cpp-flask

A C++ variant of Python Flask, including a HtmlBuilder, JSON library and Webserver, for fast and flexible webapps with a C++ backend.

TL;DR

This project can be build and installed to provide an easy to use webserver. It supports HTML template building and programming (similar to jinja2). See the examples, for a Hello World implementation to get started quickly. More examples will follow as the project matures (voicing intend, not a promise).

Project structure

The project contains 3 internal libraries and exports 1 bundle upon installation.

The internal libraries are

1. HttpServer
   • Simple entry point to set up and handle the API.
   • Offers a static run method to just make the server run with your router.
   • Offers Router, Route and SimpleRoute classes, to limit boilerplate code.
2. HtmlBuilder
   • Low effort programmable HTML parsing.
   • Automatic support for:
     • Conditionals (if, else if, else).
     • Loops (for x to y, for el in list).
     • Variables (headers, cookies, path params, forms etc. all easily accessible via JSON URIs).
     • User created filters to 'pipe' variables through.
     • Creating variables from within your HTML (set).
     • Drop in other files for reusability (include).
     • Extending other files for more convenient user interface design (extends and block).
     • Use macros to create reusable and variable code blocks (macro).
3. JsonObject
   • A user-friendly wrapper-object around RapidJSON.

Because this structure is mostly for internal architecture (keeping things organized), a single target will be available for end-users upon installation: CppFlask.

Installation

Simply running CMake build steps, should install the project and make it available for usage in your CMake project.

mkdir -p build && cd build
cmake ..
cmake --build . --target install

Building it as part of your project

If you do not want, or can't, install this project on your system. As of v0.3.0, CppFlask fully supports CMake's FetchContent functionality.

include(FetchContent)

FetchContent_Declare(
        CppFlask
        GIT_REPOSITORY https://github.com/acherrum/cpp-flask.git
        GIT_TAG        v0.4.0
        GIT_SHALLOW    TRUE
)

FetchContent_MakeAvailable(CppFlask)

And then simply link against CppFlask.

Examples

In the examples directory, a couple of examples are created, showing a lot of the flexibility of the framework.

• The main.cpp is the entry point.
• A very simple Router class describes the available API.
• Some HTML files show some of the programmable HTML.

Credits

This project is build on yhirose's cpp-httplib: https://github.com/yhirose/cpp-httplib

The idea to build this came from a C++ beginners class I taught in the summer of 2026, where a group of my students decided they wanted to build a webapp using httplib. This lead me to try out httplib for myself and while it worked, I found the syntax required a lot of boilerplate code and forms access felt unhandy. Furthermore, some students in this group had never typed any HTML code before. This is where the idea of the HtmlBuilder library came from. I already had experience with Python Flask and with these ideas combined, I set out to build a C++ version of it. The end goal: refactor some of my local webapps into this C++ version.

Furthermore, I have included a custom JsonObject library, which is a slim wrapper around Tencent's RapidJSON: https://github.com/Tencent/rapidjson I find RapidJSON very user unfriendly, so this object makes it easier to work with.

Finally, I've written some tests using GoogleTest framework: https://github.com/google/googletest Although I do advocate TDD, I am still an engineer who likes to build as he goes and tests mainly for my own sanity.

Work in progress

This is a hobby project. For now, I will not accept any contributions. Feel free to fork, but this is, for the time being, something to keep myself busy. Thank you for understanding.

Wishlist

• Improved filter handling
  • Additional arguments

Known issues

None yet. Please let me know if you encounter anything.

Version history

• 0.5.0 TBD

  • Add sort function to JsonObject for arrays (including arrays of objects).
  • Add filter support for the set command.
  • Add filter chaining.

• 0.4.1 2026-09-26

  • Patched workflow file to use Ubuntu-26.04 because of C++23 requirement.

• 0.4.0 2026-09-26

  • Fixed an issue setting multiple cookies.
  • Added SimpleRoute class to remove unnecessary class creation for simple routes.
  • Cleaned up parser handling (more SOLID), breaking INCLUDE commands: use include ( instead of include(.
  • Add support for user-injectable 'filters', allowing variables to be piped through a user injected method.
  • Add callback functionality to Router so that developers can create a shutdown route in their API - if desired.
  • Add static run method to the HttpServer class, to remove boilerplate main code and catch interrupt signals.
  • Add Router class to the main package, to remove some of that boilerplate as well.
  • Add extends command to the HtmlBuilder suite.
  • Extend supported API routes (added PUT and DELETE).
  • Added support for path_params. These are now available in the request json as params.
  • Improve block handling for passing blocks down files and allowing multiple definitions to append to each other (useful for <script> blocks per example).
  • Added macro functionality
  • Added Macro example.
  • Removed copy constructors of JsonObject, since these are prone to cause bugs.

• 0.3.0 2026-09-16

  • Made commands case-insensitive.
  • Added support for CMake's FetchContent instead of relying on installation.
  • Cleaned up the example, to also use FetchContent.

• 0.2.0 2026-09-15

  • Finished nested routes.
  • Added nested route with JSON response to example.
  • Add isEmpty() method to JsonObject.
  • Add method to add objects to JsonObject.
  • Fix parse error when END_IF is missing.
  • Refactor JsonObject::add() to JsonObject::set()
  • Add tests to confirm overwriting values works using JsonObject::set() method.
  • Add JsonObject::hasMember method.
  • Solved an issue with if-else if handling.
  • Small fix for adding child routes to the root route.
  • JsonObject should return true for isEmpty() when object is null.
  • Add support for Windows.
  • Add improved cookie support.
  • Added JSON parse error handling.

• 0.1.0 2026-09-11

  • Initial release on Github, with this README and a first example.