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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-4BEFF7BA-2A39-5601-919E-22AF08D06023" xml:lang="en"><title>Zip

    13 Compression Library Overview</title><shortdesc>The Zip Compression Library, EZLib, provides stream and file compression

    14 and decompression functionality for the Symbian platforms. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>EZLib provides classes to handle the file, stream and buffer requirements

    16 of zlib. It provides native Symbian APIs that access the zlib compression

    17 algorithms and it exports some zlib and gzio C APIs from libz.dll. EZLib can

    18 operate on streams, flat zip files (zlib format) and gzip files. </p>

    19 <section><title>Purpose</title> <p>EZLib facilitates: </p> <ul>

    20 <li id="GUID-EB810152-39F6-5B42-B9CA-092FD2DBADB5"><p>Compression and decompression

    21 of memory streams </p> </li>

    22 <li id="GUID-F1E8AD72-1E1C-5978-BBDB-FCF529238441"><p>Compression and decompression

    23 of files </p> </li>

    24 <li id="GUID-B08AB8E2-DE37-59B2-86D3-04F5385BFCE0"><p>Decompression of file

    25 archives of gzip format </p> </li>

    26 </ul> </section>

    27 <section><title>Required background</title> <p>You must be familiar with zlib,

    28 gzip compression and decompression formats and Deflate algorithms. You can

    29 find further information about each of these on the IETF (Internet Engineering

    30 Task Force) website. </p> <p> <xref href="http://www.ietf.org/rfc/rfc1950.txt" scope="external">RFC1950- zlib format</xref>  </p> <p> <xref href="http://www.ietf.org/rfc/rfc1951.txt" scope="external">RFC1951-Deflate algorithm</xref>  </p> <p> <xref href="http://www.ietf.org/rfc/rfc1952.txt" scope="external">RFC1952-gzip format</xref>  </p> </section>

    31 <section><title>Key concepts and terms</title> <dl>

    32 <dlentry>

    33 <dt>zlib</dt>

    34 <dd><p>zlib format is an open standard for lossless compressed data. It can

    35 be implemented using a number of alternative compression algorithms. </p> </dd>

    36 </dlentry>

    37 <dlentry>

    38 <dt>Compression</dt>

    39 <dd><p>Data compression is a process of encoding information using fewer bits

    40 (or other information-bearing units) using specific encoding algorithms. </p> </dd>

    41 </dlentry>

    42 <dlentry>

    43 <dt>Decompression</dt>

    44 <dd><p>Decompression is the process of reconverting compressed data into its

    45 original (or nearly original) form. </p> </dd>

    46 </dlentry>

    47 <dlentry>

    48 <dt>Stream</dt>

    49 <dd><p>A stream is an abstraction that represents a device on which input

    50 and ouput operations are performed. A stream can be considered as a source

    51 or destination of characters of indefinite length. A stream can be accessed

    52 only in sequence. </p> </dd>

    53 </dlentry>

    54 <dlentry>

    55 <dt>gzip File Format</dt>

    56 <dd><p>gzip is normally used to compress single files. Deflate is the compression

    57 algorithm used. </p> </dd>

    58 </dlentry>

    59 <dlentry>

    60 <dt>gzio</dt>

    61 <dd><p>gzio APIs are input amd output functions for gzip format. </p> </dd>

    62 </dlentry>

    63 <dlentry>

    64 <dt>zip Format</dt>

    65 <dd><p>The zip file format is both data compression and archive. A zip file

    66 contains one or more files that have been compressed where possible to reduce

    67 file size. The zip file format permits a number of compression algorithms

    68 but only Deflate is widely used and supported. </p> </dd>

    69 </dlentry>

    70 </dl> </section>

    71 <section><title>Architecture</title> <p>The Zip Compression Library (EZLib)

    72 provides C++ wrapper classes that encapsulate the functionality of version

    73 1.2.3 of the zlib library. zlib and gzio APIs are written in C. The core functionality

