bug fix: allow folder names up to length 64 in leveldb

When extracting a folder name from the byte slices used as database
keys, bytes.IndexByte() is used to find and remove trailing 0 bytes.
In case the folder name is 64 bytes long, bytes.IndexByte() returns
-1.  Before this change, syncthing crashed in this case with an
out-of-bounds slice access.

The commit fixes the problem and also introduces a test case which
checks for the presence of the bug.

internal/files/leveldb_test.go

@@ -0,0 +1,58 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package files
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestDeviceKey(t *testing.T) {
+	fld := []byte("folder6789012345678901234567890123456789012345678901234567890123")
+	dev := []byte("device67890123456789012345678901")
+	name := []byte("name")
+
+	key := deviceKey(fld, dev, name)
+
+	fld2 := deviceKeyFolder(key)
+	if bytes.Compare(fld2, fld) != 0 {
+		t.Errorf("wrong folder %q != %q", fld2, fld)
+	}
+	dev2 := deviceKeyDevice(key)
+	if bytes.Compare(dev2, dev) != 0 {
+		t.Errorf("wrong device %q != %q", dev2, dev)
+	}
+	name2 := deviceKeyName(key)
+	if bytes.Compare(name2, name) != 0 {
+		t.Errorf("wrong name %q != %q", name2, name)
+	}
+}
+
+func TestGlobalKey(t *testing.T) {
+	fld := []byte("folder6789012345678901234567890123456789012345678901234567890123")
+	name := []byte("name")
+
+	key := globalKey(fld, name)
+
+	fld2 := globalKeyFolder(key)
+	if bytes.Compare(fld2, fld) != 0 {
+		t.Errorf("wrong folder %q != %q", fld2, fld)
+	}
+	name2 := globalKeyName(key)
+	if bytes.Compare(name2, name) != 0 {
+		t.Errorf("wrong name %q != %q", name2, name)
+	}
+}