/* zlib.h -- interface of the 'zlib' general purpose compression library
  version 1.2.3, July 18th, 2005

  Copyright (C) 1995-2005 Jean-loup Gailly and Mark Adler

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Jean-loup Gailly        Mark Adler
  jloup@gzip.org          madler@alumni.caltech.edu


  The data format used by the zlib library is described by RFCs (Request for
  Comments) 1950 to 1952 in the files http://www.ietf.org/rfc/rfc1950.txt
  (zlib format), rfc1951.txt (deflate format) and rfc1952.txt (gzip format).
*/

module tango.util.compress.c.zlib;

extern (C):

enum immutable(char)* ZLIB_VERSION = "1.2.3".ptr;
enum uint  ZLIB_VERNUM  = 0x1230;

/*
     The 'zlib' compression library provides in-memory compression and
  decompression functions, including integrity checks of the uncompressed
  data.  This version of the library supports only one compression method
  (deflation) but other algorithms will be added later and will have the same
  stream interface.

     Compression can be done in a single step if the buffers are large
  enough (for example if an input file is mmap'ed), or can be done by
  repeated calls of the compression function.  In the latter case, the
  application must provide more input and/or consume the output
  (providing more output space) before each call.

     The compressed data format used by default by the in-memory functions is
  the zlib format, which is a zlib wrapper documented in RFC 1950, wrapped
  around a deflate stream, which is itself documented in RFC 1951.

     The library also supports reading and writing files in gzip (.gz) format
  with an interface similar to that of stdio using the functions that start
  with "gz".  The gzip format is different from the zlib format.  gzip is a
  gzip wrapper, documented in RFC 1952, wrapped around a deflate stream.

     This library can optionally read and write gzip streams in memory as well.

     The zlib format was designed to be compact and fast for use in memory
  and on communications channels.  The gzip format was designed for single-
  file compression on file systems, has a larger header than zlib to maintain
  directory information, and uses a different, slower check method than zlib.

     The library does not install any signal handler. The decoder checks
  the consistency of the compressed data, so the library should never
  crash even in case of corrupted input.
*/

private
{
    import tango.stdc.config : c_long, c_ulong;

    version( Posix )
    {
        import tango.stdc.posix.sys.types : z_off_t = off_t;
    }
    else
    {
        alias c_long z_off_t;
    }

    alias ubyte     Byte;
    alias uint      uInt;
    alias c_ulong   uLong;

    alias Byte      Bytef;
    alias char      charf;
    alias int       intf;
    alias uInt      uIntf;
    alias uLong     uLongf;

    alias void*     voidpc; // TODO: normally const
    alias void*     voidpf;
    alias void*     voidp;

    alias voidpf function(voidpf opaque, uInt items, uInt size) alloc_func;
    alias void   function(voidpf opaque, voidpf address)        free_func;

    struct internal_state {}
}

struct z_stream
{
    Bytef*          next_in;   /* next input byte */
    uInt            avail_in;  /* number of bytes available at next_in */
    uLong           total_in;  /* total nb of input bytes read so far */

    Bytef*          next_out;  /* next output byte should be put there */
    uInt            avail_out; /* remaining free space at next_out */
    uLong           total_out; /* total nb of bytes output so far */

    char*           msg;       /* last error message, NULL if no error */
    internal_state* state;     /* not visible by applications */

    alloc_func      zalloc;    /* used to allocate the internal state */
    free_func       zfree;     /* used to free the internal state */
    voidpf          opaque;    /* private data object passed to zalloc and zfree */

    int             data_type; /* best guess about the data type: binary or text */
    uLong           adler;     /* adler32 value of the uncompressed data */
    uLong           reserved;  /* reserved for future use */
}

alias z_stream* z_streamp;

/*
     gzip header information passed to and from zlib routines.  See RFC 1952
  for more details on the meanings of these fields.
*/
struct gz_header
{
    int     text;       /* true if compressed data believed to be text */
    uLong   time;       /* modification time */
    int     xflags;     /* extra flags (not used when writing a gzip file) */
    int     os;         /* operating system */
    Bytef*  extra;      /* pointer to extra field or Z_NULL if none */
    uInt    extra_len;  /* extra field length (valid if extra != Z_NULL) */
    uInt    extra_max;  /* space at extra (only when reading header) */
    Bytef*  name;       /* pointer to zero-terminated file name or Z_NULL */
    uInt    name_max;   /* space at name (only when reading header) */
    Bytef*  comment;    /* pointer to zero-terminated comment or Z_NULL */
    uInt    comm_max;   /* space at comment (only when reading header) */
    int     hcrc;       /* true if there was or will be a header crc */
    int     done;       /* true when done reading gzip header (not used
                           when writing a gzip file) */
}

alias gz_header* gz_headerp;

/*
   The application must update next_in and avail_in when avail_in has
   dropped to zero. It must update next_out and avail_out when avail_out
   has dropped to zero. The application must initialize zalloc, zfree and
   opaque before calling the init function. All other fields are set by the
   compression library and must not be updated by the application.

   The opaque value provided by the application will be passed as the first
   parameter for calls of zalloc and zfree. This can be useful for custom
   memory management. The compression library attaches no meaning to the
   opaque value.

   zalloc must return Z_NULL if there is not enough memory for the object.
   If zlib is used in a multi-threaded application, zalloc and zfree must be
   thread safe.

   On 16-bit systems, the functions zalloc and zfree must be able to allocate
   exactly 65536 bytes, but will not be required to allocate more than this
   if the symbol MAXSEG_64K is defined (see zconf.h). WARNING: On MSDOS,
   pointers returned by zalloc for objects of exactly 65536 bytes *must*
   have their offset normalized to zero. The default allocation function
   provided by this library ensures this (see zutil.c). To reduce memory
   requirements and avoid any allocation of 64K objects, at the expense of
   compression ratio, compile the library with -DMAX_WBITS=14 (see zconf.h).

