-
-
Notifications
You must be signed in to change notification settings - Fork 282
/
filestorage.go
404 lines (360 loc) · 11.8 KB
/
filestorage.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
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
// Copyright 2015 Matthew Holt
//
// 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 certmagic
import (
"context"
"encoding/json"
"errors"
"fmt"
"io"
"io/fs"
"log"
"os"
"path"
"path/filepath"
"runtime"
"time"
)
// FileStorage facilitates forming file paths derived from a root
// directory. It is used to get file paths in a consistent,
// cross-platform way or persisting ACME assets on the file system.
// The presence of a lock file for a given key indicates a lock
// is held and is thus unavailable.
//
// Locks are created atomically by relying on the file system to
// enforce the O_EXCL flag. Acquirers that are forcefully terminated
// will not have a chance to clean up their locks before they exit,
// so locks may become stale. That is why, while a lock is actively
// held, the contents of the lockfile are updated with the current
// timestamp periodically. If another instance tries to acquire the
// lock but fails, it can see if the timestamp within is still fresh.
// If so, it patiently waits by polling occasionally. Otherwise,
// the stale lockfile is deleted, essentially forcing an unlock.
//
// While locking is atomic, unlocking is not perfectly atomic. File
// systems offer native atomic operations when creating files, but
// not necessarily when deleting them. It is theoretically possible
// for two instances to discover the same stale lock and both proceed
// to delete it, but if one instance is able to delete the lockfile
// and create a new one before the other one calls delete, then the
// new lock file created by the first instance will get deleted by
// mistake. This does mean that mutual exclusion is not guaranteed
// to be perfectly enforced in the presence of stale locks. One
// alternative is to lock the unlock operation by using ".unlock"
// files; and we did this for some time, but those files themselves
// may become stale, leading applications into infinite loops if
// they always expect the unlock file to be deleted by the instance
// that created it. We instead prefer the simpler solution that
// implies imperfect mutual exclusion if locks become stale, but
// that is probably less severe a consequence than infinite loops.
//
// See https://github.com/caddyserver/caddy/issues/4448 for discussion.
// See commit 468bfd25e452196b140148928cdd1f1a2285ae4b for where we
// switched away from using .unlock files.
type FileStorage struct {
Path string
}
// Exists returns true if key exists in s.
func (s *FileStorage) Exists(_ context.Context, key string) bool {
_, err := os.Stat(s.Filename(key))
return !errors.Is(err, fs.ErrNotExist)
}
// Store saves value at key.
func (s *FileStorage) Store(_ context.Context, key string, value []byte) error {
filename := s.Filename(key)
err := os.MkdirAll(filepath.Dir(filename), 0700)
if err != nil {
return err
}
return os.WriteFile(filename, value, 0600)
}
// Load retrieves the value at key.
func (s *FileStorage) Load(_ context.Context, key string) ([]byte, error) {
return os.ReadFile(s.Filename(key))
}
// Delete deletes the value at key.
func (s *FileStorage) Delete(_ context.Context, key string) error {
return os.Remove(s.Filename(key))
}
// List returns all keys that match prefix.
func (s *FileStorage) List(ctx context.Context, prefix string, recursive bool) ([]string, error) {
var keys []string
walkPrefix := s.Filename(prefix)
err := filepath.Walk(walkPrefix, func(fpath string, info os.FileInfo, err error) error {
if err != nil {
return err
}
if info == nil {
return fmt.Errorf("%s: file info is nil", fpath)
}
if fpath == walkPrefix {
return nil
}
if ctxErr := ctx.Err(); ctxErr != nil {
return ctxErr
}
suffix, err := filepath.Rel(walkPrefix, fpath)
if err != nil {
return fmt.Errorf("%s: could not make path relative: %v", fpath, err)
}
keys = append(keys, path.Join(prefix, suffix))
if !recursive && info.IsDir() {
return filepath.SkipDir
}
return nil
})
return keys, err
}
// Stat returns information about key.
func (s *FileStorage) Stat(_ context.Context, key string) (KeyInfo, error) {
fi, err := os.Stat(s.Filename(key))
if err != nil {
return KeyInfo{}, err
}
return KeyInfo{
Key: key,
Modified: fi.ModTime(),
Size: fi.Size(),
IsTerminal: !fi.IsDir(),
}, nil
}
// Filename returns the key as a path on the file
// system prefixed by s.Path.
func (s *FileStorage) Filename(key string) string {
return filepath.Join(s.Path, filepath.FromSlash(key))
}
// Lock obtains a lock named by the given key. It blocks
// until the lock can be obtained or an error is returned.
func (s *FileStorage) Lock(ctx context.Context, key string) error {
filename := s.lockFilename(key)
for {
err := createLockfile(filename)
if err == nil {
// got the lock, yay
return nil
}
if !os.IsExist(err) {
// unexpected error
return fmt.Errorf("creating lock file: %v", err)
}
// lock file already exists
var meta lockMeta
f, err := os.Open(filename)
if err == nil {
err2 := json.NewDecoder(f).Decode(&meta)
f.Close()
if err2 != nil {
return fmt.Errorf("decoding lockfile contents: %w", err2)
}
}
switch {
case os.IsNotExist(err):
// must have just been removed; try again to create it
continue
case err != nil:
// unexpected error
return fmt.Errorf("accessing lock file: %v", err)
case fileLockIsStale(meta):
// lock file is stale - delete it and try again to obtain lock
// (NOTE: locking becomes imperfect if lock files are stale; known solutions
// either have potential to cause infinite loops, as in caddyserver/caddy#4448,
// or must give up on perfect mutual exclusivity; however, these cases are rare,
// so we prefer the simpler solution that avoids infinite loops)
log.Printf("[INFO][%s] Lock for '%s' is stale (created: %s, last update: %s); removing then retrying: %s",
s, key, meta.Created, meta.Updated, filename)
if err = os.Remove(filename); err != nil { // hopefully we can replace the lock file quickly!
