fix：introduce buffered response writer for webdav, fix status/error return failed. (#2544)

* fix: introduce buffered response writer for webdav, fix webdav status/error return failed.

* fix: bypass buffered writer for GET/HEAD/POST requests

server/webdav/buffered_response_writer.go

@@ -0,0 +1,46 @@
+package webdav
+
+import (
+	"net/http"
+)
+
+type bufferedResponseWriter struct {
+	statusCode int
+	data       []byte
+	header     http.Header
+}
+
+func (w *bufferedResponseWriter) Header() http.Header {
+	if w.header == nil {
+		w.header = make(http.Header)
+	}
+	return w.header
+}
+
+func (w *bufferedResponseWriter) Write(bytes []byte) (int, error) {
+	w.data = append(w.data, bytes...)
+	return len(bytes), nil
+}
+
+func (w *bufferedResponseWriter) WriteHeader(statusCode int) {
+	if w.statusCode == 0 {
+		w.statusCode = statusCode
+	}
+}
+
+func (w *bufferedResponseWriter) WriteToResponse(rw http.ResponseWriter) (int, error) {
+	h := rw.Header()
+	for k, vs := range w.header {
+		for _, v := range vs {
+			h.Add(k, v)
+		}
+	}
+	rw.WriteHeader(w.statusCode)
+	return rw.Write(w.data)
+}
+
+func newBufferedResponseWriter() *bufferedResponseWriter {
+	return &bufferedResponseWriter{
+		statusCode: 0,
+	}
+}