    74 is performed by a core library (libzcore.dll). </p> <p>EZLib provides three

    75 DLLs which encapsulate the core functionality in Symbian C++ and Open Environment

    76 APIs. </p> <ul>

    77 <li id="GUID-D8A474AF-8853-5297-AF1A-CDB87AA90CDC"><p>LIBZ.DLL: This is an

    78 Open Environment library that provides the zlib and gzio C APIs. The APIs

    79 can be used to compress and decompress zlib and gzip file formats. </p> </li>

    80 <li id="GUID-11302514-AFA7-548A-8EB2-2CD0FE34B1B5"><p>EZLIB.DLL: This provides

    81 Symbian C++ wrappers for the zlib compression and decompression APIs. It offers

    82 buffer, stream and gzip file handling classes. It also exports the C API interface

    83 provided by LIBZ.DLL with the exception of the gzio APIs. This library can

    84 be used to compress and decompress zlib and gzip file formats and memory streams. </p> </li>

    85 <li id="GUID-123ED28B-2F59-593E-B1F4-DA1E70368A0C"><p>EZIP.DLL: This provides

    86 Symbian C++ APIs for reading from and decompressing zip archives. It cannot

    87 be used to compress archives to zip archives. </p> </li>

    88 </ul> <fig id="GUID-14EAABD4-6E9D-53CA-9515-7504EF0482D7">

    89 <title>              EZLib Architecture            </title>

    90 <image href="GUID-917790B7-A71D-511C-AFAB-BB46EFD046C6_d0e151178_href.jpg" placement="inline"/>

    91 </fig> </section>

    92 <section><title>APIs</title> <p>The classes exported from <filepath>ezlib.dll</filepath> are

    93 tabulated below: </p> <table id="GUID-DD3CE37A-8241-5961-B517-03266AE463F0">

    94 <tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

    95 <thead>

    96 <row>

    97 <entry>API</entry>

    98 <entry>Description</entry>

    99 </row>

   100 </thead>

   101 <tbody>

   102 <row>

   103 <entry><p> <xref href="GUID-AEF8BCC8-6B24-3D59-AD3A-17B5203B3AA5.dita"><apiname>CEZCompressor</apiname></xref>  </p> </entry>

   104 <entry><p>Provides wrapper for ‘compress’ and ‘Deflate’ zlib APIs. </p> </entry>

   105 </row>

   106 <row>

   107 <entry><p> <xref href="GUID-BC3CEC02-B747-38FB-8B35-E7390DB06E35.dita"><apiname>CEZDecompressor</apiname></xref>  </p> </entry>

   108 <entry><p>Provides wrapper for ‘uncompress’ and ‘inflate’ zlib APIs. </p> </entry>

   109 </row>

   110 <row>

   111 <entry><p> <xref href="GUID-A54D8675-1874-3B4F-816D-001A235C0F9C.dita"><apiname>CEZFileBufferManager</apiname></xref>  </p> </entry>

   112 <entry><p>Provides basic file handling for CEZCompressor and CEZDecompressor

   113 classes. </p> </entry>

   114 </row>

   115 <row>

   116 <entry><p> <xref href="GUID-417AB4E0-FF07-34CB-A4A8-CEF31C48A162.dita"><apiname>CEZFileToGZip</apiname></xref>  </p> </entry>

   117 <entry><p>Provides implementation to compress an uncompressed file to a gzip

   118 file. </p> </entry>

   119 </row>

   120 <row>

   121 <entry><p> <xref href="GUID-20B207AF-0DEB-3B4A-8BA4-4C0D17F544AC.dita"><apiname>CEZFileToGzipBM</apiname></xref>  </p> </entry>

   122 <entry><p>Provides buffer management class for CEZFileToGZip. </p> </entry>

   123 </row>

   124 <row>

   125 <entry><p> <xref href="GUID-8DE05785-D058-3855-A11F-7132EB4DE078.dita"><apiname>CEZGZipToFile</apiname></xref>  </p> </entry>

   126 <entry><p>Provides implementation to uncompress a gzip file to an output file. </p> </entry>

   127 </row>

   128 <row>

   129 <entry><p> <xref href="GUID-2C372219-941A-3D1B-885F-8BC745827445.dita"><apiname>CEZGzipToFileBM</apiname></xref>  </p> </entry>

