Missing something when decompressing HTTP gzipped response - c++

Question

I have recently been setting up various testing environments and in this cas I nneed to read and decode a gzip response from a HTTP server. I know what I have so far works as I have tested it with wireshark and hardcoded data as outlined below, my question is what is wrong with how I am handling the gizzped data from a HTTP server?
Here is what Im using:
From this thread http://www.qtcentre.org/threads/30031-qUncompress-data-from-gzip I am using the gzipDecopress function with the data provided and seeing that it works.
QByteArray gzipDecompress( QByteArray compressData )
{
//Hardcode sample data
const char dat[40] = {
0x1F, 0x8B, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0xAA, 0x2E, 0x2E, 0x49, 0x2C, 0x29,
0x2D, 0xB6, 0x4A, 0x4B, 0xCC, 0x29, 0x4E, 0xAD, 0x05, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x03, 0x00,
0x2A, 0x63, 0x18, 0xC5, 0x0E, 0x00, 0x00, 0x00};
compressData = QByteArray::fromRawData( dat, 40);
//decompress GZIP data
//strip header and trailer
compressData.remove(0, 10);
compressData.chop(12);
const int buffersize = 16384;
quint8 buffer[buffersize];
z_stream cmpr_stream;
cmpr_stream.next_in = (unsigned char *)compressData.data();
cmpr_stream.avail_in = compressData.size();
cmpr_stream.total_in = 0;
cmpr_stream.next_out = buffer;
cmpr_stream.avail_out = buffersize;
cmpr_stream.total_out = 0;
cmpr_stream.zalloc = Z_NULL;
cmpr_stream.zalloc = Z_NULL;
if( inflateInit2(&cmpr_stream, -8 ) != Z_OK) {
qDebug() << "cmpr_stream error!";
}
QByteArray uncompressed;
do {
int status = inflate( &cmpr_stream, Z_SYNC_FLUSH );
if(status == Z_OK || status == Z_STREAM_END) {
uncompressed.append(QByteArray::fromRawData((char *)buffer, buffersize - cmpr_stream.avail_out));
cmpr_stream.next_out = buffer;
cmpr_stream.avail_out = buffersize;
} else {
inflateEnd(&cmpr_stream);
}
if(status == Z_STREAM_END) {
inflateEnd(&cmpr_stream);
break;
}
}while(cmpr_stream.avail_out == 0);
return uncompressed;
}
When the data is hardcoded as in that example, the string is decompressed. However, when I read the response from a HTTP server and store it in a QByteArray, it cannot be uncompressed. I am reading the response as follows and I can see it works when comparing the results on wireshark
//Read that length of encoded data
char EncodedData[ LengthToRead ];
memset( EncodedData, 0, LengthToRead );
recv( socketDesc, EncodedData, LengthToRead, 0 );
EndOfData = true;
//EncodedDataBytes = QByteArray((char*)EncodedData);
EncodedDataBytes = QByteArray::fromRawData(EncodedData, LengthToRead );
I assume i am missing some header or byte order when reading the response, but at the moment have no idea what. Any help very welcome!!
EDIT: So I have been looking at this a little more over the weekend and at the moment im trying to test the encode and decode of the given hex string, which is "{status:false}" in plain text. I have tried to use online gzip encoders such as http://www.txtwizard.net/compression but it returns some ascii text that does not match the hex string in the above code. When I use PHPs gzcompress( "{status:false}", 1) function it gives me non-ascii values, that I cannot copy/paste to test since they are ascii. So I am wondering if there is any standard reference for gzip encode/decode? It is definitely not in some special encoding since both firefox and wireshark can decode the packets, but my software cannot.

Answer 1

So the issue was with my gzip function, the correct function I found on this link: uncompress error when using zlib
As mentioned above by Cornstalks the infalteInit2 function needs to take MAX_WBITS+16 as its max bit size, I think that was the issue. If anybody knows any libraries or plugins to handle this please post them here! I am surprised that this had to be coded manually when it is so commonly used by HTTP clients/servers.