zlib 压缩，为什么不能用gzip解压？解决思路

/*
00480 ZEXTERN int ZEXPORT deflateInit2 OF((z_streamp strm,
00481                                      int  level,
00482                                      int  method,
00483                                      int  windowBits,
00484                                      int  memLevel,
00485                                      int  strategy));
00486 
00487      This is another version of deflateInit with more compression options. The
00488    fields next_in, zalloc, zfree and opaque must be initialized before by
00489    the caller.
00490 
00491      The method parameter is the compression method. It must be Z_DEFLATED in
00492    this version of the library.
00493 
00494      The windowBits parameter is the base two logarithm of the window size
00495    (the size of the history buffer). It should be in the range 8..15 for this
00496    version of the library. Larger values of this parameter result in better
00497    compression at the expense of memory usage. The default value is 15 if
00498    deflateInit is used instead.
00499 
00500      windowBits can also be -8..-15 for raw deflate. In this case, -windowBits
00501    determines the window size. deflate() will then generate raw deflate data
00502    with no zlib header or trailer, and will not compute an adler32 check value.
00503 
00504      windowBits can also be greater than 15 for optional gzip encoding. Add
00505    16 to windowBits to write a simple gzip header and trailer around the
00506    compressed data instead of a zlib wrapper. The gzip header will have no
00507    file name, no extra data, no comment, no modification time (set to zero),
00508    no header crc, and the operating system will be set to 255 (unknown).  If a
00509    gzip stream is being written, strm->adler is a crc32 instead of an adler32.
00510 
00511      The memLevel parameter specifies how much memory should be allocated
00512    for the internal compression state. memLevel=1 uses minimum memory but
00513    is slow and reduces compression ratio; memLevel=9 uses maximum memory
00514    for optimal speed. The default value is 8. See zconf.h for total memory
00515    usage as a function of windowBits and memLevel.
00516 
00517      The strategy parameter is used to tune the compression algorithm. Use the
00518    value Z_DEFAULT_STRATEGY for normal data, Z_FILTERED for data produced by a
00519    filter (or predictor), Z_HUFFMAN_ONLY to force Huffman encoding only (no
00520    string match), or Z_RLE to limit match distances to one (run-length
00521    encoding). Filtered data consists mostly of small values with a somewhat
00522    random distribution. In this case, the compression algorithm is tuned to
00523    compress them better. The effect of Z_FILTERED is to force more Huffman
00524    coding and less string matching; it is somewhat intermediate between
00525    Z_DEFAULT and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as fast as
00526    Z_HUFFMAN_ONLY, but give better compression for PNG image data. The strategy
00527    parameter only affects the compression ratio but not the correctness of the
00528    compressed output even if it is not set appropriately.  Z_FIXED prevents the
00529    use of dynamic Huffman codes, allowing for a simpler decoder for special
00530    applications.
00531 
00532       deflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
00533    memory, Z_STREAM_ERROR if a parameter is invalid (such as an invalid
00534    method). msg is set to null if there is no error message.  deflateInit2 does
00535    not perform any compression: this will be done by deflate().
00536 */