Feature: Add FSN type.

fsnotify.go

@@ -8,12 +8,13 @@ package fsnotify
 import "fmt"
 
 const (
-	FSN_CREATE = 1
-	FSN_MODIFY = 2
-	FSN_DELETE = 4
-	FSN_RENAME = 8
+	FSN_CREATE = 1 << iota
+	FSN_MODIFY
+	FSN_DELETE
+	FSN_RENAME
+	FSN_CLOSE_WRITE
 
-	FSN_ALL = FSN_MODIFY | FSN_DELETE | FSN_RENAME | FSN_CREATE
+	FSN_ALL = FSN_MODIFY | FSN_DELETE | FSN_RENAME | FSN_CREATE | FSN_CLOSE_WRITE
 )
 
 // Purge events from interal chan to external chan if passes filter
@@ -40,6 +41,26 @@ func (w *Watcher) purgeEvents() {
 			sendEvent = true
 		}
 
+		// In some cases, we make sure a file change is finished before we read it.
+		// So how do you do that? Try using IN_CLOSE_WRITE instead.
+		//
+		// https://stackoverflow.com/questions/32377517/inotify-event-in-modify-occurring-twice-for-tftp-put/32424150
+		// Q: What is the difference between IN_MODIFY and IN_CLOSE_WRITE?
+		// The IN_MODIFY event is emitted on a file content change (e.g. via the write() syscall)
+		// while IN_CLOSE_WRITE occurs on closing the changed file.
+		// It means each change operation causes one IN_MODIFY event (it may occur many times during manipulations with an open file)
+		// whereas IN_CLOSE_WRITE is emitted only once (on closing the file).
+		//
+		// Q: Is it better to use IN_MODIFY or IN_CLOSE_WRITE?
+		// It varies from case to case. Usually it is more suitable to use IN_CLOSE_WRITE
+		// because if emitted the all changes on the appropriate file are safely written inside the file.
+		// The IN_MODIFY event needn't mean that a file change is finished (data may remain in memory buffers in the application).
+		// On the other hand, many logs and similar files must be monitored using IN_MODIFY -
+		// in such cases where these files are permanently open and thus no IN_CLOSE_WRITE can be emitted.
+		if (fsnFlags&FSN_CLOSE_WRITE == FSN_CLOSE_WRITE) && ev.IsCloseWrite() {
+			sendEvent = true
+		}
+
 		if sendEvent {
 			w.Event <- ev
 		}
@@ -103,6 +124,10 @@ func (e *FileEvent) String() string {
 		events += "|" + "ATTRIB"
 	}
 
+	if e.IsCloseWrite() {
+		events += "|" + "CLOSE_WRITE"
+	}
+
 	if len(events) > 0 {
 		events = events[1:]
 	}

fsnotify_linux.go

@@ -47,7 +47,7 @@ const (
 	sys_IN_MOVE_SELF     uint32 = syscall.IN_MOVE_SELF
 	sys_IN_OPEN          uint32 = syscall.IN_OPEN
 
-	sys_AGNOSTIC_EVENTS = sys_IN_MOVED_TO | sys_IN_MOVED_FROM | sys_IN_CREATE | sys_IN_ATTRIB | sys_IN_MODIFY | sys_IN_MOVE_SELF | sys_IN_DELETE | sys_IN_DELETE_SELF
+	sys_AGNOSTIC_EVENTS = sys_IN_CLOSE_WRITE | sys_IN_MOVED_TO | sys_IN_MOVED_FROM | sys_IN_CREATE | sys_IN_ATTRIB | sys_IN_MODIFY | sys_IN_MOVE_SELF | sys_IN_DELETE | sys_IN_DELETE_SELF
 
 	// Special events
 	sys_IN_ISDIR      uint32 = syscall.IN_ISDIR
@@ -87,6 +87,11 @@ func (e *FileEvent) IsAttrib() bool {
 	return (e.mask & sys_IN_ATTRIB) == sys_IN_ATTRIB
 }
 
+// IsCloseWrite reports whether the FileEvent was triggered by closing the changed file.
+func (e *FileEvent) IsCloseWrite() bool {
+	return (e.mask & sys_IN_CLOSE_WRITE) == sys_IN_CLOSE_WRITE
+}
+
 type watch struct {
 	wd    uint32 // Watch descriptor (as returned by the inotify_add_watch() syscall)
 	flags uint32 // inotify flags of this watch (see inotify(7) for the list of valid flags)