This code is to perform http request that requires Digest authentication.

curl_http_get.cpp

#include <iostream>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <curl/curl.h>

#include <vector>
#include <chrono>
#include <thread>

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

class CurlGlobalObject
{
public:
    CurlGlobalObject()
    {
        curl_global_init(CURL_GLOBAL_ALL);
        std::cout << "Initialized Curl" << std::endl;
    }

    ~CurlGlobalObject()
    {
        curl_global_cleanup();
        std::cout << "Curl cleanup" << std::endl;
    }
};

CurlGlobalObject curlGlobalObject;

class CurlHttpGet
{
public:
    CURL* curlHandle;
    std::vector<uint8_t> data;

    std::string url;
    std::string username;
    std::string password;
    bool verbose;
    
    static size_t writeDataCallback(void* contents, size_t size, size_t nmemb, void* userp)
    {
        std::vector<uint8_t>* data = reinterpret_cast<std::vector<uint8_t>*>(userp);
        size_t realsize = size * nmemb;

        uint8_t* beginning = (uint8_t*)contents;
        uint8_t* ending = &(((uint8_t*)contents)[realsize]);
        std::vector<uint8_t> newData(beginning, ending);

        data->insert(data->end(), newData.begin(), newData.end());

        return realsize;
    }

    CurlHttpGet(std::string url, std::string username, std::string password, bool verbose)
        : url(url)
        , username(username)
        , password(password)
        , verbose(false)
    {
        this->curlHandle = curl_easy_init();
    }

    ~CurlHttpGet()
    {
        curl_easy_cleanup(this->curlHandle);
    }

    void setOptions()
    {
        std::string userpwd(this->username + ":" + this->password);

        curl_easy_setopt(this->curlHandle, CURLOPT_URL, this->url.c_str());
        curl_easy_setopt(this->curlHandle, CURLOPT_WRITEFUNCTION, CurlHttpGet::writeDataCallback);
        curl_easy_setopt(this->curlHandle, CURLOPT_WRITEDATA, &this->data);
        curl_easy_setopt(this->curlHandle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
        curl_easy_setopt(this->curlHandle, CURLOPT_USERPWD, userpwd.c_str());
        curl_easy_setopt(this->curlHandle, CURLOPT_FOLLOWLOCATION, 1L);
        curl_easy_setopt(this->curlHandle, CURLOPT_HTTPAUTH, CURLAUTH_DIGEST);
        curl_easy_setopt(this->curlHandle, CURLOPT_HTTPGET, 1L);
        if(this->verbose)
        {
            curl_easy_setopt(this->curlHandle, CURLOPT_VERBOSE, 1L);
        }
    }
    
    void perform()
    {
        this->setOptions();
        CURLcode res = curl_easy_perform(this->curlHandle);
        if(res != CURLE_OK)
        {
            std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
        }
        else
        {
            std::cout << "Received: " << data.size() << std::endl;;
        }

    }
};

int main(void)
{
    while(true)
    {
        CurlHttpGet httpGet("http://192.168.0.170/axis-cgi/jpg/image.cgi", "root", "pass", false);
        httpGet.perform();
        cv::Mat image = cv::imdecode(httpGet.data, 1);
        cv::imshow("DISPLAY", image);
        cv::waitKey(1);
    }
    //FILE* outputFile = fopen("output.jpg", "wb");
    //fwrite(httpGet.data.data(), sizeof(uint8_t), httpGet.data.size(), outputFile);
    //fclose(outputFile);
        

    return 0;
}