A bytes file of exactly 64 KiB stays inline: take its exact decoded length (issue 1694)

go/declaration/filereference.go

@@ -85,7 +85,9 @@ func (f *File) TravelsByDigest() bool {
 		return false
 	}
 	if f.Bytes != "" {
-		return base64.StdEncoding.DecodedLen(len(f.Bytes)) > FileReferenceThreshold
+		// DecodedLen counts padding, so the exact length is taken off the decoded bytes.
+		body, err := f.Body()
+		return err == nil && len(body) > FileReferenceThreshold
 	}
 	return len(f.Content) > FileReferenceThreshold
 }

go/declaration/filereference_test.go

@@ -111,6 +111,13 @@ func TestWhichFilesTravelByDigest(t *testing.T) {
 			t.Errorf("%s was made a reference", name)
 		}
 	}
+	exact := File{ID: "m.e", Bytes: base64.StdEncoding.EncodeToString(bytes.Repeat([]byte{7}, FileReferenceThreshold))}
+	if exact.TravelsByDigest() {
+		t.Error("a bytes file of exactly the threshold travels by digest")
+	}
+	if _, _, err := exact.AsReference(); err == nil {
+		t.Error("a bytes file of exactly the threshold was made a reference")
+	}
 	raw := bytes.Repeat([]byte{0, 1, 2}, FileReferenceThreshold)
 	f := File{ID: "m.b", Bytes: base64.StdEncoding.EncodeToString(raw)}
 	ref, body, err := f.AsReference()