allow Write during streaming mode. add Flush function

w.go

@@ -16,7 +16,12 @@ type Writer struct {
 // Write implements io.Writer.
 func (w *Writer) Write(p []byte) (n int, err error) {
 	if w.stream != nil {
-		return 0, errStreaming
+		if len(w.Buf) > 0 {
+			if w.Flush() {
+				return 0, w.stream.writeErr
+			}
+		}
+		return w.stream.writer.Write(p)
 	}
 	w.Buf = append(w.Buf, p...)
 	return len(p), nil
@@ -63,6 +68,17 @@ func (w *Writer) Grow(n int) {
 	w.Buf = buf.Bytes()
 }
 
+// Flush flushes the stream. It does nothing if not in streaming mode
+func (w *Writer) Flush() (fail bool) {
+	if w.stream != nil {
+		w.Buf, fail = w.stream.flush(w.Buf)
+		if fail {
+			return true
+		}
+	}
+	return false
+}
+
 // byte writes a single byte.
 func (w *Writer) byte(c byte) (fail bool) {
 	if w.stream == nil {

w_stream.go

@@ -94,7 +94,6 @@ func writeStreamByteseqSlow[S byteseq.Byteseq](w *Writer, s S) bool {
 		if fail {
 			return true
 		}
-
 		n := copy(w.Buf[len(w.Buf):cap(w.Buf)], s)
 		s = s[n:]
 		w.Buf = w.Buf[:len(w.Buf)+n]