Milo: Use custom config caching layer

milo/appengine/swarming/html.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package swarming
 
 import (
         "errors"
         "fmt"
         "net/http"
         "os"
 
         "golang.org/x/net/context"
         "google.golang.org/api/googleapi"
 
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/milo/appengine/common"
         "github.com/luci/luci-go/server/router"
         "github.com/luci/luci-go/server/templates"
 )
 
-const (
-        defaultSwarmingServer    = "chromium-swarm.appspot.com"
-        defaultSwarmingDevServer = "chromium-swarm-dev.appspot.com"
-)
-
 var errUnrecognizedHost = errors.New("Unregistered Swarming Host")
 
 // getSwarmingHost parses the swarming hostname out of the context.  If
 // none is specified, get the default swarming host out of the global
 // configs.
 func getSwarmingHost(c context.Context, r *http.Request) (string, error) {
-        settings, err := common.GetSettings(c)
-        if err != nil {
-                logging.WithError(err).Errorf(c, "could not get settings")
-                return "", err
-        }
+        settings := common.GetSettings(c)
         if settings.Swarming == nil {
-                err = errors.New("swarming not in settings")
+                err := errors.New("swarming not in settings")
                 logging.Errorf(c, err.Error())
                 return "", err
         }
         server := r.FormValue("server")
         // If server isn't specified, return the default host.
-        if server == "" {
+        if server == "" || server == settings.Swarming.DefaultHost {
                 return settings.Swarming.DefaultHost, nil
         }
         // If it is specified, validate the hostname.
         for _, hostname := range settings.Swarming.AllowedHosts {
                 if server == hostname {
                         return server, nil
                 }
         }
         return "", errUnrecognizedHost
 }
@@ skipping 89 matching lines @@
         return http.StatusInternalServerError
 }
 
 // isAPINotFound returns true if err is a HTTP 404 API response.
 func isAPINotFound(err error) bool {
         if apiErr, ok := err.(*googleapi.Error); ok && apiErr.Code == http.StatusNotFound {
                 return true
         }
         return false
 }