   130 <entry><p>Provides buffer management class for CEZGzipToFile. </p> </entry>

   131 </row>

   132 <row>

   133 <entry><p> <xref href="GUID-E9A5CC9F-612E-3C32-AF93-6F28D2A894EF.dita"><apiname>CEZZStream</apiname></xref>  </p> </entry>

   134 <entry><p>Provides stream handling. </p> </entry>

   135 </row>

   136 <row>

   137 <entry><p> <xref href="GUID-B90BA6D6-72A2-3EB8-B8EF-CD5408107A9E.dita"><apiname>MEZBufferManager</apiname></xref>  </p> </entry>

   138 <entry><p>Pure virtual interface class. CEZFileBufferManager derives from

   139 this class. </p> </entry>

   140 </row>

   141 </tbody>

   142 </tgroup>

   143 </table> <p>The classes exported from <filepath>ezip.dll</filepath> are tabulated

   144 below: </p> <table id="GUID-067977A4-93E7-5E09-9962-63B3FA501B42">

   145 <tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

   146 <thead>

   147 <row>

   148 <entry>API</entry>

   149 <entry>Description</entry>

   150 </row>

   151 </thead>

   152 <tbody>

   153 <row>

   154 <entry><p> <xref href="GUID-8C8DEC50-6FC8-3DED-84E1-1EA42E2A0BB8.dita"><apiname>CZipArchive</apiname></xref>  </p> </entry>

   155 <entry><p>Represents a zip archive and defines all relevant enumerations and

   156 structures. </p> </entry>

   157 </row>

   158 <row>

   159 <entry><p> <xref href="GUID-79C613E8-35F8-319B-BE8B-1411CBE5AF00.dita"><apiname>CZipFile</apiname></xref>  </p> </entry>

   160 <entry><p>Represents a zip archive contained in a single file. </p> </entry>

   161 </row>

   162 <row>

   163 <entry><p> <xref href="GUID-02A8BC62-D653-39A3-BE0C-92A5F3F43E85.dita"><apiname>CZipFileMember</apiname></xref>  </p> </entry>

   164 <entry><p>Represents a compressed file contained in a CZipFile archive file. </p> </entry>

   165 </row>

   166 <row>

   167 <entry><p> <xref href="GUID-D458AE6A-EC64-3882-BCEA-A44A43DAA99A.dita"><apiname>CZipFileMemberIterator</apiname></xref>  </p> </entry>

   168 <entry><p>Allows iteration through all the entries of an archive. </p> </entry>

   169 </row>

   170 <row>

   171 <entry><p> <xref href="GUID-62F9728B-9C39-3496-BAEB-6E1456E6F197.dita"><apiname>RZipFileMemberReaderStream</apiname></xref>  </p> </entry>

   172 <entry><p>Represents an input stream for compressed files in an archive. </p> </entry>

   173 </row>

   174 </tbody>

   175 </tgroup>

   176 </table> <p><filepath>libz.dll</filepath> provides the C open environment

   177 and hybrid applications to support the zlib library. </p></section>

   178 <section><title>Typical uses</title> <p>The typical uses of

   179 the ZIP Compression Library are: </p> <ul>

   180 <li id="GUID-374EF76C-333C-5A09-9154-42056C70DD58"><p><xref href="GUID-548CC331-8E38-5627-A925-EA386BE90258.dita"> Compression

   181 and decompression of files(gzip)</xref>  </p> </li>

   182 <li id="GUID-053B2446-7ED5-5263-AF3D-00866C829B4C"><p><xref href="GUID-84922B27-FDCF-56FD-91ED-5E0BFE3ED0E4.dita">Compression

   183 and decompression of files(zip) </xref>  </p> </li>

   184 <li id="GUID-BA9F0FBB-6B0C-51DB-8162-336C27002B79"><p><xref href="GUID-C3086910-D7B4-5549-BF65-374C8B602E8F.dita"> Compression

   185 and decompression of memory streams </xref>  </p> </li>

   186 <li id="GUID-A6DDC9BD-B8F4-52CE-BE3D-AFAC549EF9ED"><p><xref href="GUID-FDDAF8E9-4CAB-5489-B578-A5362E2140C1.dita"> Decompression

   187 of file archives </xref>  </p> </li>

   188 </ul> </section>

   189 </conbody></concept>