net/websockets/websocket_frame_parser.cc

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/websockets/websocket_frame_parser.h"

#include <algorithm>
#include <ostream>
#include <utility>
#include <vector>

#include "base/check.h"
#include "base/check_op.h"
#include "base/containers/extend.h"
#include "base/containers/span.h"
#include "base/logging.h"
#include "base/numerics/byte_conversions.h"
#include "base/numerics/safe_conversions.h"
#include "net/websockets/websocket_frame.h"

namespace {

constexpr uint8_t kFinalBit = 0x80;
constexpr uint8_t kReserved1Bit = 0x40;
constexpr uint8_t kReserved2Bit = 0x20;
constexpr uint8_t kReserved3Bit = 0x10;
constexpr uint8_t kOpCodeMask = 0xF;
constexpr uint8_t kMaskBit = 0x80;
constexpr uint8_t kPayloadLengthMask = 0x7F;
constexpr uint64_t kMaxPayloadLengthWithoutExtendedLengthField = 125;
constexpr uint64_t kPayloadLengthWithTwoByteExtendedLengthField = 126;
constexpr uint64_t kPayloadLengthWithEightByteExtendedLengthField = 127;
constexpr size_t kMaximumFrameHeaderSize =
    net::WebSocketFrameHeader::kBaseHeaderSize +
    net::WebSocketFrameHeader::kMaximumExtendedLengthSize +
    net::WebSocketFrameHeader::kMaskingKeyLength;

}  // namespace.

namespace net {

WebSocketFrameParser::WebSocketFrameParser() = default;

WebSocketFrameParser::~WebSocketFrameParser() = default;

bool WebSocketFrameParser::Decode(
    base::span<uint8_t> data_span,
    std::vector<std::unique_ptr<WebSocketFrameChunk>>* frame_chunks) {
  if (websocket_error_ != kWebSocketNormalClosure) {
    return false;
  }
  if (data_span.empty()) {
    return true;
  }

  // If we have incomplete frame header, try to decode a header combining with
  // |data|.
  bool first_chunk = false;
  if (incomplete_header_buffer_.size() > 0) {
    DCHECK(!current_frame_header_.get());
    const size_t original_size = incomplete_header_buffer_.size();
    DCHECK_LE(original_size, kMaximumFrameHeaderSize);
    base::Extend(
        incomplete_header_buffer_,
        data_span.first(std::min(data_span.size(),
                                 kMaximumFrameHeaderSize - original_size)));
    const size_t consumed = DecodeFrameHeader(incomplete_header_buffer_);
    if (websocket_error_ != kWebSocketNormalClosure)
      return false;
    if (!current_frame_header_.get())
      return true;

    DCHECK_GE(consumed, original_size);
    data_span = data_span.subspan(consumed - original_size);
    incomplete_header_buffer_.clear();
    first_chunk = true;
  }

  DCHECK(incomplete_header_buffer_.empty());
  while (data_span.size() > 0 || first_chunk) {
    if (!current_frame_header_.get()) {
      const size_t consumed = DecodeFrameHeader(data_span);
      if (websocket_error_ != kWebSocketNormalClosure)
        return false;
      // If frame header is incomplete, then carry over the remaining
      // data to the next round of Decode().
      if (!current_frame_header_.get()) {
        DCHECK(!consumed);
        base::Extend(incomplete_header_buffer_, data_span);
        // Sanity check: the size of carried-over data should not exceed
        // the maximum possible length of a frame header.
        DCHECK_LT(incomplete_header_buffer_.size(), kMaximumFrameHeaderSize);
        return true;
      }
      DCHECK_GE(data_span.size(), consumed);
      data_span = data_span.subspan(consumed);
      first_chunk = true;
    }
    DCHECK(incomplete_header_buffer_.empty());
    std::unique_ptr<WebSocketFrameChunk> frame_chunk =
        DecodeFramePayload(first_chunk, &data_span);
    first_chunk = false;
    DCHECK(frame_chunk.get());
    frame_chunks->push_back(std::move(frame_chunk));
  }
  return true;
}

size_t WebSocketFrameParser::DecodeFrameHeader(base::span<const uint8_t> data) {
  DVLOG(3) << "DecodeFrameHeader buffer size:"
           << ", data size:" << data.size();
  typedef WebSocketFrameHeader::OpCode OpCode;
  DCHECK(!current_frame_header_.get());

