pagespeed/automatic/html_detector.cc

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

//         sligocki@google.com (Shawn Ligocki)
//
// This contains HtmlDetector, which tries to heuristically guess whether
// content a server claims to be HTML actually is HTML (it sometimes isn't).

#include "pagespeed/automatic/html_detector.h"

#include "pagespeed/kernel/base/string.h"
#include "pagespeed/kernel/base/string_util.h"

namespace net_instaweb {

HtmlDetector::HtmlDetector() : already_decided_(false), probable_html_(false) {
}

HtmlDetector::~HtmlDetector() {
}

bool HtmlDetector::ConsiderInput(const StringPiece& data) {
  DCHECK(!already_decided_);

  for (int i = 0, n = data.size(); i < n; ++i) {
    unsigned char c = static_cast<unsigned char>(data[i]);
    switch (c) {
      // Ignore all leading whitespace and byte order markers.
      // See http://en.wikipedia.org/wiki/Byte_order_mark
      // Note: This test allows arbitrary orderings and combinations of the
      // byte order markers, but we do not expect many false positives.
      case ' ':
      case '\t':
      case '\n':
      case '\r':
      case 0xef:
      case 0xbb:
      case 0xbf: {
        break;
      }
      // If the first non-whitespace, non-BOM char is <, we are content that
      // this is HTML.
      case '<': {
        already_decided_ = true;
        probable_html_ = true;
        return true;
      }
      // Similarly, if it's something else, it probably isn't.
      default: {
        already_decided_ = true;
        probable_html_ = false;
        return true;
      }
    }
  }

  // Looks like we managed to get entirely whitespace --- buffer it up.
  StrAppend(&buffer_, data);

  return false;
}

void HtmlDetector::ReleaseBuffered(GoogleString* out_buffer) {
  buffer_.swap(*out_buffer);
  buffer_.clear();
}

void HtmlDetector::ForceDecision(bool is_html) {
  DCHECK(!already_decided_);
  already_decided_ = true;
  probable_html_ = is_html;
}

}  // namespace net_instaweb