The Tor Browser: mfbt/Compression.h@97036ab72558

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

     1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* This Source Code Form is subject to the terms of the Mozilla Public

     3  * License, v. 2.0. If a copy of the MPL was not distributed with this

     4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     6 /* Various simple compression/decompression functions. */

     8 #ifndef mozilla_Compression_h_

     9 #define mozilla_Compression_h_

    11 #include "mozilla/Types.h"

    12 #include "mozilla/Assertions.h"

    14 namespace mozilla {

    15 namespace Compression {

    17 /**

    18  * LZ4 is a very fast byte-wise compression algorithm.

    19  *

    20  * Compared to Google's Snappy it is faster to compress and decompress and

    21  * generally produces output of about the same size.

    22  *

    23  * Compared to zlib it compresses at about 10x the speed, decompresses at about

    24  * 4x the speed and produces output of about 1.5x the size.

    25  *

    26  */

    28 class LZ4

    29 {

    31 public:

    33   /**

    34    * Compresses 'inputSize' bytes from 'source' into 'dest'.

    35    * Destination buffer must be already allocated,

    36    * and must be sized to handle worst cases situations (input data not compressible)

    37    * Worst case size evaluation is provided by function maxCompressedSize()

    38    *

    39    * @param inputSize is the input size. Max supported value is ~1.9GB

    40    * @param return the number of bytes written in buffer dest

    41    */

    42   static MFBT_API size_t compress(const char* source, size_t inputSize, char* dest);

    44   /**

    45    * Compress 'inputSize' bytes from 'source' into an output buffer

    46    * 'dest' of maximum size 'maxOutputSize'.  If it cannot achieve it,

    47    * compression will stop, and result of the function will be zero,

    48    * 'dest' will still be written to, but since the number of input

    49    * bytes consumed is not returned the result is not usable.

    50    *

    51    * This function never writes outside of provided output buffer.

    52    *

    53    * @param inputSize is the input size. Max supported value is ~1.9GB

    54    * @param maxOutputSize is the size of the destination buffer (which must be already allocated)

    55    * @return the number of bytes written in buffer 'dest'

    56              or 0 if the compression fails

    57   */

    58   static MFBT_API size_t compressLimitedOutput(const char* source, size_t inputSize, char* dest,

    59                                                size_t maxOutputSize);

    61   /**

    62    * If the source stream is malformed, the function will stop decoding

    63    * and return a negative result, indicating the byte position of the

    64    * faulty instruction

    65    *

    66    * This function never writes outside of provided buffers, and never

    67    * modifies input buffer.

    68    *

    69    * note : destination buffer must be already allocated.

    70    *        its size must be a minimum of 'outputSize' bytes.

    71    * @param outputSize is the output size, therefore the original size

    72    * @return the number of bytes read in the source buffer

    73   */

    74   static MFBT_API bool decompress(const char* source, char* dest, size_t outputSize);

    76   /**

    77    * If the source stream is malformed, the function will stop decoding

    78    * and return false.

    79    *

    80    * This function never writes beyond dest + maxOutputSize, and is

    81    * therefore protected against malicious data packets.

    82    *

    83    * note   : Destination buffer must be already allocated.

    84    *          This version is slightly slower than the decompress

    85    *          without the maxOutputSize

    86    *

    87    * @param inputSize is the length of the input compressed data

    88    * @param maxOutputSize is the size of the destination buffer (which must be already allocated)

    89    * @param outputSize the actual number of bytes decoded in the destination buffer (necessarily <= maxOutputSize)

    91   */

    92   static MFBT_API bool decompress(const char* source, size_t inputSize, char* dest,

    93                                   size_t maxOutputSize, size_t *outputSize);

    95   /*

    96     Provides the maximum size that LZ4 may output in a "worst case"

    97     scenario (input data not compressible) primarily useful for memory

    98     allocation of output buffer.

    99     note : this function is limited by "int" range (2^31-1)

   101     @param inputSize is the input size. Max supported value is ~1.9GB

   102     @return maximum output size in a "worst case" scenario

   103   */

   104   static inline size_t maxCompressedSize(size_t inputSize)

   105   {

   106       size_t max = ((inputSize) + ((inputSize)/255) + 16);

   107       MOZ_ASSERT(max > inputSize);

   108       return max;

   109   }

   111 };

   113 } /* namespace Compression */

   114 } /* namespace mozilla */

   116 #endif /* mozilla_Compression_h_ */

The Tor Browser / file revision

mfbt/Compression.h@97036ab72558

mfbt/Compression.h