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Packets, chunks, parameters and error causes - the SCTP entities that are sent on the wire - are buffers with fields that are stored in big endian and that generally consist of a fixed header size, and a variable sized part, that can e.g. be encoded sub-fields or serialized strings. The BoundedByteReader and BoundedByteWriter utilities make it easy to read those fields with as much aid from the compiler as possible, by having compile-time assertions that fields are not accessed outside the buffer's span. There are some byte reading functionality already in modules/rtp_rtcp, but that module would be a bit unfortunate to depend on, and doesn't have the compile time bounds checking that is the biggest feature of this abstraction of an rtc::ArrayView. Bug: webrtc:12614 Change-Id: I9fc641aff22221018dda9add4e2c44853c0f64f0 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212967 Commit-Queue: Victor Boivie <boivie@webrtc.org> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Reviewed-by: Tommi <tommi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33597}
99 lines
3.4 KiB
C++
99 lines
3.4 KiB
C++
/*
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* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef NET_DCSCTP_PACKET_BOUNDED_BYTE_READER_H_
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#define NET_DCSCTP_PACKET_BOUNDED_BYTE_READER_H_
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#include <cstdint>
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#include "api/array_view.h"
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namespace dcsctp {
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// TODO(boivie): These generic functions - and possibly this entire class -
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// could be a candidate to have added to rtc_base/. They should use compiler
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// intrinsics as well.
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namespace internal {
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// Loads a 8-bit unsigned word at `data`.
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inline uint8_t LoadBigEndian8(const uint8_t* data) {
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return data[0];
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}
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// Loads a 16-bit unsigned word at `data`.
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inline uint16_t LoadBigEndian16(const uint8_t* data) {
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return (data[0] << 8) | data[1];
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}
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// Loads a 32-bit unsigned word at `data`.
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inline uint32_t LoadBigEndian32(const uint8_t* data) {
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return (data[0] << 24) | (data[1] << 16) | (data[2] << 8) | data[3];
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}
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} // namespace internal
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// BoundedByteReader wraps an ArrayView and divides it into two parts; A fixed
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// size - which is the template parameter - and a variable size, which is what
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// remains in `data` after the `FixedSize`.
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//
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// The BoundedByteReader provides methods to load/read big endian numbers from
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// the FixedSize portion of the buffer, and these are read with static bounds
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// checking, to avoid out-of-bounds accesses without a run-time penalty.
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//
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// The variable sized portion can either be used to create sub-readers, which
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// themselves would provide compile-time bounds-checking, or the entire variable
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// sized portion can be retrieved as an ArrayView.
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template <int FixedSize>
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class BoundedByteReader {
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public:
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explicit BoundedByteReader(rtc::ArrayView<const uint8_t> data) : data_(data) {
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RTC_DCHECK(data.size() >= FixedSize);
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}
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template <size_t offset>
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uint8_t Load8() const {
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static_assert(offset + sizeof(uint8_t) <= FixedSize, "Out-of-bounds");
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return internal::LoadBigEndian8(&data_[offset]);
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}
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template <size_t offset>
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uint16_t Load16() const {
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static_assert(offset + sizeof(uint16_t) <= FixedSize, "Out-of-bounds");
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static_assert((offset % sizeof(uint16_t)) == 0, "Unaligned access");
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return internal::LoadBigEndian16(&data_[offset]);
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}
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template <size_t offset>
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uint32_t Load32() const {
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static_assert(offset + sizeof(uint32_t) <= FixedSize, "Out-of-bounds");
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static_assert((offset % sizeof(uint32_t)) == 0, "Unaligned access");
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return internal::LoadBigEndian32(&data_[offset]);
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}
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template <size_t SubSize>
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BoundedByteReader<SubSize> sub_reader(size_t variable_offset) const {
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RTC_DCHECK(FixedSize + variable_offset + SubSize <= data_.size());
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rtc::ArrayView<const uint8_t> sub_span =
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data_.subview(FixedSize + variable_offset, SubSize);
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return BoundedByteReader<SubSize>(sub_span);
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}
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size_t variable_data_size() const { return data_.size() - FixedSize; }
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rtc::ArrayView<const uint8_t> variable_data() const {
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return data_.subview(FixedSize, data_.size() - FixedSize);
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}
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private:
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const rtc::ArrayView<const uint8_t> data_;
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};
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} // namespace dcsctp
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#endif // NET_DCSCTP_PACKET_BOUNDED_BYTE_READER_H_
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