Fastapi: [BUG] Tutorial websocket doc example

Created on 4 Jul 2019  路  11Comments  路  Source: tiangolo/fastapi

Describe the bug
Hi,
On the docs of websocket the last example doesn't work.

To Reproduce
Steps to reproduce the behavior:

  1. Create a file main.py with the last example on the bottom of the file

https://fastapi.tiangolo.com/tutorial/websockets/#create-a-websocket

from fastapi import Cookie, Depends, FastAPI, Header
from starlette.responses import HTMLResponse
from starlette.status import WS_1008_POLICY_VIOLATION
from starlette.websockets import WebSocket

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>WebSocket Chat</h1>
        <form action="" onsubmit="sendMessage(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="foo"/></label>
            <button onclick="connect(event)">Connect</button>
            <br>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var input = document.getElementById("itemId")
                ws = new WebSocket("ws://localhost:8000/items/" + input.value + "/ws");
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')
                    var message = document.createElement('li')
                    var content = document.createTextNode(event.data)
                    message.appendChild(content)
                    messages.appendChild(message)
                };
            }
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


async def get_cookie_or_client(
    websocket: WebSocket, session: str = Cookie(None), x_client: str = Header(None)
):
    if session is None and x_client is None:
        await websocket.close(code=WS_1008_POLICY_VIOLATION)
    return session or x_client


@app.websocket("/items/{item_id}/ws")
async def websocket_endpoint(
    websocket: WebSocket,
    item_id: int,
    q: str = None,
    cookie_or_client: str = Depends(get_cookie_or_client),
):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(
            f"Session Cookie or X-Client Header value is: {cookie_or_client}"
        )
        if q is not None:
            await websocket.send_text(f"Query parameter q is: {q}")
        await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")
  1. Run the application with the cmd:
uvicorn main:app  --log-level debug --reload
  1. Open the browser 127.0.0.01

    • the first time i connect with ItemID foo , press the button connect

    • send message hi with ItemID foo and press the button send.

      it's look like the connect fail but the second ,but the send have return code 200

      but nothing happen on the web side.

image

  1. See error

INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: Started reloader process [366952]
email-validator not installed, email fields will be treated as str.
To install, run: pip install email-validator
INFO: Started server process [366957]
INFO: Waiting for application startup.
DEBUG: None - ASGI [1] Started
DEBUG: None - ASGI [1] Sent {'type': 'lifespan.startup'}
DEBUG: None - ASGI [1] Received {'type': 'lifespan.startup.complete'}
DEBUG: ('127.0.0.1', 50056) - Connected
DEBUG: server - state = CONNECTING
DEBUG: server - event = connection_made(<TCPTransport closed=False reading=True 0x1819178>)
DEBUG: ('127.0.0.1', 50056) - ASGI [2] Started
DEBUG: ('127.0.0.1', 50056) - ASGI [2] Received {'type': 'websocket.close', 'code': 1008}
INFO: ('127.0.0.1', 50056) - "WebSocket /items/foo/ws" 403
DEBUG: ('127.0.0.1', 50056) - ASGI [2] Raised exception
ERROR: Exception in ASGI application
Traceback (most recent call last):
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py", line 147, in run_asgi
    result = await self.app(self.scope, self.asgi_receive, self.asgi_send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/middleware/message_logger.py", line 58, in __call__
    raise exc from None
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/middleware/message_logger.py", line 54, in __call__
    await self.app(scope, inner_receive, inner_send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/applications.py", line 133, in __call__
    await self.error_middleware(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/middleware/errors.py", line 87, in __call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/exceptions.py", line 49, in __call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 585, in __call__
    await route(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 265, in __call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 56, in app
    await func(session)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/fastapi/routing.py", line 148, in app
    await websocket.close(code=WS_1008_POLICY_VIOLATION)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/websockets.py", line 121, in close
    await self.send({"type": "websocket.close", "code": code})
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/websockets.py", line 70, in send
    raise RuntimeError('Cannot call "send" once a close message has been sent.')
RuntimeError: Cannot call "send" once a close message has been sent.
DEBUG: server ! failing WebSocket connection in the CONNECTING state: 1006 [no reason]
DEBUG: ('127.0.0.1', 50058) - Connected
DEBUG: server x half-closing TCP connection
DEBUG: ('127.0.0.1', 50058) - ASGI [3] Started
DEBUG: ('127.0.0.1', 50058) - ASGI [3] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('127.0.0.1', 50058) - "GET / HTTP/1.1" 200
DEBUG: ('127.0.0.1', 50058) - ASGI [3] Received {'type': 'http.response.body', 'body': '<1419 bytes>'}
DEBUG: ('127.0.0.1', 50058) - ASGI [3] Completed
DEBUG: server - event = eof_received()
DEBUG: server - event = connection_lost(None)
DEBUG: server - state = CLOSED
DEBUG: server x code = 1006, reason = [no reason]
DEBUG: ('127.0.0.1', 50058) - Disconnected
DEBUG: ('127.0.0.1', 50060) - Connected
DEBUG: ('127.0.0.1', 50060) - ASGI [4] Started
DEBUG: ('127.0.0.1', 50060) - ASGI [4] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('127.0.0.1', 50060) - "GET / HTTP/1.1" 200
DEBUG: ('127.0.0.1', 50060) - ASGI [4] Received {'type': 'http.response.body', 'body': '<1419 bytes>'}
DEBUG: ('127.0.0.1', 50060) - ASGI [4] Completed
DEBUG: ('127.0.0.1', 50060) - Disconnected

