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// Copyright (c) 2012 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 "net/third_party/quiche/src/quic/core/quic_data_writer.h"
#include <algorithm>
#include <limits>
#include "net/third_party/quiche/src/quic/core/crypto/quic_random.h"
#include "net/third_party/quiche/src/quic/core/quic_utils.h"
#include "net/third_party/quiche/src/quic/platform/api/quic_bug_tracker.h"
#include "net/third_party/quiche/src/quic/platform/api/quic_flags.h"
#include "net/third_party/quiche/src/quic/platform/api/quic_str_cat.h"
namespace quic {
QuicDataWriter::QuicDataWriter(size_t size, char* buffer, Endianness endianness)
: buffer_(buffer), capacity_(size), length_(0), endianness_(endianness) {}
QuicDataWriter::~QuicDataWriter() {}
char* QuicDataWriter::data() {
return buffer_;
}
bool QuicDataWriter::WriteUInt8(uint8_t value) {
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt16(uint16_t value) {
if (endianness_ == NETWORK_BYTE_ORDER) {
value = QuicEndian::HostToNet16(value);
}
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt32(uint32_t value) {
if (endianness_ == NETWORK_BYTE_ORDER) {
value = QuicEndian::HostToNet32(value);
}
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteUInt64(uint64_t value) {
if (endianness_ == NETWORK_BYTE_ORDER) {
value = QuicEndian::HostToNet64(value);
}
return WriteBytes(&value, sizeof(value));
}
bool QuicDataWriter::WriteBytesToUInt64(size_t num_bytes, uint64_t value) {
if (num_bytes > sizeof(value)) {
return false;
}
if (endianness_ == HOST_BYTE_ORDER) {
return WriteBytes(&value, num_bytes);
}
value = QuicEndian::HostToNet64(value);
return WriteBytes(reinterpret_cast<char*>(&value) + sizeof(value) - num_bytes,
num_bytes);
}
bool QuicDataWriter::WriteUFloat16(uint64_t value) {
uint16_t result;
if (value < (UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
// Fast path: either the value is denormalized, or has exponent zero.
// Both cases are represented by the value itself.
result = static_cast<uint16_t>(value);
} else if (value >= kUFloat16MaxValue) {
// Value is out of range; clamp it to the maximum representable.
result = std::numeric_limits<uint16_t>::max();
} else {
// The highest bit is between position 13 and 42 (zero-based), which
// corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
// hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
// and count the shifts.
uint16_t exponent = 0;
for (uint16_t offset = 16; offset > 0; offset /= 2) {
// Right-shift the value until the highest bit is in position 11.
// For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
// shift if the bit is at or above 11 + offset.
if (value >= (UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
exponent += offset;
value >>= offset;
}
}
DCHECK_GE(exponent, 1);
DCHECK_LE(exponent, kUFloat16MaxExponent);
DCHECK_GE(value, UINT64_C(1) << kUFloat16MantissaBits);
DCHECK_LT(value, UINT64_C(1) << kUFloat16MantissaEffectiveBits);
// Hidden bit (position 11) is set. We should remove it and increment the
// exponent. Equivalently, we just add it to the exponent.
// This hides the bit.
result = static_cast<uint16_t>(value + (exponent << kUFloat16MantissaBits));
}
if (endianness_ == NETWORK_BYTE_ORDER) {
result = QuicEndian::HostToNet16(result);
}
return WriteBytes(&result, sizeof(result));
}
bool QuicDataWriter::WriteStringPiece16(QuicStringPiece val) {
if (val.size() > std::numeric_limits<uint16_t>::max()) {
return false;
}
if (!WriteUInt16(static_cast<uint16_t>(val.size()))) {
return false;
}
return WriteBytes(val.data(), val.size());
}
bool QuicDataWriter::WriteStringPiece(QuicStringPiece val) {
return WriteBytes(val.data(), val.size());
}
char* QuicDataWriter::BeginWrite(size_t length) {
if (length_ > capacity_) {
return nullptr;
}
if (capacity_ - length_ < length) {
return nullptr;
}
#ifdef ARCH_CPU_64_BITS
DCHECK_LE(length, std::numeric_limits<uint32_t>::max());
#endif
return buffer_ + length_;
}
bool QuicDataWriter::WriteBytes(const void* data, size_t data_len) {
char* dest = BeginWrite(data_len);
if (!dest) {
return false;
}
memcpy(dest, data, data_len);
length_ += data_len;
return true;
}
bool QuicDataWriter::WriteRepeatedByte(uint8_t byte, size_t count) {
char* dest = BeginWrite(count);
if (!dest) {
return false;
}
memset(dest, byte, count);
length_ += count;
return true;
}
void QuicDataWriter::WritePadding() {
DCHECK_LE(length_, capacity_);
if (length_ > capacity_) {
return;
}
memset(buffer_ + length_, 0x00, capacity_ - length_);
length_ = capacity_;
}
bool QuicDataWriter::WritePaddingBytes(size_t count) {
return WriteRepeatedByte(0x00, count);
}
bool QuicDataWriter::WriteConnectionId(QuicConnectionId connection_id,
Perspective perspective) {
if (!QuicConnectionIdSupportsVariableLength(perspective)) {
uint64_t connection_id64 =
QuicEndian::HostToNet64(QuicConnectionIdToUInt64(connection_id));
return WriteBytes(&connection_id64, sizeof(connection_id64));
}
return WriteBytes(connection_id.data(), connection_id.length());
}
bool QuicDataWriter::WriteTag(uint32_t tag) {
return WriteBytes(&tag, sizeof(tag));
}
bool QuicDataWriter::WriteRandomBytes(QuicRandom* random, size_t length) {
char* dest = BeginWrite(length);
if (!dest) {
return false;
}
random->RandBytes(dest, length);
length_ += length;
return true;
}
// Converts a uint64_t into an IETF/Quic formatted Variable Length
// Integer. IETF Variable Length Integers have 62 significant bits, so
// the value to write must be in the range of 0..(2^62)-1.