   The fields total_in and total_out can be used for statistics or
   progress reports. After compression, total_in holds the total size of
   the uncompressed data and may be saved for use in the decompressor
   (particularly if the decompressor wants to decompress everything in
   a single step).
*/

                        /* constants */

enum
{
    Z_NO_FLUSH      = 0,
    Z_PARTIAL_FLUSH = 1, /* will be removed, use Z_SYNC_FLUSH instead */
    Z_SYNC_FLUSH    = 2,
    Z_FULL_FLUSH    = 3,
    Z_FINISH        = 4,
    Z_BLOCK         = 5,
}
/* Allowed flush values; see deflate() and inflate() below for details */

enum
{
    Z_OK            = 0,
    Z_STREAM_END    = 1,
    Z_NEED_DICT     = 2,
    Z_ERRNO         = -1,
    Z_STREAM_ERROR  = -2,
    Z_DATA_ERROR    = -3,
    Z_MEM_ERROR     = -4,
    Z_BUF_ERROR     = -5,
    Z_VERSION_ERROR = -6,
}
/* Return codes for the compression/decompression functions. Negative
 * values are errors, positive values are used for special but normal events.
 */

enum
{
    Z_NO_COMPRESSION      = 0,
    Z_BEST_SPEED          = 1,
    Z_BEST_COMPRESSION    = 9,
    Z_DEFAULT_COMPRESSION = -1,
}
/* compression levels */

enum
{
    Z_FILTERED            = 1,
    Z_HUFFMAN_ONLY        = 2,
    Z_RLE                 = 3,
    Z_FIXED               = 4,
    Z_DEFAULT_STRATEGY    = 0,
}
/* compression strategy; see deflateInit2() below for details */

enum
{
    Z_BINARY   = 0,
    Z_TEXT     = 1,
    Z_ASCII    = Z_TEXT,  /* for compatibility with 1.2.2 and earlier */
    Z_UNKNOWN  = 2,
}
/* Possible values of the data_type field (though see inflate()) */

enum
{
    Z_DEFLATED = 8,
}
/* The deflate compression method (the only one supported in this version) */

enum Z_NULL = null;    /* for initializing zalloc, zfree, opaque */

alias zlibVersion zlib_version;
/* for compatibility with versions < 1.0.2 */

                        /* basic functions */

const(char)* zlibVersion();
/* The application can compare zlibVersion and ZLIB_VERSION for consistency.
   If the first character differs, the library code actually used is
   not compatible with the zlib.h header file used by the application.
   This check is automatically made by deflateInit and inflateInit.
 */

/*
int deflateInit (z_streamp strm, int level);

     Initializes the internal stream state for compression. The fields
   zalloc, zfree and opaque must be initialized before by the caller.
   If zalloc and zfree are set to Z_NULL, deflateInit updates them to
   use default allocation functions.

     The compression level must be Z_DEFAULT_COMPRESSION, or between 0 and 9:
   1 gives best speed, 9 gives best compression, 0 gives no compression at
   all (the input data is simply copied a block at a time).
   Z_DEFAULT_COMPRESSION requests a default compromise between speed and
   compression (currently equivalent to level 6).

     deflateInit returns Z_OK if success, Z_MEM_ERROR if there was not
   enough memory, Z_STREAM_ERROR if level is not a valid compression level,
   Z_VERSION_ERROR if the zlib library version (zlib_version) is incompatible
   with the version assumed by the caller (ZLIB_VERSION).
   msg is set to null if there is no error message.  deflateInit does not
   perform any compression: this will be done by deflate().
*/


int deflate(z_streamp strm, int flush);
/*
    deflate compresses as much data as possible, and stops when the input
  buffer becomes empty or the output buffer becomes full. It may introduce some
  output latency (reading input without producing any output) except when
  forced to flush.

    The detailed semantics are as follows. deflate performs one or both of the
  following actions:

  - Compress more input starting at next_in and update next_in and avail_in
    accordingly. If not all input can be processed (because there is not
    enough room in the output buffer), next_in and avail_in are updated and
    processing will resume at this point for the next call of deflate().

  - Provide more output starting at next_out and update next_out and avail_out
    accordingly. This action is forced if the parameter flush is non zero.
    Forcing flush frequently degrades the compression ratio, so this parameter
    should be set only when necessary (in interactive applications).
    Some output may be provided even if flush is not set.

  Before the call of deflate(), the application should ensure that at least
  one of the actions is possible, by providing more input and/or consuming
  more output, and updating avail_in or avail_out accordingly; avail_out
  should never be zero before the call. The application can consume the
  compressed output when it wants, for example when the output buffer is full
  (avail_out == 0), or after each call of deflate(). If deflate returns Z_OK
  and with zero avail_out, it must be called again after making room in the
  output buffer because there might be more output pending.

    Normally the parameter flush is set to Z_NO_FLUSH, which allows deflate to
  decide how much data to accumualte before producing output, in order to
  maximize compression.

    If the parameter flush is set to Z_SYNC_FLUSH, all pending output is
  flushed to the output buffer and the output is aligned on a byte boundary, so
  that the decompressor can get all input data available so far. (In particular
  avail_in is zero after the call if enough output space has been provided
  before the call.)  Flushing may degrade compression for some compression
  algorithms and so it should be used only when necessary.

    If flush is set to Z_FULL_FLUSH, all output is flushed as with
  Z_SYNC_FLUSH, and the compression state is reset so that decompression can
  restart from this point if previous compressed data has been damaged or if
  random access is desired. Using Z_FULL_FLUSH too often can seriously degrade
  compression.

    If deflate returns with avail_out == 0, this function must be called again
  with the same value of the flush parameter and more output space (updated
  avail_out), until the flush is complete (deflate returns with non-zero
  avail_out). In the case of a Z_FULL_FLUSH or Z_SYNC_FLUSH, make sure that
  avail_out is greater than six to avoid repeated flush markers due to
  avail_out == 0 on return.

    If the parameter flush is set to Z_FINISH, pending input is processed,
  pending output is flushed and deflate returns with Z_STREAM_END if there
  was enough output space; if deflate returns with Z_OK, this function must be
  called again with Z_FINISH and more output space (updated avail_out) but no
  more input data, until it returns with Z_STREAM_END or an error. After
  deflate has returned Z_STREAM_END, the only possible operations on the
  stream are deflateReset or deflateEnd.

    Z_FINISH can be used immediately after deflateInit if all the compression
  is to be done in a single step. In this case, avail_out must be at least
  the value returned by deflateBound (see below). If deflate does not return
  Z_STREAM_END, then it must be called again as described above.

    deflate() sets strm->adler to the adler32 checksum of all input read
  so far (that is, total_in bytes).

    deflate() may update strm->data_type if it can make a good guess about
  the input data type (Z_BINARY or Z_TEXT). In doubt, the data is considered
  binary. This field is only for information purposes and does not affect
  the compression algorithm in any manner.

    deflate() returns Z_OK if some progress has been made (more input
  processed or more output produced), Z_STREAM_END if all input has been
  consumed and all output has been produced (only when flush is set to
  Z_FINISH), Z_STREAM_ERROR if the stream state was inconsistent (for example
  if next_in or next_out was NULL), Z_BUF_ERROR if no progress is possible
  (for example avail_in or avail_out was zero). Note that Z_BUF_ERROR is not
  fatal, and deflate() can be called again with more input and more output
  space to continue compressing.
*/


int deflateEnd(z_streamp strm);
/*
     All dynamically allocated data structures for this stream are freed.
   This function discards any unprocessed input and does not flush any
   pending output.

     deflateEnd returns Z_OK if success, Z_STREAM_ERROR if the
   stream state was inconsistent, Z_DATA_ERROR if the stream was freed
   prematurely (some input or output was discarded). In the error case,
   msg may be set but then points to a static string (which must not be
   deallocated).
*/


/*
int inflateInit(z_streamp strm);

