filter_bytecode_parser.h | Explore in Territory

/*
 * Copyright (C) 2021 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SRC_PROTOZERO_FILTERING_FILTER_BYTECODE_PARSER_H_
#define SRC_PROTOZERO_FILTERING_FILTER_BYTECODE_PARSER_H_

#include <stddef.h>
#include <stdint.h>

#include <optional>
#include <vector>

namespace protozero {

// Loads the proto-encoded bytecode in memory and allows fast lookups for tuples
// (msg_index, field_id) to tell if a given field should be allowed or not and,
// in the case of nested fields, what is the next message index to recurse into.
// This class does two things:
// 1. Expands the array of varint from the proto into a vector<uint32_t>. This
//    is to avoid performing varint decoding on every lookup, at the cost of
//    some extra memory (2KB-4KB). Note that the expanded vector is not just a
//    1:1 copy of the proto one (more below). This is to avoid O(Fields) linear
//    lookup complexity.
// 2. Creates an index of offsets to remember the start word for each message.
//    This is so we can jump to O(1) to the N-th message when recursing into a
//    nested fields, without having to scan and find the (N-1)-th END_OF_MESSAGE
//    marker.
// Overall lookups are O(1) for field ids < 128 (kDirectlyIndexLimit) and O(N),
// with N being the number of allowed field ranges for other fields.
// See comments around |word_| below for the structure of the word vector.
class FilterBytecodeParser { … };

}  // namespace protozero

#endif  // SRC_PROTOZERO_FILTERING_FILTER_BYTECODE_PARSER_H_
chromium/third_party/perfetto/src/protozero/filtering/filter_bytecode_parser.h
