Gzip string unable to concatenate to a string - html

Question

I'm a newbie in c++ and I've been trying to search for an answer to this question but can hardly found an answer I'm trying to compress an html string body with zlib in gzip compression the compression gets done successfully but when I try to concatenate it to another string it won't concatenate at all rendering the body to be blank here is the compression code:
void compress_message(){
z_stream zs;
char outbuffer[32768];
long strlen = content.size();
int ret;
string outstring;
memset(&zs, 0, sizeof(zs));
if (deflateInit2(&zs,
Z_BEST_COMPRESSION,
Z_DEFLATED,
MOD_GZIP_ZLIB_WINDOWSIZE + 16,
MOD_GZIP_ZLIB_CFACTOR,
Z_DEFAULT_STRATEGY) != Z_OK
) {
throw(std::runtime_error("deflateInit2 failed while compressing."));
}
content = "";
zs.next_in = (Bytef*) content.data();
zs.avail_in = strlen;
do {
//cout << "compressing..." << endl;
zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
zs.avail_out = sizeof(outbuffer);
ret = deflate(&zs, Z_FINISH);
if (content.size() < zs.total_out) {
// append the block to the output string
content.append(outbuffer,
zs.total_out - content.size());
}
} while (ret == Z_OK);
deflateEnd(&zs);
//cout << "original: " << content << endl;
if (ret != Z_STREAM_END) { // an error occurred that was not EOF
ostringstream oss;
oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
throw(std::runtime_error(oss.str()));
}
}
base64 conversion function:
string tobase64(string data) {
string code64,
output = "";
int i = 0,
j = 0;
unsigned int slen = data.size();
const char* bytes_to_encode;
code64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";
unsigned char char_array_3[3],
char_array_4[4];
bytes_to_encode = data.c_str();
while(slen--){
char_array_3[i++] = bytes_to_encode[j++];
if(3 == i){
char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
char_array_4[3] = char_array_3[2] & 0x3f;
for(i = 0; i < 4; i++){
output += code64[char_array_4[i]];
}
i = 0;
}
}
if (i)
{
for(j = i; j < 3; j++)
char_array_3[j] = '\0';
char_array_4[0] = ( char_array_3[0] & 0xfc) >> 2;
char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
for (j = 0; (j < i + 1); j++)
output += code64[char_array_4[j]];
while((i++ < 3))
output += '=';
}
return output;
}
the string is successfully compressed but when I concatenate it to the string response like:
string final_content = ("HTTP/1.1 200 OK\r\n"+headers+"\r\n\r\n");
content = tobase64(content);
final_content += content;
I also tried
final_content.append(content);
They both have the same result the body is never concatenated the final_content when printed only shows:
HTTP/1.1 200 OK
...
Content-type: text/html
and the compressed string is never included have been trying to find answers online and couldn't figure it out please help. I'm working this on ubuntu 18.04