浏览器研究-chromium修改源码禁用图片加载

浏览器指纹

禁用图片是为了加速和节省资源，搞并发需要把图片加载禁用掉，便于提升速度。实现这个功能的思路是在网络层加载资源url的时候进行判断，如果url的后缀有png等图片后缀就不进行加载，相当于把网络层请求给拦截下来，代码位于src\net\http\http_network_transaction.cc，代码中的Start方法就是发起请求的启动函数。

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int HttpNetworkTransaction::Start(const HttpRequestInfo* request_info,
                                  CompletionOnceCallback callback,
                                  const NetLogWithSource& net_log) {
  if (request_info->load_flags & LOAD_ONLY_FROM_CACHE)
    return ERR_CACHE_MISS;

  DCHECK(request_info->traffic_annotation.is_valid());
  DCHECK(request_info->IsConsistent());
  net_log_ = net_log;
  request_ = request_info;
  url_ = request_->url;
  // jack
  const base::CommandLine* jack_command_line =
      base::CommandLine::ForCurrentProcess();
  if (jack_command_line->HasSwitch("jack")) {
    const std::string jack_fp = jack_command_line->GetSwitchValueASCII("jack");
    absl::optional<base::Value> json_reader = base::JSONReader::Read(jack_fp);
    const std::string* enableimg =
        json_reader->GetDict().FindString("disableimg");
    if (enableimg != nullptr) {
      std::string img_value = *enableimg;
      if (img_value == "yes") {
        std::string path = url_.possibly_invalid_spec();
        if (path.find("jpg") != std::string::npos ||
            path.find("jpeg") != std::string::npos ||
            path.find("png") != std::string::npos ||
            path.find("gif") != std::string::npos ||
            path.find("bmp") != std::string::npos ||
            path.find("JPEG") != std::string::npos) {
          return ERR_BLOCKED_BY_CLIENT;
        }
      }
    }
  }
  // jack end
  network_anonymization_key_ = request_->network_anonymization_key;
#if BUILDFLAG(ENABLE_REPORTING)
  // Store values for later use in NEL report generation.
  request_method_ = request_->method;
  request_->extra_headers.GetHeader(HttpRequestHeaders::kReferer,
                                    &request_referrer_);
  request_->extra_headers.GetHeader(HttpRequestHeaders::kUserAgent,
                                    &request_user_agent_);
  request_reporting_upload_depth_ = request_->reporting_upload_depth;
#endif  // BUILDFLAG(ENABLE_REPORTING)
  start_timeticks_ = base::TimeTicks::Now();

  if (request_->load_flags & LOAD_DISABLE_CERT_NETWORK_FETCHES) {
    server_ssl_config_.disable_cert_verification_network_fetches = true;
    proxy_ssl_config_.disable_cert_verification_network_fetches = true;
  }

  if (request_->idempotency == IDEMPOTENT ||
      (request_->idempotency == DEFAULT_IDEMPOTENCY &&
       HttpUtil::IsMethodSafe(request_info->method))) {
    can_send_early_data_ = true;
  }

  if (request_->load_flags & LOAD_PREFETCH) {
    response_.unused_since_prefetch = true;
  }

  if (request_->load_flags & LOAD_RESTRICTED_PREFETCH) {
    DCHECK(response_.unused_since_prefetch);
    response_.restricted_prefetch = true;
  }

  next_state_ = STATE_NOTIFY_BEFORE_CREATE_STREAM;
  int rv = DoLoop(OK);
  if (rv == ERR_IO_PENDING)
    callback_ = std::move(callback);

  // This always returns ERR_IO_PENDING because DoCreateStream() does, but
  // GenerateNetworkErrorLoggingReportIfError() should be called here if any
  // other net::Error can be returned.
  DCHECK_EQ(rv, ERR_IO_PENDING);
  return rv;
}