Writing Data Fails With CURLOPT_WRITEFUNCTION After Many Writeback Calls - c++

Question

Essentially, I have a write callback that I set for CURLOPT_WRITEFUNCTION. I also set my pointer for writing the data to in CURLOPT_WRITEDATA.
I run an infinite while loop for around 5 seconds, then CURLOPT fails to right data to the void* up pointer defined in CURLOPT_WRITEDATA, then after that one failure it starts working again. I got tons of successful writes sprinkled with failures. Is this a memory issue, and if so, is there a way to circumvent reaching this issue altogether?
// these locations will likely be different on your local.
#include "../cygwin64/usr/include/curl/curl.h"
#include "../cygwin64/usr/include/json/json.h"
size_t write_callback(char *buf, size_t size, size_t nmemb, void* up) {
size_t num_bytes = size*nmemb;
std::string* data = (std::string*) up;
for(int i = 0; i < num_bytes; i++) {
data->push_back(buf[i]);
}
return num_bytes;
}
CURL* init_curl(struct curl_slist *headers, std::string* chunk) {
CURL *curl;
CURLcode res;
curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &write_callback);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *) chunk);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
return curl;
}
bool curl_get(struct curl_slist *headers, const std::string& url,
Json::Value* json_res) {
// this is where my data should be written to
std::string data;
CURL* curl = init_curl(headers, &data);
CURLcode res;
bool success = true;
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
res = curl_easy_perform(curl);
if(res != CURLE_OK) {
std::cout << "Could not perform get for " << url << std::endl;
std::cout << curl_easy_strerror(res) << std::endl;
success = false;
} else {
Json::Value json_data;
Json::CharReaderBuilder json_reader;
std::istringstream stream_data(data);
std::string errs;
if(Json::parseFromStream(json_reader, stream_data, &json_data, &errs)) {
std::cout << "successfully parsed JSON data for: " << url << std::endl;
*json_res = json_data;
} else {
std::cout << "failed to parse JSON data for: " << url << std::endl;
std::cout << errs << std::endl;
std::cout << json_data << std::endl;
std::cout << "finished failing" << std::endl;
success = false;
}
}
} else {
success = false;
}
curl_slist_free_all(headers);
curl_easy_cleanup(curl);
return success;
}
int main(int argc, char** argv) {
curl_global_init(CURL_GLOBAL_ALL);
struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "Accept: application/json");
while (true) {
Json::Value response;
if (curl_get(headers, "https://api.robinhood.com/quotes/?symbols=AMZN", &response)) {
std::cout << response << std::endl;
} else {
// reaches here sometimes because response (my data) is null
std::cout << "failed to get last trade price" << std::endl;
}
}
curl_global_cleanup();
return 0;
}
Expect no failures, but I get intermittent failures to right the data to my WRITEDATA chunk.