if !errors.Is(err, fs.ErrNotExist) {
return fmt.Errorf("unable to delete stale lock; deadlocked: %w", err)
}
}
continue
default:
// lockfile exists and is not stale;
// just wait a moment and try again,
// or return if context cancelled
select {
case <-time.After(fileLockPollInterval):
case <-ctx.Done():
return ctx.Err()
}
}
}
}
// Unlock releases the lock for name.
func (s *FileStorage) Unlock(_ context.Context, key string) error {
return os.Remove(s.lockFilename(key))
}
func (s *FileStorage) String() string {
return "FileStorage:" + s.Path
}
func (s *FileStorage) lockFilename(key string) string {
return filepath.Join(s.lockDir(), StorageKeys.Safe(key)+".lock")
}
func (s *FileStorage) lockDir() string {
return filepath.Join(s.Path, "locks")
}
func fileLockIsStale(meta lockMeta) bool {
ref := meta.Updated
if ref.IsZero() {
ref = meta.Created
}
// since updates are exactly every lockFreshnessInterval,
// add a grace period for the actual file read+write to
// take place
return time.Since(ref) > lockFreshnessInterval*2
}
// createLockfile atomically creates the lockfile
// identified by filename. A successfully created
// lockfile should be removed with removeLockfile.
func createLockfile(filename string) error {
err := atomicallyCreateFile(filename, true)
if err != nil {
return err
}
go keepLockfileFresh(filename)
return nil
}
// keepLockfileFresh continuously updates the lock file
// at filename with the current timestamp. It stops
// when the file disappears (happy path = lock released),
// or when there is an error at any point. Since it polls
// every lockFreshnessInterval, this function might
// not terminate until up to lockFreshnessInterval after
// the lock is released.
func keepLockfileFresh(filename string) {
defer func() {
if err := recover(); err != nil {
buf := make([]byte, stackTraceBufferSize)
buf = buf[:runtime.Stack(buf, false)]
log.Printf("panic: active locking: %v\n%s", err, buf)
}
}()
for {
time.Sleep(lockFreshnessInterval)
done, err := updateLockfileFreshness(filename)
if err != nil {
log.Printf("[ERROR] Keeping lock file fresh: %v - terminating lock maintenance (lockfile: %s)", err, filename)
return
}
if done {
return
}
}
}
// updateLockfileFreshness updates the lock file at filename
// with the current timestamp. It returns true if the parent
// loop can terminate (i.e. no more need to update the lock).
func updateLockfileFreshness(filename string) (bool, error) {
f, err := os.OpenFile(filename, os.O_RDWR, 0644)
if os.IsNotExist(err) {
return true, nil // lock released
}
if err != nil {
return true, err
}
defer f.Close()
// read contents
metaBytes, err := io.ReadAll(io.LimitReader(f, 2048))
if err != nil {
return true, err
}
var meta lockMeta
if err := json.Unmarshal(metaBytes, &meta); err != nil {
return true, err
}
// truncate file and reset I/O offset to beginning
if err := f.Truncate(0); err != nil {
return true, err
}
if _, err := f.Seek(0, io.SeekStart); err != nil {
return true, err
}
// write updated timestamp
meta.Updated = time.Now()
if err = json.NewEncoder(f).Encode(meta); err != nil {
return false, err
}
// sync to device; we suspect that sometimes file systems
// (particularly AWS EFS) don't do this on their own,
// leaving the file empty when we close it; see
// https://github.com/caddyserver/caddy/issues/3954
return false, f.Sync()
}
// atomicallyCreateFile atomically creates the file
// identified by filename if it doesn't already exist.
func atomicallyCreateFile(filename string, writeLockInfo bool) error {
// no need to check this error, we only really care about the file creation error
_ = os.MkdirAll(filepath.Dir(filename), 0700)
f, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_EXCL, 0644)
if err != nil {
return err
}
defer f.Close()
if writeLockInfo {
now := time.Now()
meta := lockMeta{
Created: now,
Updated: now,
}
if err := json.NewEncoder(f).Encode(meta); err != nil {
return err
}
// see https://github.com/caddyserver/caddy/issues/3954
if err := f.Sync(); err != nil {
return err
}
}
return nil
}
// homeDir returns the best guess of the current user's home
// directory from environment variables. If unknown, "." (the
// current directory) is returned instead.
func homeDir() string {
home := os.Getenv("HOME")
if home == "" && runtime.GOOS == "windows" {
drive := os.Getenv("HOMEDRIVE")
path := os.Getenv("HOMEPATH")
home = drive + path
if drive == "" || path == "" {
home = os.Getenv("USERPROFILE")
}
}
if home == "" {
home = "."
}
return home
}
func dataDir() string {
baseDir := filepath.Join(homeDir(), ".local", "share")
if xdgData := os.Getenv("XDG_DATA_HOME"); xdgData != "" {
baseDir = xdgData
}
return filepath.Join(baseDir, "certmagic")
}
// lockMeta is written into a lock file.
type lockMeta struct {
Created time.Time `json:"created,omitempty"`
Updated time.Time `json:"updated,omitempty"`
}
// lockFreshnessInterval is how often to update
// a lock's timestamp. Locks with a timestamp
// more than this duration in the past (plus a
// grace period for latency) can be considered
// stale.
const lockFreshnessInterval = 5 * time.Second
// fileLockPollInterval is how frequently
// to check the existence of a lock file
const fileLockPollInterval = 1 * time.Second
// Interface guard
var _ Storage = (*FileStorage)(nil)