cmd/syncthing: Add test for truncate behavior of log file (ref #4255)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4342

cmd/syncthing/monitor_test.go

@@ -0,0 +1,88 @@
+// Copyright (C) 2017 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 main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestAutoClosedFile(t *testing.T) {
+	os.RemoveAll("_autoclose")
+	defer os.RemoveAll("_autoclose")
+	os.Mkdir("_autoclose", 0755)
+	file := filepath.FromSlash("_autoclose/tmp")
+	data := []byte("hello, world\n")
+
+	// An autoclosed file that closes very quickly
+	ac := newAutoclosedFile(file, time.Millisecond, time.Millisecond)
+
+	// Write some data.
+	if _, err := ac.Write(data); err != nil {
+		t.Fatal(err)
+	}
+
+	// Wait for it to close
+	start := time.Now()
+	for {
+		time.Sleep(time.Millisecond)
+		ac.mut.Lock()
+		fd := ac.fd
+		ac.mut.Unlock()
+		if fd == nil {
+			break
+		}
+		if time.Since(start) > time.Second {
+			t.Fatal("File should have been closed after first write")
+		}
+	}
+
+	// Write more data, which should be an append.
+	if _, err := ac.Write(data); err != nil {
+		t.Fatal(err)
+	}
+
+	// Close.
+	if err := ac.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	// The file should have both writes in it.
+	bs, err := ioutil.ReadFile(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(bs) != 2*len(data) {
+		t.Fatalf("Writes failed, expected %d bytes, not %d", 2*len(data), len(bs))
+	}
+
+	// Open the file again.
+	ac = newAutoclosedFile(file, time.Second, time.Second)
+
+	// Write something
+	if _, err := ac.Write(data); err != nil {
+		t.Fatal(err)
+	}
+
+	// It should now contain only one write, because the first open
+	// should be a truncate.
+	bs, err = ioutil.ReadFile(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(bs) != len(data) {
+		t.Fatalf("Write failed, expected %d bytes, not %d", len(data), len(bs))
+	}
+
+	// Close.
+	if err := ac.Close(); err != nil {
+		t.Fatal(err)
+	}
+}