netramesh

1
// Copyright 2009 The Go Authors. All rights reserved.
2
// Use of this source code is governed by a BSD-style
3
// license that can be found in the LICENSE file.
4

5
// HTTP file system request handler
6

7
package http
8

9
import (
10
	"errors"
11
	"fmt"
12
	"io"
13
	"mime"
14
	"mime/multipart"
15
	"net/textproto"
16
	"net/url"
17
	"os"
18
	"path"
19
	"path/filepath"
20
	"sort"
21
	"strconv"
22
	"strings"
23
	"time"
24
)
25

26
// A Dir implements FileSystem using the native file system restricted to a
27
// specific directory tree.
28
//
29
// While the FileSystem.Open method takes '/'-separated paths, a Dir's string
30
// value is a filename on the native file system, not a URL, so it is separated
31
// by filepath.Separator, which isn't necessarily '/'.
32
//
33
// Note that Dir will allow access to files and directories starting with a
34
// period, which could expose sensitive directories like a .git directory or
35
// sensitive files like .htpasswd. To exclude files with a leading period,
36
// remove the files/directories from the server or create a custom FileSystem
37
// implementation.
38
//
39
// An empty Dir is treated as ".".
40
type Dir string
41

42
// mapDirOpenError maps the provided non-nil error from opening name
43
// to a possibly better non-nil error. In particular, it turns OS-specific errors
44
// about opening files in non-directories into os.ErrNotExist. See Issue 18984.
45
func mapDirOpenError(originalErr error, name string) error {
46
	if os.IsNotExist(originalErr) || os.IsPermission(originalErr) {
47
		return originalErr
48
	}
49

50
	parts := strings.Split(name, string(filepath.Separator))
51
	for i := range parts {
52
		if parts[i] == "" {
53
			continue
54
		}
55
		fi, err := os.Stat(strings.Join(parts[:i+1], string(filepath.Separator)))
56
		if err != nil {
57
			return originalErr
58
		}
59
		if !fi.IsDir() {
60
			return os.ErrNotExist
61
		}
62
	}
63
	return originalErr
64
}
65

66
func (d Dir) Open(name string) (File, error) {
67
	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
68
		return nil, errors.New("http: invalid character in file path")
69
	}
70
	dir := string(d)
71
	if dir == "" {
72
		dir = "."
73
	}
74
	fullName := filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name)))
75
	f, err := os.Open(fullName)
76
	if err != nil {
77
		return nil, mapDirOpenError(err, fullName)
78
	}
79
	return f, nil
80
}
81

82
// A FileSystem implements access to a collection of named files.
83
// The elements in a file path are separated by slash ('/', U+002F)
84
// characters, regardless of host operating system convention.
85
type FileSystem interface {
86
	Open(name string) (File, error)
87
}
88

89
// A File is returned by a FileSystem's Open method and can be
90
// served by the FileServer implementation.
91
//
92
// The methods should behave the same as those on an *os.File.
93
type File interface {
94
	io.Closer
95
	io.Reader
96
	io.Seeker
97
	Readdir(count int) ([]os.FileInfo, error)
98
	Stat() (os.FileInfo, error)
99
}
100

101
func dirList(w ResponseWriter, r *Request, f File) {
102
	dirs, err := f.Readdir(-1)
103
	if err != nil {
104
		logf(r, "http: error reading directory: %v", err)
105
		Error(w, "Error reading directory", StatusInternalServerError)
106
		return
107
	}
108
	sort.Slice(dirs, func(i, j int) bool { return dirs[i].Name() < dirs[j].Name() })
109

110
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
111
	fmt.Fprintf(w, "<pre>\n")
112
	for _, d := range dirs {
113
		name := d.Name()
114
		if d.IsDir() {
115
			name += "/"
116
		}
117
		// name may contain '?' or '#', which must be escaped to remain
118
		// part of the URL path, and not indicate the start of a query
119
		// string or fragment.
120
		url := url.URL{Path: name}
121
		fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
122
	}
123
	fmt.Fprintf(w, "</pre>\n")
124
}
125

