POST http://<host>:<port>/execute Content-Type: application/json { "language": "c", // "c" or "cpp" "code_b64": "<base64-encoded source>", // full source file, UTF-8 → base64 "compile_cmd": "gcc", // custom compiler binary "flags": "-o output -lm", // flags appended after source filename "stdin": "42\nhello\n" // optional stdin for the program }

# server.py import base64, subprocess, tempfile, os from fastapi import FastAPI from fastapi.middleware.cors import CORSMiddleware from fastapi.responses import StreamingResponse from pydantic import BaseModel app = FastAPI() # Allow browser requests from any origin (needed for local use) app.add_middleware( CORSMiddleware, allow_origins=["*"], allow_methods=["*"], allow_headers=["*"], ) class ExecRequest(BaseModel): language: str # "c" or "cpp" code_b64: str # base64-encoded source code compile_cmd: str = "gcc" flags: str = "-o output -lm" stdin: str = "" @app.post("/execute") async def execute(req: ExecRequest): # Decode base64 source src = base64.b64decode(req.code_b64).decode("utf-8") ext = ".c" if req.language == "c" else ".cpp" def stream(): with tempfile.TemporaryDirectory() as tmpdir: src_file = os.path.join(tmpdir, "main" + ext) out_bin = os.path.join(tmpdir, "output") with open(src_file, "w") as f: f.write(src) # Build compile command cmd = req.compile_cmd.split() + [src_file] + req.flags.split() # Replace "-o output" placeholder with actual path cmd = [out_bin if p == "output" else p for p in cmd] if "-o" not in cmd: cmd += ["-o", out_bin] # Compile comp = subprocess.run( cmd, capture_output=True, text=True, timeout=30 ) if comp.returncode != 0: yield f"[Compile Error]\n{comp.stderr or comp.stdout}" return yield "[Compiled OK]\n" # Run try: proc = subprocess.Popen( [out_bin], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True, cwd=tmpdir, ) stdout, _ = proc.communicate( input=req.stdin, timeout=10 ) yield stdout if proc.returncode != 0: yield f"\n[Exit code: {proc.returncode}]" except subprocess.TimeoutExpired: proc.kill() yield "\n[Timeout: program ran > 10 seconds]" return StreamingResponse(stream(), media_type="text/plain")

C examples: gcc → standard GCC clang → Clang compiler tcc → Tiny C Compiler (very fast) musl-gcc → musl libc static linking zig cc → Zig's bundled C compiler C++ examples: g++ → standard G++ clang++ → Clang C++ g++-13 → specific GCC version em++ → Emscripten (WASM) Flags examples (C): -O2 -Wall -lm -lpthread Flags examples (C++): -std=c++20 -O2 -Wall -lstdc++fs