HTTP client in C++: making requests correctly from A to Z

HTTP client in C++: making requests correctly from A to Z

In the modern world of software development, the ability to interact with remote servers via HTTP is a fundamental skill. Whether it's downloading data from an API, submitting forms, or working with web services, C++ provides several powerful tools for creating HTTP clients. In this article, we will break down how to make HTTP requests correctly in C++, look at popular libraries, and write working code examples.

Why C++ for HTTP requests?

C++ does not have built-in HTTP support in the standard library, unlike Python or JavaScript. However, this is not a problem: there are time-tested libraries that allow you to easily and efficiently send requests. The main options are:

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• libcurl (cURL) — the most popular cross-platform library.
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• Boost.Beast — a modern library based on Boost.Asio.
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• WinHTTP — a built-in solution for Windows.
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• Qt Network — for Qt projects.
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In this article, we will focus on the first two, as they are the most versatile and suitable for most tasks.

1. HTTP client using libcurl

libcurl is a time-tested library that supports HTTP, HTTPS, FTP, and many other protocols. It is easy to use and well-documented.

Installing libcurl

For Linux (Ubuntu/Debian):

sudo apt-get install libcurl4-openssl-dev

For Windows, you can download pre-built binaries from the official curl.se website or use vcpkg:

vcpkg install curl

Simple GET request

Let's write a basic example of fetching data from a server:

#include <iostream>\n#include <string>\n#include <curl/curl.h>\n\n// Callback function for writing data\nstatic size_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {\n    size_t totalSize = size * nmemb;\n    output->append((char*)contents, totalSize);\n    return totalSize;\n}\n\nint main() {\n    CURL* curl = curl_easy_init();\n    if (!curl) {\n        std::cerr << "CURL initialization error" << std::endl;\n        return 1;\n    }\n\n    std::string response;\n    curl_easy_setopt(curl, CURLOPT_URL, "https://jsonplaceholder.typicode.com/posts/1");\n    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);\n    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);\n    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L); // Disable SSL verification for testing\n\n    CURLcode res = curl_easy_perform(curl);\n    if (res != CURLE_OK) {\n        std::cerr << "Request error: " << curl_easy_strerror(res) << std::endl;\n    } else {\n        std::cout << "Server response:\\n" << response << std::endl;\n    }\n\n    curl_easy_cleanup(curl);\n    return 0;\n}

Compile with the -lcurl flag:

g++ -o http_client http_client.cpp -lcurl

POST request with JSON sending

Now let's add data sending:

#include <iostream>\n#include <string>\n#include <curl/curl.h>\n\nint main() {\n    CURL* curl = curl_easy_init();\n    if (!curl) return 1;\n\n    std::string response;\n    std::string jsonData = R"({"title": "foo", "body": "bar", "userId": 1})";\n\n    struct curl_slist* headers = nullptr;\n    headers = curl_slist_append(headers, "Content-Type: application/json");\n\n    curl_easy_setopt(curl, CURLOPT_URL, "https://jsonplaceholder.typicode.com/posts");\n    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, jsonData.c_str());\n    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);\n    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCal