-
Notifications
You must be signed in to change notification settings - Fork 6
/
assets.go
329 lines (276 loc) · 11.4 KB
/
assets.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
// MIT License
//
// Copyright (c) 2016 Rick Beton
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
package servefiles
import (
"fmt"
"io/fs"
"math/rand"
"mime"
"net/http"
"os"
"path/filepath"
"strconv"
"strings"
"sync"
"time"
"github.com/rickb777/path"
"github.com/spf13/afero"
)
// This needs to track the same string in net/http (which is unlikely ever to change)
const indexPage = "index.html"
// Assets sets the options for asset handling. Use AssetHandler to create the handler(s) you need.
type Assets struct {
// Choose a number greater than zero to strip off some leading segments from the URL path. This helps if
// you want, say, a sequence number in the URL so that only has the effect of managing far-future cache
// control. Use zero for default behaviour.
UnwantedPrefixSegments int
// Set the expiry duration for assets. This will be set via headers in the response. This should never be
// negative. Use zero to disable asset caching in clients and proxies.
MaxAge time.Duration
// Configurable http.Handler which is called when no matching route is found. If it is not set,
// http.NotFound is used.
NotFound http.Handler
// the local filesystem (remember that all paths are relative to its root)
fs fs.FS
server http.Handler
expiryElasticity time.Duration
timestamp int64
timestampExpiry string
lock *sync.Mutex
}
// Type conformance proof
var _ http.Handler = &Assets{}
//-------------------------------------------------------------------------------------------------
// NewAssetHandler creates an Assets value. The parameter is the directory containing the asset files;
// this can be absolute or relative to the directory in which the server process is started.
//
// This function cleans (i.e. normalises) the asset path.
func NewAssetHandler(assetPath string) *Assets {
cleanAssetPath := path.Clean(assetPath)
Debugf("NewAssetHandler %s\n", cleanAssetPath)
filesystem := os.DirFS(cleanAssetPath).(fs.StatFS)
return NewAssetHandlerIoFS(filesystem)
}
// NewAssetHandlerFS creates an Assets value for a given filesystem.
func NewAssetHandlerFS(fs afero.Fs) *Assets {
return &Assets{
fs: afero.NewIOFS(fs),
server: http.FileServer(afero.NewHttpFs(fs)),
lock: &sync.Mutex{},
}
}
// NewAssetHandlerIoFS creates an Assets value for a given filesystem.
// Implementations include os.DirFS.
func NewAssetHandlerIoFS(fs fs.FS) *Assets {
return &Assets{
fs: fs,
server: http.FileServer(http.FS(fs)),
lock: &sync.Mutex{},
}
}
// StripOff alters the handler to strip off a specified number of segments from the path before
// looking for the matching asset. For example, if StripOff(2) has been applied, the requested
// path "/a/b/c/d/doc.js" would be shortened to "c/d/doc.js".
//
// The returned handler is a new copy of the original one.
func (a Assets) StripOff(unwantedPrefixSegments int) *Assets {
if unwantedPrefixSegments < 0 {
panic("Negative unwantedPrefixSegments")
}
a.UnwantedPrefixSegments = unwantedPrefixSegments
return &a
}
// WithMaxAge alters the handler to set the specified max age on the served assets.
//
// The returned handler is a new copy of the original one.
func (a Assets) WithMaxAge(maxAge time.Duration) *Assets {
if maxAge < 0 {
panic("Negative maxAge")
}
a.MaxAge = maxAge
return &a
}
// WithNotFound alters the handler so that 404-not found cases are passed to a specified
// handler. Without this, the default handler is the one provided in the net/http package.
//
// The returned handler is a new copy of the original one.
func (a Assets) WithNotFound(notFound http.Handler) *Assets {
a.NotFound = notFound
return &a
}
//-------------------------------------------------------------------------------------------------
// Calculate the 'Expires' value using an approximation that reduces unimportant re-calculation.
// We don't need to do this accurately because the 'Cache-Control' maxAge value takes precedence
// anyway. So the value is cached and shared between requests for a short while.
