C++ LibCurl retry on error - c++

Question

I want to retry a curl connection in my C++ program for 5 times. When it fails 5 times in a row, it should stop the execution of the program. However, it stops after the first error at this point. I am able to catch the error, however I don't know how to execute the previous curl connection. E.g., with jQuery I can use something like $.ajax(this);. For LibCurl in C++ I am looking for a similar solution.
My current LibCurl code is shown below, note that I use multiple curl connections which all have other settings, therefore I would like a general approach which I can use for all my LibCurl errors within my LibcurlError function which is also included below.
curl = curl_easy_init();
if (curl) {
CurlResponse = "";
host = "http://google.com";
LibcurlHeaders = curl_slist_append(NULL, "Expect:");
if (ProxyAddress.length() > 0) {
curl_easy_setopt(curl, CURLOPT_PROXY, ProxyAddress.c_str());
}
curl_easy_setopt(curl, CURLOPT_URL, (host).c_str());
curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1);
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER , 1);
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST , 1);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, LibcurlHeaders);
res = curl_easy_perform(curl);
curl_slist_free_all(LibcurlHeaders);
if (res != CURLE_OK) {
//AT THIS POINT I WOULD LIKE TO RETRY FOR 5 TIMES WHICH I WOULD LIKE TO CATCH IN MY LibcurlError FUNCTION.
LibcurlError(curl_easy_strerror(res), host);
}
curl_easy_cleanup(curl);
}
curl_global_cleanup();
void LibcurlError(string error, string host) {
//IF FAILED FOR LESS THEN 5 TIMES IN A ROW -> RETRY CURL
//ELSE I WOULD LIKE TO EXECUTE MY ORIGINAL CODE WHICH IS STATED BELOW
Message = "LibCurl Error: ";
if (error == "Couldn't resolve host name") {
Message.append("Couldn't connect to the server of ");
if (host.find("google.com") != string::npos) {
Message.append("Google");
}
else {
Message.append("'" + host + "'");
}
}
else {
Message.append("'" + error + "'");
}
cout << Message << endl;
system("pause");
exit(0);
}

Answer 1

There is no CURL method that specifically does this because it can be accomplished by repeated calls to curl_easy_perform.
Here is how you would write the code in your question (the relevant part at least) using loops to retry the CURL request repeatedly:
#include <unistd.h>
#include <curl/curl.h>
/*
* This is the maximum number of times CURL will run
*/
const int max_attempts = 5;
curl = curl_easy_init();
if (curl) {
CurlResponse = "";
host = "http://google.com";
LibcurlHeaders = curl_slist_append(NULL, "Expect:");
if (ProxyAddress.length() > 0) {
curl_easy_setopt(curl, CURLOPT_PROXY, ProxyAddress.c_str());
}
curl_easy_setopt(curl, CURLOPT_URL, (host).c_str());
curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1);
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER , 1);
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST , 1);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, LibcurlHeaders);
for (int i = 1; i <= max_attempts &&
(res = curl_easy_perform(curl)) != CURLE_OK; i++) {
/*
* At this point, you would sleep
* for some seconds between requests
*/
const int sleep_secs = 1;
sleep(sleep_secs);
}
// As others have mentioned, you should delete this line:
//curl_slist_free_all(LibcurlHeaders);
if (res != CURLE_OK) {
// The max retries have all failed
LibcurlError(curl_easy_strerror(res), host);
}
else {
// The request has succeeded in the first `max_retries` attempts
// ...
}
curl_easy_cleanup(curl);
}
curl_global_cleanup();