How to download from url and return contents as a string (using libcurl)

http_client.cpp

#include "http_client.h"

#include <memory>

std::string http_client::get_from_url(const std::string & a_url)
{
    std::string result;

    auto curl_deleter = [](CURL * curl_easy_handle) 
                        {
                            curl_easy_cleanup(curl_easy_handle);
                        };

    std::unique_ptr<CURL, decltype(curl_deleter)> curl_handle(curl_easy_init(), curl_deleter);

    curl_easy_setopt(curl_handle.get(), CURLOPT_URL, a_url.c_str());
    curl_easy_setopt(curl_handle.get(), CURLOPT_WRITEFUNCTION, http_client::curl_writefunction_callback);
    curl_easy_setopt(curl_handle.get(), CURLOPT_WRITEDATA, &result);
    CURLcode curl_easy_perform_result = curl_easy_perform(curl_handle.get());

    return result;
}

size_t http_client::curl_writefunction_callback(void * a_buffer, size_t a_size, size_t a_nmemb, void * a_userp)
{
    size_t resulting_size = a_size * a_nmemb;

    std::string * result_string = static_cast<std::string *>(a_userp);
    char * buffer_char_ptr = static_cast<char *>(a_buffer);

    try {
        result_string->append(buffer_char_ptr, resulting_size);
    }
    catch (const std::length_error&) {
        return 0;
    }

    return resulting_size;
}

http_client.h

#ifndef HTTP_CLIENT_H
#define HTTP_CLIENT_H

#include <string>

#include <curl/curl.h>

class http_client 
{
public:
    static std::string get_from_url(const std::string& a_url);

private:
    static size_t curl_writefunction_callback(void * a_buffer, size_t a_size, size_t a_nmemb, void * a_userp);
};

#endif HTTP_CLIENT_H