net/http ServeMux clears query when redirecting

[Maydell]

What version of Go are you using (go version)?

What operating system and processor architecture are you using (go env)?

go version go1.7.1 linux/amd64

What did you do?

package main

import "net/http"

func main() {
	http.HandleFunc("/route/", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusInternalServerError)
	})

	http.ListenAndServe(":8080", nil)
}

I made a request to the above server as follows
curl "localhost:8080/route?test=a" -v

What did you expect to see?

As described in the docs, I expected the server to redirect me to path /route/?test=a

What did you see instead?

Instead the server redirected me to path /route/, ignoring the query provided in the original request.

*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /route?test=a HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.43.0
> Accept: */*
> 
< HTTP/1.1 301 Moved Permanently
< Location: /route/
< Date: Thu, 08 Dec 2016 18:22:54 GMT
< Content-Length: 42
< Content-Type: text/html; charset=utf-8
< 
<a href="/route/">Moved Permanently</a>.

* Connection #0 to host localhost left intact

[bradfitz]

Dup of #17841