     Initializes the internal stream state for decompression. The fields
   next_in, avail_in, zalloc, zfree and opaque must be initialized before by
   the caller. If next_in is not Z_NULL and avail_in is large enough (the exact
   value depends on the compression method), inflateInit determines the
   compression method from the zlib header and allocates all data structures
   accordingly; otherwise the allocation will be deferred to the first call of
   inflate.  If zalloc and zfree are set to Z_NULL, inflateInit updates them to
   use default allocation functions.

     inflateInit returns Z_OK if success, Z_MEM_ERROR if there was not enough
   memory, Z_VERSION_ERROR if the zlib library version is incompatible with the
   version assumed by the caller.  msg is set to null if there is no error
   message. inflateInit does not perform any decompression apart from reading
   the zlib header if present: this will be done by inflate().  (So next_in and
   avail_in may be modified, but next_out and avail_out are unchanged.)
*/


int inflate(z_streamp strm, int flush);
/*
    inflate decompresses as much data as possible, and stops when the input
  buffer becomes empty or the output buffer becomes full. It may introduce
  some output latency (reading input without producing any output) except when
  forced to flush.

  The detailed semantics are as follows. inflate performs one or both of the
  following actions:

  - Decompress more input starting at next_in and update next_in and avail_in
    accordingly. If not all input can be processed (because there is not
    enough room in the output buffer), next_in is updated and processing
    will resume at this point for the next call of inflate().

  - Provide more output starting at next_out and update next_out and avail_out
    accordingly.  inflate() provides as much output as possible, until there
    is no more input data or no more space in the output buffer (see below
    about the flush parameter).

  Before the call of inflate(), the application should ensure that at least
  one of the actions is possible, by providing more input and/or consuming
  more output, and updating the next_* and avail_* values accordingly.
  The application can consume the uncompressed output when it wants, for
  example when the output buffer is full (avail_out == 0), or after each
  call of inflate(). If inflate returns Z_OK and with zero avail_out, it
  must be called again after making room in the output buffer because there
  might be more output pending.

    The flush parameter of inflate() can be Z_NO_FLUSH, Z_SYNC_FLUSH,
  Z_FINISH, or Z_BLOCK. Z_SYNC_FLUSH requests that inflate() flush as much
  output as possible to the output buffer. Z_BLOCK requests that inflate() stop
  if and when it gets to the next deflate block boundary. When decoding the
  zlib or gzip format, this will cause inflate() to return immediately after
  the header and before the first block. When doing a raw inflate, inflate()
  will go ahead and process the first block, and will return when it gets to
  the end of that block, or when it runs out of data.

    The Z_BLOCK option assists in appending to or combining deflate streams.
  Also to assist in this, on return inflate() will set strm->data_type to the
  number of unused bits in the last byte taken from strm->next_in, plus 64
  if inflate() is currently decoding the last block in the deflate stream,
  plus 128 if inflate() returned immediately after decoding an end-of-block
  code or decoding the complete header up to just before the first byte of the
  deflate stream. The end-of-block will not be indicated until all of the
  uncompressed data from that block has been written to strm->next_out.  The
  number of unused bits may in general be greater than seven, except when
  bit 7 of data_type is set, in which case the number of unused bits will be
  less than eight.

    inflate() should normally be called until it returns Z_STREAM_END or an
  error. However if all decompression is to be performed in a single step
  (a single call of inflate), the parameter flush should be set to
  Z_FINISH. In this case all pending input is processed and all pending
  output is flushed; avail_out must be large enough to hold all the
  uncompressed data. (The size of the uncompressed data may have been saved
  by the compressor for this purpose.) The next operation on this stream must
  be inflateEnd to deallocate the decompression state. The use of Z_FINISH
  is never required, but can be used to inform inflate that a faster approach
  may be used for the single inflate() call.

     In this implementation, inflate() always flushes as much output as
  possible to the output buffer, and always uses the faster approach on the
  first call. So the only effect of the flush parameter in this implementation
  is on the return value of inflate(), as noted below, or when it returns early
  because Z_BLOCK is used.

     If a preset dictionary is needed after this call (see inflateSetDictionary
  below), inflate sets strm->adler to the adler32 checksum of the dictionary
  chosen by the compressor and returns Z_NEED_DICT; otherwise it sets
  strm->adler to the adler32 checksum of all output produced so far (that is,
  total_out bytes) and returns Z_OK, Z_STREAM_END or an error code as described
  below. At the end of the stream, inflate() checks that its computed adler32
  checksum is equal to that saved by the compressor and returns Z_STREAM_END
  only if the checksum is correct.

    inflate() will decompress and check either zlib-wrapped or gzip-wrapped
  deflate data.  The header type is detected automatically.  Any information
  contained in the gzip header is not retained, so applications that need that
  information should instead use raw inflate, see inflateInit2() below, or
  inflateBack() and perform their own processing of the gzip header and
  trailer.

    inflate() returns Z_OK if some progress has been made (more input processed
  or more output produced), Z_STREAM_END if the end of the compressed data has
  been reached and all uncompressed output has been produced, Z_NEED_DICT if a
  preset dictionary is needed at this point, Z_DATA_ERROR if the input data was
  corrupted (input stream not conforming to the zlib format or incorrect check
  value), Z_STREAM_ERROR if the stream structure was inconsistent (for example
  if next_in or next_out was NULL), Z_MEM_ERROR if there was not enough memory,
  Z_BUF_ERROR if no progress is possible or if there was not enough room in the
  output buffer when Z_FINISH is used. Note that Z_BUF_ERROR is not fatal, and
  inflate() can be called again with more input and more output space to
  continue decompressing. If Z_DATA_ERROR is returned, the application may then
  call inflateSync() to look for a good compression block if a partial recovery
  of the data is desired.
*/


int inflateEnd(z_streamp strm);
/*
     All dynamically allocated data structures for this stream are freed.
   This function discards any unprocessed input and does not flush any
   pending output.

     inflateEnd returns Z_OK if success, Z_STREAM_ERROR if the stream state
   was inconsistent. In the error case, msg may be set but then points to a
   static string (which must not be deallocated).
*/

                        /* Advanced functions */

/*
    The following functions are needed only in some special applications.
*/

/*
int deflateInit2 (z_streamp strm,
                                  int       level,
                                  int       method,
                                  int       windowBits,
                                  int       memLevel,
                                  int       strategy);

     This is another version of deflateInit with more compression options. The
   fields next_in, zalloc, zfree and opaque must be initialized before by
   the caller.

     The method parameter is the compression method. It must be Z_DEFLATED in
   this version of the library.

     The windowBits parameter is the base two logarithm of the window size
   (the size of the history buffer). It should be in the range 8..15 for this
   version of the library. Larger values of this parameter result in better
   compression at the expense of memory usage. The default value is 15 if
   deflateInit is used instead.

     windowBits can also be -8..-15 for raw deflate. In this case, -windowBits
   determines the window size. deflate() will then generate raw deflate data
   with no zlib header or trailer, and will not compute an adler32 check value.

     windowBits can also be greater than 15 for optional gzip encoding. 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).  If a
   gzip stream is being written, strm->adler is a crc32 instead of an adler32.

