SplitHTTP: Do not produce too large upload (#3691)

transport/pipe/impl.go

@@ -46,6 +46,14 @@ var (
 	errSlowDown   = errors.New("slow down")
 )
 
+func (p *pipe) Len() int32 {
+    data := p.data
+    if data == nil {
+        return 0
+    }
+    return data.Len()
+}
+
 func (p *pipe) getState(forRead bool) error {
 	switch p.state {
 	case open:

transport/pipe/writer.go

@@ -19,6 +19,10 @@ func (w *Writer) Close() error {
 	return w.pipe.Close()
 }
 
+func (w *Writer) Len() int32 {
+    return w.pipe.Len()
+}
+
 // Interrupt implements common.Interruptible.
 func (w *Writer) Interrupt() {
 	w.pipe.Interrupt()