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/*
* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef NET_DCSCTP_PACKET_TLV_TRAIT_H_
#define NET_DCSCTP_PACKET_TLV_TRAIT_H_
#include <stdint.h>
#include <string.h>
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <optional>
#include <string>
#include <vector>
#include "api/array_view.h"
#include "net/dcsctp/packet/bounded_byte_reader.h"
#include "net/dcsctp/packet/bounded_byte_writer.h"
namespace dcsctp {
namespace tlv_trait_impl {
// Logging functions, only to be used by TLVTrait, which is a templated class.
void ReportInvalidSize(size_t actual_size, size_t expected_size);
void ReportInvalidType(int actual_type, int expected_type);
void ReportInvalidFixedLengthField(size_t value, size_t expected);
void ReportInvalidVariableLengthField(size_t value, size_t available);
void ReportInvalidPadding(size_t padding_bytes);
void ReportInvalidLengthMultiple(size_t length, size_t alignment);
} // namespace tlv_trait_impl
// Various entities in SCTP are padded data blocks, with a type and length
// field at fixed offsets, all stored in a 4-byte header.
//
// See e.g. https://tools.ietf.org/html/rfc4960#section-3.2 and
// https://tools.ietf.org/html/rfc4960#section-3.2.1
//
// These are helper classes for writing and parsing that data, which in SCTP is
// called Type-Length-Value, or TLV.
//
// This templated class is configurable - a struct passed in as template
// parameter with the following expected members:
// * kType - The type field's value
// * kTypeSizeInBytes - The type field's width in bytes.
// Either 1 or 2.
// * kHeaderSize - The fixed size header
// * kVariableLengthAlignment - The size alignment on the variable data. Set
// to zero (0) if no variable data is used.
//
// This class is to be used as a trait
// (https://en.wikipedia.org/wiki/Trait_(computer_programming)) that adds a few
// public and protected members and which a class inherits from when it
// represents a type-length-value object.
template <typename Config>
class TLVTrait {
private:
static constexpr size_t kTlvHeaderSize = 4;
protected:
static constexpr size_t kHeaderSize = Config::kHeaderSize;
static_assert(Config::kTypeSizeInBytes == 1 || Config::kTypeSizeInBytes == 2,
"kTypeSizeInBytes must be 1 or 2");
static_assert(Config::kHeaderSize >= kTlvHeaderSize,
"HeaderSize must be >= 4 bytes");
static_assert((Config::kHeaderSize % 4 == 0),
"kHeaderSize must be an even multiple of 4 bytes");
static_assert((Config::kVariableLengthAlignment == 0 ||
Config::kVariableLengthAlignment == 1 ||
Config::kVariableLengthAlignment == 2 ||
Config::kVariableLengthAlignment == 4 ||
Config::kVariableLengthAlignment == 8),
"kVariableLengthAlignment must be an allowed value");
// Validates the data with regards to size, alignment and type.
// If valid, returns a bounded buffer.
static std::optional<BoundedByteReader<Config::kHeaderSize>> ParseTLV(
webrtc::ArrayView<const uint8_t> data) {
if (data.size() < Config::kHeaderSize) {
tlv_trait_impl::ReportInvalidSize(data.size(), Config::kHeaderSize);
return std::nullopt;
}
BoundedByteReader<kTlvHeaderSize> tlv_header(data);
const int type = (Config::kTypeSizeInBytes == 1)
? tlv_header.template Load8<0>()
: tlv_header.template Load16<0>();
if (type != Config::kType) {
tlv_trait_impl::ReportInvalidType(type, Config::kType);
return std::nullopt;
}
const uint16_t length = tlv_header.template Load16<2>();
if (Config::kVariableLengthAlignment == 0) {
// Don't expect any variable length data at all.
if (length != Config::kHeaderSize || data.size() != Config::kHeaderSize) {
tlv_trait_impl::ReportInvalidFixedLengthField(length,
Config::kHeaderSize);
return std::nullopt;
}
} else {
// Expect variable length data - verify its size alignment.
if (length > data.size() || length < Config::kHeaderSize) {
tlv_trait_impl::ReportInvalidVariableLengthField(length, data.size());
return std::nullopt;
}
const size_t padding = data.size() - length;
if (padding > 3) {
// https://tools.ietf.org/html/rfc4960#section-3.2
// "This padding MUST NOT be more than 3 bytes in total"
tlv_trait_impl::ReportInvalidPadding(padding);
return std::nullopt;
}
if (!ValidateLengthAlignment(length, Config::kVariableLengthAlignment)) {
tlv_trait_impl::ReportInvalidLengthMultiple(
length, Config::kVariableLengthAlignment);
return std::nullopt;
}
}
return BoundedByteReader<Config::kHeaderSize>(data.subview(0, length));
}
// Allocates space for data with a static header size, as defined by
// `Config::kHeaderSize` and a variable footer, as defined by `variable_size`
// (which may be 0) and writes the type and length in the header.
static BoundedByteWriter<Config::kHeaderSize> AllocateTLV(
std::vector<uint8_t>& out,
size_t variable_size = 0) {
const size_t offset = out.size();
const size_t size = Config::kHeaderSize + variable_size;
out.resize(offset + size);
BoundedByteWriter<kTlvHeaderSize> tlv_header(
webrtc::ArrayView<uint8_t>(out.data() + offset, kTlvHeaderSize));
if (Config::kTypeSizeInBytes == 1) {
tlv_header.template Store8<0>(static_cast<uint8_t>(Config::kType));
} else {
tlv_header.template Store16<0>(Config::kType);
}
tlv_header.template Store16<2>(size);
return BoundedByteWriter<Config::kHeaderSize>(
webrtc::ArrayView<uint8_t>(out.data() + offset, size));
}
private:
static bool ValidateLengthAlignment(uint16_t length, size_t alignment) {
// This is to avoid MSVC believing there could be a "mod by zero", when it
// certainly can't.
if (alignment == 0) {
return true;
}
return (length % alignment) == 0;
}
};
} // namespace dcsctp
#endif // NET_DCSCTP_PACKET_TLV_TRAIT_H_
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