT in MySQL(5.7+).
        for (++i; i < path_str.len && path[i] == ' '; ++i);  // skip whitespaces
        if (i == path_str.len) {
          string msg = Substitute("Failed to parse json path '$0': Found a trailing '.'",
              AnyValUtil::ToString(path_str));
          ctx->SetError(msg.c_str());
          return StringVal::null();
        }
        if (path[i] == '*') {
          i = ProcessWildcardKey(ctx, path_str, ++i, &queue, &allocator);
          if (i < 0) return StringVal::null();
          break;
        }
        const uint8_t* start = path + i;
        const uint8_t* end = FindEndOfIdentifier(start, path_end);
        // Set error if looking for an empty key
        if (end == nullptr) {