net/http: add AllowQuerySemicolons [freeze exception]

[rsc]

Over in #25192 (comment), @AGWA makes the suggestion to add to net/http a standard Handler wrapper to allow semicolons for people who want to opt into that. The function would be something like:

func AllowQuerySemicolons(h http.Handler) http.Handler {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
                if r.URL.RawQuery != "" {
                        r2 := new(http.Request)
                        *r2 = *r
                        r2.URL = new(url.URL)
                        *r2.URL = *r.URL
                        r2.URL.RawQuery = strings.ReplaceAll(r.URL.RawQuery, ";", "&")
                        h.ServeHTTP(w, r2)
                } else {
                        h.ServeHTTP(w, r)
                }
        })
}

It seems like a nice way to reduce the pain of the semicolon change itself in #25192. We should consider adding it for Go 1.17 (even though we are in the freeze).

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[rsc]

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

[rsc]

No change in consensus, so accepted. 🎉
This issue now tracks the work of implementing the proposal.
— rsc for the proposal review group

[dmitshur]

Thank you for making this freeze exception request. It is approved.

[gopherbot]

Change https://golang.org/cl/326309 mentions this issue: net/http: add AllowQuerySemicolons