Merge pull request #6 from srid/bug99139_copytruncate

copytruncate support,

truncation detection for both inotify and polling file watchers along with test cases, plus a fix for issue #5.

CHANGES.md

@@ -1,6 +1,8 @@
 # May, 2013
 
 * Recognize deletions/renames when using polling file watcher (PR #1)
+* Detect file truncation
+* Fix potential race condition when reopening the file (issue 5)
 
 # Feb, 2013
 

tail.go

@@ -13,8 +13,8 @@ import (
 )
 
 type Line struct {
-	Text     string
+	Text string
-	Time     time.Time
+	Time time.Time
 }
 
 // Tail configuration
@@ -102,8 +102,7 @@ func (tail *Tail) reopen() error {
 		if err != nil {
 			if os.IsNotExist(err) {
 				log.Printf("Waiting for %s to appear...", tail.Filename)
-				err := tail.watcher.BlockUntilExists()
+				if err := tail.watcher.BlockUntilExists(); err != nil {
-				if err != nil {
 					return fmt.Errorf("Failed to detect creation of %s: %s", tail.Filename, err)
 				}
 				continue
@@ -157,7 +156,7 @@ func (tail *Tail) tailFileSync() {
 					for _, line := range partitionString(string(line), tail.MaxLineSize) {
 						tail.Lines <- &Line{line, now}
 					}
-				}else{
+				} else {
 					tail.Lines <- &Line{string(line), now}
 				}
 			}
@@ -187,10 +186,10 @@ func (tail *Tail) tailFileSync() {
 					if !ok {
 						changes = nil // XXX: how to kill changes' goroutine?
 
-						// File got deleted/renamed
+						// File got deleted/renamed/truncated.
 						if tail.ReOpen {
 							// TODO: no logging in a library?
-							log.Printf("Re-opening moved/deleted file %s ...", tail.Filename)
+							log.Printf("Re-opening moved/deleted/truncated file %s ...", tail.Filename)
 							err := tail.reopen()
 							if err != nil {
 								tail.close()

tail_test.go

@@ -14,6 +14,7 @@ import (
 )
 
 func init() {
+	// Clear the temporary test directory
 	err := os.RemoveAll(".test")
 	if err != nil {
 		panic(err)
@@ -84,7 +85,7 @@ func _TestReOpen(_t *testing.T, poll bool) {
 	var name string
 	if poll {
 		name = "reopen-polling"
-	}else {
+	} else {
 		name = "reopen-inotify"
 	}
 	t := NewTailTest(name, _t)
@@ -122,18 +123,71 @@ func _TestReOpen(_t *testing.T, poll bool) {
 	<-time.After(100 * time.Millisecond)
 	t.RemoveFile("test.txt")
 
+	println("Stopping (REOPEN)...")
 	tail.Stop()
 }
 
 // The use of polling file watcher could affect file rotation
 // (detected via renames), so test these explicitly.
 
-func TestReOpenWithPoll(_t *testing.T) {
+func TestReOpenInotify(_t *testing.T) {
+	_TestReOpen(_t, false)
+}
+
+func TestReOpenPolling(_t *testing.T) {
 	_TestReOpen(_t, true)
 }
 
-func TestReOpenWithoutPoll(_t *testing.T) {
+func _TestReSeek(_t *testing.T, poll bool) {
-	_TestReOpen(_t, false)
+	var name string
+	if poll {
+		name = "reseek-polling"
+	} else {
+		name = "reseek-inotify"
+	}
+	t := NewTailTest(name, _t)
+	t.CreateFile("test.txt", "a really long string goes here\nhello\nworld\n")
+	tail := t.StartTail(
+		"test.txt",
+		Config{Follow: true, ReOpen: true, Poll: poll, Location: -1})
+
+	go t.VerifyTailOutput(tail, []string{
+		"a really long string goes here", "hello", "world", "h311o", "w0r1d", "endofworld"})
+
+	// truncate now
+	<-time.After(100 * time.Millisecond)
+	if poll {
+		// Give polling a chance to read the just-written lines (more;
+		// data), before we truncate the file again below.
+		<-time.After(POLL_DURATION)
+	}
+	println("truncating..")
+	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")
+
+	println("Stopping (RESEEK)...")
+	tail.Stop()
+}
+
+// The use of polling file watcher could affect file rotation
+// (detected via renames), so test these explicitly.
+
+func TestReSeekInotify(_t *testing.T) {
+	_TestReSeek(_t, false)
+}
+
+func TestReSeekPolling(_t *testing.T) {
+	_TestReSeek(_t, true)
 }
 
 // Test library
@@ -150,6 +204,10 @@ func NewTailTest(name string, t *testing.T) TailTest {
 	if err != nil {
 		tt.Fatal(err)
 	}
+
+	// Use a smaller poll duration for faster test runs.
+	POLL_DURATION = 25 * time.Millisecond
+
 	return tt
 }
 
@@ -188,6 +246,18 @@ 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_TRUNC|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 {
@@ -203,7 +273,7 @@ func (t TailTest) VerifyTailOutput(tail *Tail, lines []string) {
 			err := tail.Wait()
 			if err != nil {
 				t.Fatal("tail ended early with error: %v", err)
-			}else{
+			} else {
 				t.Fatalf("tail ended early; expecting more: %v", lines[idx:])
 			}
 		}
@@ -211,7 +281,8 @@ 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

watch.go

@@ -6,14 +6,14 @@ import (
 	"github.com/howeyc/fsnotify"
 	"os"
 	"path/filepath"
-	"time"
 	"sync"
+	"time"
 )
 
