Add webhook example

Author: hermanzdosilovic

examples/1000_http_callback_aka_webhook/.github/demo.gif

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+# HTTP Callbacks (a.k.a. Webhooks)
+![demo.gif](.github/demo.gif)
+
+```bash
+pip install -r requirements.txt
+./main.py
+```
+
+In this example we are creating a HTTP server that has two routes:
+1. `GET /` - triggers the creation of submission on Judge0
+2. `PUT /callback` - called by Judge0 once the submission is done
+
+When you run the HTTP server you should visit `http://localhost:8000` and that will create a new submission on Judge0. This submission will have a `callback_url` attribute set which Judge0 will call `PUT` HTTP verb once the submission is done.
+
+For this to work the `callback_url` must be publicly accessible, so in this example we are using a free service https://localhost.run that allows us to expose your local HTTP server and make it available on the internet and accessible by Judge0.
+
+Once the submission is done Judge0 will call our second route `PUT /callback` and in your terminal you should see the result.

examples/1000_http_callback_aka_webhook/README.md

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+#!/usr/bin/env python3
+from fastapi import FastAPI, Depends
+from pydantic import BaseModel
+
+import uvicorn
+import asyncio
+import judge0
+
+
+class CallbackResponse(BaseModel):
+    created_at: str
+    finished_at: str
+    language: dict
+    status: dict
+    stdout: str
+
+
+class AppContext:
+    def __init__(self):
+        self.public_url = ""
+
+
+LOCAL_SERVER_PORT = 8000
+
+app = FastAPI()
+app_context = AppContext()
+
+
+def get_app_context():
+    return app_context
+
+
+@app.get("/")
+async def root(app_context=Depends(get_app_context)):
+    if not app_context.public_url:
+        return {
+            "message": "Public URL is not available yet. Try again after a few seconds."
+        }
+
+    submission = judge0.Submission(
+        source_code="print('Hello, World!')",
+        language_id=judge0.PYTHON,
+        callback_url=f"{app_context.public_url}/callback",
+    )
+
+    return judge0.async_execute(submissions=submission)
+
+
+@app.put("/callback")
+async def callback(response: CallbackResponse):
+    print(f"Received: {response}")
+
+
+# We are using free service from https://localhost.run to get a public URL for our local server.
+# This approach is not recommended for production use. It is only for demonstration purposes
+# since domain names change regularly and there is a speed limit for the free service.
+async def run_ssh_tunnel():
+    app_context = get_app_context()
+
+    command = [
+        "ssh",
+        "-o",
+        "StrictHostKeyChecking=no",
+        "-o",
+        "ServerAliveInterval=30",
+        "-R",
+        f"80:localhost:{LOCAL_SERVER_PORT}",
+        "localhost.run",
+    ]
+
+    process = await asyncio.create_subprocess_exec(
+        *command, stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.STDOUT
+    )
+
+    while True:
+        line = await process.stdout.readline()
+        if not line:
+            break
+
+        decoded_line = line.decode().strip()
+        if decoded_line.endswith(".lhr.life"):
+            app_context.public_url = decoded_line.split()[-1].strip()
+
+    await process.wait()
+
+
+async def run_server():
+    config = uvicorn.Config(
+        app, host="127.0.0.1", port=LOCAL_SERVER_PORT, workers=5, loop="asyncio"
+    )
+    server = uvicorn.Server(config)
+    await server.serve()
+
+
+async def main():
+    await asyncio.gather(run_ssh_tunnel(), run_server())
+
+
+if __name__ == "__main__":
+    asyncio.run(main())

examples/1000_http_callback_aka_webhook/main.py

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+fastapi==0.115.4
+uvicorn==0.32.0