Zip +Compression Library Overview

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.

Purpose

EZLib facilitates:

Compression and decompression +of memory streams
Compression and decompression +of files
Decompression of file +archives of gzip format

Required background

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.

RFC1950- zlib format

RFC1951-Deflate algorithm

RFC1952-gzip format

Key concepts and terms

zlib: zlib format is an open standard for lossless compressed data. It can +be implemented using a number of alternative compression algorithms.
Compression: Data compression is a process of encoding information using fewer bits +(or other information-bearing units) using specific encoding algorithms.
Decompression: Decompression is the process of reconverting compressed data into its +original (or nearly original) form.
Stream: 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.
gzip File Format: gzip is normally used to compress single files. Deflate is the compression +algorithm used.
gzio: gzio APIs are input amd output functions for gzip format.
zip Format: 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.

Architecture

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).

EZLib provides three +DLLs which encapsulate the core functionality in Symbian C++ and Open Environment +APIs.

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.
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.
EZIP.DLL: This provides +Symbian C++ APIs for reading from and decompressing zip archives. It cannot +be used to compress archives to zip archives.

+ EZLib Architecture + +

APIs

The classes exported from ezlib.dll are +tabulated below:

+ + + +API +Description + + + + +

CEZCompressor

Provides wrapper for ‘compress’ and ‘Deflate’ zlib APIs.

+ + +

CEZDecompressor

Provides wrapper for ‘uncompress’ and ‘inflate’ zlib APIs.

+ + +

CEZFileBufferManager

Provides basic file handling for CEZCompressor and CEZDecompressor +classes.

+ + +

CEZFileToGZip

Provides implementation to compress an uncompressed file to a gzip +file.

+ + +

CEZFileToGzipBM

Provides buffer management class for CEZFileToGZip.

+ + +

CEZGZipToFile

Provides implementation to uncompress a gzip file to an output file.

+ + +

CEZGzipToFileBM

Provides buffer management class for CEZGzipToFile.

+ + +

CEZZStream

Provides stream handling.

+ + +

MEZBufferManager

Pure virtual interface class. CEZFileBufferManager derives from +this class.

+ + + +

The classes exported from ezip.dll are tabulated +below:

+ + + +API +Description + + + + +

CZipArchive

Represents a zip archive and defines all relevant enumerations and +structures.

+ + +

CZipFile

Represents a zip archive contained in a single file.

+ + +

CZipFileMember

Represents a compressed file contained in a CZipFile archive file.

+ + +

CZipFileMemberIterator

Allows iteration through all the entries of an archive.

+ + +

RZipFileMemberReaderStream

Represents an input stream for compressed files in an archive.

+ + + +

libz.dll provides the C open environment +and hybrid applications to support the zlib library.

Typical uses

The typical uses of +the ZIP Compression Library are:

Compression +and decompression of files(gzip)
Compression +and decompression of files(zip)
Compression +and decompression of memory streams
Decompression +of file archives