components/metrics/compression_utils.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "components/metrics/compression_utils.h"
   6
   7 #include <vector>
   8
   9 #include "base/basictypes.h"
  10 #include "base/logging.h"
  11 #include "base/sys_byteorder.h"
  12 #include "third_party/zlib/zlib.h"
  13
  14 namespace {
  15
  16 // The difference in bytes between a zlib header and a gzip header.
  17 const size_t kGzipZlibHeaderDifferenceBytes = 16;
  18
  19 // Pass an integer greater than the following get a gzip header instead of a
  20 // zlib header when calling deflateInit2() and inflateInit2().
  21 const int kWindowBitsToGetGzipHeader = 16;
  22
  23 // This describes the amount of memory zlib uses to compress data. It can go
  24 // from 1 to 9, with 8 being the default. For details, see:
  25 // http://www.zlib.net/manual.html (search for memLevel).
  26 const int kZlibMemoryLevel = 8;
  27
  28 // This code is taken almost verbatim from third_party/zlib/compress.c. The only
  29 // difference is deflateInit2() is called which sets the window bits to be > 16.
  30 // That causes a gzip header to be emitted rather than a zlib header.
  31 int GzipCompressHelper(Bytef* dest,
  32                        uLongf* dest_length,
  33                        const Bytef* source,
  34                        uLong source_length) {
  35   z_stream stream;
  36
  37   stream.next_in = bit_cast<Bytef*>(source);
  38   stream.avail_in = static_cast<uInt>(source_length);
  39   stream.next_out = dest;
  40   stream.avail_out = static_cast<uInt>(*dest_length);
  41   if (static_cast<uLong>(stream.avail_out) != *dest_length)
  42     return Z_BUF_ERROR;
  43
  44   stream.zalloc = static_cast<alloc_func>(0);
  45   stream.zfree = static_cast<free_func>(0);
  46   stream.opaque = static_cast<voidpf>(0);
  47
  48   gz_header gzip_header;
  49   memset(&gzip_header, 0, sizeof(gzip_header));
  50   int err = deflateInit2(&stream,
  51                          Z_DEFAULT_COMPRESSION,
  52                          Z_DEFLATED,
  53                          MAX_WBITS + kWindowBitsToGetGzipHeader,
  54                          kZlibMemoryLevel,
  55                          Z_DEFAULT_STRATEGY);
  56   if (err != Z_OK)
  57     return err;
  58
  59   err = deflateSetHeader(&stream, &gzip_header);
  60   if (err != Z_OK)
  61     return err;
  62
  63   err = deflate(&stream, Z_FINISH);
  64   if (err != Z_STREAM_END) {
  65     deflateEnd(&stream);
  66     return err == Z_OK ? Z_BUF_ERROR : err;
  67   }
  68   *dest_length = stream.total_out;
  69
  70   err = deflateEnd(&stream);
  71   return err;
  72 }
  73
  74 // This code is taken almost verbatim from third_party/zlib/uncompr.c. The only
  75 // difference is inflateInit2() is called which sets the window bits to be > 16.
  76 // That causes a gzip header to be parsed rather than a zlib header.
  77 int GzipUncompressHelper(Bytef* dest,
  78                          uLongf* dest_length,
  79                          const Bytef* source,
  80                          uLong source_length) {
  81   z_stream stream;
  82
  83   stream.next_in = bit_cast<Bytef*>(source);
  84   stream.avail_in = static_cast<uInt>(source_length);
  85   if (static_cast<uLong>(stream.avail_in) != source_length)
  86     return Z_BUF_ERROR;
  87
  88   stream.next_out = dest;
  89   stream.avail_out = static_cast<uInt>(*dest_length);
  90   if (static_cast<uLong>(stream.avail_out) != *dest_length)
  91     return Z_BUF_ERROR;
  92
  93   stream.zalloc = static_cast<alloc_func>(0);
  94   stream.zfree = static_cast<free_func>(0);
  95
  96   int err = inflateInit2(&stream, MAX_WBITS + kWindowBitsToGetGzipHeader);
  97   if (err != Z_OK)
  98     return err;
  99
 100   err = inflate(&stream, Z_FINISH);
 101   if (err != Z_STREAM_END) {
 102     inflateEnd(&stream);
 103     if (err == Z_NEED_DICT || (err == Z_BUF_ERROR && stream.avail_in == 0))
 104       return Z_DATA_ERROR;
 105     return err;
 106   }
 107   *dest_length = stream.total_out;
 108
 109   err = inflateEnd(&stream);
 110   return err;
 111 }
 112
 113 // Returns the uncompressed size from GZIP-compressed |compressed_data|.
 114 uint32 GetUncompressedSize(const std::string& compressed_data) {
 115   // The uncompressed size is stored in the last 4 bytes of |input| in LE.
 116   uint32 size;
 117   if (compressed_data.length() < sizeof(size))
 118     return 0;
 119   memcpy(&size, &compressed_data[compressed_data.length() - sizeof(size)],
 120          sizeof(size));
 121   return base::ByteSwapToLE32(size);
 122 }
 123
 124 }  // namespace
 125
 126 namespace metrics {
 127
 128 bool GzipCompress(const std::string& input, std::string* output) {
 129   const uLongf input_size = static_cast<uLongf>(input.size());
 130   std::vector<Bytef> compressed_data(kGzipZlibHeaderDifferenceBytes +
 131                                      compressBound(input_size));
 132
 133   uLongf compressed_size = static_cast<uLongf>(compressed_data.size());
 134   if (GzipCompressHelper(&compressed_data.front(),
 135                          &compressed_size,
 136                          bit_cast<const Bytef*>(input.data()),
 137                          input_size) != Z_OK) {
 138     return false;
 139   }
 140
 141   compressed_data.resize(compressed_size);
 142   output->assign(compressed_data.begin(), compressed_data.end());
 143   DCHECK_EQ(input.size(), GetUncompressedSize(*output));
 144   return true;
 145 }
 146
 147 bool GzipUncompress(const std::string& input, std::string* output) {
 148   output->resize(GetUncompressedSize(input));
 149   uLongf uncompressed_size = static_cast<uLongf>(output->length());
 150   return GzipUncompressHelper(bit_cast<Bytef*>(output->data()),
 151                               &uncompressed_size,
 152                               bit_cast<const Bytef*>(input.data()),
 153                               static_cast<uLongf>(input.length())) == Z_OK;
 154 }
 155
 156 }  // namespace metrics