     The memLevel parameter specifies how much memory should be allocated
   for the internal compression state. memLevel=1 uses minimum memory but
   is slow and reduces compression ratio; memLevel=9 uses maximum memory
   for optimal speed. The default value is 8. See zconf.h for total memory
   usage as a function of windowBits and memLevel.

     The strategy parameter is used to tune the compression algorithm. Use the
   value Z_DEFAULT_STRATEGY for normal data, Z_FILTERED for data produced by a
   filter (or predictor), Z_HUFFMAN_ONLY to force Huffman encoding only (no
   string match), or Z_RLE to limit match distances to one (run-length
   encoding). Filtered data consists mostly of small values with a somewhat
   random distribution. In this case, the compression algorithm is tuned to
   compress them better. The effect of Z_FILTERED is to force more Huffman
   coding and less string matching; it is somewhat intermediate between
   Z_DEFAULT and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as fast as
   Z_HUFFMAN_ONLY, but give better compression for PNG image data. The strategy
   parameter only affects the compression ratio but not the correctness of the
   compressed output even if it is not set appropriately.  Z_FIXED prevents the
   use of dynamic Huffman codes, allowing for a simpler decoder for special
   applications.

      deflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
   memory, Z_STREAM_ERROR if a parameter is invalid (such as an invalid
   method). msg is set to null if there is no error message.  deflateInit2 does
   not perform any compression: this will be done by deflate().
*/

int deflateSetDictionary(z_streamp strm,
                         Bytef*    dictionary,
                         uInt      dictLength);
/*
     Initializes the compression dictionary from the given byte sequence
   without producing any compressed output. This function must be called
   immediately after deflateInit, deflateInit2 or deflateReset, before any
   call of deflate. The compressor and decompressor must use exactly the same
   dictionary (see inflateSetDictionary).

     The dictionary should consist of strings (byte sequences) that are likely
   to be encountered later in the data to be compressed, with the most commonly
   used strings preferably put towards the end of the dictionary. Using a
   dictionary is most useful when the data to be compressed is short and can be
   predicted with good accuracy; the data can then be compressed better than
   with the default empty dictionary.

     Depending on the size of the compression data structures selected by
   deflateInit or deflateInit2, a part of the dictionary may in effect be
   discarded, for example if the dictionary is larger than the window size in
   deflate or deflate2. Thus the strings most likely to be useful should be
   put at the end of the dictionary, not at the front. In addition, the
   current implementation of deflate will use at most the window size minus
   262 bytes of the provided dictionary.

     Upon return of this function, strm->adler is set to the adler32 value
   of the dictionary; the decompressor may later use this value to determine
   which dictionary has been used by the compressor. (The adler32 value
   applies to the whole dictionary even if only a subset of the dictionary is
   actually used by the compressor.) If a raw deflate was requested, then the
   adler32 value is not computed and strm->adler is not set.

     deflateSetDictionary returns Z_OK if success, or Z_STREAM_ERROR if a
   parameter is invalid (such as NULL dictionary) or the stream state is
   inconsistent (for example if deflate has already been called for this stream
   or if the compression method is bsort). deflateSetDictionary does not
   perform any compression: this will be done by deflate().
*/

int deflateCopy(z_streamp dest,
                z_streamp source);
/*
     Sets the destination stream as a complete copy of the source stream.

     This function can be useful when several compression strategies will be
   tried, for example when there are several ways of pre-processing the input
   data with a filter. The streams that will be discarded should then be freed
   by calling deflateEnd.  Note that deflateCopy duplicates the internal
   compression state which can be quite large, so this strategy is slow and
   can consume lots of memory.

     deflateCopy returns Z_OK if success, Z_MEM_ERROR if there was not
   enough memory, Z_STREAM_ERROR if the source stream state was inconsistent
   (such as zalloc being NULL). msg is left unchanged in both source and
   destination.
*/

int deflateReset(z_streamp strm);
/*
     This function is equivalent to deflateEnd followed by deflateInit,
   but does not free and reallocate all the internal compression state.
   The stream will keep the same compression level and any other attributes
   that may have been set by deflateInit2.

      deflateReset returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent (such as zalloc or state being NULL).
*/

int deflateParams(z_streamp strm,
                  int       level,
                  int       strategy);
/*
     Dynamically update the compression level and compression strategy.  The
   interpretation of level and strategy is as in deflateInit2.  This can be
   used to switch between compression and straight copy of the input data, or
   to switch to a different kind of input data requiring a different
   strategy. If the compression level is changed, the input available so far
   is compressed with the old level (and may be flushed); the new level will
   take effect only at the next call of deflate().

     Before the call of deflateParams, the stream state must be set as for
   a call of deflate(), since the currently available input may have to
   be compressed and flushed. In particular, strm->avail_out must be non-zero.

     deflateParams returns Z_OK if success, Z_STREAM_ERROR if the source
   stream state was inconsistent or if a parameter was invalid, Z_BUF_ERROR
   if strm->avail_out was zero.
*/

int deflateTune(z_streamp strm,
                int       good_length,
                int       max_lazy,
                int       nice_length,
                int       max_chain);
/*
     Fine tune deflate's internal compression parameters.  This should only be
   used by someone who understands the algorithm used by zlib's deflate for
   searching for the best matching string, and even then only by the most
   fanatic optimizer trying to squeeze out the last compressed bit for their
   specific input data.  Read the deflate.c source code for the meaning of the
   max_lazy, good_length, nice_length, and max_chain parameters.

     deflateTune() can be called after deflateInit() or deflateInit2(), and
   returns Z_OK on success, or Z_STREAM_ERROR for an invalid deflate stream.
 */

uLong deflateBound(z_streamp strm,
                   uLong     sourceLen);
/*
     deflateBound() returns an upper bound on the compressed size after
   deflation of sourceLen bytes.  It must be called after deflateInit()
   or deflateInit2().  This would be used to allocate an output buffer
   for deflation in a single pass, and so would be called before deflate().
*/

int deflatePrime(z_streamp strm,
                 int       bits,
                 int       value);
/*
     deflatePrime() inserts bits in the deflate output stream.  The intent
  is that this function is used to start off the deflate output with the
  bits leftover from a previous deflate stream when appending to it.  As such,
  this function can only be used for raw deflate, and must be used before the
  first deflate() call after a deflateInit2() or deflateReset().  bits must be
  less than or equal to 16, and that many of the least significant bits of
  value will be inserted in the output.

      deflatePrime returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent.
*/

int deflateSetHeader(z_streamp  strm,
                     gz_headerp head);
/*
      deflateSetHeader() provides gzip header information for when a gzip
   stream is requested by deflateInit2().  deflateSetHeader() may be called
   after deflateInit2() or deflateReset() and before the first call of
   deflate().  The text, time, os, extra field, name, and comment information
   in the provided gz_header structure are written to the gzip header (xflag is
   ignored -- the extra flags are set according to the compression level).  The
   caller must assure that, if not Z_NULL, name and comment are terminated with
   a zero byte, and that if extra is not Z_NULL, that extra_len bytes are
   available there.  If hcrc is true, a gzip header crc is included.  Note that
   the current versions of the command-line version of gzip (up through version
   1.3.x) do not support header crc's, and will report that it is a "multi-part
   gzip file" and give up.

