Source file src/net/http/fs.go

Documentation: net/http

		 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  	"io/fs"
		14  	"mime"
		15  	"mime/multipart"
		16  	"net/textproto"
		17  	"net/url"
		18  	"os"
		19  	"path"
		20  	"path/filepath"
		21  	"sort"
		22  	"strconv"
		23  	"strings"
		24  	"time"
		25  )
		26  
		27  // A Dir implements FileSystem using the native file system restricted to a
		28  // specific directory tree.
		29  //
		30  // While the FileSystem.Open method takes '/'-separated paths, a Dir's string
		31  // value is a filename on the native file system, not a URL, so it is separated
		32  // by filepath.Separator, which isn't necessarily '/'.
		33  //
		34  // Note that Dir could expose sensitive files and directories. Dir will follow
		35  // symlinks pointing out of the directory tree, which can be especially dangerous
		36  // if serving from a directory in which users are able to create arbitrary symlinks.
		37  // Dir will also allow access to files and directories starting with a period,
		38  // which could expose sensitive directories like .git or sensitive files like
		39  // .htpasswd. To exclude files with a leading period, remove the files/directories
		40  // from the server or create a custom FileSystem implementation.
		41  //
		42  // An empty Dir is treated as ".".
		43  type Dir string
		44  
		45  // mapDirOpenError maps the provided non-nil error from opening name
		46  // to a possibly better non-nil error. In particular, it turns OS-specific errors
		47  // about opening files in non-directories into fs.ErrNotExist. See Issue 18984.
		48  func mapDirOpenError(originalErr error, name string) error {
		49  	if errors.Is(originalErr, fs.ErrNotExist) || errors.Is(originalErr, fs.ErrPermission) {
		50  		return originalErr
		51  	}
		52  
		53  	parts := strings.Split(name, string(filepath.Separator))
		54  	for i := range parts {
		55  		if parts[i] == "" {
		56  			continue
		57  		}
		58  		fi, err := os.Stat(strings.Join(parts[:i+1], string(filepath.Separator)))
		59  		if err != nil {
		60  			return originalErr
		61  		}
		62  		if !fi.IsDir() {
		63  			return fs.ErrNotExist
		64  		}
		65  	}
		66  	return originalErr
		67  }
		68  
		69  // Open implements FileSystem using os.Open, opening files for reading rooted
		70  // and relative to the directory d.
		71  func (d Dir) Open(name string) (File, error) {
		72  	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
		73  		return nil, errors.New("http: invalid character in file path")
		74  	}
		75  	dir := string(d)
		76  	if dir == "" {
		77  		dir = "."
		78  	}
		79  	fullName := filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name)))
		80  	f, err := os.Open(fullName)
		81  	if err != nil {
		82  		return nil, mapDirOpenError(err, fullName)
		83  	}
		84  	return f, nil
		85  }
		86  
		87  // A FileSystem implements access to a collection of named files.
		88  // The elements in a file path are separated by slash ('/', U+002F)
		89  // characters, regardless of host operating system convention.
		90  // See the FileServer function to convert a FileSystem to a Handler.
		91  //
		92  // This interface predates the fs.FS interface, which can be used instead:
		93  // the FS adapter function converts an fs.FS to a FileSystem.
		94  type FileSystem interface {
		95  	Open(name string) (File, error)
		96  }
		97  
		98  // A File is returned by a FileSystem's Open method and can be
		99  // served by the FileServer implementation.
	 100  //
	 101  // The methods should behave the same as those on an *os.File.
	 102  type File interface {
	 103  	io.Closer
	 104  	io.Reader
	 105  	io.Seeker
	 106  	Readdir(count int) ([]fs.FileInfo, error)
	 107  	Stat() (fs.FileInfo, error)
	 108  }
	 109  
	 110  type anyDirs interface {
	 111  	len() int
	 112  	name(i int) string
	 113  	isDir(i int) bool
	 114  }
	 115  
	 116  type fileInfoDirs []fs.FileInfo
	 117  
	 118  func (d fileInfoDirs) len() int					{ return len(d) }
	 119  func (d fileInfoDirs) isDir(i int) bool	{ return d[i].IsDir() }
	 120  func (d fileInfoDirs) name(i int) string { return d[i].Name() }
	 121  
	 122  type dirEntryDirs []fs.DirEntry
	 123  
	 124  func (d dirEntryDirs) len() int					{ return len(d) }
	 125  func (d dirEntryDirs) isDir(i int) bool	{ return d[i].IsDir() }
	 126  func (d dirEntryDirs) name(i int) string { return d[i].Name() }
	 127  
	 128  func dirList(w ResponseWriter, r *Request, f File) {
	 129  	// Prefer to use ReadDir instead of Readdir,
	 130  	// because the former doesn't require calling
	 131  	// Stat on every entry of a directory on Unix.
