Zip file format.

zip_file_format

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>

#pragma warning(disable:4996)


/************************************************************************/
/* Zip file struct                                                      */
/*                                                                      */
/* FileEntry0,[..., FileEntryN] +  DirEntry0,[..., DirEntryN]           */
/*                                         + DigitalSignature + EndEntry*/
/*     [FileEntryHeader + Data + [DataDesc]]                            */
/************************************************************************/


#pragma pack(push) 
#pragma pack(2)

struct ZipDate
{
	unsigned short Mday:5;           /* day of the month - [1,31] */
	unsigned short Mon:4;            /* months since January - [0,11] */
	unsigned short Year:7;           /* years - [1980..2044] */	
};

struct ZipTime
{
	unsigned short Sec:5;            /* seconds after the minute - [0,59] */
	unsigned short Min:6;            /* minutes after the hour - [0,59] */
	unsigned short Hour:5;           /* hours since midnight - [0,23] */	
};

#define ZIP_FILE_MAGIC_NUMBER 0x04034b50

struct ZipFileEntryHeader {
	//unsigned long  m_MagicNumber;          /* Magic number                    4 bytes, must be 0x04034b50 */
	unsigned short m_VersionNeeded;        /* version needed to extract       2 bytes */
	unsigned short m_Flag;                 /* general purpose bit flag        2 bytes */
	unsigned short m_CompressionMethod;    /* compression method              2 bytes */
	ZipTime        m_LastModTime;          /* last mod file time in Dos fmt   2 bytes */
	ZipDate        m_LastModDate;          /* last mod file time in Dos date  2 bytes */
	unsigned long  m_CRC;                  /* crc-32                          4 bytes */
	unsigned long  m_CompressedSize;       /* compressed size                 4 bytes */
	unsigned long  m_UncompressedSize;     /* uncompressed size               4 bytes */
	unsigned short m_FilenameSize;         /* filename length                 2 bytes */
	unsigned short m_FileExtraSize;        /* extra field length              2 bytes */
	/* file name (variable size) */
	/* extra field (variable size) */
};


/**
* This part only availably when the 3rd bit is 1 of 'm_Flag' in 'ZipEntryHeader'
*/
struct ZipDataDesc {
	unsigned long m_CRC;                   /* crc-32                          4 bytes */
	unsigned long  m_CompressedSize;       /* compressed size                 4 bytes */
	unsigned long  m_UncompressedSize;     /* uncompressed size               4 bytes */
};


#define ZIP_DIR_MAGIC_NUMBER 0x02014b50

struct ZipDirEntry {
    //unsigned long  m_MagicNumber;           /* Magic number                    4 bytes  (0x02014b50) */
	unsigned short m_VersionMade;           /* version made by                 2 bytes */
	unsigned short m_VersionNeeded;         /* version needed to extract       2 bytes */
	unsigned short m_Flag;                  /* general purpose bit flag        2 bytes */
	unsigned short m_CompressionMethod;     /* compression method              2 bytes */
	ZipTime        m_LastModTime;          /* last mod file time in Dos fmt   2 bytes */
	ZipDate        m_LastModData;          /* last mod file time in Dos fmt   2 bytes */
	unsigned long  m_CRC;                  /* crc-32                          4 bytes */
	unsigned long  m_CompressedSize;       /* compressed size                 4 bytes */
	unsigned long  m_UncompressedSize;     /* uncompressed size               4 bytes */
	unsigned short m_FilenameSize;         /* filename length                 2 bytes */
	unsigned short m_FileExtraSize;        /* extra field length              2 bytes */
	unsigned short m_FileCommentSize;      /* file comment length             2 bytes */
	unsigned short m_DiskNumberStart;      /* disk number start               2 bytes */
	unsigned short m_InternalFileAttribute;/* internal file attributes        2 bytes */
	unsigned long m_ExternalFileAttribute; /* external file attributes        4 bytes */
	unsigned long m_OffsetOfLocalHeader;   /* relative offset of local header 4 bytes */
	/* file name (variable size)   */
	/* extra field (variable size) */
	/* file comment (variable size) */
};


#define ZIP_DIR_SIGN_MAGIC_NUMBER 0x05054b50

struct ZipDirSignature {
	//unsigned long  m_MagicNumber;           /*header signature                4 bytes  (0x05054b50) */
	unsigned short m_DataSize;              /* size of data                    2 bytes */
	/* signature data (variable size) */
};