      If deflateSetHeader is not used, the default gzip header has text false,
   the time set to zero, and os set to 255, with no extra, name, or comment
   fields.  The gzip header is returned to the default state by deflateReset().

      deflateSetHeader returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent.
*/

/*
int inflateInit2(z_streamp strm,
                 int       windowBits);

     This is another version of inflateInit with an extra parameter. The
   fields next_in, avail_in, zalloc, zfree and opaque must be initialized
   before by the caller.

     The windowBits parameter is the base two logarithm of the maximum window
   size (the size of the history buffer).  It should be in the range 8..15 for
   this version of the library. The default value is 15 if inflateInit is used
   instead. windowBits must be greater than or equal to the windowBits value
   provided to deflateInit2() while compressing, or it must be equal to 15 if
   deflateInit2() was not used. If a compressed stream with a larger window
   size is given as input, inflate() will return with the error code
   Z_DATA_ERROR instead of trying to allocate a larger window.

     windowBits can also be -8..-15 for raw inflate. In this case, -windowBits
   determines the window size. inflate() will then process raw deflate data,
   not looking for a zlib or gzip header, not generating a check value, and not
   looking for any check values for comparison at the end of the stream. This
   is for use with other formats that use the deflate compressed data format
   such as zip.  Those formats provide their own check values. If a custom
   format is developed using the raw deflate format for compressed data, it is
   recommended that a check value such as an adler32 or a crc32 be applied to
   the uncompressed data as is done in the zlib, gzip, and zip formats.  For
   most applications, the zlib format should be used as is. Note that comments
   above on the use in deflateInit2() applies to the magnitude of windowBits.

     windowBits can also be greater than 15 for optional gzip decoding. Add
   32 to windowBits to enable zlib and gzip decoding with automatic header
   detection, or add 16 to decode only the gzip format (the zlib format will
   return a Z_DATA_ERROR).  If a gzip stream is being decoded, strm->adler is
   a crc32 instead of an adler32.

     inflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
   memory, Z_STREAM_ERROR if a parameter is invalid (such as a null strm). msg
   is set to null if there is no error message.  inflateInit2 does not perform
   any decompression apart from reading the zlib header if present: this will
   be done by inflate(). (So next_in and avail_in may be modified, but next_out
   and avail_out are unchanged.)
*/

int inflateSetDictionary(z_streamp strm,
                         Bytef*    dictionary,
                         uInt      dictLength);
/*
     Initializes the decompression dictionary from the given uncompressed byte
   sequence. This function must be called immediately after a call of inflate,
   if that call returned Z_NEED_DICT. The dictionary chosen by the compressor
   can be determined from the adler32 value returned by that call of inflate.
   The compressor and decompressor must use exactly the same dictionary (see
   deflateSetDictionary).  For raw inflate, this function can be called
   immediately after inflateInit2() or inflateReset() and before any call of
   inflate() to set the dictionary.  The application must insure that the
   dictionary that was used for compression is provided.

     inflateSetDictionary returns Z_OK if success, Z_STREAM_ERROR if a
   parameter is invalid (such as NULL dictionary) or the stream state is
   inconsistent, Z_DATA_ERROR if the given dictionary doesn't match the
   expected one (incorrect adler32 value). inflateSetDictionary does not
   perform any decompression: this will be done by subsequent calls of
   inflate().
*/

int inflateSync(z_streamp strm);
/*
    Skips invalid compressed data until a full flush point (see above the
  description of deflate with Z_FULL_FLUSH) can be found, or until all
  available input is skipped. No output is provided.

    inflateSync returns Z_OK if a full flush point has been found, Z_BUF_ERROR
  if no more input was provided, Z_DATA_ERROR if no flush point has been found,
  or Z_STREAM_ERROR if the stream structure was inconsistent. In the success
  case, the application may save the current current value of total_in which
  indicates where valid compressed data was found. In the error case, the
  application may repeatedly call inflateSync, providing more input each time,
  until success or end of the input data.
*/

int inflateCopy(z_streamp dest,
                z_streamp source);
/*
     Sets the destination stream as a complete copy of the source stream.

     This function can be useful when randomly accessing a large stream.  The
   first pass through the stream can periodically record the inflate state,
   allowing restarting inflate at those points when randomly accessing the
   stream.

     inflateCopy returns Z_OK if success, Z_MEM_ERROR if there was not
   enough memory, Z_STREAM_ERROR if the source stream state was inconsistent
   (such as zalloc being NULL). msg is left unchanged in both source and
   destination.
*/

int inflateReset(z_streamp strm);
/*
     This function is equivalent to inflateEnd followed by inflateInit,
   but does not free and reallocate all the internal decompression state.
   The stream will keep attributes that may have been set by inflateInit2.

      inflateReset returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent (such as zalloc or state being NULL).
*/

int inflatePrime(z_streamp strm,
                 int       bits,
                 int       value);
/*
     This function inserts bits in the inflate input stream.  The intent is
  that this function is used to start inflating at a bit position in the
  middle of a byte.  The provided bits will be used before any bytes are used
  from next_in.  This function should only be used with raw inflate, and
  should be used before the first inflate() call after inflateInit2() or
  inflateReset().  bits must be less than or equal to 16, and that many of the
  least significant bits of value will be inserted in the input.

      inflatePrime returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent.
*/

int inflateGetHeader(z_streamp  strm,
                     gz_headerp head);
/*
      inflateGetHeader() requests that gzip header information be stored in the
   provided gz_header structure.  inflateGetHeader() may be called after
   inflateInit2() or inflateReset(), and before the first call of inflate().
   As inflate() processes the gzip stream, head->done is zero until the header
   is completed, at which time head->done is set to one.  If a zlib stream is
   being decoded, then head->done is set to -1 to indicate that there will be
   no gzip header information forthcoming.  Note that Z_BLOCK can be used to
   force inflate() to return immediately after header processing is complete
   and before any actual data is decompressed.