Expected behavior
expected to appear the send bold message on the web page.

Environment:

  • OS: centos 7
  • FastAPI Version [e.g. 0.3.0], get it with: fastapi==0.31.0
import fastapi
print(fastapi.__version__)
0.31.0
  • Python version, get it with:
python --version
Python 3.7.3
answered bug
Source
picture Ben621

Most helpful comment

Thanks for the discussion here everyone! :coffee:

It was updated and simplified as part of https://github.com/tiangolo/fastapi/pull/1540

You can check the new docs here: https://fastapi.tiangolo.com/advanced/websockets/#using-depends-and-others :rocket:

I'm re-opening the issue to give time for the author of the issue to confirm and close it :nerd_face:

picture tiangolo on 13 Jun 2020
👍3

All 11 comments

@BenjPy ,
Just add event.preventDefault() in the beginning of connect js function.
The problem here is when you are trying to make websocket connection, browser refreshes page and closes websocket connection.
So connect function should looks like this:

function connect(event) {
    event.preventDefault()
    var input = document.getElementById("itemId")
    ws = new WebSocket("ws://localhost:8000/items/" + input.value + "/ws");
    ws.onmessage = function(event) {
        var messages = document.getElementById('messages')
        var message = document.createElement('li')
        var content = document.createTextNode(event.data)
        message.appendChild(content)
        messages.appendChild(message)
    };
}
alj06ka picture alj06ka on 5 Jul 2019
👍1

@alj06ka ,
still nothing appear , when added the line on the web page
it's look like the first time the Websocket fail to connect

see on below the js code

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>WebSocket Chat</h1>
        <form action="" onsubmit="sendMessage(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="foo"/></label>
            <button onclick="connect(event)">Connect</button>
            <br>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                event.preventDefault()
                var input = document.getElementById("itemId")
                ws = new WebSocket("ws://127.0.0.1:8000/items/" + input.value + "/ws");
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')
                    var message = document.createElement('li')
                    var content = document.createTextNode(event.data)
                    message.appendChild(content)
                    messages.appendChild(message)
                };
            }
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""

