7d3c49a171
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}
101 lines
3.3 KiB
C++
101 lines
3.3 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_WRITER_H_
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#define NET_DCSCTP_PACKET_BOUNDED_BYTE_WRITER_H_
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#include <algorithm>
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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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// Stores a 8-bit unsigned word at `data`.
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inline void StoreBigEndian8(uint8_t* data, uint8_t val) {
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data[0] = val;
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}
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// Stores a 16-bit unsigned word at `data`.
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inline void StoreBigEndian16(uint8_t* data, uint16_t val) {
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data[0] = val >> 8;
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data[1] = val;
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}
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// Stores a 32-bit unsigned word at `data`.
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inline void StoreBigEndian32(uint8_t* data, uint32_t val) {
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data[0] = val >> 24;
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data[1] = val >> 16;
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data[2] = val >> 8;
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data[3] = val;
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}
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} // namespace internal
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// BoundedByteWriter 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 BoundedByteWriter provides methods to write big endian numbers to the
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// FixedSize portion of the buffer, and these are written 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-writers, which
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// themselves would provide compile-time bounds-checking, or data can be copied
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// to it.
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template <int FixedSize>
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class BoundedByteWriter {
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public:
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explicit BoundedByteWriter(rtc::ArrayView<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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void Store8(uint8_t value) {
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static_assert(offset + sizeof(uint8_t) <= FixedSize, "Out-of-bounds");
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internal::StoreBigEndian8(&data_[offset], value);
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}
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template <size_t offset>
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void Store16(uint16_t value) {
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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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internal::StoreBigEndian16(&data_[offset], value);
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}
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template <size_t offset>
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void Store32(uint32_t value) {
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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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internal::StoreBigEndian32(&data_[offset], value);
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}
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template <size_t SubSize>
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BoundedByteWriter<SubSize> sub_writer(size_t variable_offset) {
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RTC_DCHECK(FixedSize + variable_offset + SubSize <= data_.size());
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return BoundedByteWriter<SubSize>(
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data_.subview(FixedSize + variable_offset, SubSize));
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}
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void CopyToVariableData(rtc::ArrayView<const uint8_t> source) {
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memcpy(data_.data() + FixedSize, source.data(),
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std::min(source.size(), data_.size() - FixedSize));
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}
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private:
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rtc::ArrayView<uint8_t> data_;
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};
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} // namespace dcsctp
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#endif // NET_DCSCTP_PACKET_BOUNDED_BYTE_WRITER_H_
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