Websocket shouldUpgrade() fail causes empty reply from server about vapor

[gwynne]

Without the -f flag, curl is not reporting the actual status code from the server in your example - try using the -v flag to see the full protocol exchange, including the actual response code for the empty replies.

[challfry]

Adding the -f and -v flags:

curl -f -v --include \
     --header "Connection: Upgrade" \
     --header "Upgrade: websocket" \
     --header "Host: 127.0.0.1" \
     --header "Origin: http://127.0.0.1:8080" \
     --header "Sec-WebSocket-Key: SGVsbG8sIHdvcmxkIQ==" \
     --header "Sec-WebSocket-Version: 13" \
     http://127.0.0.1:8080/throwsocket
*   Trying 127.0.0.1:8080...
* Connected to 127.0.0.1 (127.0.0.1) port 8080
> GET /throwsocket HTTP/1.1
> Host: 127.0.0.1
> User-Agent: curl/8.4.0
> Accept: */*
> Connection: Upgrade
> Upgrade: websocket
> Origin: http://127.0.0.1:8080
> Sec-WebSocket-Key: SGVsbG8sIHdvcmxkIQ==
> Sec-WebSocket-Version: 13
> 
* Empty reply from server
* Closing connection
curl: (52) Empty reply from server

[gwynne]

Ah ha, literally no response at all, not even an HTTP status line. My apologies for my partial misread of your original post! That is definitely incorrect behavior 😕.

[challfry]

More information that's likely related. When calling a ws route, the middleware futures (or async completions; the part that runs on the way out of the middleware stack) all fire before the "shouldUpgrade" closure is called. Oddly, as the middlewares unwind they all receive a Response object with a 101 status. This means that e.g. ErrorMiddleware never sees an error response when shouldUpgrade() returns an error, because ErrorMiddleware exits before shouldUpgrade gets to run.

Later, after shouldUpgrade throws an error or returns nil the future chain enters the .failure state, the Response object with the 101 status disappears, and eventually NIO closes the channel. I wish I could understand NIO better to figure out which part was where things go wrong, but alas.