pb: Do not exceed the specified total transfer bytes (#2685)

mc, via minio-go, can retries some requests for many reasons, such as, network
disconnect. This commit ensures that the progress bar does not show transfered
bytes greater then the total transfered bytes to avoid confusing users.

cmd/progress-bar.go

@@ -17,8 +17,6 @@
 package cmd
 
 import (
-	"errors"
-	"io"
 	"runtime"
 	"strings"
 	"time"
@@ -32,10 +30,6 @@ import (
 // progress extender.
 type progressBar struct {
 	*pb.ProgressBar
-	reader       io.Reader
-	readerLength int64
-	bytesRead    int64
-	isResume     bool
 }
 
 // newProgressBar - instantiate a progress bar.
@@ -102,18 +96,17 @@ func (p *progressBar) Set64(length int64) *progressBar {
 	return p
 }
 
-func (p *progressBar) Seek(offset int64, whence int) (n int64, err error) {
-	switch whence {
-	case io.SeekStart:
-		p.ProgressBar = p.ProgressBar.Set64(offset)
-		return offset, nil
-	case io.SeekCurrent:
-		return p.ProgressBar.Add64(offset), nil
-	case io.SeekEnd:
-		p.ProgressBar.Set64(p.ProgressBar.Total - offset)
-		return p.ProgressBar.Total - offset, nil
-	}
-	return 0, errors.New("invalid argument")
+func (p *progressBar) Read(buf []byte) (n int, err error) {
+	defer func() {
+		// After updating the internal progress bar, make sure that its
+		// current progress doesn't exceed the specified total progress
+		currentProgress := p.ProgressBar.Get()
+		if currentProgress > p.ProgressBar.Total {
+			p.ProgressBar.Set64(p.ProgressBar.Total)
+		}
+	}()
+
+	return p.ProgressBar.Read(buf)
 }
 
 func (p *progressBar) SetTotal(total int64) *progressBar {