Sebastián Ramírez
6 years ago
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GitHub
GitHub
7 changed files with 147 additions and 0 deletions
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from fastapi import FastAPI |
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from starlette.responses import HTMLResponse |
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from starlette.websockets import WebSocket |
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app = FastAPI() |
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html = """ |
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<!DOCTYPE html> |
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<html> |
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<head> |
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<title>Chat</title> |
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</head> |
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<body> |
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<h1>WebSocket Chat</h1> |
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<form action="" onsubmit="sendMessage(event)"> |
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<input type="text" id="messageText" autocomplete="off"/> |
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<button>Send</button> |
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</form> |
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<ul id='messages'> |
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</ul> |
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<script> |
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var ws = new WebSocket("ws://localhost:8000/ws"); |
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ws.onmessage = function(event) { |
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var messages = document.getElementById('messages') |
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var message = document.createElement('li') |
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var content = document.createTextNode(event.data) |
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message.appendChild(content) |
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messages.appendChild(message) |
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}; |
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function sendMessage(event) { |
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var input = document.getElementById("messageText") |
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ws.send(input.value) |
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input.value = '' |
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event.preventDefault() |
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} |
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</script> |
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</body> |
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</html> |
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""" |
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@app.get("/") |
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async def get(): |
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return HTMLResponse(html) |
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@app.websocket_route("/ws") |
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async def websocket_endpoint(websocket: WebSocket): |
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await websocket.accept() |
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while True: |
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data = await websocket.receive_text() |
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await websocket.send_text(f"Message text was: {data}") |
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await websocket.close() |
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You can use <a href="https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API" target="_blank">WebSockets</a> with **FastAPI**. |
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## WebSockets client |
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### In production |
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In your production system, you probably have a frontend created with a modern framework like React, Vue.js or Angular. |
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And to communicate using WebSockets with your backend you would probably use your frontend's utilities. |
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Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code. |
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Or you might have any other way to communicate with the WebSocket endpoint. |
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--- |
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But for this example, we'll use a very simple HTML document with some JavaScript, all inside a long string. |
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This, of course, is not optimal and you wouldn't use it for production. |
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In production you would have one of the options above. |
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But it's the simplest way to focus on the server-side of WebSockets and have a working example: |
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```Python hl_lines="2 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 42 43 44" |
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{!./src/websockets/tutorial001.py!} |
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``` |
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## Create a `websocket_route` |
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In your **FastAPI** application, create a `websocket_route`: |
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```Python hl_lines="3 47 48" |
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{!./src/websockets/tutorial001.py!} |
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``` |
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!!! tip |
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In this example we are importing `WebSocket` from `starlette.websockets` to use it in the type declaration in the WebSocket route function. |
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That is not required, but it's recommended as it will provide you completion and checks inside the function. |
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!!! info |
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This `websocket_route` we are using comes directly from <a href="https://www.starlette.io/applications/" target="_blank">Starlette</a>. |
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That's why the naming convention is not the same as with other API path operations (`get`, `post`, etc). |
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## Await for messages and send messages |
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In your WebSocket route you can `await` for messages and send messages. |
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```Python hl_lines="49 50 51 52 53" |
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{!./src/websockets/tutorial001.py!} |
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``` |
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You can receive and send binary, text, and JSON data. |
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To learn more about the options, check Starlette's documentation for: |
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* <a href="https://www.starlette.io/applications/" target="_blank">Applications (`websocket_route`)</a>. |
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* <a href="https://www.starlette.io/websockets/" target="_blank">The `WebSocket` class</a>. |
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* <a href="https://www.starlette.io/endpoints/#websocketendpoint" target="_blank">Class-based WebSocket handling</a>. |
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## Test it |
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If your file is named `main.py`, run your application with: |
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```bash |
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uvicorn main:app --debug |
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``` |
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Open your browser at <a href="http://127.0.0.1:8000" target="_blank">http://127.0.0.1:8000</a>. |
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You will see a simple page like: |
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<img src="/img/tutorial/websockets/image01.png"> |
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You can type messages in the input box, and send them: |
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<img src="/img/tutorial/websockets/image02.png"> |
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And your **FastAPI** application with WebSockets will respond back: |
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<img src="/img/tutorial/websockets/image03.png"> |
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You can send (and receive) many messages: |
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<img src="/img/tutorial/websockets/image04.png"> |
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And all of them will use the same WebSocket connection. |
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