all: Refactor cmd/syncthing creating lib/syncthing (ref #4085) (#5805)

* add skeleton for lib/syncthing

* copy syncthingMain to lib/syncthing (verbatim)

* Remove code to deduplicate copies of syncthingMain

* fix simple build errors

* move stuff from main to syncthing with minimal mod

* merge runtime options

* actually use syncthing.App

* pass io.writer to lib/syncthing for auditing

* get rid of env stuff in lib/syncthing

* add .Error() and comments

* review: Remove fs interactions from lib

* and go 1.13 happened

* utility functions

lib/syncthing/auditservice_test.go

@@ -0,0 +1,54 @@
+// Copyright (C) 2015 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 syncthing
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/syncthing/syncthing/lib/events"
+)
+
+func TestAuditService(t *testing.T) {
+	buf := new(bytes.Buffer)
+	service := newAuditService(buf)
+
+	// Event sent before start, will not be logged
+	events.Default.Log(events.ConfigSaved, "the first event")
+
+	go service.Serve()
+	service.WaitForStart()
+
+	// Event that should end up in the audit log
+	events.Default.Log(events.ConfigSaved, "the second event")
+
+	// We need to give the events time to arrive, since the channels are buffered etc.
+	time.Sleep(10 * time.Millisecond)
+
+	service.Stop()
+	service.WaitForStop()
+
+	// This event should not be logged, since we have stopped.
+	events.Default.Log(events.ConfigSaved, "the third event")
+
+	result := buf.String()
+	t.Log(result)
+
+	if strings.Contains(result, "first event") {
+		t.Error("Unexpected first event")
+	}
+
+	if !strings.Contains(result, "second event") {
+		t.Error("Missing second event")
+	}
+
+	if strings.Contains(result, "third event") {
+		t.Error("Missing third event")
+	}
+}