Make HTTP middleware easier to use

appengine/cmd/milo/settings/settings.go

Index: appengine/cmd/milo/settings/settings.go
diff --git a/appengine/cmd/milo/settings/settings.go b/appengine/cmd/milo/settings/settings.go
index d7fb7399be6c4f605603306a8383b8dbb479a508..f51b78345358131a951e420a433de1d525f96cb3 100644
--- a/appengine/cmd/milo/settings/settings.go
+++ b/appengine/cmd/milo/settings/settings.go
@@ -10,13 +10,13 @@ import (
 	"fmt"
 	"net/http"
 
-	"github.com/julienschmidt/httprouter"
 	"github.com/luci/gae/service/datastore"
 	"github.com/luci/luci-go/appengine/cmd/milo/model"
 	"github.com/luci/luci-go/appengine/cmd/milo/resp"
 	"github.com/luci/luci-go/server/auth"
 	"github.com/luci/luci-go/server/auth/identity"
 	"github.com/luci/luci-go/server/auth/xsrf"
+	"github.com/luci/luci-go/server/router"
 	"golang.org/x/net/context"
 )
 
@@ -75,31 +75,31 @@ func getCookieSettings(c context.Context, r *http.Request) *model.UserConfig {
 
 // ChangeSettings is invoked in a POST request to settings and changes either
 // the user settings in the datastore, or the cookies if user is anon.
-func ChangeSettings(c context.Context, h http.ResponseWriter, r *http.Request, p httprouter.Params) {
+func ChangeSettings(c *router.Context) {
 	// First, check XSRF token.
-	err := xsrf.Check(c, r.FormValue("xsrf_token"))
+	err := xsrf.Check(c.Context, c.Request.FormValue("xsrf_token"))
 	if err != nil {
-		h.WriteHeader(http.StatusUnauthorized)
-		h.Write([]byte("Failed XSRF check."))
+		c.Writer.WriteHeader(http.StatusUnauthorized)
+		c.Writer.Write([]byte("Failed XSRF check."))
 		return
 	}
 
 	u := &updateReq{
-		Theme: r.FormValue("theme"),
+		Theme: c.Request.FormValue("theme"),
 	}
 	validateUpdate(u)
-	s := getUserSettings(c)
+	s := getUserSettings(c.Context)
 	if s == nil {
 		// User doesn't exist, just respond with a cookie.
-		s = getCookieSettings(c, r)
+		s = getCookieSettings(c.Context, c.Request)
 		s.Theme = u.Theme
-		setCookieSettings(h, s)
+		setCookieSettings(c.Writer, s)
 	} else {
-		changeUserSettings(c, u)
+		changeUserSettings(c.Context, u)
 	}
 
 	// Redirect to the GET endpoint.
-	http.Redirect(h, r, r.URL.String(), http.StatusSeeOther)
+	http.Redirect(c.Writer, c.Request, c.Request.URL.String(), http.StatusSeeOther)
 }
 
 // setCookieSettings sets the cfg object as a base64 json serialized string.