Milo: Add themed page for errors

milo/appengine/buildbot/master.go

Index: milo/appengine/buildbot/master.go
diff --git a/milo/appengine/buildbot/master.go b/milo/appengine/buildbot/master.go
index 6fcef9219291e4fa81ae5969f850fc238d3dc4a9..7fe602b56455ba6eafed04670f9503a78391361d 100644
--- a/milo/appengine/buildbot/master.go
+++ b/milo/appengine/buildbot/master.go
@@ -16,6 +16,8 @@ import (
 	"github.com/luci/luci-go/common/logging"
 	"github.com/luci/luci-go/milo/api/resp"
 	"github.com/luci/luci-go/milo/appengine/settings"
+	"github.com/luci/luci-go/server/auth"
+	"github.com/luci/luci-go/server/auth/identity"
 
 	"golang.org/x/net/context"
 )
@@ -36,12 +38,26 @@ func decodeMasterEntry(
 
 // getMasterEntry feches the named master and does an ACL check on the
 // current user.
+// It returns:
+// User not logged in, master found, master public: 200
+// User not logged in, master not found: 401
+// User not logged in, master internal: 401
+// User logged in, master found, master internal: 200
+// User logged in, master not found: 404
+// User logged in, master found, master internal: 404
+// Other error: 500
 func getMasterEntry(c context.Context, name string) (*buildbotMasterEntry, error) {
 	entry := buildbotMasterEntry{Name: name}
 	err := ds.Get(c, &entry)
+	cu := auth.CurrentUser(c)
+
 	switch {
 	case err == ds.ErrNoSuchEntity:
-		return nil, errMasterNotFound
+		if cu.Identity == identity.AnonymousIdentity {

[estaab, 2016/12/01 00:04:34]

It seems pretty dangerous to have the auth checking code duplicated. If the
logic changes and we forget to update one we can get into trouble. Can you make
this a CheckAccess() method that's shared between both access sites?

[hinoka, 2016/12/01 02:08:54]

Done.

+			return nil, errNotAuth
+		} else {
+			return nil, errMasterNotFound
+		}
 	case err != nil:
 		logging.WithError(err).Errorf(
 			c, "Encountered error while fetching entry for %s:\n%s", name, err)
@@ -55,7 +71,11 @@ func getMasterEntry(c context.Context, name string) (*buildbotMasterEntry, error
 			return nil, err
 		}
 		if !allowed {
-			return nil, errMasterNotFound
+			if cu.Identity == identity.AnonymousIdentity {
+				return nil, errNotAuth
+			} else {
+				return nil, errMasterNotFound
+			}
 		}
 	}