amoeba
amoeba

Reputation: 105

zlib inflate data error

I am having some trouble inflating a simple HTML file using zlib that has been compressed using gzip.

The file is below along with the steps I am taking to open it as well as the inflation function I am attempting to use. When I run the function I get zlib's error code Z_DATA_ERROR. From what I can tell I have stuck faithfully to zlib's usage example (found here) but nonetheless I am having some trouble.

The inflation routine doesn't turn up an error until after the inflate() method is called and the function returns in the switch statement, but I haven't been able to track down just what the problem is.

Any help here would be much appreciated.

Compressed file:

<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>TEST</title>
</head>

<body>
<ul>
   <li>hello</li>
   <li>I</li>
   <li>am</li>
   <li>a</li>
   <li>test</li>
   <li>web</li>
   <li>page</li>
</ul>
</body>
</html>

Note: These are the file contents before gzip compression.

File opening: sourcefile here is then passed in inf().

FILE *sourcefile;
sourcefile = fopen("/Users/me/pathtofile/test.html.gz", "r");

Inflate routine:

inf(FILE *source, FILE *dest){

int chunk = 16384;

//setup zlib variables
int return_val;
unsigned have;
z_stream z_strm;
unsigned char in[chunk];
unsigned char out[chunk];

//allocate inflate state
z_strm.zalloc = Z_NULL;
z_strm.zfree = Z_NULL;
z_strm.opaque = Z_NULL;
z_strm.avail_in = 0;
z_strm.next_in = Z_NULL;

return_val = inflateInit(&z_strm);
if(return_val != Z_OK){
    return return_val;
}

cout << "zlib setup complete" << endl;

//decompress
do{
    z_strm.avail_in = fread(in, 1, chunk, source);

    //check for error
    if (ferror(source)){
        (void)inflateEnd(&z_strm);
        return Z_ERRNO;
    }

    if(z_strm.avail_in == 0){
        break;
    }
    z_strm.next_in = in;

    cout << "inflate loop") << endl;

    //inflate the data
    do{
        z_strm.avail_out = chunk;
        z_strm.next_out = out;

        return_val = inflate(&z_strm, Z_NO_FLUSH);
        assert(return_val != Z_STREAM_ERROR);

        cout << "switch statement start" << endl;

        switch(return_val){
            case Z_NEED_DICT:
                return_val = Z_DATA_ERROR;
                cout << "case: Z_NEED_DICT" << endl;
            case Z_DATA_ERROR:
                cout<< "case: Z_DATA_ERROR" << endl;
            case Z_MEM_ERROR:
                cout << "case: Z_MEM_ERROR" << endl;
                void(inflateEnd(&z_strm));
                return return_val;
        }

        cout << "switch statement end" << endl;

        have = chunk - z_strm.avail_out;

        if(fwrite(out, 1, have, dest) != have || ferror(dest)){
            (void)inflateEnd(&z_strm);
            return Z_ERRNO;
        }

    }while(z_strm.avail_out == 0);

}while(return_val != Z_STREAM_END);
}

Upvotes: 1

Views: 5852

Answers (2)

sam
sam

Reputation: 1401

The main reason could be you have wrong initialization inflateInit2(&z_strm,15+32) and for inflate inflate(&z_strm, Z_SYNC_FLUSH ); Could solve your problem .

Upvotes: 0

Mark Adler
Mark Adler

Reputation: 112239

You need to use inflateInit2() instead of inflateInit() to request decoding of the gzip format. zlib by default is looking for the zlib format.

Upvotes: 1

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