From ba36bda4bde582e8fb05d166aa79c963052ba806 Mon Sep 17 00:00:00 2001
From: Nakul Chander <nakul@stackrox.com>
Date: Fri, 27 Aug 2021 14:45:07 -0700
Subject: [PATCH 1/2] File watcher may not capture any changes that occured
 before the watcher was started

---
 watch/inotify.go | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/watch/inotify.go b/watch/inotify.go
index cbd11ad..7d85d56 100644
--- a/watch/inotify.go
+++ b/watch/inotify.go
@@ -79,6 +79,13 @@ func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChange
 
 		events := Events(fw.Filename)
 
+		// Check to see the file hasn't been modified already before the watcher started
+		fi, deleted := fw.checkAndNotifyIfModifiedInBetween(changes)
+		if deleted {
+			return
+		}
+		fw.Size = fi.Size()
+
 		for {
 			prevSize := fw.Size
 
@@ -134,3 +141,27 @@ func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChange
 
 	return changes, nil
 }
+
+func (fw *InotifyFileWatcher) checkAndNotifyIfModifiedInBetween(changes *FileChanges) (os.FileInfo, bool) {
+	fi, err := os.Stat(fw.Filename)
+	if err != nil {
+		if os.IsNotExist(err) {
+			RemoveWatch(fw.Filename)
+			changes.NotifyDeleted()
+			return nil, true
+		}
+		util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
+	}
+
+	if fw.Size > 0 && fw.Size > fi.Size() { // old file size was larger than now => truncated
+		changes.NotifyTruncated()
+	} else if fw.Size != fi.Size() {
+		changes.NotifyModified()
+	}
+	// there is a corner case of file that was truncated and replaced with exact same amount of bytes, which would
+	// result in no notification. However any subsequent writes will capture that
+	// If the file isn't expected to be written to often and those events cannot be missed, recommend using Polling watcher
+	// instead of inotify
+
+	return fi, false
+}

From a6a562443980db637c984089f8635ed7a71752a6 Mon Sep 17 00:00:00 2001
From: Nakul Chander <nakul@stackrox.com>
Date: Tue, 31 Aug 2021 12:50:14 -0700
Subject: [PATCH 2/2] review comments & gofmt

---
 util/util.go     |  9 +++++++--
 watch/inotify.go | 15 ++++++++-------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/util/util.go b/util/util.go
index b64caa2..9c466c7 100644
--- a/util/util.go
+++ b/util/util.go
@@ -17,14 +17,19 @@ type Logger struct {
 
 var LOGGER = &Logger{log.New(os.Stderr, "", log.LstdFlags)}
 
-// fatal is like panic except it displays only the current goroutine's stack.
+// Fatal is like panic except it displays only the current goroutine's stack.
 func Fatal(format string, v ...interface{}) {
 	// https://github.com/nxadm/log/blob/master/log.go#L45
 	LOGGER.Output(2, fmt.Sprintf("FATAL -- "+format, v...)+"\n"+string(debug.Stack()))
 	os.Exit(1)
 }
 
-// partitionString partitions the string into chunks of given size,
+// Error logs an error message with the current goroutine stack and returns. It doesn't quit.
+func Error(format string, v ...interface{}) {
+	LOGGER.Output(2, fmt.Sprintf("ERROR -- "+format, v...)+"\n"+string(debug.Stack()))
+}
+
+// PartitionString partitions the string into chunks of given size,
 // with the last chunk of variable size.
 func PartitionString(s string, chunkSize int) []string {
 	if chunkSize <= 0 {
diff --git a/watch/inotify.go b/watch/inotify.go
index 7d85d56..6ffab80 100644
--- a/watch/inotify.go
+++ b/watch/inotify.go
@@ -11,7 +11,7 @@ import (
 
 	"github.com/nxadm/tail/util"
 
-    "github.com/fsnotify/fsnotify"
+	"github.com/fsnotify/fsnotify"
 	"gopkg.in/tomb.v1"
 )
 
@@ -145,15 +145,16 @@ func (fw *InotifyFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChange
 func (fw *InotifyFileWatcher) checkAndNotifyIfModifiedInBetween(changes *FileChanges) (os.FileInfo, bool) {
 	fi, err := os.Stat(fw.Filename)
 	if err != nil {
-		if os.IsNotExist(err) {
-			RemoveWatch(fw.Filename)
-			changes.NotifyDeleted()
-			return nil, true
+		if !os.IsNotExist(err) {
+			util.Error("Failed to stat file %v: %v", fw.Filename, err)
+			// Treat it as a deleted file as we cannot read it anyway.
 		}
-		util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
+		_ = RemoveWatch(fw.Filename)
+		changes.NotifyDeleted()
+		return nil, true
 	}
 
-	if fw.Size > 0 && fw.Size > fi.Size() { // old file size was larger than now => truncated
+	if fw.Size > fi.Size() { // old file size was larger than now => truncated
 		changes.NotifyTruncated()
 	} else if fw.Size != fi.Size() {
 		changes.NotifyModified()