docker: support for requesting chunks without end offset

if the specified length for the range is set to -1, then request all
the data possible by using the "Range: <unit>=<range-start>-" syntax
for the HTTP range.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

docker/docker_image_src.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"mime"
 	"mime/multipart"
 	"net/http"
@@ -342,8 +343,18 @@ func (s *dockerImageSource) GetBlobAt(ctx context.Context, info types.BlobInfo,
 	headers := make(map[string][]string)
 
 	rangeVals := make([]string, 0, len(chunks))
+	lastFound := false
 	for _, c := range chunks {
-		rangeVals = append(rangeVals, fmt.Sprintf("%d-%d", c.Offset, c.Offset+c.Length-1))
+		if lastFound {
+			return nil, nil, fmt.Errorf("invalid chunk requested: %v", c)
+		}
+		// If the Length is set to -1, then request anything after the specified offset.
+		if c.Length == math.MaxUint64 {
+			lastFound = true
+			rangeVals = append(rangeVals, fmt.Sprintf("%d-", c.Offset))
+		} else {
+			rangeVals = append(rangeVals, fmt.Sprintf("%d-%d", c.Offset, c.Offset+c.Length-1))
+		}
 	}
 
 	headers["Range"] = []string{fmt.Sprintf("bytes=%s", strings.Join(rangeVals, ","))}