  // Header needs 2 bytes at minimum.
  if (data.size() < 2)
    return 0;
  size_t current = 0;
  const uint8_t first_byte = data[current++];
  const uint8_t second_byte = data[current++];

  const bool final = (first_byte & kFinalBit) != 0;
  const bool reserved1 = (first_byte & kReserved1Bit) != 0;
  const bool reserved2 = (first_byte & kReserved2Bit) != 0;
  const bool reserved3 = (first_byte & kReserved3Bit) != 0;
  const OpCode opcode = first_byte & kOpCodeMask;

  uint64_t payload_length = second_byte & kPayloadLengthMask;
  if (payload_length == kPayloadLengthWithTwoByteExtendedLengthField) {
    if (data.size() < current + 2)
      return 0;
    uint16_t payload_length_16 =
        base::U16FromBigEndian(data.subspan(current).first<2>());
    current += 2;
    payload_length = payload_length_16;
    if (payload_length <= kMaxPayloadLengthWithoutExtendedLengthField) {
      websocket_error_ = kWebSocketErrorProtocolError;
      return 0;
    }
  } else if (payload_length == kPayloadLengthWithEightByteExtendedLengthField) {
    if (data.size() < current + 8)
      return 0;
    payload_length = base::U64FromBigEndian(data.subspan(current).first<8>());
    current += 8;
    if (payload_length <= UINT16_MAX ||
        payload_length > static_cast<uint64_t>(INT64_MAX)) {
      websocket_error_ = kWebSocketErrorProtocolError;
      return 0;
    }
    if (payload_length > static_cast<uint64_t>(INT32_MAX)) {
      websocket_error_ = kWebSocketErrorMessageTooBig;
      return 0;
    }
  }
  DCHECK_EQ(websocket_error_, kWebSocketNormalClosure);

  WebSocketMaskingKey masking_key = {};
  const bool masked = (second_byte & kMaskBit) != 0;
  static constexpr size_t kMaskingKeyLength =
      WebSocketFrameHeader::kMaskingKeyLength;
  if (masked) {
    if (data.size() < current + kMaskingKeyLength)
      return 0;
    base::as_writable_byte_span(masking_key.key)
        .copy_from(data.subspan(current, kMaskingKeyLength));
    current += kMaskingKeyLength;
  }

  current_frame_header_ = std::make_unique<WebSocketFrameHeader>(opcode);
  current_frame_header_->final = final;
  current_frame_header_->reserved1 = reserved1;
  current_frame_header_->reserved2 = reserved2;
  current_frame_header_->reserved3 = reserved3;
  current_frame_header_->masked = masked;
  current_frame_header_->masking_key = masking_key;
  current_frame_header_->payload_length = payload_length;
  DCHECK_EQ(0u, frame_offset_);
  return current;
}

std::unique_ptr<WebSocketFrameChunk> WebSocketFrameParser::DecodeFramePayload(
    bool first_chunk,
    base::span<uint8_t>* data) {
  // The cast here is safe because |payload_length| is already checked to be
  // less than std::numeric_limits<int>::max() when the header is parsed.
  const auto chunk_data_size = static_cast<uint64_t>(
      std::min(uint64_t{data->size()},
               current_frame_header_->payload_length - frame_offset_));

  auto frame_chunk = std::make_unique<WebSocketFrameChunk>();
  if (first_chunk) {
    frame_chunk->header = current_frame_header_->Clone();
  }
  frame_chunk->final_chunk = false;
  if (chunk_data_size) {
    const auto split_point = base::checked_cast<size_t>(chunk_data_size);
    frame_chunk->payload = base::as_writable_chars(data->first(split_point));
    *data = data->subspan(split_point);
    frame_offset_ += chunk_data_size;
  }

  DCHECK_LE(frame_offset_, current_frame_header_->payload_length);
  if (frame_offset_ == current_frame_header_->payload_length) {
    frame_chunk->final_chunk = true;
    current_frame_header_.reset();
    frame_offset_ = 0;
  }

  return frame_chunk;
}

}  // namespace net