see the log on below

INFO: ('127.0.0.1', 59388) - "WebSocket /items/foo/ws" 403
DEBUG: ('127.0.0.1', 59388) - ASGI [13] Raised exception
ERROR: Exception in ASGI application
Traceback (most recent call last):
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/protocols/websockets/websockets_impl.py                                                             ", line 147, in run_asgi
    result = await self.app(self.scope, self.asgi_receive, self.asgi_send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/middleware/message_logger.py", line 58,                                                              in __call__
    raise exc from None
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/uvicorn/middleware/message_logger.py", line 54,                                                              in __call__
    await self.app(scope, inner_receive, inner_send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/applications.py", line 133, in __call                                                             __
    await self.error_middleware(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/middleware/errors.py", line 87, in __                                                             call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/exceptions.py", line 49, in __call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 585, in __call__
    await route(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 265, in __call__
    await self.app(scope, receive, send)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/routing.py", line 56, in app
    await func(session)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/fastapi/routing.py", line 148, in app
    await websocket.close(code=WS_1008_POLICY_VIOLATION)
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/websockets.py", line 121, in close
    await self.send({"type": "websocket.close", "code": code})
  File "/data/experiments/realtime_web_socket/lib/python3.7/site-packages/starlette/websockets.py", line 70, in send
    raise RuntimeError('Cannot call "send" once a close message has been sent.')
RuntimeError: Cannot call "send" once a close message has been sent.
DEBUG: server ! failing WebSocket connection in the CONNECTING state: 1006 [no reason]
DEBUG: server x half-closing TCP connection
DEBUG: server - event = eof_received()
DEBUG: server - event = connection_lost(None)
DEBUG: server - state = CLOSED
DEBUG: server x code = 1006, reason = [no reason]
DEBUG: ('127.0.0.1', 59390) - Connected
DEBUG: ('127.0.0.1', 59390) - ASGI [14] Started
DEBUG: ('127.0.0.1', 59390) - ASGI [14] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('127.0.0.1', 59390) - "GET / HTTP/1.1" 200
DEBUG: ('127.0.0.1', 59390) - ASGI [14] Received {'type': 'http.response.body', 'body': '<1458 bytes>'}
DEBUG: ('127.0.0.1', 59390) - ASGI [14] Completed
DEBUG: ('127.0.0.1', 59390) - ASGI [15] Started
DEBUG: ('127.0.0.1', 59390) - ASGI [15] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('127.0.0.1', 59390) - "GET / HTTP/1.1" 200
DEBUG: ('127.0.0.1', 59390) - ASGI [15] Received {'type': 'http.response.body', 'body': '<1458 bytes>'}
DEBUG: ('127.0.0.1', 59390) - ASGI [15] Completed
DEBUG: ('127.0.0.1', 59390) - Disconnected
DEBUG: ('127.0.0.1', 59448) - Connected
DEBUG: ('127.0.0.1', 59448) - ASGI [16] Started
DEBUG: ('127.0.0.1', 59448) - ASGI [16] Received {'type': 'http.response.start', 'status': 200, 'headers': '<...>'}
INFO: ('127.0.0.1', 59448) - "GET / HTTP/1.1" 200
DEBUG: ('127.0.0.1', 59448) - ASGI [16] Received {'type': 'http.response.body', 'body': '<1458 bytes>'}
DEBUG: ('127.0.0.1', 59448) - ASGI [16] Completed
Ben621 picture Ben621 on 5 Jul 2019

@BenjPy ,
Looks like this window is still reloading...
Actually, I think, that separation onto two forms will help you:

<form action="" onsubmit="connect(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="foo"/></label>
            <button>Connect</button>
</form>
<form action="" onsubmit="sendMessage(event)">
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
</form>

It's not a good way, but it's okay to try out websockets.

alj06ka picture alj06ka on 5 Jul 2019

@alj06ka ,
Hi, still nothing appear on the web page.

Ben621 picture Ben621 on 7 Jul 2019

@BenjPy ,
Hi, actually, problem was not in page reloading. I find out, that this example shows how to pass cookie or header params as well. So, you can see dependency cookie_or_client. It means, that you must pass session param in Cookie, or x-client param in Header on websocket connection request. So if you pass it, everything works correctly.
Here is my code of this example:

import uvicorn

from fastapi import Cookie, Depends, FastAPI, Header
from starlette.responses import HTMLResponse
from starlette.status import WS_1008_POLICY_VIOLATION
from starlette.websockets import WebSocket

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>WebSocket Chat</h1>
        <form action="" onsubmit="sendMessage(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="foo"/></label>
            <button onclick="connect(event)">Connect</button>
            <br>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
            var ws = null;
            function connect(event) {
                event.preventDefault()
                var input = document.getElementById("itemId")
                document.cookie = "session=Test;path=/"
                ws = new WebSocket("ws://localhost:8000/items/" + input.value + "/ws");
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')
                    var message = document.createElement('li')
                    var content = document.createTextNode(event.data)
                    message.appendChild(content)
                    messages.appendChild(message)
                };
            }
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


async def get_cookie_or_client(
    websocket: WebSocket, session: str = Cookie(None), x_client: str = Header(None)
):
    if session is None and x_client is None:
        await websocket.close(code=WS_1008_POLICY_VIOLATION)
    return session or x_client


@app.websocket("/items/{item_id}/ws")
async def websocket_endpoint(
    websocket: WebSocket,
    item_id: int,
    q: str = None,
    cookie_or_client: str = Depends(get_cookie_or_client),
):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(
            f"Session Cookie or X-Client Header value is: {cookie_or_client}"
        )
        if q is not None:
            await websocket.send_text(f"Query parameter q is: {q}")
        await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")

if __name__ == '__main__':
    uvicorn.run(app, host='localhost', port=8000)
alj06ka picture alj06ka on 7 Jul 2019

@alj06ka
work, thank you
need to change item_id to str 

@app.websocket("/items/{item_id}/ws")
async def websocket_endpoint(
    websocket: WebSocket,
    item_id: str,
    q: str = None,
    cookie_or_client: str = Depends(get_cookie_or_client),
):

it's possible to update the doc ?

