/
watcher.go
216 lines (182 loc) · 5.73 KB
/
watcher.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
/*
Copyright 2017 The Kubernetes Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package filesystem
import (
"context"
"fmt"
"time"
"github.com/fsnotify/fsnotify"
)
// FSWatcher is a callback-based filesystem watcher abstraction for fsnotify.
type FSWatcher interface {
// Initializes the watcher with the given watch handlers.
// Called before all other methods.
Init(FSEventHandler, FSErrorHandler) error
// Starts listening for events and errors.
// When an event or error occurs, the corresponding handler is called.
Run()
// Add a filesystem path to watch
AddWatch(path string) error
}
// FSEventHandler is called when a fsnotify event occurs.
type FSEventHandler func(event fsnotify.Event)
// FSErrorHandler is called when a fsnotify error occurs.
type FSErrorHandler func(err error)
type fsnotifyWatcher struct {
watcher *fsnotify.Watcher
eventHandler FSEventHandler
errorHandler FSErrorHandler
}
var _ FSWatcher = &fsnotifyWatcher{}
// NewFsnotifyWatcher returns an implementation of FSWatcher that continuously listens for
// fsnotify events and calls the event handler as soon as an event is received.
func NewFsnotifyWatcher() FSWatcher {
return &fsnotifyWatcher{}
}
func (w *fsnotifyWatcher) AddWatch(path string) error {
return w.watcher.Add(path)
}
func (w *fsnotifyWatcher) Init(eventHandler FSEventHandler, errorHandler FSErrorHandler) error {
var err error
w.watcher, err = fsnotify.NewWatcher()
if err != nil {
return err
}
w.eventHandler = eventHandler
w.errorHandler = errorHandler
return nil
}
func (w *fsnotifyWatcher) Run() {
go func() {
defer w.watcher.Close()
for {
select {
case event := <-w.watcher.Events:
if w.eventHandler != nil {
w.eventHandler(event)
}
case err := <-w.watcher.Errors:
if w.errorHandler != nil {
w.errorHandler(err)
}
}
}
}()
}
type watchAddRemover interface {
Add(path string) error
Remove(path string) error
}
type noopWatcher struct{}
func (noopWatcher) Add(path string) error { return nil }
func (noopWatcher) Remove(path string) error { return nil }
// WatchUntil watches the specified path for changes and blocks until ctx is canceled.
// eventHandler() must be non-nil, and pollInterval must be greater than 0.
// eventHandler() is invoked whenever a change event is observed or pollInterval elapses.
// errorHandler() is invoked (if non-nil) whenever an error occurs initializing or watching the specified path.
//
// If path is a directory, only the directory and immediate children are watched.
//
// If path does not exist or cannot be watched, an error is passed to errorHandler() and eventHandler() is called at pollInterval.
//
// Multiple observed events may collapse to a single invocation of eventHandler().
//
// eventHandler() is invoked immediately after successful initialization of the filesystem watch,
// in case the path changed concurrent with calling WatchUntil().
func WatchUntil(ctx context.Context, pollInterval time.Duration, path string, eventHandler func(), errorHandler func(err error)) {
if pollInterval <= 0 {
panic(fmt.Errorf("pollInterval must be > 0"))
}
if eventHandler == nil {
panic(fmt.Errorf("eventHandler must be non-nil"))
}
if errorHandler == nil {
errorHandler = func(err error) {}
}
// Initialize watcher, fall back to no-op
var (
eventsCh chan fsnotify.Event
errorCh chan error
watcher watchAddRemover
)
if w, err := fsnotify.NewWatcher(); err != nil {
errorHandler(fmt.Errorf("error creating file watcher, falling back to poll at interval %s: %w", pollInterval, err))
watcher = noopWatcher{}
} else {
watcher = w
eventsCh = w.Events
errorCh = w.Errors
defer func() {
_ = w.Close()
}()
}
// Initialize background poll
t := time.NewTicker(pollInterval)
defer t.Stop()
attemptPeriodicRewatch := false
// Start watching the path
if err := watcher.Add(path); err != nil {
errorHandler(err)
attemptPeriodicRewatch = true
} else {
// Invoke handle() at least once after successfully registering the listener,
// in case the file changed concurrent with calling WatchUntil.
eventHandler()
}
for {
select {
case <-ctx.Done():
return
case <-t.C:
// Prioritize exiting if context is canceled
if ctx.Err() != nil {
return
}
// Try to re-establish the watcher if we previously got a watch error
if attemptPeriodicRewatch {
_ = watcher.Remove(path)
if err := watcher.Add(path); err != nil {
errorHandler(err)
} else {
attemptPeriodicRewatch = false
}
}
// Handle
eventHandler()
case e := <-eventsCh:
// Prioritize exiting if context is canceled
if ctx.Err() != nil {
return
}
// Try to re-establish the watcher for events which dropped the existing watch
if e.Name == path && (e.Has(fsnotify.Remove) || e.Has(fsnotify.Rename)) {
_ = watcher.Remove(path)
if err := watcher.Add(path); err != nil {
errorHandler(err)
attemptPeriodicRewatch = true
}
}
// Handle
eventHandler()
case err := <-errorCh:
// Prioritize exiting if context is canceled
if ctx.Err() != nil {
return
}
// If the error occurs in response to calling watcher.Add, re-adding here could hot-loop.
// The periodic poll will attempt to re-establish the watch.
errorHandler(err)
attemptPeriodicRewatch = true
}
}
}