pagespeed/kernel/base/hasher.h

/*
 * 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.
 */

//
// Interface for a hash function.

#ifndef PAGESPEED_KERNEL_BASE_HASHER_H_
#define PAGESPEED_KERNEL_BASE_HASHER_H_

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

namespace net_instaweb {

class Hasher {
 public:
  // The passed in max_chars will be used to limit the length of
  // Hash() and HashSizeInChars()
  explicit Hasher(int max_chars);
  virtual ~Hasher();

  // Computes a web64-encoded hash of a single string.  This
  // operation is thread-safe.
  //
  // This is implemented in terms of RawHash, and honors the length limit
  // passed in to the constructor.
  GoogleString Hash(const StringPiece& content) const;

  // Return string length of hashes produced by this hasher's Hash
  // method.
  //
  // This is implemented in terms of RawHashSizeInBytes() and the length limit
  // passed in to the constructor.
  int HashSizeInChars() const;

  // Uses first 64-bits of hash to make a uint64 version of hash.
  uint64 HashToUint64(const StringPiece& content) const;

  // Computes a binary hash of the given content. The returned value
  // is not printable as it is the direct binary encoding of the hash.
  // This operation is thread-safe.
  virtual GoogleString RawHash(const StringPiece& content) const = 0;

  // The number of bytes RawHash will produce.
  virtual int RawHashSizeInBytes() const = 0;

 private:
  int max_chars_;  // limit on length of Hash/HashSizeInChars set by subclass.

  DISALLOW_COPY_AND_ASSIGN(Hasher);
};

}  // namespace net_instaweb

#endif  // PAGESPEED_KERNEL_BASE_HASHER_H_