      The text, time, xflags, and os fields are filled in with the gzip header
   contents.  hcrc is set to true if there is a header CRC.  (The header CRC
   was valid if done is set to one.)  If extra is not Z_NULL, then extra_max
   contains the maximum number of bytes to write to extra.  Once done is true,
   extra_len contains the actual extra field length, and extra contains the
   extra field, or that field truncated if extra_max is less than extra_len.
   If name is not Z_NULL, then up to name_max characters are written there,
   terminated with a zero unless the length is greater than name_max.  If
   comment is not Z_NULL, then up to comm_max characters are written there,
   terminated with a zero unless the length is greater than comm_max.  When
   any of extra, name, or comment are not Z_NULL and the respective field is
   not present in the header, then that field is set to Z_NULL to signal its
   absence.  This allows the use of deflateSetHeader() with the returned
   structure to duplicate the header.  However if those fields are set to
   allocated memory, then the application will need to save those pointers
   elsewhere so that they can be eventually freed.

      If inflateGetHeader is not used, then the header information is simply
   discarded.  The header is always checked for validity, including the header
   CRC if present.  inflateReset() will reset the process to discard the header
   information.  The application would need to call inflateGetHeader() again to
   retrieve the header from the next gzip stream.

      inflateGetHeader returns Z_OK if success, or Z_STREAM_ERROR if the source
   stream state was inconsistent.
*/

/*
int inflateBackInit(z_streamp strm,
                    int       windowBits,
                    ubyte*    window);

     Initialize the internal stream state for decompression using inflateBack()
   calls.  The fields zalloc, zfree and opaque in strm must be initialized
   before the call.  If zalloc and zfree are Z_NULL, then the default library-
   derived memory allocation routines are used.  windowBits is the base two
   logarithm of the window size, in the range 8..15.  window is a caller
   supplied buffer of that size.  Except for special applications where it is
   assured that deflate was used with small window sizes, windowBits must be 15
   and a 32K byte window must be supplied to be able to decompress general
   deflate streams.

     See inflateBack() for the usage of these routines.

     inflateBackInit will return Z_OK on success, Z_STREAM_ERROR if any of
   the paramaters are invalid, Z_MEM_ERROR if the internal state could not
   be allocated, or Z_VERSION_ERROR if the version of the library does not
   match the version of the header file.
*/

alias uint function(void*, ubyte**)      in_func;
alias int  function(void*, ubyte*, uint) out_func;

int inflateBack(z_streamp strm,
                in_func   in_fn,
                void*     in_desc,
                out_func  out_fn,
                void*     out_desc);
/*
     inflateBack() does a raw inflate with a single call using a call-back
   interface for input and output.  This is more efficient than inflate() for
   file i/o applications in that it avoids copying between the output and the
   sliding window by simply making the window itself the output buffer.  This
   function trusts the application to not change the output buffer passed by
   the output function, at least until inflateBack() returns.

     inflateBackInit() must be called first to allocate the internal state
   and to initialize the state with the user-provided window buffer.
   inflateBack() may then be used multiple times to inflate a complete, raw
   deflate stream with each call.  inflateBackEnd() is then called to free
   the allocated state.

     A raw deflate stream is one with no zlib or gzip header or trailer.
   This routine would normally be used in a utility that reads zip or gzip
   files and writes out uncompressed files.  The utility would decode the
   header and process the trailer on its own, hence this routine expects
   only the raw deflate stream to decompress.  This is different from the
   normal behavior of inflate(), which expects either a zlib or gzip header and
   trailer around the deflate stream.

     inflateBack() uses two subroutines supplied by the caller that are then
   called by inflateBack() for input and output.  inflateBack() calls those
   routines until it reads a complete deflate stream and writes out all of the
   uncompressed data, or until it encounters an error.  The function's
   parameters and return types are defined above in the in_func and out_func
   aliass.  inflateBack() will call in(in_desc, &buf) which should return the
   number of bytes of provided input, and a pointer to that input in buf.  If
   there is no input available, in() must return zero--buf is ignored in that
   case--and inflateBack() will return a buffer error.  inflateBack() will call
   out(out_desc, buf, len) to write the uncompressed data buf[0..len-1].  out()
   should return zero on success, or non-zero on failure.  If out() returns
   non-zero, inflateBack() will return with an error.  Neither in() nor out()
   are permitted to change the contents of the window provided to
   inflateBackInit(), which is also the buffer that out() uses to write from.
   The length written by out() will be at most the window size.  Any non-zero
   amount of input may be provided by in().

     For convenience, inflateBack() can be provided input on the first call by
   setting strm->next_in and strm->avail_in.  If that input is exhausted, then
   in() will be called.  Therefore strm->next_in must be initialized before
   calling inflateBack().  If strm->next_in is Z_NULL, then in() will be called
   immediately for input.  If strm->next_in is not Z_NULL, then strm->avail_in
   must also be initialized, and then if strm->avail_in is not zero, input will
   initially be taken from strm->next_in[0 .. strm->avail_in - 1].

     The in_desc and out_desc parameters of inflateBack() is passed as the
   first parameter of in() and out() respectively when they are called.  These
   descriptors can be optionally used to pass any information that the caller-
   supplied in() and out() functions need to do their job.

     On return, inflateBack() will set strm->next_in and strm->avail_in to
   pass back any unused input that was provided by the last in() call.  The
   return values of inflateBack() can be Z_STREAM_END on success, Z_BUF_ERROR
   if in() or out() returned an error, Z_DATA_ERROR if there was a format
   error in the deflate stream (in which case strm->msg is set to indicate the
   nature of the error), or Z_STREAM_ERROR if the stream was not properly
   initialized.  In the case of Z_BUF_ERROR, an input or output error can be
   distinguished using strm->next_in which will be Z_NULL only if in() returned
   an error.  If strm->next is not Z_NULL, then the Z_BUF_ERROR was due to
   out() returning non-zero.  (in() will always be called before out(), so
   strm->next_in is assured to be defined if out() returns non-zero.)  Note
   that inflateBack() cannot return Z_OK.
*/

int inflateBackEnd(z_streamp strm);
/*
     All memory allocated by inflateBackInit() is freed.

     inflateBackEnd() returns Z_OK on success, or Z_STREAM_ERROR if the stream
   state was inconsistent.
*/

uLong zlibCompileFlags();
/* Return flags indicating compile-time options.