 // FileWatcher monitors file-level events.
 type FileWatcher interface {
 	// BlockUntilExists blocks until the missing file comes into
-	// existence. If the file already exists, block until it is recreated.
+	// existence. If the file already exists, returns immediately.
 	BlockUntilExists() error
 
 	// ChangeEvents returns a channel of events corresponding to the
@@ -24,10 +24,11 @@ type FileWatcher interface {
 // InotifyFileWatcher uses inotify to monitor file changes.
 type InotifyFileWatcher struct {
 	Filename string
+	Size     int64
 }
 
 func NewInotifyFileWatcher(filename string) *InotifyFileWatcher {
-	fw := &InotifyFileWatcher{filename}
+	fw := &InotifyFileWatcher{filename, 0}
 	return fw
 }
 
@@ -37,11 +38,23 @@ func (fw *InotifyFileWatcher) BlockUntilExists() error {
 		return err
 	}
 	defer w.Close()
-	err = w.WatchFlags(filepath.Dir(fw.Filename), fsnotify.FSN_CREATE)
+
+	dirname := filepath.Dir(fw.Filename)
+
+	// Watch for new files to be created in the parent directory.
+	err = w.WatchFlags(dirname, fsnotify.FSN_CREATE)
 	if err != nil {
 		return err
 	}
 	defer w.RemoveWatch(filepath.Dir(fw.Filename))
+
+	// Do a real check now as the file might have been created before
+	// calling `WatchFlags` above.
+	if _, err = os.Stat(fw.Filename); !os.IsNotExist(err) {
+		// file exists, or stat returned an error.
+		return err
+	}
+
 	for {
 		evt := <-w.Event
 		if evt.Name == fw.Filename {
@@ -52,7 +65,7 @@ func (fw *InotifyFileWatcher) BlockUntilExists() error {
 }
 
 // ChangeEvents returns a channel that gets updated when the file is ready to be read.
-func (fw *InotifyFileWatcher) ChangeEvents(_ os.FileInfo) chan bool {
+func (fw *InotifyFileWatcher) ChangeEvents(fi os.FileInfo) chan bool {
 	w, err := fsnotify.NewWatcher()
 	if err != nil {
 		panic(err)
@@ -64,20 +77,36 @@ func (fw *InotifyFileWatcher) ChangeEvents(_ os.FileInfo) chan bool {
 
 	ch := make(chan bool)
 
+	fw.Size = fi.Size()
+
 	go func() {
+		defer w.Close()
+		defer w.RemoveWatch(fw.Filename)
+		defer close(ch)
+
 		for {
+			prevSize := fw.Size
+
 			evt := <-w.Event
 			switch {
 			case evt.IsDelete():
 				fallthrough
 
 			case evt.IsRename():
-				close(ch)
-				w.RemoveWatch(fw.Filename)
-				w.Close()
 				return
 
 			case evt.IsModify():
+				fi, err := os.Stat(fw.Filename)
+				if err != nil {
+					// XXX: no panic here
+					panic(err)
+				}
+				fw.Size = fi.Size()
+
+				if prevSize > 0 && prevSize > fw.Size {
+					return
+				}
+
 				// send only if channel is empty.
 				select {
 				case ch <- true:
@@ -93,22 +122,21 @@ func (fw *InotifyFileWatcher) ChangeEvents(_ os.FileInfo) chan bool {
 // PollingFileWatcher polls the file for changes.
 type PollingFileWatcher struct {
 	Filename string
+	Size     int64
 }
 
 func NewPollingFileWatcher(filename string) *PollingFileWatcher {
-	fw := &PollingFileWatcher{filename}
+	fw := &PollingFileWatcher{filename, 0}
 	return fw
 }
 
 var POLL_DURATION time.Duration
 
-// BlockUntilExists blocks until the file comes into existence. If the
-// file already exists, then block until it is created again.
 func (fw *PollingFileWatcher) BlockUntilExists() error {
 	for {
 		if _, err := os.Stat(fw.Filename); err == nil {
 			return nil
-		}else if !os.IsNotExist(err) {
+		} else if !os.IsNotExist(err) {
 			return err
 		}
 		time.Sleep(POLL_DURATION)
@@ -132,7 +160,10 @@ func (fw *PollingFileWatcher) ChangeEvents(origFi os.FileInfo) chan bool {
 		}()
 	}
 
+	fw.Size = origFi.Size()
+
 	go func() {
+		prevSize := fw.Size
 		for {
 			select {
 			case <-stop:
@@ -157,6 +188,13 @@ func (fw *PollingFileWatcher) ChangeEvents(origFi os.FileInfo) chan bool {
 				continue
 			}
 
+			// Was the file truncated?
+			fw.Size = fi.Size()
+			if prevSize > 0 && prevSize > fw.Size {
+				once.Do(stopAndClose)
+				continue
+			}
+
 			// If the file was changed since last check, notify.
 			modTime := fi.ModTime()
 			if modTime != prevModTime {