JSON response split up over multiple cURL callbacks - c++

Question

Messing around with the League of Legends API.
I've had an issue for a couple of days now so I've simplified what's going on. I'm sending off a URL via cURL which should return a block of Json. The URL opens fine in my browser and displays the expected data. However for some strange reason, cURL (or the API?) is sending data to my callback function multiple times.
A few snippets of what returns:
Starts with - {"20278403":[{"name":"Pop...
Ends with - {"name":"Karthus's Overlords","ti
Literally cuts out with "ti. A new callback then begins, continuing on with the old data:
Starts with - er":"PLATINUM","que...
Ends with - "isInactive":false}]}]}
As you may notice, the correct termination for Json is present with the second callback's output. I know the suggestion will be 'why not just shove it all into one string and parse it after?' - the problem is that I need to send off several requests as you can only request X many players data at a time. So it's difficult to tell where one request's Json begins and the other ends!
Most importantly - does anyone know why this is happening? It seems extremely bizarre to return data across multiple callbacks.
If it helps.. Just a generic cURL call:
curl_easy_setopt(m_pCurl, CURLOPT_URL, "https://euw...")
curl_easy_setopt(m_pCurl, CURLOPT_WRITEFUNCTION, &DataSuccessCB);
curl_easy_perform(m_pCurl);
size_t CAPIReader::DataSuccessCB(char* cBuffer, size_t iSize, size_t nmemb, void* userData)
{
string sBuffer = string(cBuffer);
vStrVec.push_back(sBuffer); // vector holding all the returned json strings - intended to have a whole block of json in each one!
return (iSize * nmemb);
}
Thanks.

Answer 1

This is the normal behaviour of libcurl, you could see this in the getinmemory.c sample. I suppose that cURL callback the function when data are available from the socket. So if the TCP message is fragmented, the callback is called several times.
A possible solution to concatenate the message is to transmit a pointer to the string to fill :
size_t CAPIReader::DataSuccessCB(char* cBuffer, size_t iSize, size_t nmemb, void* userData)
{
std::string & buffer = *(std::string*)userData;
buffer.append((char*)contents,nmemb*iSize);
return (iSize * nmemb);
}
std::string data;
curl_easy_setopt(m_pCurl, CURLOPT_URL, "https://euw...")
curl_easy_setopt(m_pCurl, CURLOPT_WRITEFUNCTION, &DataSuccessCB);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&data);
if(curl_easy_perform(m_pCurl) == CURLE_OK)
{
// Parse the JSON data in data string
}