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

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

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

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

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

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

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

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

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

of memory streams </p> </li>

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

of files </p> </li>

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

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

</ul> </section>

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

gzip compression and decompression formats and Deflate algorithms. You can

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

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>

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

<dlentry>

<dt>zlib</dt>

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

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

</dlentry>

<dlentry>

<dt>Compression</dt>

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

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

</dlentry>

<dlentry>

<dt>Decompression</dt>

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

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

</dlentry>

<dlentry>

<dt>Stream</dt>

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

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

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

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

</dlentry>

<dlentry>

<dt>gzip File Format</dt>

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

algorithm used. </p> </dd>

</dlentry>

<dlentry>

<dt>gzio</dt>

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

</dlentry>

<dlentry>

<dt>zip Format</dt>

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

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

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

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

</dlentry>

</dl> </section>

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

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

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

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

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

APIs. </p> <ul>

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

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

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

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

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

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

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

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

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

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

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

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

<title>              EZLib Architecture            </title>

<image href="GUID-917790B7-A71D-511C-AFAB-BB46EFD046C6_d0e163507_href.jpg" placement="inline"/>

</fig> </section>

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

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

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

<thead>

<row>

<entry>API</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

classes. </p> </entry>

</row>

<row>

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

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

file. </p> </entry>

</row>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

this class. </p> </entry>

</row>

</tbody>

</tgroup>

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

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

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

<thead>

<row>

<entry>API</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

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

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

structures. </p> </entry>

</row>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

</row>

<row>

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

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

</row>

</tbody>

</tgroup>

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

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

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

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

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

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

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

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

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

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

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

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

</ul> </section>