?? bug report

When running parcel serve where the --port is the same as the --hmr-port (the default behavior AFAIK), the WebSocket proxy (i.e. .proxyrc ) no longer functions properly.

?? Configuration

$ cat .proxyrc.json

{
	
"/ws"
: {
		
"target"
: 
"
http://localhost:1235/
"
,
		
"ws"
: 
true

	}
}

Running this command exhibits the bug:

parcel index.html

?? Expected Behavior

WebSocket proxy should work. When the browser connects to ws://localhost:1234/ws , it should be proxied to localhost:1235/ws using http-proxy-middleware

?? Current Behavior

When the browser establishes the WebSocket connection to ws://localhost:1234/ws , parcel indicates that the web browser immediately disconnects:

$ parcel --port 1234 --hmr-port 1234 index.html

Server running at http://localhost:1234
? Built in 1.76s
console: [HPM] Upgrading to WebSocket
console: [HPM] Client disconnected

On the WebSocket server running in Go on port 1235, I get an error that seems to indicate that the socket is closed:

failed to get reader: failed to read frame header: EOF

On the browser (Firefox), I get a message like this:

The connection to ws://localhost:1234/ws was interrupted while the page was loading.

which occurs on the line where I create the new WebSocket(...) .

?? Possible Solution

Everything runs fine without parcel . If I parcel build and bypass the parcel server and HMR server, it works.

Running Parcel with a different HMR port also seems to work (note that HMR port is set to 1236 ):

parcel --port 1234 --hmr-port 1236 index.html

$ parcel --port 1234 --hmr-port 1236 index.html

Server running at http://localhost:1234
? Built in 392ms
console: [HPM] Upgrading to WebSocket

... and in this case, it all works splendidly.

This seems to indicate that parcel serve does not properly handle WebSocket proxying with http-proxy-middleware when the HMR server is running on the same port as the normal parcel HTTP server.

?? Context

I'm just trying to run parcel serve [entry_point] and have it work (ideally without a separate HMR port).

?? Code Sample

I can provide a sample upon request, but it will take time.

?? Your Environment