lib/db: Refactor key handling (ref #5198) (#5199)

This breaks out the key generation stuff into a separate type. It's
cleaner on its own, and it prepares for future stuff.

lib/db/keyer_test.go

@@ -0,0 +1,80 @@
+// Copyright (C) 2018 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package db
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestDeviceKey(t *testing.T) {
+	fld := []byte("folder6789012345678901234567890123456789012345678901234567890123")
+	dev := []byte("device67890123456789012345678901")
+	name := []byte("name")
+
+	db := OpenMemory()
+
+	key := db.keyer.GenerateDeviceFileKey(nil, fld, dev, name)
+
+	fld2, ok := db.keyer.FolderFromDeviceFileKey(key)
+	if !ok {
+		t.Fatal("unexpectedly not found")
+	}
+	if !bytes.Equal(fld2, fld) {
+		t.Errorf("wrong folder %q != %q", fld2, fld)
+	}
+	dev2, ok := db.keyer.DeviceFromDeviceFileKey(key)
+	if !ok {
+		t.Fatal("unexpectedly not found")
+	}
+	if !bytes.Equal(dev2, dev) {
+		t.Errorf("wrong device %q != %q", dev2, dev)
+	}
+	name2 := db.keyer.NameFromDeviceFileKey(key)
+	if !bytes.Equal(name2, name) {
+		t.Errorf("wrong name %q != %q", name2, name)
+	}
+}
+
+func TestGlobalKey(t *testing.T) {
+	fld := []byte("folder6789012345678901234567890123456789012345678901234567890123")
+	name := []byte("name")
+
+	db := OpenMemory()
+
+	key := db.keyer.GenerateGlobalVersionKey(nil, fld, name)
+
+	fld2, ok := db.keyer.FolderFromGlobalVersionKey(key)
+	if !ok {
+		t.Error("should have been found")
+	}
+	if !bytes.Equal(fld2, fld) {
+		t.Errorf("wrong folder %q != %q", fld2, fld)
+	}
+	name2 := db.keyer.NameFromGlobalVersionKey(key)
+	if !bytes.Equal(name2, name) {
+		t.Errorf("wrong name %q != %q", name2, name)
+	}
+
+	_, ok = db.keyer.FolderFromGlobalVersionKey([]byte{1, 2, 3, 4, 5})
+	if ok {
+		t.Error("should not have been found")
+	}
+}
+
+func TestSequenceKey(t *testing.T) {
+	fld := []byte("folder6789012345678901234567890123456789012345678901234567890123")
+
+	db := OpenMemory()
+
+	const seq = 1234567890
+	key := db.keyer.GenerateSequenceKey(nil, fld, seq)
+	outSeq := db.keyer.SequenceFromSequenceKey(key)
+	if outSeq != seq {
+		t.Errorf("sequence number mangled, %d != %d", outSeq, seq)
+	}
+}