The Web as a Data Source: Automating HTTP with C++ and libcurl (2002)

The Web as a Data Source: Automating HTTP with C++ and libcurl

By late 2002, the web has grown into a massive repository of information. If your C++ desktop application isn't talking to a web server for updates or data, it's already obsolete. But for we developers, the real challenge is testing our web apps. Clicking 'Refresh' in Internet Explorer 6.0 and visually checking the HTML is not 'Quality Assurance'.

We need to automate our requests. The industry standard for this is libcurl, Daniel Stenberg's masterpiece of a multi-protocol library. It’s fast, it’s stable, and it’s become the backbone of modern C++ network development.

The Basic libcurl Workflow

The curl_easy interface is what you'll use 90% of the time. You initialize a handle, set some options, and perform the request.

#include <curl/curl.h>
#include <iostream>

size_t WriteCallback(void* contents, size_t size, size_t nmemb, void* userp) {
    ((std::string*)userp)->append((char*)contents, size * nmemb);
    return size * nmemb;
}

int main() {
    CURL* curl;
    CURLcode res;
    std::string readBuffer;

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://www.google.com");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
        
        // Execute the GET request
        res = curl_easy_perform(curl);
        
        if(res == CURLE_OK) {
            std::cout << "Successfully retrieved " << readBuffer.size() << " bytes." << std::endl;
        }

        curl_easy_cleanup(curl);
    }
    return 0;
}

Handling Forms and POST Requests

In 2002, we're doing a lot of automated login testing. This requires sending application/x-www-form-urlencoded data via POST.

// Within your curl setup...
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "user=admin&pass=secret123&login=1");
curl_easy_setopt(curl, CURLOPT_POST, 1L);

Managing Cookies and State

The web is stateless, but our applications aren't. If you're testing a shopping cart or a user session, you must handle cookies. libcurl makes this trivial with its 'cookie jar'.

// Load existing cookies and save new ones automatically
curl_easy_setopt(curl, CURLOPT_COOKIEJAR, "cookies.txt");
curl_easy_setopt(curl, CURLOPT_COOKIEFILE, "cookies.txt");

Multithreaded Scrapers: The libcurl 'Multi' Interface

If you're building a real-world scraper (like a search engine bot or a price comparison engine), the easy interface won't cut it-it's blocking. For 2002-era performance, you need the curl_multi interface. This allows you to handle hundreds of transfers in parallel on a single thread using non-blocking I/O.

This approach is significantly faster than launching a separate thread per connection, especially on the Windows 2000/XP kernels which still have non-trivial thread creation costs. Pair libcurl with a robust HTML parser like libxml2 and you can transform any website into a structured data feed.

Aunimeda designs and builds scalable software architectures - from system design to implementation and ongoing engineering.

Contact us to discuss architecture for your project. See also: Custom Software Development, Web Development