func (a *Assets) expires() string {
if a.expiryElasticity == 0 {
// lazy initialisation
a.expiryElasticity = 1 + a.MaxAge/100
}
now := time.Now().UTC()
unix := now.Unix()
if unix > a.timestamp {
later := now.Add(a.MaxAge + a.expiryElasticity) // add expiryElasticity to avoid negative expiry
a.lock.Lock()
defer a.lock.Unlock()
// cache the formatted string for one second to avoid repeated formatting
// race condition is ignored here, but note the order below
a.timestampExpiry = later.Format(time.RFC1123)
a.timestamp = unix + int64(a.expiryElasticity)
}
return a.timestampExpiry
}
//-------------------------------------------------------------------------------------------------
type fileData struct {
resource string
code code
fi os.FileInfo
}
func calculateEtag(fi os.FileInfo) string {
if fi == nil {
return ""
}
return fmt.Sprintf(`"%x-%x"`, fi.ModTime().Unix(), fi.Size())
}
func handleSaturatedServer(header http.Header, resource string, err error) fileData {
// Possibly the server is under heavy load and ran out of file descriptors
backoff := 2 + rand.Int31()%4 // 2–6 seconds to prevent a stampede
header.Set("Retry-After", strconv.Itoa(int(backoff)))
return fileData{resource, ServiceUnavailable, nil}
}
func (a *Assets) checkResource(resource string, header http.Header) fileData {
d, err := fs.Stat(a.fs, removeLeadingSlash(resource))
if err != nil {
if os.IsNotExist(err) {
// gzipped does not exist; original might but this gets checked later
Debugf("Assets checkResource 404 %s\n", resource)
return fileData{"", NotFound, nil}
} else if os.IsPermission(err) {
// incorrectly assembled gzipped asset is treated as an error
Debugf("Assets checkResource 403 %s\n", resource)
return fileData{resource, Forbidden, nil}
}
Debugf("Assets handleSaturatedServer 503 %s\n", resource)
return handleSaturatedServer(header, resource, err)
}
if d.IsDir() {
// directory edge case is simply passed on to the standard library
return fileData{resource, Directory, nil}
}
Debugf("Assets checkResource 100 %s\n", resource)
return fileData{resource, Continue, d}
}
func removeLeadingSlash(name string) string {
if len(name) > 0 && name[0] == '/' {
name = name[1:]
}
return name
}
func (a *Assets) chooseResource(header http.Header, req *http.Request) (string, code) {
resource := path.Drop(req.URL.Path, a.UnwantedPrefixSegments)
if strings.HasSuffix(resource, "/") {
resource += indexPage
}
Debugf("Assets chooseResource %s %s %s\n", req.Method, req.URL.Path, resource)
if a.MaxAge > 0 {
header.Set("Expires", a.expires())
header.Set("Cache-Control", fmt.Sprintf("public, max-age=%d", a.MaxAge/time.Second))
}
acceptEncoding := commaSeparatedList(req.Header.Get("Accept-Encoding"))
if acceptEncoding.Contains("br") {
brotli := resource + ".br"
fdbr := a.checkResource(brotli, header)
if fdbr.code == Continue {
ext := filepath.Ext(resource)
header.Set("Content-Type", mime.TypeByExtension(ext))
// the standard library sometimes overrides the content type via sniffing
header.Set("X-Content-Type-Options", "nosniff")
header.Set("Content-Encoding", "br")
header.Add("Vary", "Accept-Encoding")
// weak etag because the representation is not the original file but a compressed variant
header.Set("ETag", "W/"+calculateEtag(fdbr.fi))
return brotli, Continue
}
}
if acceptEncoding.Contains("gzip") {
gzipped := resource + ".gz"
fdgz := a.checkResource(gzipped, header)
if fdgz.code == Continue {
ext := filepath.Ext(resource)
header.Set("Content-Type", mime.TypeByExtension(ext))
// the standard library sometimes overrides the content type via sniffing
header.Set("X-Content-Type-Options", "nosniff")
header.Set("Content-Encoding", "gzip")
header.Add("Vary", "Accept-Encoding")
// weak etag because the representation is not the original file but a compressed variant
header.Set("ETag", "W/"+calculateEtag(fdgz.fi))
return gzipped, Continue
}
}
// no intervention; the file will be served normally by the standard api
fd := a.checkResource(resource, header)
if fd.code > 0 {
// strong etag because the representation is the original file
header.Set("ETag", calculateEtag(fd.fi))
}
return fd.resource, fd.code
}
// ServeHTTP implements the http.Handler interface. Note that it (a) handles
// headers for compression, expiry etc, and then (b) calls the standard
// http.ServeHTTP handler for each request. This ensures that it follows
// all the standard logic paths implemented there, including conditional
// requests and content negotiation.
func (a *Assets) ServeHTTP(w http.ResponseWriter, req *http.Request) {
resource, code := a.chooseResource(w.Header(), req)
if code == NotFound && a.NotFound != nil {
// use the provided not-found handler
Debugf("Assets ServeHTTP (not found) %s %s R:%+v W:%+v\n", req.Method, req.URL.Path, req.Header, w.Header())
// ww has silently dropped the headers and body from the built-in handler in this case,
// so complete the response using the original handler.
w.Header().Set("X-Content-Type-Options", "nosniff")
a.NotFound.ServeHTTP(w, req)
return
}
if code >= 400 {
Debugf("Assets ServeHTTP (error %d) %s %s R:%+v W:%+v\n", code, req.Method, req.URL.Path, req.Header, w.Header())
http.Error(w, code.String(), int(code))
return
}
original := req.URL.Path
req.URL.Path = resource
// Conditional requests and content negotiation are handled in the standard net/http API.
// Note that req.URL remains unchanged, even if prefix stripping is turned on, because the resource is
// the only value that matters.
Debugf("Assets ServeHTTP (ok %d) %s %s (was %s) R:%+v W:%+v\n", code, req.Method, req.URL.Path, original, req.Header, w.Header())
a.server.ServeHTTP(w, req)
// leave the path as we found it, in case middleware depends on the original value
req.URL.Path = original
}
//-------------------------------------------------------------------------------------------------
// Printer is something that allows formatted printing. This is only used for diagnostics.
type Printer func(format string, v ...interface{})
// Debugf is a function that allows diagnostics to be emitted. By default it does very
// little and has almost no impact. Set it to some other function (e.g. using log.Printf) to
// see the diagnostics.
var Debugf Printer = func(format string, v ...interface{}) {}
// example (paste this into setup code elsewhere)
//var servefiles.Debugf Printer = log.Printf