Ben621 picture Ben621 on 7 Jul 2019
🎉3

I just had the same problem, and looks like the doc hasn't been edited yet as of Mar. 3rd 2020.
The code above seems like a decent fix, which has worked for me too.

harplife picture harplife on 3 Mar 2020

I still have this problem:

from fastapi import Cookie, Depends, FastAPI, Header, WebSocket, status

app = FastAPI()


async def get_cookie_or_client(
    websocket: WebSocket, session: str = Cookie(None), x_client: str = Header(None)
):
    if session is None and x_client is None:
        await websocket.close(code=status.WS_1008_POLICY_VIOLATION)
    return session or x_client


@app.websocket("/ws")
async def websocket_endpoint(
    websocket: WebSocket, cookie_or_client: str = Depends(get_cookie_or_client),
):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()

        await websocket.send_text(f"Message text was: {data}")
naveenreddyin picture naveenreddyin on 2 Apr 2020

After I tried, I found some strange.
For example in get_cookie_or_client part, it check session and x_client is None and then server will wait for websocket connection close, but it's wired because the session is not connecting, why server need to wait?

So I change this part to check if session or client is not None, then close connection.
And it could work now.

After I look test case in unit test, I found that it will fill session or header manually in unit test, but there isn't any part that will create session or header in tutorial002.
I add cookie in get function, and it work.

from fastapi import Cookie, Depends, FastAPI, Header, WebSocket, status
from fastapi.responses import HTMLResponse

app = FastAPI()

html = """
<!DOCTYPE html>
<html>
    <head>
        <title>Chat</title>
    </head>
    <body>
        <h1>WebSocket Chat</h1>
        <form action="" onsubmit="sendMessage(event)">
            <label>Item ID: <input type="text" id="itemId" autocomplete="off" value="1"/></label>
            <button onclick="connect(event)">Connect</button>
            <br>
            <label>Message: <input type="text" id="messageText" autocomplete="off"/></label>
            <button>Send</button>
        </form>
        <ul id='messages'>
        </ul>
        <script>
        var ws = null;
            function connect(event) {
                var input = document.getElementById("itemId")
                ws = new WebSocket("ws://localhost:8000/items/" + input.value + "/ws");
                ws.onmessage = function(event) {
                    var messages = document.getElementById('messages')
                    var message = document.createElement('li')
                    var content = document.createTextNode(event.data)
                    message.appendChild(content)
                    messages.appendChild(message)
                };
                event.preventDefault()
            }
            function sendMessage(event) {
                var input = document.getElementById("messageText")
                ws.send(input.value)
                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""



@app.get("/")
async def get(*, session: str = Cookie(None)):
    response = HTMLResponse(html)
    response.set_cookie(key="session", value="fake-cookie-session-value")
    return response


async def get_cookie_or_client(
    websocket: WebSocket, session: str = Cookie(None), x_client: str = Header(None)
):
    print(session)
    if session is None and x_client is None:
        await websocket.close(code=status.WS_1008_POLICY_VIOLATION)
    return session or x_client


@app.websocket("/items/{item_id}/ws")
async def websocket_endpoint(
    websocket: WebSocket,
    item_id: int,
    q: str = None,
    cookie_or_client: str = Depends(get_cookie_or_client),
):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(
            f"Session Cookie or X-Client Header value is: {cookie_or_client}"
        )
        if q is not None:
            await websocket.send_text(f"Query parameter q is: {q}")
        await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")
ChihSeanHsu picture ChihSeanHsu on 9 Jun 2020

Thanks for the discussion here everyone! :coffee:

It was updated and simplified as part of https://github.com/tiangolo/fastapi/pull/1540

You can check the new docs here: https://fastapi.tiangolo.com/advanced/websockets/#using-depends-and-others :rocket:

I'm re-opening the issue to give time for the author of the issue to confirm and close it :nerd_face:

tiangolo picture tiangolo on 13 Jun 2020
👍3

Assuming the original issue was solved, it will be automatically closed now. But feel free to add more comments or create new issues.

github-actions[bot] picture github-actions[bot] on 24 Jun 2020
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