C++ ZLib GZipStream Decompression NULL terminated - c++

Question

There are a lot of questions out there revolving around zlib and GZipStreams but none that I've found answer this question. I'm using a C# GZipStream to send compressed data to a client. It reads the compressed data in entirely then tries to decompress it. However, each time inflate() is called in the loop it only gets the NULL terminated string. When sending a binary this is a pretty huge problem.
Before I show you code, I just wanted to say that if I write the received compressed bytes to a .gz file and use gzFile/gzopen/gzread/gzclose everything works perfectly. That means all the data is coming in properly. I want to read in the compressed data, decompress it in memory, and have the contents in a variable.
I think the issue is that inflate() is writing to a char* which is NULL terminated. I just don't know how to get it to be a string. I do fully anticipate this being a major oversight and a simple fix. Thanks for any help!
Here's the decompression code:
bool DecompressString(const std::string& message, std::string& dMsg)
{
int bufferSize = 512;
int messageSize = message.size() + 1;
//decompress string
z_stream zs;
memset(&zs, 0, sizeof(zs));
zs.zalloc = Z_NULL;
zs.zfree = Z_NULL;
zs.opaque = Z_NULL;
zs.next_in = (Bytef*)message.data();
zs.avail_in = messageSize;
int ret = Z_OK;
unsigned char* outbuffer = new unsigned char[bufferSize];
if (inflateInit2(&zs, 16+MAX_WBITS) == Z_OK)
{
do {
zs.next_out = outbuffer;
zs.avail_out = bufferSize;
ret = inflate(&zs, Z_NO_FLUSH);
if (ret < 0) return false;
std::stringstream tmpString;
tmpString << outbuffer;
if (dMsg.size() < zs.total_out) {
dMsg.append(tmpString.str().substr(0, zs.total_out - dMsg.size()));
}
} while (ret == Z_OK);
}
inflateEnd(&zs);
delete[] outbuffer;
//"\n<EOF>" is appended by sender to signify the end of file. This removes it
if (dMsg.find("\n<EOF>") != -1)
dMsg = dMsg.substr(0, dMsg.find("\n<EOF>"));
return true;
}
Working code from solution:
bool DecompressString(const std::string& message, std::string& dMsg)
{
int bufferSize = 512;
int messageSize = message.size() + 1;
//decompress string
z_stream zs;
memset(&zs, 0, sizeof(zs));
zs.zalloc = Z_NULL;
zs.zfree = Z_NULL;
zs.opaque = Z_NULL;
zs.next_in = (Bytef*)message.data();
zs.avail_in = messageSize;
int ret = Z_OK;
unsigned char* outbuffer = new unsigned char[bufferSize];
if (inflateInit2(&zs, 16+MAX_WBITS) == Z_OK)
{
// get the decompressed bytes blockwise using repeated calls to inflate
do {
zs.next_out = outbuffer;
zs.avail_out = bufferSize;
ret = inflate(&zs, Z_NO_FLUSH);
if (ret < 0) return false;
//Here's the difference
if (dMsg.size() < zs.total_out)
dMsg.append(reinterpret_cast<char*>(outbuffer), bufferSize);
//End
} while (ret == Z_OK);
}
inflateEnd(&zs);
delete[] outbuffer;
if (dMsg.find("\n<EOF>") != -1)
dMsg = dMsg.substr(0, dMsg.find("\n<EOF>"));
return true;
}

Answer 1

string is not a problem in itself, it can handle binary data.
It is this line that assumes a zero-terminated c-string:
tmpString << outbuffer;
Replace it with
tmpString.append(outbuffer, bufferSize);