    Type sizes, two bits each, 00 = 16 bits, 01 = 32, 10 = 64, 11 = other:
     1.0: size of uInt
     3.2: size of uLong
     5.4: size of voidpf (pointer)
     7.6: size of z_off_t

    Compiler, assembler, and debug options:
     8: DEBUG
     9: ASMV or ASMINF -- use ASM code
     10: ZLIB_WINAPI -- exported functions use the WINAPI calling convention
     11: 0 (reserved)

    One-time table building (smaller code, but not thread-safe if true):
     12: BUILDFIXED -- build static block decoding tables when needed
     13: DYNAMIC_CRC_TABLE -- build CRC calculation tables when needed
     14,15: 0 (reserved)

    Library content (indicates missing functionality):
     16: NO_GZCOMPRESS -- gz* functions cannot compress (to avoid linking
                          deflate code when not needed)
     17: NO_GZIP -- deflate can't write gzip streams, and inflate can't detect
                    and decode gzip streams (to avoid linking crc code)
     18-19: 0 (reserved)

    Operation variations (changes in library functionality):
     20: PKZIP_BUG_WORKAROUND -- slightly more permissive inflate
     21: FASTEST -- deflate algorithm with only one, lowest compression level
     22,23: 0 (reserved)

    The sprintf variant used by gzprintf (zero is best):
     24: 0 = vs*, 1 = s* -- 1 means limited to 20 arguments after the format
     25: 0 = *nprintf, 1 = *printf -- 1 means gzprintf() not secure!
     26: 0 = returns value, 1 = void -- 1 means inferred string length returned

    Remainder:
     27-31: 0 (reserved)
 */


                        /* utility functions */

/*
     The following utility functions are implemented on top of the
   basic stream-oriented functions. To simplify the interface, some
   default options are assumed (compression level and memory usage,
   standard memory allocation functions). The source code of these
   utility functions can easily be modified if you need special options.
*/

int compress(Bytef*  dest,
             uLongf* destLen,
             Bytef*  source,
             uLong   sourceLen);
/*
     Compresses the source buffer into the destination buffer.  sourceLen is
   the byte length of the source buffer. Upon entry, destLen is the total
   size of the destination buffer, which must be at least the value returned
   by compressBound(sourceLen). Upon exit, destLen is the actual size of the
   compressed buffer.
     This function can be used to compress a whole file at once if the
   input file is mmap'ed.
     compress returns Z_OK if success, Z_MEM_ERROR if there was not
   enough memory, Z_BUF_ERROR if there was not enough room in the output
   buffer.
*/

int compress2(Bytef*  dest,
              uLongf* destLen,
              Bytef*  source,
              uLong   sourceLen,
              int     level);
/*
     Compresses the source buffer into the destination buffer. The level
   parameter has the same meaning as in deflateInit.  sourceLen is the byte
   length of the source buffer. Upon entry, destLen is the total size of the
   destination buffer, which must be at least the value returned by
   compressBound(sourceLen). Upon exit, destLen is the actual size of the
   compressed buffer.

     compress2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
   memory, Z_BUF_ERROR if there was not enough room in the output buffer,
   Z_STREAM_ERROR if the level parameter is invalid.
*/

uLong compressBound(uLong sourceLen);
/*
     compressBound() returns an upper bound on the compressed size after
   compress() or compress2() on sourceLen bytes.  It would be used before
   a compress() or compress2() call to allocate the destination buffer.
*/

int uncompress(Bytef*  dest,
               uLongf* destLen,
               Bytef*  source,
               uLong   sourceLen);
/*
     Decompresses the source buffer into the destination buffer.  sourceLen is
   the byte length of the source buffer. Upon entry, destLen is the total
   size of the destination buffer, which must be large enough to hold the
   entire uncompressed data. (The size of the uncompressed data must have
   been saved previously by the compressor and transmitted to the decompressor
   by some mechanism outside the scope of this compression library.)
   Upon exit, destLen is the actual size of the compressed buffer.
     This function can be used to decompress a whole file at once if the
   input file is mmap'ed.

     uncompress returns Z_OK if success, Z_MEM_ERROR if there was not
   enough memory, Z_BUF_ERROR if there was not enough room in the output
   buffer, or Z_DATA_ERROR if the input data was corrupted or incomplete.
*/


alias voidp gzFile;

gzFile gzopen(char* path, char* mode);
/*
     Opens a gzip (.gz) file for reading or writing. The mode parameter
   is as in fopen ("rb" or "wb") but can also include a compression level
   ("wb9") or a strategy: 'f' for filtered data as in "wb6f", 'h' for
   Huffman only compression as in "wb1h", or 'R' for run-length encoding
   as in "wb1R". (See the description of deflateInit2 for more information
   about the strategy parameter.)

     gzopen can be used to read a file which is not in gzip format; in this
   case gzread will directly read from the file without decompression.

     gzopen returns NULL if the file could not be opened or if there was
   insufficient memory to allocate the (de)compression state; errno
   can be checked to distinguish the two cases (if errno is zero, the
   zlib error is Z_MEM_ERROR).  */

gzFile gzdopen(int fd, char* mode);
/*
     gzdopen() associates a gzFile with the file descriptor fd.  File
   descriptors are obtained from calls like open, dup, creat, pipe or
   fileno (in the file has been previously opened with fopen).
   The mode parameter is as in gzopen.
     The next call of gzclose on the returned gzFile will also close the
   file descriptor fd, just like fclose(fdopen(fd), mode) closes the file
   descriptor fd. If you want to keep fd open, use gzdopen(dup(fd), mode).
     gzdopen returns NULL if there was insufficient memory to allocate
   the (de)compression state.
*/

int gzsetparams(gzFile file, int level, int strategy);
/*
     Dynamically update the compression level or strategy. See the description
   of deflateInit2 for the meaning of these parameters.
     gzsetparams returns Z_OK if success, or Z_STREAM_ERROR if the file was not
   opened for writing.
*/

int gzread(gzFile file, voidp buf, uint len);
/*
     Reads the given number of uncompressed bytes from the compressed file.
   If the input file was not in gzip format, gzread copies the given number
   of bytes into the buffer.
     gzread returns the number of uncompressed bytes actually read (0 for
   end of file, -1 for error). */

int gzwrite(gzFile file, voidpc buf, uint len);
/*
     Writes the given number of uncompressed bytes into the compressed file.
   gzwrite returns the number of uncompressed bytes actually written
   (0 in case of error).
*/

int gzprintf (gzFile file, const(char)* format, ...);
/*
     Converts, formats, and writes the args to the compressed file under
   control of the format string, as in fprintf. gzprintf returns the number of
   uncompressed bytes actually written (0 in case of error).  The number of
   uncompressed bytes written is limited to 4095. The caller should assure that
   this limit is not exceeded. If it is exceeded, then gzprintf() will return
   return an error (0) with nothing written. In this case, there may also be a
   buffer overflow with unpredictable consequences, which is possible only if
   zlib was compiled with the insecure functions sprintf() or vsprintf()
   because the secure snprintf() or vsnprintf() functions were not available.
*/

int gzputs(gzFile file, const(char)* s);
/*
      Writes the given null-terminated string to the compressed file, excluding
   the terminating null character.
      gzputs returns the number of characters written, or -1 in case of error.
*/

char* gzgets(gzFile file, char* buf, int len);
/*
      Reads bytes from the compressed file until len-1 characters are read, or
   a newline character is read and transferred to buf, or an end-of-file
   condition is encountered.  The string is then terminated with a null
   character.
      gzgets returns buf, or Z_NULL in case of error.
*/

int gzputc(gzFile file, int c);
/*
      Writes c, converted to an unsigned char, into the compressed file.
   gzputc returns the value that was written, or -1 in case of error.
*/

