Programming

When I gzopen & gzread from a gzip file, it works OK. But I when I try to uncompress the same data from memory (either by reading to memory with fread or mmap()ing) using decompress, I get Z_DATA_ERROR. Is it because gzip file has some kind of headers that uncompress doesn't want?

How can I get around this?

Code:

fp = fopen("file.gz", "r");
buf = mmap(0,len,PROT_READ,MAP_SHARED,fileno(fp),0);
assert(buf);

if(uncompress(out,&outsize,buf,len) == Z_DATA_ERROR) fprintf(stderr,"boh\n");

I read somewhere that header is 8 bytes, so I tried

Code:

uncompress(out,&outsize,buf+8,len-8)

but it didn't make any difference either.

OK, I figured it out.

zlib function uncompress uses inflateInit(), which accepts zlib format, not gzip. I've changed inflateInit() to inflateInit2() and it worked.

However, for 2nd argument of inflateInit2(), I've tried various numbers but it worked for only 24,30,47. Which means at least 16MB of buffer! How can I get around this now?

That is strange, since it's only supposed to accept values of 8...15. What error do you get when you use other values?

mmh,
some time ago i used a library call libfz (?) it supports fzopen() that let you read or write any compressed file without much problems.

just my 2 cents, happy hacking