upload: add TeeReader to count bytes during upload (#54)

We occasionally see an EOF error when attempting to upload to S3
storage. An EOF from io.ReadCloser interfaces typically indicates that
no more input is available. This commit is adding a TeeReader to count
the number of bytes that were read from the local input file when
attempting to upload -- this should help us diagnose upload errors where
segments seem to be missing from s3 buckets.

core/uploader.go

@@ -18,6 +18,15 @@ import (
 	"github.com/livepeer/go-tools/drivers"
 )
 
+type ByteCounter struct {
+	Count int64
+}
+
+func (bc *ByteCounter) Write(p []byte) (n int, err error) {
+	bc.Count += int64(len(p))
+	return n, nil
+}
+
 func newExponentialBackOffExecutor() *backoff.ExponentialBackOff {
 	backOff := backoff.NewExponentialBackOff()
 	backOff.InitialInterval = 200 * time.Millisecond
@@ -55,6 +64,7 @@ func Upload(input io.Reader, outputURI *url.URL, waitBetweenWrites, writeTimeout
 		}
 	}
 
+	byteCounter := &ByteCounter{}
 	if strings.HasSuffix(output, ".ts") || strings.HasSuffix(output, ".mp4") {
 		// For segments we just write them in one go here and return early.
 		// (Otherwise the incremental write logic below caused issues with clipping since it results in partial segments being written.)
@@ -63,16 +73,19 @@ func Upload(input io.Reader, outputURI *url.URL, waitBetweenWrites, writeTimeout
 			return nil, fmt.Errorf("failed to read file")
 		}
 
+		// To count how many bytes we are trying to read then write (upload) to s3 storage
+		teeReader := io.TeeReader(bytes.NewReader(fileContents), byteCounter)
+
 		var out *drivers.SaveDataOutput
 		err = backoff.Retry(func() error {
-			out, err = session.SaveData(context.Background(), "", bytes.NewReader(fileContents), fields, segmentWriteTimeout)
+			out, err = session.SaveData(context.Background(), "", teeReader, fields, segmentWriteTimeout)
 			if err != nil {
-				glog.Errorf("failed upload attempt for %s: %v", outputURI.Redacted(), err)
+				glog.Errorf("failed upload attempt for %s (%d bytes): %v", outputURI.Redacted(), byteCounter.Count, err)
 			}
 			return err
 		}, UploadRetryBackoff())
 		if err != nil {
-			return nil, fmt.Errorf("failed to upload video %s: %w", outputURI.Redacted(), err)
+			return nil, fmt.Errorf("failed to upload video %s: (%d bytes) %w", outputURI.Redacted(), byteCounter.Count, err)
 		}
 
 		if err = extractThumb(session, output, fileContents); err != nil {