internal/frontend: preserve query parameters when redirecting /v1beta/ to /v1/

Fixes golang/go#81045

Change-Id: Ic3d914069bb9e3536f313c292fe98c48b90b6808
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/824864
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Ethan Lee <ethanalee@google.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/frontend/frontend_test.go

diff --git a/internal/frontend/frontend_test.go b/internal/frontend/frontend_test.go
index c155e33..3084546 100644
--- a/internal/frontend/frontend_test.go
+++ b/internal/frontend/frontend_test.go
@@ -169,6 +169,17 @@
 			t.Errorf("got Location = %q, want %q", got, "/v1/moo")
 		}
 	})
+
+	t.Run("redirect /v1beta/ path with query", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		handler.ServeHTTP(w, httptest.NewRequest("GET", "/v1beta/search?q=uuid&limit=25", nil))
+		if w.Code != http.StatusMovedPermanently {
+			t.Errorf("got status code = %d, want %d", w.Code, http.StatusMovedPermanently)
+		}
+		if got, want := w.Header().Get("Location"), "/v1/search?q=uuid&limit=25"; got != want {
+			t.Errorf("got Location = %q, want %q", got, want)
+		}
+	})
 }
 
 func TestAPIUnknownEndpoint(t *testing.T) {

internal/frontend/server.go

diff --git a/internal/frontend/server.go b/internal/frontend/server.go
index 1ba3db3..9bcf822 100644
--- a/internal/frontend/server.go
+++ b/internal/frontend/server.go
@@ -266,8 +266,12 @@
 		http.Redirect(w, r, "/v1/api", http.StatusMovedPermanently)
 	}))
 	handle("/v1beta/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		path := strings.Replace(r.URL.Path, "/v1beta/", "/v1/", 1)
-		http.Redirect(w, r, path, http.StatusMovedPermanently)
+		u := *r.URL
+		u.Path = strings.Replace(u.Path, "/v1beta/", "/v1/", 1)
+		if u.RawPath != "" {
+			u.RawPath = strings.Replace(u.RawPath, "/v1beta/", "/v1/", 1)
+		}
+		http.Redirect(w, r, u.String(), http.StatusMovedPermanently)
 	}))
 	handle("/v1/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		api.ServeError(w, r, api.BadRequest("unknown API endpoint",