cf Workbench

A local Codeforces-style workbench for writing, running, and stress-testing C++ solutions.

Features - Quick start - How it works - Documentation

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About

cf is a self-hosted workbench for competitive programming in C++. It pairs a browser IDE (a Next.js app under web/) with a server-side execution engine that compiles and runs your code against the real C++ toolchain on your machine. Everything runs locally: there is no sandbox VM, no remote judge, and no account.

The workbench is built to make the macOS toolchain a first-class target. The #include <bits/stdc++.h> idiom is a GCC/libstdc++ detail that Apple clang does not ship, so the repository bundles a portable shim at include/bits/stdc++.h and every compile is invoked with -I include. The same flag is used by the web engine and the Makefile, so code that compiles in the UI compiles from the terminal too.

This is a stable release: the engine, the UI, and the build tooling are feature complete and the production build (npm run build) passes clean.

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Features

• C++ editor with Prism syntax highlighting, a synced line-number gutter, soft-tab handling, and an adjustable font. Editor contents persist to localStorage across reloads.
• Insertable templates (Minimal, A + B, Fast I/O + helpers, Brute force, Generator) plus a Settings panel for the language standard, per-run time limit, and extra compiler flags.
• Run panel that POSTs to /api/run with custom stdin and renders the verdict, exit code, elapsed wall-clock time, compiler, and a scrollable raw terminal log of stdout / stderr / compile errors.
• Tests panel to add, edit, delete, and paste-and-split sample cases, then Run all via /api/test for per-case AC / WA / TLE / RE / CE badges with an expandable, whitespace-tolerant diff.
• Stress panel that compiles a solution, a brute force, and a generator, runs them for a configurable number of iterations, and surfaces the first failing input. It degrades gracefully if the endpoint is unavailable.
• Problems sidebar to save, load, rename, and delete problems and their test cases, persisted as JSON under web/data/.
• Keyboard shortcuts: Cmd/Ctrl+Enter runs, Cmd/Ctrl+Shift+Enter runs all tests, Cmd/Ctrl+S saves the current problem.

See docs/features.md for the complete feature guide.

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Quick start

Prerequisites

• A working C++ compiler. Apple clang (clang++ / c++) or GCC (g++) both work. On macOS, install the Xcode Command Line Tools: xcode-select --install.
• Node.js 20 or newer (the web app targets Next.js 16).

Run the workbench

git clone https://github.com/mbn-code/cf.git
cd cf/web
npm install
npm run dev

Open http://localhost:3000. The editor loads with an A + B program and a 2 3 -> 5 sample test, so you can click Run and see a result immediately.

For a production build:

npm run build
npm run start

Build from the terminal

The repository also ships a portable Makefile that uses the same compiler detection and -I include flag as the engine:

make build FILE=src/solution.cpp   # compile one source
make run   FILE=src/solution.cpp   # compile and run with a timeout
make test  FILE=myproblem          # compile and diff vs src/myproblem/input.txt

Full setup, build, and test instructions are in docs/development.md.

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How it works

cf/
|- web/                         Next.js workbench (UI + API)
|  |- app/
|  |  |- page.tsx               Workbench shell (editor, panels, shortcuts)
|  |  |- api/
|  |  |  |- _engine/            Server execution engine (Node built-ins only)
|  |  |  |  |- cpp.ts           Compiler detection, compile, run, time-limit, caps
|  |  |  |  |- compare.ts       Whitespace-tolerant output comparison + diff
|  |  |  |  |- store.ts         JSON problem store under web/data
|  |  |  |- run/                POST /api/run    - compile + run once
|  |  |  |- test/               POST /api/test   - run many cases, AC/WA/...
|  |  |  |- stress/             POST /api/stress - solution vs brute + generator
|  |  |  |- problems/           CRUD for saved problems
|  |  |  |- {config,problem-text,solution,template}/
|  |  |- components/            Editor, Run/Tests/Stress panels, sidebar, badges
|  |  |- lib/                   Typed API client, localStorage helpers, templates
|  |- data/problems/           Saved problems (one JSON file per problem)
|- include/bits/stdc++.h        Portable <bits/stdc++.h> shim for clang/libc++
|- Makefile                     Portable terminal build/run/test
|- docs/                        This documentation

The execution engine compiles each submission to a unique os.tmpdir() directory with -std=gnu++17 -O2 -I include, measures wall-clock time inside Node with process.hrtime.bigint(), enforces the time limit with SIGKILL (reported as TLE), caps stdin / stdout / stderr at 4 MiB, and distinguishes compile errors (CE) from runtime errors (RE) and spawn failures. Output comparison tolerates trailing whitespace and trailing blank lines.

A deeper walkthrough lives in docs/architecture.md.

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Documentation

Document	Contents
docs/features.md	Full feature guide for every panel and setting.
docs/architecture.md	The execution engine, the macOS shim, and the data store.
docs/api.md	Request / response contract for every /api/* route.
docs/development.md	Install, run, build, and the Playwright e2e suite.
docs/troubleshooting.md	Compiler-not-found, time limits, and macOS notes.

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Command-line tools

Alongside the workbench, the repository ships a Bash CLI (scripts/cf) and the Makefile for terminal-first workflows:

Command	Description
cf template <name>	Scaffold src/<name>/ with a solution and sample files.
cf <name> [input]	Compile and run a solution with file or inline input.
cf test	Run a solution against its sample cases with timeout protection.
cf serve [problem]	Start the web workbench.
cf update	Pull the latest toolkit and re-run setup (see docs/UPDATE_COMMAND.md).

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Contributing

Contributions are welcome. See CONTRIBUTING.md for details.

License

Released under the MIT License. See LICENSE.