mfbt/Compression.h
author Jim Chen <nchen@mozilla.com>
Wed, 20 Jun 2018 16:46:20 -0400
changeset 423113 2806729c61eaac199ad4670788c4008079a99f34
parent 380562 35dcbab0bdbd7cdf7ecc33460390d9fe13672fd5
child 448947 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1469683 - 1. Fix crash tests; r=esawin Specify individual sessions in crash tests (i.e. "mainSession.waitUntilCalled" instead of "sessionRule.waitUntilCalled"), so that the tests assert behavior on the correct session, and not inadvertently on the cached session. Also, under x86 debug builds, Gecko installs an "ah_crap_handler" for SIGSEGV that waits for a long time, which causes our crash tests to time out. Therefore, ignore crash tests under x86 debug. MozReview-Commit-ID: DdtmRBLmPGp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Various simple compression/decompression functions. */

#ifndef mozilla_Compression_h_
#define mozilla_Compression_h_

#include "mozilla/Assertions.h"
#include "mozilla/Types.h"

namespace mozilla {
namespace Compression {

/**
 * LZ4 is a very fast byte-wise compression algorithm.
 *
 * Compared to Google's Snappy it is faster to compress and decompress and
 * generally produces output of about the same size.
 *
 * Compared to zlib it compresses at about 10x the speed, decompresses at about
 * 4x the speed and produces output of about 1.5x the size.
 */

class LZ4
{
public:
  /**
   * Compresses |aInputSize| bytes from |aSource| into |aDest|. Destination
   * buffer must be already allocated, and must be sized to handle worst cases
   * situations (input data not compressible). Worst case size evaluation is
   * provided by function maxCompressedSize()
   *
   * @param aInputSize is the input size. Max supported value is ~1.9GB
   * @return the number of bytes written in buffer |aDest|
   */
  static MFBT_API size_t
  compress(const char* aSource, size_t aInputSize, char* aDest);

  /**
   * Compress |aInputSize| bytes from |aSource| into an output buffer
   * |aDest| of maximum size |aMaxOutputSize|.  If it cannot achieve it,
   * compression will stop, and result of the function will be zero,
   * |aDest| will still be written to, but since the number of input
   * bytes consumed is not returned the result is not usable.
   *
   * This function never writes outside of provided output buffer.
   *
   * @param aInputSize is the input size. Max supported value is ~1.9GB
   * @param aMaxOutputSize is the size of the destination buffer (which must
   *   be already allocated)
   * @return the number of bytes written in buffer |aDest| or 0 if the
   *   compression fails
   */
  static MFBT_API size_t
  compressLimitedOutput(const char* aSource, size_t aInputSize, char* aDest,
                        size_t aMaxOutputSize);

  /**
   * If the source stream is malformed, the function will stop decoding
   * and return false.
   *
   * This function never writes outside of provided buffers, and never
   * modifies input buffer.
   *
   * Note: destination buffer must be already allocated, and its size must be a
   *       minimum of |aOutputSize| bytes.
   *
   * @param aOutputSize is the output size, therefore the original size
   * @return true on success, false on failure
   */
  static MFBT_API MOZ_MUST_USE bool
  decompress(const char* aSource, char* aDest, size_t aOutputSize);

  /**
   * If the source stream is malformed, the function will stop decoding
   * and return false.
   *
   * This function never writes beyond aDest + aMaxOutputSize, and is
   * therefore protected against malicious data packets.
   *
   * Note: Destination buffer must be already allocated.  This version is
   *       slightly slower than the decompress without the aMaxOutputSize.
   *
   * @param aInputSize is the length of the input compressed data
   * @param aMaxOutputSize is the size of the destination buffer (which must be
   *   already allocated)
   * @param aOutputSize the actual number of bytes decoded in the destination
   *   buffer (necessarily <= aMaxOutputSize)
   * @return true on success, false on failure
   */
  static MFBT_API MOZ_MUST_USE bool
  decompress(const char* aSource, size_t aInputSize, char* aDest,
             size_t aMaxOutputSize, size_t* aOutputSize);

  /**
   * If the source stream is malformed, the function will stop decoding
   * and return false.
   *
   * This function never writes beyond aDest + aMaxOutputSize, and is
   * therefore protected against malicious data packets. It also ignores
   * unconsumed input upon reaching aMaxOutputSize and can therefore be used
   * for partial decompression.
   *
   * Note: Destination buffer must be already allocated.  This version is
   *       slightly slower than the decompress without the aMaxOutputSize.
   *
   * @param aInputSize is the length of the input compressed data
   * @param aMaxOutputSize is the size of the destination buffer (which must be
   *   already allocated)
   * @param aOutputSize the actual number of bytes decoded in the destination
   *   buffer (necessarily <= aMaxOutputSize)
   * @return true on success, false on failure
   */
  static MFBT_API MOZ_MUST_USE bool
  decompressPartial(const char* aSource, size_t aInputSize, char* aDest,
                    size_t aMaxOutputSize, size_t* aOutputSize);

  /*
   * Provides the maximum size that LZ4 may output in a "worst case"
   * scenario (input data not compressible) primarily useful for memory
   * allocation of output buffer.
   * note : this function is limited by "int" range (2^31-1)
   *
   * @param aInputSize is the input size. Max supported value is ~1.9GB
   * @return maximum output size in a "worst case" scenario
   */
  static inline size_t maxCompressedSize(size_t aInputSize)
  {
    size_t max = (aInputSize + (aInputSize / 255) + 16);
    MOZ_ASSERT(max > aInputSize);
    return max;
  }
};

} /* namespace Compression */
} /* namespace mozilla */

#endif /* mozilla_Compression_h_ */