126
// ServeContent replies to the request using the content in the
127
// provided ReadSeeker. The main benefit of ServeContent over io.Copy
128
// is that it handles Range requests properly, sets the MIME type, and
129
// handles If-Match, If-Unmodified-Since, If-None-Match, If-Modified-Since,
130
// and If-Range requests.
131
//
132
// If the response's Content-Type header is not set, ServeContent
133
// first tries to deduce the type from name's file extension and,
134
// if that fails, falls back to reading the first block of the content
135
// and passing it to DetectContentType.
136
// The name is otherwise unused; in particular it can be empty and is
137
// never sent in the response.
138
//
139
// If modtime is not the zero time or Unix epoch, ServeContent
140
// includes it in a Last-Modified header in the response. If the
141
// request includes an If-Modified-Since header, ServeContent uses
142
// modtime to decide whether the content needs to be sent at all.
143
//
144
// The content's Seek method must work: ServeContent uses
145
// a seek to the end of the content to determine its size.
146
//
147
// If the caller has set w's ETag header formatted per RFC 7232, section 2.3,
148
// ServeContent uses it to handle requests using If-Match, If-None-Match, or If-Range.
149
//
150
// Note that *os.File implements the io.ReadSeeker interface.
151
func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, content io.ReadSeeker) {
152
	sizeFunc := func() (int64, error) {
153
		size, err := content.Seek(0, io.SeekEnd)
154
		if err != nil {
155
			return 0, errSeeker
156
		}
157
		_, err = content.Seek(0, io.SeekStart)
158
		if err != nil {
159
			return 0, errSeeker
160
		}
161
		return size, nil
162
	}
163
	serveContent(w, req, name, modtime, sizeFunc, content)
164
}
165

166
// errSeeker is returned by ServeContent's sizeFunc when the content
167
// doesn't seek properly. The underlying Seeker's error text isn't
168
// included in the sizeFunc reply so it's not sent over HTTP to end
169
// users.
170
var errSeeker = errors.New("seeker can't seek")
171

172
// errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
173
// all of the byte-range-spec values is greater than the content size.
174
var errNoOverlap = errors.New("invalid range: failed to overlap")
175

176
// if name is empty, filename is unknown. (used for mime type, before sniffing)
177
// if modtime.IsZero(), modtime is unknown.
178
// content must be seeked to the beginning of the file.
179
// The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
180
func serveContent(w ResponseWriter, r *Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
181
	setLastModified(w, modtime)
182
	done, rangeReq := checkPreconditions(w, r, modtime)
183
	if done {
184
		return
185
	}
186

187
	code := StatusOK
188

189
	// If Content-Type isn't set, use the file's extension to find it, but
190
	// if the Content-Type is unset explicitly, do not sniff the type.
191
	ctypes, haveType := w.Header()["Content-Type"]
192
	var ctype string
193
	if !haveType {
194
		ctype = mime.TypeByExtension(filepath.Ext(name))
195
		if ctype == "" {
196
			// read a chunk to decide between utf-8 text and binary
197
			var buf [sniffLen]byte
198
			n, _ := io.ReadFull(content, buf[:])
199
			ctype = DetectContentType(buf[:n])
200
			_, err := content.Seek(0, io.SeekStart) // rewind to output whole file
201
			if err != nil {
202
				Error(w, "seeker can't seek", StatusInternalServerError)
203
				return
204
			}
205
		}
206
		w.Header().Set("Content-Type", ctype)
207
	} else if len(ctypes) > 0 {
208
		ctype = ctypes[0]
209
	}
210

211
	size, err := sizeFunc()
212
	if err != nil {
213
		Error(w, err.Error(), StatusInternalServerError)
214
		return
215
	}
216

