add more descriptive errors

Signed-off-by: Tw <tw19881113@gmail.com>

caddyhttp/httpserver/error.go

@@ -0,0 +1,44 @@
+package httpserver
+
+import (
+	"fmt"
+)
+
+var (
+	_ error = NonHijackerError{}
+	_ error = NonFlusherError{}
+	_ error = NonCloseNotifierError{}
+)
+
+// 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)
+}