HTTP Client in C++: Making Requests Properly from A to Z

HTTP Client in C++: Making Requests Properly from A to Z

In the modern world of programming, interacting with remote servers via the HTTP protocol is one of the basic tasks. Whether it's getting data from an API, sending a form, or downloading a file — the ability to work with HTTP requests is essential for every C++ developer. In this article, we will look at how to create a full-fledged HTTP client in C++, review popular libraries, and best practices.

Why do you need an HTTP client in C++?

Unlike languages with built-in HTTP libraries (Python, JavaScript), C++ does not have a standard tool for working with HTTP in the standard library. However, this is not a problem, as there are several powerful and time-tested solutions:

• libcurl — the most popular and powerful library for working with URLs
• cpprestsdk (Casablanca) — a modern asynchronous library from Microsoft
• Boost.Beast — a library based on Boost.Asio for low-level work

In this article, we will focus on libcurl and cpprestsdk, as the most commonly used solutions.

Basics of working with libcurl

libcurl is a time-tested library that supports many protocols, including HTTP/1.1, HTTP/2, FTP, and others. It is written in C but has excellent bindings for C++.

Installing libcurl

Installing libcurl depends on your operating system:

# Ubuntu/Debiansudo apt-get install libcurl4-openssl-dev

# macOS (via Homebrew)brew install curl

# Windows (via vcpkg)vcpkg install curl

Simple GET request with libcurl

Let's start with a basic example — sending a GET request and receiving a response:

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

// Callback function for writing datasize_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {    size_t totalSize = size * nmemb;    output->append(static_cast<char*>(contents), totalSize);    return totalSize;}

int main() {    CURL* curl = curl_easy_init();    if (!curl) {        std::cerr << "CURL initialization error" << std::endl;        return 1;    }

    std::string response;        curl_easy_setopt(curl, CURLOPT_URL, "https://jsonplaceholder.typicode.com/posts/1");    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);        CURLcode res = curl_easy_perform(curl);        if (res != CURLE_OK) {        std::cerr << "Request error: " << curl_easy_strerror(res) << std::endl;    } else {        std::cout << "Server response:" << std::endl;        std::cout << response << std::endl;    }        curl_easy_cleanup(curl);    return 0;}

Sending a POST request with data

POST requests are used to send data to the server. Let's look at an example with JSON data:

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

size_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {    size_t totalSize = size * nmemb;    output->append(static_cast<char*>(contents), totalSize);    return totalSize;}

int main() {    CURL* curl = curl_easy_init();    if (!curl) return 1;

    std::string response;    std::string jsonData = R"({"title": "foo", "body": "bar", "userId": 1})";        struct curl_slist* headers = nullptr;    headers = curl_slist_append(headers, "Content-Type: application/json");        curl_easy_setopt(curl, CURLOPT_URL, "https://jsonplaceholder.typicode.com/posts");    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, jsonData.c_str());    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);    curl_easy_