217
	// handle Content-Range header.
218
	sendSize := size
219
	var sendContent io.Reader = content
220
	if size >= 0 {
221
		ranges, err := parseRange(rangeReq, size)
222
		if err != nil {
223
			if err == errNoOverlap {
224
				w.Header().Set("Content-Range", fmt.Sprintf("bytes */%d", size))
225
			}
226
			Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
227
			return
228
		}
229
		if sumRangesSize(ranges) > size {
230
			// The total number of bytes in all the ranges
231
			// is larger than the size of the file by
232
			// itself, so this is probably an attack, or a
233
			// dumb client. Ignore the range request.
234
			ranges = nil
235
		}
236
		switch {
237
		case len(ranges) == 1:
238
			// RFC 7233, Section 4.1:
239
			// "If a single part is being transferred, the server
240
			// generating the 206 response MUST generate a
241
			// Content-Range header field, describing what range
242
			// of the selected representation is enclosed, and a
243
			// payload consisting of the range.
244
			// ...
245
			// A server MUST NOT generate a multipart response to
246
			// a request for a single range, since a client that
247
			// does not request multiple parts might not support
248
			// multipart responses."
249
			ra := ranges[0]
250
			if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
251
				Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
252
				return
253
			}
254
			sendSize = ra.length
255
			code = StatusPartialContent
256
			w.Header().Set("Content-Range", ra.contentRange(size))
257
		case len(ranges) > 1:
258
			sendSize = rangesMIMESize(ranges, ctype, size)
259
			code = StatusPartialContent
260

261
			pr, pw := io.Pipe()
262
			mw := multipart.NewWriter(pw)
263
			w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
264
			sendContent = pr
265
			defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
266
			go func() {
267
				for _, ra := range ranges {
268
					part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
269
					if err != nil {
270
						pw.CloseWithError(err)
271
						return
272
					}
273
					if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
274
						pw.CloseWithError(err)
275
						return
276
					}
277
					if _, err := io.CopyN(part, content, ra.length); err != nil {
278
						pw.CloseWithError(err)
279
						return
280
					}
281
				}
282
				mw.Close()
283
				pw.Close()
284
			}()
285
		}
286

287
		w.Header().Set("Accept-Ranges", "bytes")
288
		if w.Header().Get("Content-Encoding") == "" {
289
			w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
290
		}
291
	}
292

293
	w.WriteHeader(code)
294

295
	if r.Method != "HEAD" {
296
		io.CopyN(w, sendContent, sendSize)
297
	}
298
}
299

300
// scanETag determines if a syntactically valid ETag is present at s. If so,
301
// the ETag and remaining text after consuming ETag is returned. Otherwise,
302
// it returns "", "".
303
func scanETag(s string) (etag string, remain string) {
304
	s = textproto.TrimString(s)
305
	start := 0
306
	if strings.HasPrefix(s, "W/") {
307
		start = 2
308
	}
309
	if len(s[start:]) < 2 || s[start] != '"' {
310
		return "", ""
311
	}
312
	// ETag is either W/"text" or "text".
313
	// See RFC 7232 2.3.
314
	for i := start + 1; i < len(s); i++ {
315
		c := s[i]
316
		switch {
317
		// Character values allowed in ETags.
318
		case c == 0x21 || c >= 0x23 && c <= 0x7E || c >= 0x80:
319
		case c == '"':
320
			return s[:i+1], s[i+1:]
321
		default:
322
			return "", ""
323
		}
324
	}
325
	return "", ""
326
}
327

328
// etagStrongMatch reports whether a and b match using strong ETag comparison.
329
// Assumes a and b are valid ETags.
330
func etagStrongMatch(a, b string) bool {
331
	return a == b && a != "" && a[0] == '"'
332
}
333

334
// etagWeakMatch reports whether a and b match using weak ETag comparison.
335
// Assumes a and b are valid ETags.
336
func etagWeakMatch(a, b string) bool {
337
	return strings.TrimPrefix(a, "W/") == strings.TrimPrefix(b, "W/")
338
}
339

340
// condResult is the result of an HTTP request precondition check.
341
// See https://tools.ietf.org/html/rfc7232 section 3.
342
type condResult int
343

344
const (
345
	condNone condResult = iota
346
	condTrue
347
	condFalse
348
)
349

