net/http/httputil: add WebSocket support to ReverseProxy

[bradfitz]

Add WebSocket support to ReverseProxy.

I have code for this that I use myself in various projects, but I keep forgetting to add it to Go.

[nhooyr]

This would need to be off by default in case current clients rely on the lack of support to prevent websocket connections.

[bradfitz]

@nhooyr, that seems like a stretch. We'd document it in the release notes and say how to disable it if people wanted to. But if the two sides negotiate it and the Go user expressed their intent to wire up the two sides with a ReverseProxy, I don't think it's crazy to say we'd wire it up all the way.

[nhooyr]

@bradfitz Fair enough. Its extremely unlikely anyone would not want WebSockets support anyway.

[nhooyr]

@bradfitz Could you post the code for this, I've written something similar myself, want to make sure I'm doing it right.

[nhooyr]

We should also support arbitrary upgrades instead of just WebSockets.

[nhooyr]

@bradfitz In fact, if you post it, I'd love to work on the CL for this.

[bradfitz]

@nhooyr, I'll send it myself, as I already have the code. It won't save me any time to hand it to you to hand back to me. You can review it once it's on Gerrit, though.

[gopherbot]

Change https://golang.org/cl/131279 mentions this issue: net/http: make Transport return Writable Response.Body on WebSocket upgrade

[bradfitz]

I decided to implement this a different way, not using my existing code. Instead, I sent https://golang.org/cl/131279 to add Transport support for WebSockets, so the ReverseProxy code won't need to separately dial the backend.