Fix parsing of indefinite empty structures

ber.go

@@ -220,14 +220,6 @@ func readObject(ber []byte, offset int) (asn1Object, int, error) {
 	} else {
 		var subObjects []asn1Object
 		for (offset < contentEnd) || indefinite {
-			var subObj asn1Object
-			var err error
-			subObj, offset, err = readObject(ber, offset)
-			if err != nil {
-				return nil, 0, err
-			}
-			subObjects = append(subObjects, subObj)
-
 			if indefinite {
 				terminated, err := isIndefiniteTermination(ber, offset)
 				if err != nil {
@@ -238,6 +230,14 @@ func readObject(ber []byte, offset int) (asn1Object, int, error) {
 					break
 				}
 			}
+
+			var subObj asn1Object
+			var err error
+			subObj, offset, err = readObject(ber, offset)
+			if err != nil {
+				return nil, 0, err
+			}
+			subObjects = append(subObjects, subObj)
 		}
 		obj = asn1Structured{
 			tagBytes: ber[tagStart:tagEnd],

ber_test.go

@@ -39,6 +39,35 @@ func TestBer2Der(t *testing.T) {
 	}
 }
 
+func TestBer2Der_EmptyIndefinite(t *testing.T) {
+	// indefinite length fixture without content (actual 0-length)
+	ber := []byte{0x30, 0x80, 0x00, 0x00}
+	expected := []byte{0x30, 0x00}
+	der, err := ber2der(ber)
+	if err != nil {
+		t.Fatalf("ber2der failed with error: %v", err)
+	}
+	if !bytes.Equal(der, expected) {
+		t.Errorf("ber2der result did not match.\n\tExpected: % X\n\tActual: % X", expected, der)
+	}
+
+	if der2, err := ber2der(der); err != nil {
+		t.Errorf("ber2der on DER bytes failed with error: %v", err)
+	} else {
+		if !bytes.Equal(der, der2) {
+			t.Error("ber2der is not idempotent")
+		}
+	}
+	var thing struct {
+	}
+	rest, err := asn1.Unmarshal(der, &thing)
+	if err != nil {
+		t.Errorf("Cannot parse resulting DER because: %v", err)
+	} else if len(rest) > 0 {
+		t.Errorf("Resulting DER has trailing data: % X", rest)
+	}
+}
+
 func TestBer2Der_Negatives(t *testing.T) {
 	fixtures := []struct {
 		Input         []byte