use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/mholt/caddy/caddyhttp/httpserver/error.go

@@ -0,0 +1,70 @@
+// Copyright 2015 Light Code Labs, LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package httpserver
+
+import (
+	"fmt"
+)
+
+var (
+	_ error = NonHijackerError{}
+	_ error = NonFlusherError{}
+	_ error = NonCloseNotifierError{}
+	_ error = NonPusherError{}
+)
+
+// NonHijackerError is more descriptive error caused by a non hijacker
+type NonHijackerError struct {
+	// underlying type which doesn't implement Hijack
+	Underlying interface{}
+}
+
+// Implement Error
+func (h NonHijackerError) Error() string {
+	return fmt.Sprintf("%T is not a hijacker", h.Underlying)
+}
+
+// NonFlusherError is more descriptive error caused by a non flusher
+type NonFlusherError struct {
+	// underlying type which doesn't implement Flush
+	Underlying interface{}
+}
+
+// Implement Error
+func (f NonFlusherError) Error() string {
+	return fmt.Sprintf("%T is not a flusher", f.Underlying)
+}
+
+// NonCloseNotifierError is more descriptive error caused by a non closeNotifier
+type NonCloseNotifierError struct {
+	// underlying type which doesn't implement CloseNotify
+	Underlying interface{}
+}
+
+// Implement Error
+func (c NonCloseNotifierError) Error() string {
+	return fmt.Sprintf("%T is not a closeNotifier", c.Underlying)
+}
+
+// NonPusherError is more descriptive error caused by a non pusher
+type NonPusherError struct {
+	// underlying type which doesn't implement pusher
+	Underlying interface{}
+}
+
+// Implement Error
+func (c NonPusherError) Error() string {
+	return fmt.Sprintf("%T is not a pusher", c.Underlying)
+}