root/net/quic/quic_data_reader.cc

DEFINITIONS

1. pos_
2. ReadUInt16
3. ReadUInt32
4. ReadUInt48
5. ReadUInt64
6. ReadUInt128
7. ReadUFloat16
8. ReadStringPiece16
9. ReadStringPiece
10. ReadRemainingPayload
11. PeekRemainingPayload
12. ReadBytes
13. IsDoneReading
14. BytesRemaining
15. CanRead
16. OnFailure

// 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/quic/quic_data_reader.h"

#include "net/base/int128.h"
#include "net/quic/quic_protocol.h"

using base::StringPiece;

namespace net {

QuicDataReader::QuicDataReader(const char* data, const size_t len)
    : data_(data),
      len_(len),
      pos_(0) {
}

bool QuicDataReader::ReadUInt16(uint16* result) {
  return ReadBytes(result, sizeof(*result));
}

bool QuicDataReader::ReadUInt32(uint32* result) {
  return ReadBytes(result, sizeof(*result));
}

bool QuicDataReader::ReadUInt48(uint64* result) {
  uint32 lo;
  if (!ReadUInt32(&lo)) {
    return false;
  }

  uint16 hi;
  if (!ReadUInt16(&hi)) {
    return false;
  }

  *result = hi;
  *result <<= 32;
  *result += lo;

  return true;
}

bool QuicDataReader::ReadUInt64(uint64* result) {
  return ReadBytes(result, sizeof(*result));
}

bool QuicDataReader::ReadUInt128(uint128* result) {
  uint64 high_hash;
  uint64 low_hash;

  if (!ReadUInt64(&low_hash)) {
    return false;
  }
  if (!ReadUInt64(&high_hash)) {
    return false;
  }

  *result = uint128(high_hash, low_hash);
  return true;
}

bool QuicDataReader::ReadUFloat16(uint64* result) {
  uint16 value;
  if (!ReadUInt16(&value)) {
    return false;
  }

  *result = value;
  if (*result < (1 << kUFloat16MantissaEffectiveBits)) {
    // Fast path: either the value is denormalized (no hidden bit), or
    // normalized (hidden bit set, exponent offset by one) with exponent zero.
    // Zero exponent offset by one sets the bit exactly where the hidden bit is.
    // So in both cases the value encodes itself.
    return true;
  }

  uint16 exponent = value >> kUFloat16MantissaBits;  // No sign extend on uint!
  // After the fast pass, the exponent is at least one (offset by one).
  // Un-offset the exponent.
  --exponent;
  DCHECK_GE(exponent, 1);
  DCHECK_LE(exponent, kUFloat16MaxExponent);
  // Here we need to clear the exponent and set the hidden bit. We have already
  // decremented the exponent, so when we subtract it, it leaves behind the
  // hidden bit.
  *result -= exponent << kUFloat16MantissaBits;
  *result <<= exponent;
  DCHECK_GE(value, 1 << kUFloat16MantissaEffectiveBits);
  DCHECK_LE(value, kUFloat16MaxValue);
  return true;
}

bool QuicDataReader::ReadStringPiece16(StringPiece* result) {
  // Read resultant length.
  uint16 result_len;
  if (!ReadUInt16(&result_len)) {
    // OnFailure() already called.
    return false;
  }

  return ReadStringPiece(result, result_len);
}

bool QuicDataReader::ReadStringPiece(StringPiece* result, size_t size) {
  // Make sure that we have enough data to read.
  if (!CanRead(size)) {
    OnFailure();
    return false;
  }

  // Set result.
  result->set(data_ + pos_, size);

  // Iterate.
  pos_ += size;

  return true;
}

StringPiece QuicDataReader::ReadRemainingPayload() {
  StringPiece payload = PeekRemainingPayload();
  pos_ = len_;
  return payload;
}

StringPiece QuicDataReader::PeekRemainingPayload() {
  return StringPiece(data_ + pos_, len_ - pos_);
}

bool QuicDataReader::ReadBytes(void* result, size_t size) {
  // Make sure that we have enough data to read.
  if (!CanRead(size)) {
    OnFailure();
    return false;
  }

  // Read into result.
  memcpy(result, data_ + pos_, size);

  // Iterate.
  pos_ += size;

  return true;
}

bool QuicDataReader::IsDoneReading() const {
  return len_ == pos_;
}

size_t QuicDataReader::BytesRemaining() const {
  return len_ - pos_;
}

bool QuicDataReader::CanRead(size_t bytes) const {
  return bytes <= (len_ - pos_);
}

void QuicDataReader::OnFailure() {
  // Set our iterator to the end of the buffer so that further reads fail
  // immediately.
  pos_ = len_;
}

}  // namespace net