	 132  	var dirs anyDirs
	 133  	var err error
	 134  	if d, ok := f.(fs.ReadDirFile); ok {
	 135  		var list dirEntryDirs
	 136  		list, err = d.ReadDir(-1)
	 137  		dirs = list
	 138  	} else {
	 139  		var list fileInfoDirs
	 140  		list, err = f.Readdir(-1)
	 141  		dirs = list
	 142  	}
	 143  
	 144  	if err != nil {
	 145  		logf(r, "http: error reading directory: %v", err)
	 146  		Error(w, "Error reading directory", StatusInternalServerError)
	 147  		return
	 148  	}
	 149  	sort.Slice(dirs, func(i, j int) bool { return dirs.name(i) < dirs.name(j) })
	 150  
	 151  	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	 152  	fmt.Fprintf(w, "<pre>\n")
	 153  	for i, n := 0, dirs.len(); i < n; i++ {
	 154  		name := dirs.name(i)
	 155  		if dirs.isDir(i) {
	 156  			name += "/"
	 157  		}
	 158  		// name may contain '?' or '#', which must be escaped to remain
	 159  		// part of the URL path, and not indicate the start of a query
	 160  		// string or fragment.
	 161  		url := url.URL{Path: name}
	 162  		fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
	 163  	}
	 164  	fmt.Fprintf(w, "</pre>\n")
	 165  }
	 166  
	 167  // ServeContent replies to the request using the content in the
	 168  // provided ReadSeeker. The main benefit of ServeContent over io.Copy
	 169  // is that it handles Range requests properly, sets the MIME type, and
	 170  // handles If-Match, If-Unmodified-Since, If-None-Match, If-Modified-Since,
	 171  // and If-Range requests.
	 172  //
	 173  // If the response's Content-Type header is not set, ServeContent
	 174  // first tries to deduce the type from name's file extension and,
	 175  // if that fails, falls back to reading the first block of the content
	 176  // and passing it to DetectContentType.
	 177  // The name is otherwise unused; in particular it can be empty and is
	 178  // never sent in the response.
	 179  //
	 180  // If modtime is not the zero time or Unix epoch, ServeContent
	 181  // includes it in a Last-Modified header in the response. If the
	 182  // request includes an If-Modified-Since header, ServeContent uses
	 183  // modtime to decide whether the content needs to be sent at all.
	 184  //
	 185  // The content's Seek method must work: ServeContent uses
	 186  // a seek to the end of the content to determine its size.
	 187  //
	 188  // If the caller has set w's ETag header formatted per RFC 7232, section 2.3,
	 189  // ServeContent uses it to handle requests using If-Match, If-None-Match, or If-Range.
	 190  //
	 191  // Note that *os.File implements the io.ReadSeeker interface.
	 192  func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, content io.ReadSeeker) {
	 193  	sizeFunc := func() (int64, error) {
	 194  		size, err := content.Seek(0, io.SeekEnd)
	 195  		if err != nil {
	 196  			return 0, errSeeker
	 197  		}
	 198  		_, err = content.Seek(0, io.SeekStart)
	 199  		if err != nil {
	 200  			return 0, errSeeker
	 201  		}
	 202  		return size, nil
	 203  	}
	 204  	serveContent(w, req, name, modtime, sizeFunc, content)
	 205  }
	 206  
	 207  // errSeeker is returned by ServeContent's sizeFunc when the content
	 208  // doesn't seek properly. The underlying Seeker's error text isn't
	 209  // included in the sizeFunc reply so it's not sent over HTTP to end
	 210  // users.
	 211  var errSeeker = errors.New("seeker can't seek")
	 212  
	 213  // errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
	 214  // all of the byte-range-spec values is greater than the content size.
	 215  var errNoOverlap = errors.New("invalid range: failed to overlap")
	 216  
	 217  // if name is empty, filename is unknown. (used for mime type, before sniffing)
	 218  // if modtime.IsZero(), modtime is unknown.
	 219  // content must be seeked to the beginning of the file.
	 220  // The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
	 221  func serveContent(w ResponseWriter, r *Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
	 222  	setLastModified(w, modtime)
	 223  	done, rangeReq := checkPreconditions(w, r, modtime)
	 224  	if done {
	 225  		return
	 226  	}
	 227  
	 228  	code := StatusOK
	 229  
	 230  	// If Content-Type isn't set, use the file's extension to find it, but
	 231  	// if the Content-Type is unset explicitly, do not sniff the type.