#define ZIP_DIR_END_MAGIC_NUMBER 0x06054b50

struct ZipEndDir {
	//unsigned long  m_MagicNumber;      /* end of central dir signature    4 bytes  (0x06054b50) */
	unsigned short m_DiskNumber;       /* number of this disk             2 bytes */
	unsigned short m_DiskNumWithStart; /* number of the disk with the start of the central directory  2 bytes */
	unsigned short m_DiskEntryCount;   /* total number of entries in the	central directory on this disk  2 bytes */
	unsigned short m_EntryCount;       /* total number of entries in	the central directory           2 bytes  */
	unsigned long  m_DirCount;         /* size of the central directory   4 bytes */
	unsigned long  m_DiskOffset;       /* offset of start of central directory with respect to the starting disk number        4 bytes */
	unsigned short m_Comment;          /* .ZIP file comment length        2 bytes */
	/* .ZIP file comment       (variable size) */
};


#pragma pack(pop)





int main(int argc, char** argv)
{
	FILE* fp = ::fopen( "Test.zip", "rb" );

    unsigned long  magic_number = 0;
	char szFileName[256];

	::fread( &magic_number, sizeof(unsigned long), 1, fp );
	while( ZIP_FILE_MAGIC_NUMBER==magic_number ) {
		printf( "A local file: " );
		ZipFileEntryHeader zip_local_header;
		::fread( &zip_local_header, sizeof(ZipFileEntryHeader), 1, fp );		
		if( zip_local_header.m_FilenameSize> 0 ) {
			::fread(szFileName, zip_local_header.m_FilenameSize, 1, fp );
			szFileName[zip_local_header.m_FilenameSize] = 0;
			printf( " name:%s.", szFileName );
			if( (zip_local_header.m_Flag & 0x00000001) ) {  //an encrypt data
				printf( " encrypted." );
			}
		}

		if( zip_local_header.m_FileExtraSize> 0 ) {
			::fseek(fp, zip_local_header.m_FileExtraSize, SEEK_CUR);
		}		

		// file data
		::fseek(fp, zip_local_header.m_CompressedSize, SEEK_CUR);

		printf( "\n" );
		::fread( &magic_number, sizeof(unsigned long), 1, fp );
		if( 0x08074b50==magic_number || (zip_local_header.m_Flag & (0x00000001<<3)) ) {
			if( 0x08074b50!=magic_number )
				::fseek(fp, -4, SEEK_CUR);
			//when the 3rd bit is 1 of 'm_Flag' in 'ZipEntryHeader'
			ZipDataDesc data_desc;
			::fread( &data_desc, sizeof(ZipDataDesc), 1, fp );
			zip_local_header.m_CRC = data_desc.m_CRC;
			zip_local_header.m_CompressedSize = data_desc.m_CompressedSize;
			zip_local_header.m_UncompressedSize = data_desc.m_UncompressedSize;
			::fread( &magic_number, sizeof(unsigned long), 1, fp );
		}
	}

	while( ZIP_DIR_MAGIC_NUMBER==magic_number ) {
		printf( "A dir: " );
		ZipDirEntry zip_dir;
		::fread( &zip_dir, sizeof(ZipDirEntry), 1, fp );

		if( zip_dir.m_FilenameSize> 0 ) {
			::fread(szFileName, zip_dir.m_FilenameSize, 1, fp );
			szFileName[zip_dir.m_FilenameSize] = 0;
			printf( "name:%s.", szFileName );
		}

		if( zip_dir.m_FileExtraSize> 0 ) {
			::fseek(fp, zip_dir.m_FileExtraSize, SEEK_CUR);
		}

		if( zip_dir.m_FileCommentSize> 0 ) {
			::fseek(fp, zip_dir.m_FileCommentSize, SEEK_CUR);
		}
		printf( "\n" );

		::fread( &magic_number, sizeof(unsigned long), 1, fp );
	}

	while( ZIP_DIR_SIGN_MAGIC_NUMBER==magic_number ) {
		printf( "A dir sign.\n" );
		ZipDirSignature zip_dir_sign;
		::fread( &zip_dir_sign, sizeof(ZipDirSignature), 1, fp );

		if( zip_dir_sign.m_DataSize> 0 ) {
			::fseek(fp, zip_dir_sign.m_DataSize, SEEK_CUR);
		}

		::fread( &magic_number, sizeof(unsigned long), 1, fp );
	}

	if( ZIP_DIR_END_MAGIC_NUMBER==magic_number ) {
		printf( "A dir end." );
		ZipEndDir zip_dir_end;
		::fread( &zip_dir_end, sizeof(ZipEndDir), 1, fp );

		if( zip_dir_end.m_Comment> 0 ) {
			::fread(szFileName, zip_dir_end.m_Comment, 1, fp );
			szFileName[zip_dir_end.m_Comment] = 0;
			printf( " Comment:%s.", szFileName );
		}
		printf( "\n" );
	}

	::fclose( fp );
	return 0;
}