350
func checkIfMatch(w ResponseWriter, r *Request) condResult {
351
	im := r.Header.Get("If-Match")
352
	if im == "" {
353
		return condNone
354
	}
355
	for {
356
		im = textproto.TrimString(im)
357
		if len(im) == 0 {
358
			break
359
		}
360
		if im[0] == ',' {
361
			im = im[1:]
362
			continue
363
		}
364
		if im[0] == '*' {
365
			return condTrue
366
		}
367
		etag, remain := scanETag(im)
368
		if etag == "" {
369
			break
370
		}
371
		if etagStrongMatch(etag, w.Header().get("Etag")) {
372
			return condTrue
373
		}
374
		im = remain
375
	}
376

377
	return condFalse
378
}
379

380
func checkIfUnmodifiedSince(r *Request, modtime time.Time) condResult {
381
	ius := r.Header.Get("If-Unmodified-Since")
382
	if ius == "" || isZeroTime(modtime) {
383
		return condNone
384
	}
385
	if t, err := ParseTime(ius); err == nil {
386
		// The Date-Modified header truncates sub-second precision, so
387
		// use mtime < t+1s instead of mtime <= t to check for unmodified.
388
		if modtime.Before(t.Add(1 * time.Second)) {
389
			return condTrue
390
		}
391
		return condFalse
392
	}
393
	return condNone
394
}
395

396
func checkIfNoneMatch(w ResponseWriter, r *Request) condResult {
397
	inm := r.Header.get("If-None-Match")
398
	if inm == "" {
399
		return condNone
400
	}
401
	buf := inm
402
	for {
403
		buf = textproto.TrimString(buf)
404
		if len(buf) == 0 {
405
			break
406
		}
407
		if buf[0] == ',' {
408
			buf = buf[1:]
409
		}
410
		if buf[0] == '*' {
411
			return condFalse
412
		}
413
		etag, remain := scanETag(buf)
414
		if etag == "" {
415
			break
416
		}
417
		if etagWeakMatch(etag, w.Header().get("Etag")) {
418
			return condFalse
419
		}
420
		buf = remain
421
	}
422
	return condTrue
423
}
424

425
func checkIfModifiedSince(r *Request, modtime time.Time) condResult {
426
	if r.Method != "GET" && r.Method != "HEAD" {
427
		return condNone
428
	}
429
	ims := r.Header.Get("If-Modified-Since")
430
	if ims == "" || isZeroTime(modtime) {
431
		return condNone
432
	}
433
	t, err := ParseTime(ims)
434
	if err != nil {
435
		return condNone
436
	}
437
	// The Date-Modified header truncates sub-second precision, so
438
	// use mtime < t+1s instead of mtime <= t to check for unmodified.
439
	if modtime.Before(t.Add(1 * time.Second)) {
440
		return condFalse
441
	}
442
	return condTrue
443
}
444

445
func checkIfRange(w ResponseWriter, r *Request, modtime time.Time) condResult {
446
	if r.Method != "GET" && r.Method != "HEAD" {
447
		return condNone
448
	}
449
	ir := r.Header.get("If-Range")
450
	if ir == "" {
451
		return condNone
452
	}
453
	etag, _ := scanETag(ir)
454
	if etag != "" {
455
		if etagStrongMatch(etag, w.Header().Get("Etag")) {
456
			return condTrue
457
		} else {
458
			return condFalse
459
		}
460
	}
461
	// The If-Range value is typically the ETag value, but it may also be
462
	// the modtime date. See golang.org/issue/8367.
463
	if modtime.IsZero() {
464
		return condFalse
465
	}
466
	t, err := ParseTime(ir)
467
	if err != nil {
468
		return condFalse
469
	}
470
	if t.Unix() == modtime.Unix() {
471
		return condTrue
472
	}
473
	return condFalse
474
}
475

476
var unixEpochTime = time.Unix(0, 0)
477

478
// isZeroTime reports whether t is obviously unspecified (either zero or Unix()=0).
479
func isZeroTime(t time.Time) bool {
480
	return t.IsZero() || t.Equal(unixEpochTime)
481
}
482

483
func setLastModified(w ResponseWriter, modtime time.Time) {
484
	if !isZeroTime(modtime) {
485
		w.Header().Set("Last-Modified", modtime.UTC().Format(TimeFormat))
486
	}
487
}
488

