Uncompress() of 'zlib' returns Z_DATA_ERROR

Question

I made a simple function which takes a gzipped file, and extracts somewhere. For testing purposes i'm using a text file which had been gzipped through a generic utility gzip. But for some reason the Uncompress() returns an error Z_DATA_ERROR.

I walked in a debugger till the function, and it surely gets the right data(a whole file content, it's just 37 bytes), so it seems to be one of two: the frightful zlib-bug is stealing your time for now, or I am missing something important and then I really sorry.

#include <zlib.h>
#include <cstdio>

int UngzipFile(FILE* Dest, FILE* Source){
    #define IN_SIZE 256
    #define OUT_SIZE 2048
    bool EOFReached=false;
    Bytef in[IN_SIZE];
    Bytef out[OUT_SIZE];
    while(!EOFReached){//for no eof
        uLong In_ReadCnt = fread(in,1,IN_SIZE,Source);//read a bytes from a file to input buffer
        if(In_ReadCnt!=IN_SIZE){
            if(!feof(Source) ){
                perror("ERR");
                return 0;
            }
            else    EOFReached=true;
        }
        uLong OutReadCnt = OUT_SIZE;//upon exit 'uncompress' this will have actual uncompressed size
        int err = uncompress(out, &OutReadCnt, in, In_ReadCnt);//uncompress the bytes to output
        if(err!=Z_OK){
            printf("An error ocurred in GZIP, errcode is %i\n", err);
            return 0;
        }
        if(fwrite(out,1,OutReadCnt,Dest)!=OUT_SIZE ){//write to a 'Dest' file
            perror("ERR");
            return 0;
        }
    }
    return 1;
} 

int main(int argc, char** argv) {
    FILE* In = fopen("/tmp/Kawabunga.gz", "r+b");
    FILE* Out = fopen("/tmp/PureKawabunga", "w+b");
    if(!In || !Out){
        perror("");
        return 1;
    }
    if(!UngzipFile(Out,In))printf("An error encountered\n");
}

Answer 1

You should use inflate(), not uncompress(). In inflateInit2(), you can specify the gzip format (or auto-detection of the zlib or gzip format). See the documentation in zlib.h.

You can take the source code for uncompress() in zlib and make a simple change to use inflateInit2() instead of inflateInit() to create your own gzipuncompress(), or whatever you'd like to call it.