HOWTO decompress a gzip archive
emCompress-Pro provides the capability to decompress streams that are compressed in various formats, but it does not provide out-of-the-box container support.
Recognizing that customers may possibly want to deal with encapsulated streams, this code can be used with emCompress-Pro to check the integrity of a a gzip archive that contains files compressed with the DEFLATE algorithm:
/*********************************************************************
* (c) SEGGER Microcontroller GmbH *
* The Embedded Experts *
* www.segger.com *
**********************************************************************
-------------------------- END-OF-HEADER -----------------------------
File : CX_GZip.c
Purpose : List the content of a gzip-compressed file.
*/
/*********************************************************************
*
* #include Section
*
**********************************************************************
*/
#include "CX_Int.h"
#include "SEGGER_MEM.h"
#include "SEGGER_UTIL.h"
#include "SEGGER_CRC.h"
#include <stdio.h>
#include <stdlib.h>
/*********************************************************************
*
* Defines, fixed
*
**********************************************************************
*/
#define FTEXT 0x01
#define FHCRC 0x02
#define FEXTRA 0x04
#define FNAME 0x08
#define FCOMMENT 0x10
/*********************************************************************
*
* Local types
*
**********************************************************************
*/
typedef struct {
U32 ISize;
U32 CalcISize;
U32 CRC;
U32 CalcCRC;
} MEMBER_INFO;
/*********************************************************************
*
* Static data
*
**********************************************************************
*/
static SEGGER_MEM_CONTEXT _StaticAllocator;
/*********************************************************************
*
* Static code
*
**********************************************************************
*/
/*********************************************************************
*
* _PrintSignOn()
*
* Function description
* Displays the application's help information on stderr.
*/
static void _PrintSignOn(void) {
printf("\n");
printf("emCompress-Flex GZip Checker V%s ", CX_GetVersionText());
printf("compiled " __DATE__ " " __TIME__ "\n");
printf("%s www.segger.com\n\n", CX_GetCopyrightText());
}
/*********************************************************************
*
* _DecompressBlocks()
*
* Function description
* Decompress DEFLATE blocks.
*
* Parameters
* pFile - Pointer to input file.
* pInfo - Pointer to member information.
*/
static void _DecompressBlocks(FILE *pFile, MEMBER_INFO *pInfo) {
CX_DECODE_CONTEXT C;
CX_PARAS Paras;
CX_STREAM Stream;
int Status;
U8 ByteIn;
U8 ByteOut;
int Overread;
//
Paras.WindowSize = 32768;
Paras.MinLen = 3;
Paras.MaxLen = 258;
Paras.BlockLen = 0;
//
pInfo->ISize = 0;
pInfo->CalcISize = 0;
pInfo->CRC = 0;
pInfo->CalcCRC = 0xFFFFFFFF;
//
Stream.AvailIn = 0;
Stream.AvailOut = 0;
CX_DECODE_Init(&C, &CX_DEFLATE_Decode, &_StaticAllocator, &Paras);
for (;;) {
if (Stream.AvailIn == 0) {
if (fread(&ByteIn, 1, 1, pFile) > 0) {
Stream.pIn = &ByteIn;
Stream.AvailIn = 1;
}
}
Stream.pOut = &ByteOut;
Stream.AvailOut = 1;
//
Status = CX_DECODE_Process(&C, &Stream, feof(pFile) ? CX_FLUSH_END : CX_FLUSH_NONE);
if (Status < 0) {
printf("%s\n", CX_GetErrorText(Status));
exit(100);
}
if (Stream.AvailOut == 0) {
pInfo->CalcISize++;
pInfo->CalcCRC = SEGGER_CRC_Calc_EDB88320(&ByteOut, 1, pInfo->CalcCRC);
}
if (Status == 1) {
break;
}
}
//
pInfo->CalcCRC = ~pInfo->CalcCRC;
//
Overread = CX_DECODE_GetBufferLen(&C) + Stream.AvailIn;
fseek(pFile, -Overread, SEEK_CUR);
//
CX_DECODE_Exit(&C);
}
/*********************************************************************
*
* _PrintListing()
*
* Function description
* Displays the content of a file, ensures compressed data
* can be decompressed.
*
* Parameters
* pFile - Pointer to input file.