489
func writeNotModified(w ResponseWriter) {
490
	// RFC 7232 section 4.1:
491
	// a sender SHOULD NOT generate representation metadata other than the
492
	// above listed fields unless said metadata exists for the purpose of
493
	// guiding cache updates (e.g., Last-Modified might be useful if the
494
	// response does not have an ETag field).
495
	h := w.Header()
496
	delete(h, "Content-Type")
497
	delete(h, "Content-Length")
498
	if h.Get("Etag") != "" {
499
		delete(h, "Last-Modified")
500
	}
501
	w.WriteHeader(StatusNotModified)
502
}
503

504
// checkPreconditions evaluates request preconditions and reports whether a precondition
505
// resulted in sending StatusNotModified or StatusPreconditionFailed.
506
func checkPreconditions(w ResponseWriter, r *Request, modtime time.Time) (done bool, rangeHeader string) {
507
	// This function carefully follows RFC 7232 section 6.
508
	ch := checkIfMatch(w, r)
509
	if ch == condNone {
510
		ch = checkIfUnmodifiedSince(r, modtime)
511
	}
512
	if ch == condFalse {
513
		w.WriteHeader(StatusPreconditionFailed)
514
		return true, ""
515
	}
516
	switch checkIfNoneMatch(w, r) {
517
	case condFalse:
518
		if r.Method == "GET" || r.Method == "HEAD" {
519
			writeNotModified(w)
520
			return true, ""
521
		} else {
522
			w.WriteHeader(StatusPreconditionFailed)
523
			return true, ""
524
		}
525
	case condNone:
526
		if checkIfModifiedSince(r, modtime) == condFalse {
527
			writeNotModified(w)
528
			return true, ""
529
		}
530
	}
531

532
	rangeHeader = r.Header.get("Range")
533
	if rangeHeader != "" && checkIfRange(w, r, modtime) == condFalse {
534
		rangeHeader = ""
535
	}
536
	return false, rangeHeader
537
}
538

539
// name is '/'-separated, not filepath.Separator.
540
func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirect bool) {
541
	const indexPage = "/index.html"
542

543
	// redirect .../index.html to .../
544
	// can't use Redirect() because that would make the path absolute,
545
	// which would be a problem running under StripPrefix
546
	if strings.HasSuffix(r.URL.Path, indexPage) {
547
		localRedirect(w, r, "./")
548
		return
549
	}
550

551
	f, err := fs.Open(name)
552
	if err != nil {
553
		msg, code := toHTTPError(err)
554
		Error(w, msg, code)
555
		return
556
	}
557
	defer f.Close()
558

559
	d, err := f.Stat()
560
	if err != nil {
561
		msg, code := toHTTPError(err)
562
		Error(w, msg, code)
563
		return
564
	}
565

566
	if redirect {
567
		// redirect to canonical path: / at end of directory url
568
		// r.URL.Path always begins with /
569
		url := r.URL.Path
570
		if d.IsDir() {
571
			if url[len(url)-1] != '/' {
572
				localRedirect(w, r, path.Base(url)+"/")
573
				return
574
			}
575
		} else {
576
			if url[len(url)-1] == '/' {
577
				localRedirect(w, r, "../"+path.Base(url))
578
				return
579
			}
580
		}
581
	}
582

583
	// redirect if the directory name doesn't end in a slash
584
	if d.IsDir() {
585
		url := r.URL.Path
586
		if url[len(url)-1] != '/' {
587
			localRedirect(w, r, path.Base(url)+"/")
588
			return
589
		}
590
	}
591

592
	// use contents of index.html for directory, if present
593
	if d.IsDir() {
594
		index := strings.TrimSuffix(name, "/") + indexPage
595
		ff, err := fs.Open(index)
596
		if err == nil {
597
			defer ff.Close()
598
			dd, err := ff.Stat()
599
			if err == nil {
600
				name = index
601
				d = dd
602
				f = ff
603
			}
604
		}
605
	}
606

