[Client] Fix error in parsing of 'Range' header.

* Result of regexp.FindStringSubmatch must be checked to be not nil.
Otherwise it leads to `index out of range`.
* Range header regexp is compiled only once to speedup (5x) the header parsing.

Signed-off-by: Anton Tiurin <noxiouz@yandex.ru>

client/client.go

@@ -67,6 +67,10 @@ type Client interface {
 	CancelBlobUpload(location string) error
 }
 
+var (
+	patternRangeHeader = regexp.MustCompile("bytes=0-(\\d+)/(\\d+)")
+)
+
 // New returns a new Client which operates against a registry with the
 // given base endpoint
 // This endpoint should not include /v2/ or any part of the url after this.
@@ -553,15 +557,18 @@ func (r *clientImpl) CancelBlobUpload(location string) error {
 // parseRangeHeader parses out the offset and length from a returned Range
 // header
 func parseRangeHeader(byteRangeHeader string) (int, int, error) {
-	r := regexp.MustCompile("bytes=0-(\\d+)/(\\d+)")
-	submatches := r.FindStringSubmatch(byteRangeHeader)
-	offset, err := strconv.ParseInt(submatches[1], 10, 0)
+	submatches := patternRangeHeader.FindStringSubmatch(byteRangeHeader)
+	if submatches == nil || len(submatches) < 3 {
+		return 0, 0, fmt.Errorf("Malformed Range header")
+	}
+
+	offset, err := strconv.Atoi(submatches[1])
 	if err != nil {
 		return 0, 0, err
 	}
-	length, err := strconv.ParseInt(submatches[2], 10, 0)
+	length, err := strconv.Atoi(submatches[2])
 	if err != nil {
 		return 0, 0, err
 	}
-	return int(offset), int(length), nil
+	return offset, length, nil
 }

client/client_test.go

@@ -19,6 +19,37 @@ type testBlob struct {
 	contents []byte
 }
 
+func TestRangeHeaderParser(t *testing.T) {
+	const (
+		malformedRangeHeader = "bytes=0-A/C"
+		emptyRangeHeader     = ""
+		rFirst               = 100
+		rSecond              = 200
+	)
+
+	var (
+		wellformedRangeHeader = fmt.Sprintf("bytes=0-%d/%d", rFirst, rSecond)
+	)
+
+	if _, _, err := parseRangeHeader(malformedRangeHeader); err == nil {
+		t.Fatalf("malformedRangeHeader: error expected, got nil")
+	}
+
+	if _, _, err := parseRangeHeader(emptyRangeHeader); err == nil {
+		t.Fatalf("emptyRangeHeader: error expected, got nil")
+	}
+
+	first, second, err := parseRangeHeader(wellformedRangeHeader)
+	if err != nil {
+		t.Fatalf("wellformedRangeHeader: unexpected error %v", err)
+	}
+
+	if first != rFirst || second != rSecond {
+		t.Fatalf("Range has been parsed unproperly: %d/%d", first, second)
+	}
+
+}
+
 func TestPush(t *testing.T) {
 	name := "hello/world"
 	tag := "sometag"