*
* Syntax
* From [RFC 1952], each member has the following structure:
*
* +---+---+---+---+---+---+---+---+---+---+
* |ID1|ID2|CM |FLG| MTIME |XFL|OS | (more-->)
* +---+---+---+---+---+---+---+---+---+---+
*
* (if FLG.FEXTRA set)
*
* +---+---+=================================+
* | XLEN |...XLEN bytes of "extra field"...| (more-->)
* +---+---+=================================+
*
* (if FLG.FNAME set)
*
* +=========================================+
* |...original file name, zero-terminated...| (more-->)
* +=========================================+
*
* (if FLG.FCOMMENT set)
*
* +===================================+
* |...file comment, zero-terminated...| (more-->)
* +===================================+
*
* (if FLG.FHCRC set)
*
* +---+---+
* | CRC16 |
* +---+---+
*
* +=======================+
* |...compressed blocks...| (more-->)
* +=======================+
*
* 0 1 2 3 4 5 6 7
* +---+---+---+---+---+---+---+---+
* | CRC32 | ISIZE |
* +---+---+---+---+---+---+---+---+
*/
static void _PrintListing(FILE *pFile) {
MEMBER_INFO Info;
U8 aHeader[10];
U8 aCRC[4];
U8 aISize[4];
char aName[256];
char c;
unsigned i;
//
printf(" Size CRC\n");
printf("File name Computed Stored Computed Stored Status\n");
printf("------------------- -------- -------- -------- -------- -----------\n");
//
for (;;) {
//
fread(aHeader, 1, sizeof(aHeader), pFile);
if (feof(pFile)) {
return;
}
if (ferror(pFile)) {
perror("Can't read input file");
exit(100);
}
//
if (aHeader[0] != 0x1F || aHeader[1]!= 0x8B) {
printf("Incorrect ID bytes for a gzip file\n");
exit(100);
}
if (aHeader[2] != 0x08) {
printf("Compression method is not DEFLATE\n");
exit(100);
}
//
if (aHeader[3] & FEXTRA) {
fseek(pFile, aHeader[8], SEEK_CUR);
}
if (aHeader[3] & FNAME) {
i = 0;
do {
fread(&c, 1, 1, pFile);
if (i < sizeof(aName)) {
aName[i++] = c;
}
} while (c != 0);
aName[sizeof(aName)-1] = '\0';
} else {
strcpy(aName, "<stdin>");
}
if (aHeader[3] & FCOMMENT) {
do {
fread(&c, 1, 1, pFile);
} while (c != 0);
aName[sizeof(aName)-1] = '\0';
}
if (aHeader[3] & FHCRC) {
fread(&c, 1, 1, pFile);
fread(&c, 1, 1, pFile);
}
//
_DecompressBlocks(pFile, &Info);
//
fread(aCRC, 1, 4, pFile);
fread(aISize, 1, 4, pFile);
Info.CRC = SEGGER_RdU32LE(aCRC);
Info.ISize = SEGGER_RdU32LE(aISize);
//
printf("%-20s %8u %8u %08X %08X ",
aName,
Info.ISize,
Info.CalcISize,
Info.CRC,
Info.CalcCRC);
if (Info.ISize == Info.CalcISize && Info.CRC == Info.CalcCRC) {
printf("OK\n");
} else {
printf("Mismatch\n");
exit(100);
}
}
}
/*********************************************************************
*
* Public code
*
**********************************************************************
*/
/*********************************************************************
*
* main()
*
* Function description
* Application entry point.
*
* Parameters
* argc - Argument count.
* argv - Argument vector.
*
* Return value
* Exit status.
*/
int main(int argc, char **argv) {
FILE *pFile;
//
SEGGER_MEM_SYSTEM_HEAP_Init(&_StaticAllocator);
//
_PrintSignOn();
if (argc != 2) {
printf("Syntax: %s <filename>\n", argv[0]);
exit(100);
}
//
pFile = fopen(argv[1], "rb");
if (pFile == NULL) {
printf("%s: can't open '%s' for reading\n", argv[0], argv[1]);
exit(100);
}
//
_PrintListing(pFile);
fclose(pFile);
exit(0);
}
/*************************** End of file ****************************/