607
	// Still a directory? (we didn't find an index.html file)
608
	if d.IsDir() {
609
		if checkIfModifiedSince(r, d.ModTime()) == condFalse {
610
			writeNotModified(w)
611
			return
612
		}
613
		w.Header().Set("Last-Modified", d.ModTime().UTC().Format(TimeFormat))
614
		dirList(w, r, f)
615
		return
616
	}
617

618
	// serveContent will check modification time
619
	sizeFunc := func() (int64, error) { return d.Size(), nil }
620
	serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, f)
621
}
622

623
// toHTTPError returns a non-specific HTTP error message and status code
624
// for a given non-nil error value. It's important that toHTTPError does not
625
// actually return err.Error(), since msg and httpStatus are returned to users,
626
// and historically Go's ServeContent always returned just "404 Not Found" for
627
// all errors. We don't want to start leaking information in error messages.
628
func toHTTPError(err error) (msg string, httpStatus int) {
629
	if os.IsNotExist(err) {
630
		return "404 page not found", StatusNotFound
631
	}
632
	if os.IsPermission(err) {
633
		return "403 Forbidden", StatusForbidden
634
	}
635
	// Default:
636
	return "500 Internal Server Error", StatusInternalServerError
637
}
638

639
// localRedirect gives a Moved Permanently response.
640
// It does not convert relative paths to absolute paths like Redirect does.
641
func localRedirect(w ResponseWriter, r *Request, newPath string) {
642
	if q := r.URL.RawQuery; q != "" {
643
		newPath += "?" + q
644
	}
645
	w.Header().Set("Location", newPath)
646
	w.WriteHeader(StatusMovedPermanently)
647
}
648

649
// ServeFile replies to the request with the contents of the named
650
// file or directory.
651
//
652
// If the provided file or directory name is a relative path, it is
653
// interpreted relative to the current directory and may ascend to
654
// parent directories. If the provided name is constructed from user
655
// input, it should be sanitized before calling ServeFile.
656
//
657
// As a precaution, ServeFile will reject requests where r.URL.Path
658
// contains a ".." path element; this protects against callers who
659
// might unsafely use filepath.Join on r.URL.Path without sanitizing
660
// it and then use that filepath.Join result as the name argument.
661
//
662
// As another special case, ServeFile redirects any request where r.URL.Path
663
// ends in "/index.html" to the same path, without the final
664
// "index.html". To avoid such redirects either modify the path or
665
// use ServeContent.
666
//
667
// Outside of those two special cases, ServeFile does not use
668
// r.URL.Path for selecting the file or directory to serve; only the
669
// file or directory provided in the name argument is used.
670
func ServeFile(w ResponseWriter, r *Request, name string) {
671
	if containsDotDot(r.URL.Path) {
672
		// Too many programs use r.URL.Path to construct the argument to
673
		// serveFile. Reject the request under the assumption that happened
674
		// here and ".." may not be wanted.
675
		// Note that name might not contain "..", for example if code (still
676
		// incorrectly) used filepath.Join(myDir, r.URL.Path).
677
		Error(w, "invalid URL path", StatusBadRequest)
678
		return
679
	}
680
	dir, file := filepath.Split(name)
681
	serveFile(w, r, Dir(dir), file, false)
682
}
683

684
func containsDotDot(v string) bool {
685
	if !strings.Contains(v, "..") {
686
		return false
687
	}
688
	for _, ent := range strings.FieldsFunc(v, isSlashRune) {
689
		if ent == ".." {
690
			return true
691
		}
692
	}
693
	return false
694
}
695

696
func isSlashRune(r rune) bool { return r == '/' || r == '\\' }
697

698
type fileHandler struct {
699
	root FileSystem
700
}
701

702
// FileServer returns a handler that serves HTTP requests
703
// with the contents of the file system rooted at root.
704
//
705
// To use the operating system's file system implementation,
706
// use http.Dir:
707
//
708
//     http.Handle("/", http.FileServer(http.Dir("/tmp")))
709
//
710
// As a special case, the returned file server redirects any request
711
// ending in "/index.html" to the same path, without the final
712
// "index.html".
713
func FileServer(root FileSystem) Handler {
714
	return &fileHandler{root}
715
}
716

