proxyReader: don't SetTotal inside Read

bar.go

@@ -85,12 +85,20 @@ func newBar(container *Progress, bs *bState) *Bar {
 }
 
 // ProxyReader wraps r with metrics required for progress tracking.
-// Panics if r is nil.
+// If r is 'unknown total/size' reader it's mandatory to call
+// (*Bar).SetTotal(-1, true) method after (Reader).Read returns io.EOF.
+// Panics if r is nil. If bar is already completed or aborted, returns
+// nil.
 func (b *Bar) ProxyReader(r io.Reader) io.ReadCloser {
 	if r == nil {
 		panic("expected non nil io.Reader")
 	}
-	return b.newProxyReader(r)
+	select {
+	case <-b.done:
+		return nil
+	default:
+		return b.newProxyReader(r)
+	}
 }
 
 // ID returs id of the bar.

proxyreader.go

@@ -14,9 +14,6 @@ type proxyReader struct {
 func (x proxyReader) Read(p []byte) (int, error) {
 	n, err := x.ReadCloser.Read(p)
 	x.bar.IncrBy(n)
-	if err == io.EOF {
-		go x.bar.SetTotal(-1, true)
-	}
 	return n, err
 }
 
@@ -28,9 +25,6 @@ type proxyWriterTo struct {
 func (x proxyWriterTo) WriteTo(w io.Writer) (int64, error) {
 	n, err := x.wt.WriteTo(w)
 	x.bar.IncrInt64(n)
-	if err == io.EOF {
-		go x.bar.SetTotal(-1, true)
-	}
 	return n, err
 }