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Archived:Getting trailer and header info from GZIP files using Symbian C++

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__NOTOC__
 
__NOTOC__
 
__NOEDITSECTION__
 
__NOEDITSECTION__
 
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{{KBCS}}
 
{|style="background:#eceff2" width="660px" border="1" cellpadding="5" cellspacing="0"  
 
{|style="background:#eceff2" width="660px" border="1" cellpadding="5" cellspacing="0"  
 
|-
 
|-
|'''ID''' ||  
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|'''ID''' || CS000948
|'''Creation date''' || May 6, 2008
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|'''Creation date''' || May 14, 2008
 
|-
 
|-
 
|'''Platform''' || S60 3rd Edition, FP1
 
|'''Platform''' || S60 3rd Edition, FP1
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==Overview==
 
==Overview==
  
This snippet shows how to get the trailer and the header info from gzip files.
+
This snippet shows how to get the trailer and the header info from GZIP files.
  
The trailer part of gzip file should contain following data:
+
The trailer part of GZIP file should contain the following data:
  
 
* CRC32  
 
* CRC32  
* input size (calculated from the original uncompressed data)
+
* Input size (calculated from the original uncompressed data)
  
The actual gzip header is defined to contain following fields:
+
The actual GZIP header is defined to contain the following fields:
  
* fixed value for ID1 = 31
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* Fixed value for ID1 = 31
* fixed value for ID2 = 139
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* Fixed value for ID2 = 139
* compression method (8 is the standard)
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* Compression method (8 is the standard)
* flags (0 = no flags are set)
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* Flags (0 = no flags are set)
* modification time  (time stamp in Unix format)
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* Modification time  (time stamp in Unix format)
* extra flags (maximum compression - fastest algorithm)
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* Extra flags (maximum compression - fastest algorithm)
 
* Operating System
 
* Operating System
  
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==Postconditions==
 
==Postconditions==
The trailer and header info from the given gzip file is printed to the console.
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The trailer and header info from the given GZIP file is printed to the console.
  
 
==See also==
 
==See also==
  
[[Compressing_and_decompressing_gzip_files]]
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[[CS000949 - Compressing and decompressing GZIP files]]
  
The gzip format is specified in the page http://www.faqs.org/rfcs/rfc1952.html.
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The GZIP format is specified in http://www.faqs.org/rfcs/rfc1952.html.
  
  
[[Category:Symbian C++]][[Category:Code Examples]][[Category:Files/Data]]
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[[Category:Symbian C++]][[Category:Code Examples]][[Category:Files/Data]][[Category:S60 3rd Edition, Feature Pack 1]]

Revision as of 14:22, 14 May 2008


Template:KBCS

ID CS000948 Creation date May 14, 2008
Platform S60 3rd Edition, FP1 Tested on devices Nokia N93
Category Symbian C++ Subcategory Files/Data


Keywords (APIs, classes, methods, functions): RFile, EZGZipFile, TEZGZipHeader, TEZGZipTrailer, RFile::Open(),EZGZipFile::IsGzipFileL(), EZGZipFile::LocateAndReadTrailerL(), EZGZipFile::ReadHeaderL(),EZGZipFile::EFText,EZGZipFile::EFHcrc, EZGZipFile::EFExtra,EZGZipFile::EFName,EZGZipFile::EFComment

Overview

This snippet shows how to get the trailer and the header info from GZIP files.

The trailer part of GZIP file should contain the following data:

  • CRC32
  • Input size (calculated from the original uncompressed data)

The actual GZIP header is defined to contain the following fields:

  • Fixed value for ID1 = 31
  • Fixed value for ID2 = 139
  • Compression method (8 is the standard)
  • Flags (0 = no flags are set)
  • Modification time (time stamp in Unix format)
  • Extra flags (maximum compression - fastest algorithm)
  • Operating System

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY efsrv.lib
LIBRARY ezlib.lib

Header file

Source file

#include <ezgzip.h>
#include <f32file.h>
 
 
void GetGZipFileTrailerAndHeaderInfoL(RFs& aRfs, const TDesC& aFileName)
{
RFile file;
TEZGZipHeader header;
TEZGZipTrailer trailer;
 
if (!EZGZipFile::IsGzipFileL(aRfs,aFileName))
{
_LIT(KIsNotGZipFile,"File:%S is not in GZip format\n");
console->Printf(KIsNotGZipFile,&aFileName);
console->Getch();
User::Leave(KErrGeneral);
}
 
EZGZipFile::LocateAndReadTrailerL(aRfs, aFileName, trailer);
_LIT(KTrailer,"CRC32 = %d size = %d\n");
console->Printf(KTrailer,trailer.iCrc32,trailer.iSize);
 
User::LeaveIfError(file.Open(aRfs,aFileName,EFileStream | EFileRead | EFileShareAny));
EZGZipFile::ReadHeaderL(file, header);
 
_LIT(KFileId1,"ID1 = %d\n");
console->Printf(KFileId1,header.iId1);
_LIT(KFileId2,"ID2 = %d\n");
console->Printf(KFileId2,header.iId2);
_LIT(KCompressionMethod,"compression method = %d\n");
console->Printf(KCompressionMethod,header.iCompressionMethod);
_LIT(KFlags,"flags = %d\n");
console->Printf(KFlags,header.iFlags);
_LIT(KTimeStamp,"time stamp = %d\n");
console->Printf(KTimeStamp,header.iTime);
_LIT(KExtraFlags,"extra flags %d\n");
console->Printf(KExtraFlags,header.iExtraFlags);
_LIT(KOS,"OS %d\n");
console->Printf(KOS,header.iOs);
 
if (header.iFlags & EZGZipFile::EFText)
{
_LIT(KText,"text flag set\n");
console->Printf(KText);
}
 
if (header.iFlags & EZGZipFile::EFHcrc)
{
_LIT(KCrc16,"CRC16 = %d\n");
console->Printf(KCrc16,header.iCrc);
}
 
if (header.iFlags & EZGZipFile::EFExtra)
{
_LIT(KExtraLength,"extra length %d\n");
console->Printf(KExtraLength,header.iXlen);
HBufC *buf = HBufC::NewLC(header.iExtra->Length());
buf->Des().Copy(*header.iExtra);
console->Printf(*buf);
CleanupStack::PopAndDestroy(); //buf
}
 
if (header.iFlags & EZGZipFile::EFName)
{
_LIT(KFName,"fname: %S\n");
HBufC *buf = HBufC::NewLC(header.iFname->Length());
buf->Des().Copy(*header.iFname);
console->Printf(KFName,buf);
CleanupStack::PopAndDestroy(); //buf
}
 
if (header.iFlags & EZGZipFile::EFComment)
{
_LIT(KComment,"comment: %S\n");
HBufC *buf = HBufC::NewLC(header.iComment->Length());
buf->Des().Copy(*header.iComment);
console->Printf(KComment,buf);
CleanupStack::PopAndDestroy(); //buf
}
}

Postconditions

The trailer and header info from the given GZIP file is printed to the console.

See also

CS000949 - Compressing and decompressing GZIP files

The GZIP format is specified in http://www.faqs.org/rfcs/rfc1952.html.

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