717
func (f *fileHandler) ServeHTTP(w ResponseWriter, r *Request) {
718
	upath := r.URL.Path
719
	if !strings.HasPrefix(upath, "/") {
720
		upath = "/" + upath
721
		r.URL.Path = upath
722
	}
723
	serveFile(w, r, f.root, path.Clean(upath), true)
724
}
725

726
// httpRange specifies the byte range to be sent to the client.
727
type httpRange struct {
728
	start, length int64
729
}
730

731
func (r httpRange) contentRange(size int64) string {
732
	return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
733
}
734

735
func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
736
	return textproto.MIMEHeader{
737
		"Content-Range": {r.contentRange(size)},
738
		"Content-Type":  {contentType},
739
	}
740
}
741

742
// parseRange parses a Range header string as per RFC 7233.
743
// errNoOverlap is returned if none of the ranges overlap.
744
func parseRange(s string, size int64) ([]httpRange, error) {
745
	if s == "" {
746
		return nil, nil // header not present
747
	}
748
	const b = "bytes="
749
	if !strings.HasPrefix(s, b) {
750
		return nil, errors.New("invalid range")
751
	}
752
	var ranges []httpRange
753
	noOverlap := false
754
	for _, ra := range strings.Split(s[len(b):], ",") {
755
		ra = strings.TrimSpace(ra)
756
		if ra == "" {
757
			continue
758
		}
759
		i := strings.Index(ra, "-")
760
		if i < 0 {
761
			return nil, errors.New("invalid range")
762
		}
763
		start, end := strings.TrimSpace(ra[:i]), strings.TrimSpace(ra[i+1:])
764
		var r httpRange
765
		if start == "" {
766
			// If no start is specified, end specifies the
767
			// range start relative to the end of the file.
768
			i, err := strconv.ParseInt(end, 10, 64)
769
			if err != nil {
770
				return nil, errors.New("invalid range")
771
			}
772
			if i > size {
773
				i = size
774
			}
775
			r.start = size - i
776
			r.length = size - r.start
777
		} else {
778
			i, err := strconv.ParseInt(start, 10, 64)
779
			if err != nil || i < 0 {
780
				return nil, errors.New("invalid range")
781
			}
782
			if i >= size {
783
				// If the range begins after the size of the content,
784
				// then it does not overlap.
785
				noOverlap = true
786
				continue
787
			}
788
			r.start = i
789
			if end == "" {
790
				// If no end is specified, range extends to end of the file.
791
				r.length = size - r.start
792
			} else {
793
				i, err := strconv.ParseInt(end, 10, 64)
794
				if err != nil || r.start > i {
795
					return nil, errors.New("invalid range")
796
				}
797
				if i >= size {
798
					i = size - 1
799
				}
800
				r.length = i - r.start + 1
801
			}
802
		}
803
		ranges = append(ranges, r)
804
	}
805
	if noOverlap && len(ranges) == 0 {
806
		// The specified ranges did not overlap with the content.
807
		return nil, errNoOverlap
808
	}
809
	return ranges, nil
810
}
811

812
// countingWriter counts how many bytes have been written to it.
813
type countingWriter int64
814

815
func (w *countingWriter) Write(p []byte) (n int, err error) {
816
	*w += countingWriter(len(p))
817
	return len(p), nil
818
}
819

820
// rangesMIMESize returns the number of bytes it takes to encode the
821
// provided ranges as a multipart response.
822
func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
823
	var w countingWriter
824
	mw := multipart.NewWriter(&w)
825
	for _, ra := range ranges {
826
		mw.CreatePart(ra.mimeHeader(contentType, contentSize))
827
		encSize += ra.length
828
	}
829
	mw.Close()
830
	encSize += int64(w)
831
	return
832
}
833

834
func sumRangesSize(ranges []httpRange) (size int64) {
835
	for _, ra := range ranges {
836
		size += ra.length
837
	}
838
	return
839
}
840