Support gzip in folly/io:compression

Summary: gzip files can be easier to work with operationally than raw zlib thanks to gzip+gunzip.  zlib supports adding/stripping the gzip header; expose that through a new CodecType.

Reviewed By: chipturner

Differential Revision: D2759554

fb-gh-sync-id: 67e0f5f88e087d363db1c349cabb909fb3f00417

folly/io/Compression.cpp

@@ -469,7 +469,7 @@ std::unique_ptr<Codec> ZlibCodec::create(int level, CodecType type) {
 }
 
 ZlibCodec::ZlibCodec(int level, CodecType type) : Codec(type) {
-  DCHECK(type == CodecType::ZLIB);
+  DCHECK(type == CodecType::ZLIB || type == CodecType::GZIP);
   switch (level) {
   case COMPRESSION_LEVEL_FASTEST:
     level = 1;
@@ -534,7 +534,22 @@ std::unique_ptr<IOBuf> ZlibCodec::doCompress(const IOBuf* data) {
   stream.zfree = nullptr;
   stream.opaque = nullptr;
 
-  int rc = deflateInit(&stream, level_);
+  // Using deflateInit2() to support gzip.  "The windowBits parameter is the
+  // base two logarithm of the maximum window size (...) The default value is
+  // 15 (...) Add 16 to windowBits to write a simple gzip header and trailer
+  // around the compressed data instead of a zlib wrapper. The gzip header
+  // will have no file name, no extra data, no comment, no modification time
+  // (set to zero), no header crc, and the operating system will be set to 255
+  // (unknown)."
+  int windowBits = 15 + (type() == CodecType::GZIP ? 16 : 0);
+  // All other parameters (method, memLevel, strategy) get default values from
+  // the zlib manual.
+  int rc = deflateInit2(&stream,
+                        level_,
+                        Z_DEFLATED,
+                        windowBits,
+                        /* memLevel */ 8,
+                        Z_DEFAULT_STRATEGY);
   if (rc != Z_OK) {
     throw std::runtime_error(to<std::string>(
         "ZlibCodec: deflateInit error: ", rc, ": ", stream.msg));
@@ -614,7 +629,11 @@ std::unique_ptr<IOBuf> ZlibCodec::doUncompress(const IOBuf* data,
   stream.zfree = nullptr;
   stream.opaque = nullptr;
 
-  int rc = inflateInit(&stream);
+  // "The windowBits parameter is the base two logarithm of the maximum window
+  // size (...) The default value is 15 (...) add 16 to decode only the gzip
+  // format (the zlib format will return a Z_DATA_ERROR)."
+  int windowBits = 15 + (type() == CodecType::GZIP ? 16 : 0);
+  int rc = inflateInit2(&stream, windowBits);
   if (rc != Z_OK) {
     throw std::runtime_error(to<std::string>(
         "ZlibCodec: inflateInit error: ", rc, ": ", stream.msg));
@@ -1063,6 +1082,12 @@ std::unique_ptr<Codec> getCodec(CodecType type, int level) {
 #else
     nullptr,
 #endif
+
+#if FOLLY_HAVE_LIBZ
+    ZlibCodec::create,
+#else
+    nullptr,
+#endif
   };
 
   size_t idx = static_cast<size_t>(type);

folly/io/Compression.h

@@ -80,7 +80,14 @@ enum class CodecType {
    */
   ZSTD_BETA = 8,
 
-  NUM_CODEC_TYPES = 9,
+  /**
+   * Use gzip compression.  This is the same compression algorithm as ZLIB but
+   * gzip-compressed files tend to be easier to work with from the command line.
+   * Levels supported: 0 = no compression, 1 = fast, ..., 9 = best; default = 6
+   */
+  GZIP = 9,
+
+  NUM_CODEC_TYPES = 10,
 };
 
 class Codec {

folly/io/test/CompressionTest.cpp

@@ -129,6 +129,7 @@ TEST(CompressionTestNeedsUncompressedLength, Simple) {
   EXPECT_FALSE(getCodec(CodecType::LZMA2_VARINT_SIZE)
     ->needsUncompressedLength());
   EXPECT_TRUE(getCodec(CodecType::ZSTD_BETA)->needsUncompressedLength());
+  EXPECT_FALSE(getCodec(CodecType::GZIP)->needsUncompressedLength());
 }
 
 class CompressionTest
@@ -182,7 +183,8 @@ INSTANTIATE_TEST_CASE_P(
                                      CodecType::LZ4_VARINT_SIZE,
                                      CodecType::LZMA2,
                                      CodecType::LZMA2_VARINT_SIZE,
-                                     CodecType::ZSTD_BETA)));
+                                     CodecType::ZSTD_BETA,
+                                     CodecType::GZIP)));
 
 class CompressionVarintTest
     : public testing::TestWithParam<std::tr1::tuple<int, CodecType>> {