-
Notifications
You must be signed in to change notification settings - Fork 0
/
archive_cache.go
226 lines (190 loc) · 5.89 KB
/
archive_cache.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
package historyarchive
import (
"io"
"os"
"path"
lru "github.com/hashicorp/golang-lru"
log "github.com/shantanu-hashcash/go/support/log"
"github.com/shantanu-hashcash/go/support/storage"
)
type CacheOptions struct {
Cache bool
Path string
MaxFiles uint
Log *log.Entry
}
type ArchiveBucketCache struct {
path string
lru *lru.Cache
log *log.Entry
}
// MakeArchiveBucketCache creates a cache on the disk at the given path that
// acts as an LRU cache, mimicking a particular upstream.
func MakeArchiveBucketCache(opts CacheOptions) (*ArchiveBucketCache, error) {
log_ := opts.Log
if opts.Log == nil {
log_ = log.WithField("subservice", "fs-cache")
}
log_ = log_.
WithField("path", opts.Path).
WithField("cap", opts.MaxFiles)
if _, err := os.Stat(opts.Path); err == nil || os.IsExist(err) {
log_.Warnf("Cache directory already exists, removing")
os.RemoveAll(opts.Path)
}
backend := &ArchiveBucketCache{
path: opts.Path,
log: log_,
}
cache, err := lru.NewWithEvict(int(opts.MaxFiles), backend.onEviction)
if err != nil {
return &ArchiveBucketCache{}, err
}
backend.lru = cache
log_.Info("Bucket cache initialized")
return backend, nil
}
// GetFile retrieves the file contents from the local cache if present.
// Otherwise, it returns the same result as the upstream, adding that result
// into the local cache if possible. It returns a 3-tuple of a reader (which may
// be nil on an error), an indication of whether or not it was *found* in the
// cache, and any error.
func (abc *ArchiveBucketCache) GetFile(
filepath string,
upstream storage.Storage,
) (io.ReadCloser, bool, error) {
L := abc.log.WithField("key", filepath)
localPath := path.Join(abc.path, filepath)
// If the lockfile exists, we should defer to the remote source but *not*
// update the cache, as it means there's an in-progress sync of the same
// file.
_, statErr := os.Stat(NameLockfile(localPath))
if statErr == nil || os.IsExist(statErr) {
L.Info("Incomplete file in on-disk cache: deferring")
reader, err := upstream.GetFile(filepath)
return reader, false, err
} else if _, ok := abc.lru.Get(localPath); !ok {
L.Info("File does not exist in the cache: downloading")
// Since it's not on-disk, pull it from the remote backend, shove it
// into the cache, and write it to disk.
remote, err := upstream.GetFile(filepath)
if err != nil {
return remote, false, err
}
local, err := abc.createLocal(filepath)
if err != nil {
// If there's some local FS error, we can still continue with the
// remote version, so just log it and continue.
L.WithError(err).Warn("Creating cache file failed")
return remote, false, nil
}
return teeReadCloser(remote, local, func() error {
L.Debug("Download complete: removing lockfile")
return os.Remove(NameLockfile(localPath))
}), false, nil
}
L.Info("Found file in cache")
// The cache claims it exists, so just give it a read and send it.
local, err := os.Open(localPath)
if err != nil {
// Uh-oh, the cache and the disk are not in sync somehow? Let's evict
// this value and try again (recurse) w/ the remote version.
L.WithError(err).Warn("Opening cached file failed")
abc.lru.Remove(localPath)
return abc.GetFile(filepath, upstream)
}
return local, true, nil
}
func (abc *ArchiveBucketCache) Exists(filepath string) bool {
localPath := path.Join(abc.path, filepath)
// First, check if the file exists in the cache.
if abc.lru.Contains(localPath) {
return true
}
// If it doesn't, it may still exist on the disk which is still a cheaper
// check than going upstream.
//
// Note that this means the cache and disk are out of sync (perhaps due to
// other archives using the same cache location) so we can update it. This
// situation is well-handled by `GetFile`.
_, statErr := os.Stat(localPath)
if statErr == nil || os.IsExist(statErr) {
abc.lru.Add(localPath, struct{}{})
return true
}
return false
}
// Close purges the cache and cleans up the filesystem.
func (abc *ArchiveBucketCache) Close() error {
abc.lru.Purge()
return os.RemoveAll(abc.path)
}
// Evict removes a file from the cache and the filesystem.
func (abc *ArchiveBucketCache) Evict(filepath string) {
log.WithField("key", filepath).Info("Evicting file from the disk")
abc.lru.Remove(path.Join(abc.path, filepath))
}
func (abc *ArchiveBucketCache) onEviction(key, value interface{}) {
path := key.(string)
os.Remove(NameLockfile(path)) // just in case
if err := os.Remove(path); err != nil { // best effort removal
abc.log.WithError(err).
WithField("key", path).
Warn("Removal failed after cache eviction")
}
}
func (abc *ArchiveBucketCache) createLocal(filepath string) (*os.File, error) {
localPath := path.Join(abc.path, filepath)
if err := os.MkdirAll(path.Dir(localPath), 0755 /* drwxr-xr-x */); err != nil {
return nil, err
}
local, err := os.Create(localPath) /* mode -rw-rw-rw- */
if err != nil {
return nil, err
}
_, err = os.Create(NameLockfile(localPath))
if err != nil {
return nil, err
}
abc.lru.Add(localPath, struct{}{}) // just use the cache as an array
return local, nil
}
func NameLockfile(file string) string {
return file + ".lock"
}
// The below is a helper interface so that we can use io.TeeReader to write
// data locally immediately as we read it remotely.
type trc struct {
io.Reader
close func() error
closed bool // prevents a double-close
}
func (t trc) Close() error {
if t.closed {
return nil
}
return t.close()
}
func teeReadCloser(r io.ReadCloser, w io.WriteCloser, onClose func() error) io.ReadCloser {
closer := trc{
Reader: io.TeeReader(r, w),
closed: false,
}
closer.close = func() error {
if closer.closed {
return nil
}
// Always run all closers, but return the first error
err1 := r.Close()
err2 := w.Close()
err3 := onClose()
closer.closed = true
if err1 != nil {
return err1
} else if err2 != nil {
return err2
}
return err3
}
return closer
}