add (failing) tests for copytruncate detection

tail_test.go

@@ -128,13 +128,59 @@ func _TestReOpen(_t *testing.T, poll bool) {
 // The use of polling file watcher could affect file rotation
 // (detected via renames), so test these explicitly.
 
+func TestReOpenWithoutPoll(_t *testing.T) {
+	_TestReOpen(_t, false)
+}
+
 func TestReOpenWithPoll(_t *testing.T) {
 	_TestReOpen(_t, true)
 }
 
-func TestReOpenWithoutPoll(_t *testing.T) {
-	_TestReOpen(_t, false)
+
+func _TestReSeek(_t *testing.T, poll bool) {
+	var name string
+	if poll {
+		name = "reseek-polling"
+	}else {
+		name = "reseek-inotify"
 	}
+	t := NewTailTest(name, _t)
+	t.CreateFile("test.txt", "hello\nworld\n")
+	tail := t.StartTail(
+		"test.txt",
+		Config{Follow: true, ReOpen: true, Poll: poll, Location: -1})
+	
+	go t.VerifyTailOutput(tail, []string{"hello", "world", "h311o", "w0r1d", "endofworld"})
+
+	// truncate now
+	<-time.After(100 * time.Millisecond)
+	t.TruncateFile("test.txt", "h311o\nw0r1d\nendofworld\n")
+	// XXX: is this required for this test function?
+	if poll {
+		// Give polling a chance to read the just-written lines (more;
+		// data), before we recreate the file again below.
+		<-time.After(POLL_DURATION)
+	}
+
+	// Delete after a reasonable delay, to give tail sufficient time
+	// to read all lines.
+	<-time.After(100 * time.Millisecond)
+	t.RemoveFile("test.txt")
+
+	tail.Stop()
+}
+
+// The use of polling file watcher could affect file rotation
+// (detected via renames), so test these explicitly.
+
+func TestReSeekWithoutPoll(_t *testing.T) {
+	_TestReSeek(_t, false)
+}
+
+func TestReSeekWithPoll(_t *testing.T) {
+	_TestReSeek(_t, true)
+}
+
 
 // Test library
 
@@ -188,6 +234,18 @@ func (t TailTest) AppendFile(name string, contents string) {
 	}
 }
 
+func (t TailTest) TruncateFile(name string, contents string) {
+	f, err := os.OpenFile(t.path+"/"+name, os.O_WRONLY, 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	_, err = f.WriteString(contents)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func (t TailTest) StartTail(name string, config Config) *Tail {
 	tail, err := TailFile(t.path+"/"+name, config)
 	if err != nil {
@@ -211,7 +269,8 @@ func (t TailTest) VerifyTailOutput(tail *Tail, lines []string) {
 			t.Fatalf("tail.Lines returned nil; not possible")
 		}
 		if tailedLine.Text != line {
-			t.Fatalf("mismatch; %s != %s", tailedLine.Text, line)
+			t.Fatalf("mismatch; %s (actual) != %s (expected)",
+				tailedLine.Text, line)
 		}
 	}
 	line, ok := <-tail.Lines