Fix deadlock when stopping on non-empty file/buffer

tail.go

@@ -137,7 +137,7 @@ func TailFile(filename string, config Config) (*Tail, error) {
 	return t, nil
 }
 
-// Return the file's current position, like stdio's ftell().
+// Tell returns the file's current position, like stdio's ftell().
 // But this value is not very accurate.
 // One line from the chan(tail.Lines) may have been read,
 // so it may have lost one line.
@@ -355,10 +355,9 @@ func (tail *Tail) waitForChanges() error {
 			tail.Logger.Printf("Successfully reopened %s", tail.Filename)
 			tail.openReader()
 			return nil
-		} else {
-			tail.Logger.Printf("Stopping tail as file no longer exists: %s", tail.Filename)
-			return ErrStop
 		}
+		tail.Logger.Printf("Stopping tail as file no longer exists: %s", tail.Filename)
+		return ErrStop
 	case <-tail.changes.Truncated:
 		// Always reopen truncated files (Follow is true)
 		tail.Logger.Printf("Re-opening truncated file %s ...", tail.Filename)
@@ -371,7 +370,6 @@ func (tail *Tail) waitForChanges() error {
 	case <-tail.Dying():
 		return ErrStop
 	}
-	panic("unreachable")
 }
 
 func (tail *Tail) openReader() {
@@ -412,7 +410,11 @@ func (tail *Tail) sendLine(line string) bool {
 
 	for _, line := range lines {
 		tail.lineNum++
-		tail.Lines <- &Line{line, tail.lineNum, now, nil}
+		select {
+		case tail.Lines <- &Line{line, tail.lineNum, now, nil}:
+		case <-tail.Dying():
+			return true
+		}
 	}
 
 	if tail.Config.RateLimiter != nil {

tail_test.go

@@ -97,6 +97,15 @@ func TestStop(t *testing.T) {
 	tail.Cleanup()
 }
 
+func TestStopNonEmptyFile(t *testing.T) {
+	tailTest := NewTailTest("maxlinesize", t)
+	tailTest.CreateFile("test.txt", "hello\nthere\nworld\n")
+	tail := tailTest.StartTail("test.txt", Config{})
+	tail.Stop()
+	tail.Cleanup()
+	// success here is if it doesn't panic.
+}
+
 func TestStopAtEOF(t *testing.T) {
 	tailTest := NewTailTest("maxlinesize", t)
 	tailTest.CreateFile("test.txt", "hello\nthere\nworld\n")
@@ -330,7 +339,7 @@ func TestTell(t *testing.T) {
 		Follow:   false,
 		Location: &SeekInfo{0, io.SeekStart}}
 	tail := tailTest.StartTail("test.txt", config)
-	// read noe line
+	// read one line
 	line := <-tail.Lines
 	if line.Num != 1 {
 		tailTest.Errorf("expected line to have number 1 but got %d", line.Num)
@@ -339,8 +348,7 @@ func TestTell(t *testing.T) {
 	if err != nil {
 		tailTest.Errorf("Tell return error: %s", err.Error())
 	}
-	tail.Done()
-	// tail.close()
+	tail.Stop()
 
 	config = Config{
 		Follow:   false,
@@ -359,7 +367,7 @@ func TestTell(t *testing.T) {
 		break
 	}
 	tailTest.RemoveFile("test.txt")
-	tail.Done()
+	tail.Stop()
 	tail.Cleanup()
 }