Boost.HTTP

HTTP powers the web, but implementing it correctly is surprisingly hard. Boost.HTTP is a portable C++ library that provides containers and algorithms for the HTTP/1.1 protocol, giving you RFC-compliant message handling without the usual implementation headaches.

What This Library Does

Provides modifiable containers for HTTP requests and responses
Parses incoming HTTP messages with configurable limits
Serializes outgoing messages with automatic chunked encoding
Handles content encodings (gzip, deflate, brotli)
Offers an Express.js-style router for request dispatch
Enforces RFC 9110 compliance to prevent common security issues

What This Library Does Not Do

Network I/O — this is a Sans-I/O library by design
HTTP/2 or HTTP/3 protocol support
TLS/SSL handling
Cookie management or session state
Full HTTP client/server implementation (see Boost.Beast2 for I/O)

Target Audience

This library is for C++ developers who need precise control over HTTP message handling. You should have:

Familiarity with TCP/IP networking concepts
Understanding of the HTTP request/response model
Experience with C++ move semantics and memory management

Design Philosophy

The library follows a Sans-I/O architecture that separates protocol logic from network operations. This design choice yields several benefits:

Reusability. The same protocol code works with any I/O framework — Asio, io_uring, or platform-specific APIs. Write the HTTP logic once, integrate it anywhere.

Testability. Tests run as pure function calls without sockets, timers, or network delays. Coverage is higher, execution is faster, results are deterministic.

Security. The parser is strict by default. Malformed input that could enable request smuggling or header injection is rejected immediately.

Requirements

C++11 compiler (see tested compilers below)
Boost libraries (core, system, optional)
Link to the static or dynamic library

The library supports -fno-exceptions and detects this automatically.

Tested Compilers

GCC: 5 to 14 (except 8.0.1)
Clang: 3.9, 4 to 18
MSVC: 14.1 to 14.42

Code Conventions

Code examples in this documentation assume these declarations are in effect:

#include <boost/http.hpp>

using namespace boost::http;

Quick Example

#include <boost/http.hpp>

using namespace boost::http;

int main()
{
    // Build a request
    request req(method::get, "/api/users");
    req.set(field::host, "example.com");
    req.set(field::accept, "application/json");

    // Build a response
    response res(status::ok);
    res.set(field::content_type, "application/json");
    res.set(field::content_length, "42");

    // Access the serialized form
    std::cout << req.buffer();
    std::cout << res.buffer();
}

Output:

GET /api/users HTTP/1.1
Host: example.com
Accept: application/json

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 42

Next Steps

Introduction to HTTP — understand HTTP sessions and message flow
Containers — work with requests, responses, and fields
Parsing — parse incoming HTTP messages
Serializing — produce outgoing HTTP messages
Router — dispatch requests to handlers

Acknowledgments

This library wouldn’t be where it is today without the help of Peter Dimov for design advice and general assistance.

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