Make HTTP middleware easier to use

server/settings/admin/index.go

Index: server/settings/admin/index.go
diff --git a/server/settings/admin/index.go b/server/settings/admin/index.go
index aa5d6d6501acd25d3c9a0c346427e5de98d7229c..1ce99c0ba7bf9433e3dc83ffe2ff5f2b5653a7b4 100644
--- a/server/settings/admin/index.go
+++ b/server/settings/admin/index.go
@@ -5,15 +5,13 @@
 package admin
 
 import (
-	"net/http"
 	"sort"
 	"time"
 
 	"github.com/dustin/go-humanize"
-	"github.com/julienschmidt/httprouter"
-	"golang.org/x/net/context"
 
 	"github.com/luci/luci-go/common/clock"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/settings"
 	"github.com/luci/luci-go/server/templates"
 )
@@ -29,12 +27,13 @@ func (a pageIndexEntries) Len() int           { return len(a) }
 func (a pageIndexEntries) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 func (a pageIndexEntries) Less(i, j int) bool { return a[i].Title < a[j].Title }
 
-func indexPage(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+func indexPage(c *router.Context) {
 	entries := pageIndexEntries{}
 	for id, p := range settings.GetUIPages() {
-		title, err := p.Title(c)
+		title, err := p.Title(c.Context)
 		if err != nil {
-			replyError(c, rw, err)
+			replyError(c.Context, c.Writer, err)
+			c.Abort()
 			return
 		}
 		entries = append(entries, pageIndexEntry{
@@ -46,18 +45,19 @@ func indexPage(c context.Context, rw http.ResponseWriter, r *http.Request, p htt
 
 	// Grab timestamp when last settings change hits all instances.
 	consistencyTime := time.Time{}
-	if s := settings.GetSettings(c); s != nil {
+	if s := settings.GetSettings(c.Context); s != nil {
 		if storage, _ := s.GetStorage().(settings.EventualConsistentStorage); storage != nil {
 			var err error
-			if consistencyTime, err = storage.GetConsistencyTime(c); err != nil {
-				replyError(c, rw, err)
+			if consistencyTime, err = storage.GetConsistencyTime(c.Context); err != nil {
+				replyError(c.Context, c.Writer, err)
+				c.Abort()
 				return
 			}
 		}
 	}
 
-	now := clock.Now(c).UTC()
-	templates.MustRender(c, rw, "pages/index.html", templates.Args{
+	now := clock.Now(c.Context).UTC()
+	templates.MustRender(c.Context, c.Writer, "pages/index.html", templates.Args{
 		"Entries":               entries,
 		"WaitingForConsistency": !consistencyTime.IsZero() && now.Before(consistencyTime),
 		"TimeToConsistency":     humanize.RelTime(consistencyTime, now, "", ""),