//
// Performance notes
//
// Measurements and experiments showed that unrolling the four cases
// like this and dereferencing next_ as we do (*(next_+n)) gains about
// 10% over making a loop and dereferencing it as *(next_++)
//
// Using a register for next didn't help.
//
// Branches are ordered to increase the likelihood of the first being
// taken.
//
// Low-level optimization is useful here because this function will be
// called frequently, leading to outsize benefits.
bool QuicDataWriter::WriteVarInt62(uint64_t value) {
DCHECK_EQ(endianness_, NETWORK_BYTE_ORDER);
size_t remaining = capacity_ - length_;
char* next = buffer_ + length_;
if ((value & kVarInt62ErrorMask) == 0) {
// We know the high 2 bits are 0 so |value| is legal.
// We can do the encoding.
if ((value & kVarInt62Mask8Bytes) != 0) {
// Someplace in the high-4 bytes is a 1-bit. Do an 8-byte
// encoding.
if (remaining >= 8) {
*(next + 0) = ((value >> 56) & 0x3f) + 0xc0;
*(next + 1) = (value >> 48) & 0xff;
*(next + 2) = (value >> 40) & 0xff;
*(next + 3) = (value >> 32) & 0xff;
*(next + 4) = (value >> 24) & 0xff;
*(next + 5) = (value >> 16) & 0xff;
*(next + 6) = (value >> 8) & 0xff;
*(next + 7) = value & 0xff;
length_ += 8;
return true;
}
return false;
}
// The high-order-4 bytes are all 0, check for a 1, 2, or 4-byte
// encoding
if ((value & kVarInt62Mask4Bytes) != 0) {
// The encoding will not fit into 2 bytes, Do a 4-byte
// encoding.
if (remaining >= 4) {
*(next + 0) = ((value >> 24) & 0x3f) + 0x80;
*(next + 1) = (value >> 16) & 0xff;
*(next + 2) = (value >> 8) & 0xff;
*(next + 3) = value & 0xff;
length_ += 4;
return true;
}
return false;
}
// The high-order bits are all 0. Check to see if the number
// can be encoded as one or two bytes. One byte encoding has
// only 6 significant bits (bits 0xffffffff ffffffc0 are all 0).
// Two byte encoding has more than 6, but 14 or less significant
// bits (bits 0xffffffff ffffc000 are 0 and 0x00000000 00003fc0
// are not 0)
if ((value & kVarInt62Mask2Bytes) != 0) {
// Do 2-byte encoding
if (remaining >= 2) {
*(next + 0) = ((value >> 8) & 0x3f) + 0x40;
*(next + 1) = (value)&0xff;
length_ += 2;
return true;
}
return false;
}
if (remaining >= 1) {
// Do 1-byte encoding
*next = (value & 0x3f);
length_ += 1;
return true;
}
return false;
}
// Can not encode, high 2 bits not 0
return false;
}
// static
int QuicDataWriter::GetVarInt62Len(uint64_t value) {
if ((value & kVarInt62ErrorMask) != 0) {
QUIC_BUG << "Attempted to encode a value, " << value
<< ", that is too big for VarInt62";
return 0;
}
if ((value & kVarInt62Mask8Bytes) != 0) {
return 8;
}
if ((value & kVarInt62Mask4Bytes) != 0) {
return 4;
}
if ((value & kVarInt62Mask2Bytes) != 0) {
return 2;
}
return 1;
}
bool QuicDataWriter::WriteStringPieceVarInt62(
const QuicStringPiece& string_piece) {
if (!WriteVarInt62(string_piece.size())) {
return false;
}
if (!string_piece.empty()) {
if (!WriteBytes(string_piece.data(), string_piece.size())) {
return false;
}
}
return true;
}
QuicString QuicDataWriter::DebugString() const {
return QuicStrCat(" { capacity: ", capacity_, ", length: ", length_, " }");
}
} // namespace quic