int gzgetc (gzFile file);
/*
      Reads one byte from the compressed file. gzgetc returns this byte
   or -1 in case of end of file or error.
*/

int gzungetc(int c, gzFile file);
/*
      Push one character back onto the stream to be read again later.
   Only one character of push-back is allowed.  gzungetc() returns the
   character pushed, or -1 on failure.  gzungetc() will fail if a
   character has been pushed but not read yet, or if c is -1. The pushed
   character will be discarded if the stream is repositioned with gzseek()
   or gzrewind().
*/

int gzflush(gzFile file, int flush);
/*
     Flushes all pending output into the compressed file. The parameter
   flush is as in the deflate() function. The return value is the zlib
   error number (see function gzerror below). gzflush returns Z_OK if
   the flush parameter is Z_FINISH and all output could be flushed.
     gzflush should be called only when strictly necessary because it can
   degrade compression.
*/

z_off_t gzseek (gzFile file, z_off_t offset, int whence);
/*
      Sets the starting position for the next gzread or gzwrite on the
   given compressed file. The offset represents a number of bytes in the
   uncompressed data stream. The whence parameter is defined as in lseek(2);
   the value SEEK_END is not supported.
     If the file is opened for reading, this function is emulated but can be
   extremely slow. If the file is opened for writing, only forward seeks are
   supported; gzseek then compresses a sequence of zeroes up to the new
   starting position.

      gzseek returns the resulting offset location as measured in bytes from
   the beginning of the uncompressed stream, or -1 in case of error, in
   particular if the file is opened for writing and the new starting position
   would be before the current position.
*/

int gzrewind(gzFile file);
/*
     Rewinds the given file. This function is supported only for reading.

   gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET)
*/

z_off_t gztell (gzFile file);
/*
     Returns the starting position for the next gzread or gzwrite on the
   given compressed file. This position represents a number of bytes in the
   uncompressed data stream.

   gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR)
*/

int gzeof(gzFile file);
/*
     Returns 1 when EOF has previously been detected reading the given
   input stream, otherwise zero.
*/

int gzdirect(gzFile file);
/*
     Returns 1 if file is being read directly without decompression, otherwise
   zero.
*/

int gzclose(gzFile file);
/*
     Flushes all pending output if necessary, closes the compressed file
   and deallocates all the (de)compression state. The return value is the zlib
   error number (see function gzerror below).
*/

const(char)* gzerror(gzFile file, int* errnum);
/*
     Returns the error message for the last error which occurred on the
   given compressed file. errnum is set to zlib error number. If an
   error occurred in the file system and not in the compression library,
   errnum is set to Z_ERRNO and the application may consult errno
   to get the exact error code.
*/

void gzclearerr(gzFile file);
/*
     Clears the error and end-of-file flags for file. This is analogous to the
   clearerr() function in stdio. This is useful for continuing to read a gzip
   file that is being written concurrently.
*/

                        /* checksum functions */

/*
     These functions are not related to compression but are exported
   anyway because they might be useful in applications using the
   compression library.
*/

uLong adler32(uLong adler, Bytef* buf, uInt len);
/*
     Update a running Adler-32 checksum with the bytes buf[0..len-1] and
   return the updated checksum. If buf is NULL, this function returns
   the required initial value for the checksum.
   An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
   much faster. Usage example:

     uLong adler = adler32(0L, Z_NULL, 0);

     while (read_buffer(buffer, length) != EOF) {
       adler = adler32(adler, buffer, length);
     }
     if (adler != original_adler) error();
*/

uLong adler32_combine(uLong adler1, uLong adler2, z_off_t len2);
/*
     Combine two Adler-32 checksums into one.  For two sequences of bytes, seq1
   and seq2 with lengths len1 and len2, Adler-32 checksums were calculated for
   each, adler1 and adler2.  adler32_combine() returns the Adler-32 checksum of
   seq1 and seq2 concatenated, requiring only adler1, adler2, and len2.
*/

uLong crc32(uLong crc, Bytef* buf, uInt len);
/*
     Update a running CRC-32 with the bytes buf[0..len-1] and return the
   updated CRC-32. If buf is NULL, this function returns the required initial
   value for the for the crc. Pre- and post-conditioning (one's complement) is
   performed within this function so it shouldn't be done by the application.
   Usage example:

     uLong crc = crc32(0L, Z_NULL, 0);

     while (read_buffer(buffer, length) != EOF) {
       crc = crc32(crc, buffer, length);
     }
     if (crc != original_crc) error();
*/

uLong crc32_combine(uLong crc1, uLong crc2, z_off_t len2);

/*
     Combine two CRC-32 check values into one.  For two sequences of bytes,
   seq1 and seq2 with lengths len1 and len2, CRC-32 check values were
   calculated for each, crc1 and crc2.  crc32_combine() returns the CRC-32
   check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and
   len2.
*/


                        /* various hacks, don't look :) */

/* deflateInit and inflateInit are macros to allow checking the zlib version
 * and the compiler's view of z_stream:
 */
int deflateInit_(z_streamp  strm,
                 int        level,
                 const(char)*      ver,
                 int        stream_size);
int inflateInit_(z_streamp  strm,
                 const(char)*      ver,
                 int        stream_size);
int deflateInit2_(z_streamp strm,
                  int       level,
                  int       method,
                  int       windowBits,
                  int       memLevel,
                  int       strategy,
                  const(char)*     ver,
                  int       stream_size);
int inflateInit2_(z_streamp strm,
                  int       windowBits,
                  const(char)*     ver,
                  int       stream_size);
int inflateBackInit_(z_streamp strm,
                     int       windowBits,
                     ubyte*    window,
                     const(char)*     ver,
                     int       stream_size);

extern (D) int deflateInit(z_streamp  strm,
                           int        level)
{
    return deflateInit_(strm,
                        level,
                        ZLIB_VERSION,
                        z_stream.sizeof);
}

extern (D) int inflateInit(z_streamp  strm)
{
    return inflateInit_(strm,
                        ZLIB_VERSION,
                        z_stream.sizeof);
}

extern (D) int deflateInit2(z_streamp strm,
                           int       level,
                           int       method,
                           int       windowBits,
                           int       memLevel,
                           int       strategy)
{
    return deflateInit2_(strm,
                         level,
                         method,
                         windowBits,
                         memLevel,
                         strategy,
                         ZLIB_VERSION,
                         z_stream.sizeof);
}

extern (D) int inflateInit2(z_streamp strm,
                            int       windowBits)
{
    return inflateInit2_(strm,
                         windowBits,
                         ZLIB_VERSION,
                         z_stream.sizeof);
}

extern (D) int inflateBackInit(z_streamp strm,
                               int       windowBits,
                               ubyte*    window)
{
    return inflateBackInit_(strm,
                            windowBits,
                            window,
                            ZLIB_VERSION,
                            z_stream.sizeof);
}

const(char)*   zError(int);
int     inflateSyncPoint(z_streamp z);
uLongf* get_crc_table();