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writer.cc
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writer.cc
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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/cbor/writer.h"
#include <string>
#include "base/numerics/safe_conversions.h"
#include "base/strings/string_piece.h"
#include "components/cbor/constants.h"
namespace cbor {
Writer::~Writer() {}
// static
base::Optional<std::vector<uint8_t>> Writer::Write(const Value& node,
size_t max_nesting_level) {
std::vector<uint8_t> cbor;
Writer writer(&cbor);
if (writer.EncodeCBOR(node, base::checked_cast<int>(max_nesting_level)))
return cbor;
return base::nullopt;
}
Writer::Writer(std::vector<uint8_t>* cbor) : encoded_cbor_(cbor) {}
bool Writer::EncodeCBOR(const Value& node, int max_nesting_level) {
if (max_nesting_level < 0)
return false;
switch (node.type()) {
case Value::Type::NONE: {
StartItem(Value::Type::BYTE_STRING, 0);
return true;
}
case Value::Type::INVALID_UTF8:
NOTREACHED() << constants::kUnsupportedMajorType;
return false;
// Represents unsigned integers.
case Value::Type::UNSIGNED: {
int64_t value = node.GetUnsigned();
StartItem(Value::Type::UNSIGNED, static_cast<uint64_t>(value));
return true;
}
// Represents negative integers.
case Value::Type::NEGATIVE: {
int64_t value = node.GetNegative();
StartItem(Value::Type::NEGATIVE, static_cast<uint64_t>(-(value + 1)));
return true;
}
// Represents a byte string.
case Value::Type::BYTE_STRING: {
const Value::BinaryValue& bytes = node.GetBytestring();
StartItem(Value::Type::BYTE_STRING,
base::strict_cast<uint64_t>(bytes.size()));
// Add the bytes.
encoded_cbor_->insert(encoded_cbor_->end(), bytes.begin(), bytes.end());
return true;
}
case Value::Type::STRING: {
base::StringPiece string = node.GetString();
StartItem(Value::Type::STRING,
base::strict_cast<uint64_t>(string.size()));
// Add the characters.
encoded_cbor_->insert(encoded_cbor_->end(), string.begin(), string.end());
return true;
}
// Represents an array.
case Value::Type::ARRAY: {
const Value::ArrayValue& array = node.GetArray();
StartItem(Value::Type::ARRAY, array.size());
for (const auto& value : array) {
if (!EncodeCBOR(value, max_nesting_level - 1))
return false;
}
return true;
}
// Represents a map.
case Value::Type::MAP: {
const Value::MapValue& map = node.GetMap();
StartItem(Value::Type::MAP, map.size());
for (const auto& value : map) {
if (!EncodeCBOR(value.first, max_nesting_level - 1))
return false;
if (!EncodeCBOR(value.second, max_nesting_level - 1))
return false;
}
return true;
}
case Value::Type::TAG:
NOTREACHED() << constants::kUnsupportedMajorType;
return false;
// Represents a simple value.
case Value::Type::SIMPLE_VALUE: {
const Value::SimpleValue simple_value = node.GetSimpleValue();
StartItem(Value::Type::SIMPLE_VALUE,
base::checked_cast<uint64_t>(simple_value));
return true;
}
}
// This is needed because, otherwise, MSVC complains that not all paths return
// a value. We should be able to remove it once MSVC builders are gone.
NOTREACHED();
return false;
}
void Writer::StartItem(Value::Type type, uint64_t size) {
encoded_cbor_->push_back(base::checked_cast<uint8_t>(
static_cast<unsigned>(type) << constants::kMajorTypeBitShift));
SetUint(size);
}
void Writer::SetAdditionalInformation(uint8_t additional_information) {
DCHECK(!encoded_cbor_->empty());
DCHECK_EQ(additional_information & constants::kAdditionalInformationMask,
additional_information);
encoded_cbor_->back() |=
(additional_information & constants::kAdditionalInformationMask);
}
void Writer::SetUint(uint64_t value) {
size_t count = GetNumUintBytes(value);
int shift = -1;
// Values under 24 are encoded directly in the initial byte.
// Otherwise, the last 5 bits of the initial byte contains the length
// of unsigned integer, which is encoded in following bytes.
switch (count) {
case 0:
SetAdditionalInformation(base::checked_cast<uint8_t>(value));
break;
case 1:
SetAdditionalInformation(constants::kAdditionalInformation1Byte);
shift = 0;
break;
case 2:
SetAdditionalInformation(constants::kAdditionalInformation2Bytes);
shift = 1;
break;
case 4:
SetAdditionalInformation(constants::kAdditionalInformation4Bytes);
shift = 3;
break;
case 8:
SetAdditionalInformation(constants::kAdditionalInformation8Bytes);
shift = 7;
break;
default:
NOTREACHED();
break;
}
for (; shift >= 0; shift--) {
encoded_cbor_->push_back(0xFF & (value >> (shift * 8)));
}
}
size_t Writer::GetNumUintBytes(uint64_t value) {
if (value < 24) {
return 0;
} else if (value <= 0xFF) {
return 1;
} else if (value <= 0xFFFF) {
return 2;
} else if (value <= 0xFFFFFFFF) {
return 4;
}
return 8;
}
} // namespace cbor