message_filter.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_MESSAGE_FILTER_H_
#define SRC_PROTOZERO_FILTERING_MESSAGE_FILTER_H_

#include <stdint.h>

#include <memory>
#include <string>
#include <unordered_map>

#include "src/protozero/filtering/filter_bytecode_parser.h"
#include "src/protozero/filtering/message_tokenizer.h"
#include "src/protozero/filtering/string_filter.h"

namespace protozero {

// A class to filter binary-encoded proto messages using an allow-list of field
// ids, also known as "filter bytecode". The filter determines which fields are
// allowed to be passed through in output and strips all the other fields.
// See go/trace-filtering for full design.
// This class takes in input:
// 1) The filter bytecode, loaded once via the LoadFilterBytecode() method.
// 2) A proto-encoded binary message. The message doesn't have to be contiguous,
//    it can be passed as an array of arbitrarily chunked fragments.
// The FilterMessage*() method returns in output a proto message, stripping out
// all unknown fields. If the input is malformed (e.g., unknown proto field wire
// types, lengths out of bound) the whole filtering failed and the |error| flag
// of the FilteredMessage object is set to true.
// The filtering operation is based on rewriting a copy of the message into a
// self-allocated buffer, which is then returned in the output. The input buffer
// is NOT altered.
// Note also that the process of rewriting the protos gets rid of most redundant
// varint encoding (if present). So even if all fields are allow-listed, the
// output might NOT be bitwise identical to the input (but it will be
// semantically equivalent).
// Furthermore the enable_field_usage_tracking() method allows to keep track of
// a histogram of allowed / denied fields. It slows down filtering and is
// intended only on host tools.
class MessageFilter { … };

}  // namespace protozero

#endif  // SRC_PROTOZERO_FILTERING_MESSAGE_FILTER_H_
chromium/third_party/perfetto/src/protozero/filtering/message_filter.h