	 232  	ctypes, haveType := w.Header()["Content-Type"]
	 233  	var ctype string
	 234  	if !haveType {
	 235  		ctype = mime.TypeByExtension(filepath.Ext(name))
	 236  		if ctype == "" {
	 237  			// read a chunk to decide between utf-8 text and binary
	 238  			var buf [sniffLen]byte
	 239  			n, _ := io.ReadFull(content, buf[:])
	 240  			ctype = DetectContentType(buf[:n])
	 241  			_, err := content.Seek(0, io.SeekStart) // rewind to output whole file
	 242  			if err != nil {
	 243  				Error(w, "seeker can't seek", StatusInternalServerError)
	 244  				return
	 245  			}
	 246  		}
	 247  		w.Header().Set("Content-Type", ctype)
	 248  	} else if len(ctypes) > 0 {
	 249  		ctype = ctypes[0]
	 250  	}
	 251  
	 252  	size, err := sizeFunc()
	 253  	if err != nil {
	 254  		Error(w, err.Error(), StatusInternalServerError)
	 255  		return
	 256  	}
	 257  
	 258  	// handle Content-Range header.
	 259  	sendSize := size
	 260  	var sendContent io.Reader = content
	 261  	if size >= 0 {
	 262  		ranges, err := parseRange(rangeReq, size)
	 263  		if err != nil {
	 264  			if err == errNoOverlap {
	 265  				w.Header().Set("Content-Range", fmt.Sprintf("bytes */%d", size))
	 266  			}
	 267  			Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
	 268  			return
	 269  		}
	 270  		if sumRangesSize(ranges) > size {
	 271  			// The total number of bytes in all the ranges
	 272  			// is larger than the size of the file by
	 273  			// itself, so this is probably an attack, or a
	 274  			// dumb client. Ignore the range request.
	 275  			ranges = nil
	 276  		}
	 277  		switch {
	 278  		case len(ranges) == 1:
	 279  			// RFC 7233, Section 4.1:
	 280  			// "If a single part is being transferred, the server
	 281  			// generating the 206 response MUST generate a
	 282  			// Content-Range header field, describing what range
	 283  			// of the selected representation is enclosed, and a
	 284  			// payload consisting of the range.
	 285  			// ...
	 286  			// A server MUST NOT generate a multipart response to
	 287  			// a request for a single range, since a client that
	 288  			// does not request multiple parts might not support
	 289  			// multipart responses."
	 290  			ra := ranges[0]
	 291  			if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
	 292  				Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
	 293  				return
	 294  			}
	 295  			sendSize = ra.length
	 296  			code = StatusPartialContent
	 297  			w.Header().Set("Content-Range", ra.contentRange(size))
	 298  		case len(ranges) > 1:
	 299  			sendSize = rangesMIMESize(ranges, ctype, size)
	 300  			code = StatusPartialContent
	 301  
	 302  			pr, pw := io.Pipe()
	 303  			mw := multipart.NewWriter(pw)
	 304  			w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
	 305  			sendContent = pr
	 306  			defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
	 307  			go func() {
	 308  				for _, ra := range ranges {
	 309  					part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
	 310  					if err != nil {
	 311  						pw.CloseWithError(err)
	 312  						return
	 313  					}
	 314  					if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
	 315  						pw.CloseWithError(err)
	 316  						return
	 317  					}
	 318  					if _, err := io.CopyN(part, content, ra.length); err != nil {
	 319  						pw.CloseWithError(err)
	 320  						return
	 321  					}
	 322  				}
	 323  				mw.Close()
	 324  				pw.Close()
	 325  			}()
	 326  		}
	 327  
	 328  		w.Header().Set("Accept-Ranges", "bytes")
	 329  		if w.Header().Get("Content-Encoding") == "" {
	 330  			w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
	 331  		}
	 332  	}
	 333  
	 334  	w.WriteHeader(code)
	 335  
	 336  	if r.Method != "HEAD" {
	 337  		io.CopyN(w, sendContent, sendSize)
	 338  	}
	 339  }
	 340  
	 341  // scanETag determines if a syntactically valid ETag is present at s. If so,
	 342  // the ETag and remaining text after consuming ETag is returned. Otherwise,
	 343  // it returns "", "".
	 344  func scanETag(s string) (etag string, remain string) {
	 345  	s = textproto.TrimString(s)
	 346  	start := 0
	 347  	if strings.HasPrefix(s, "W/") {
	 348  		start = 2
	 349  	}
	 350  	if len(s[start:]) < 2 || s[start] != '"' {
	 351  		return "", ""
	 352  	}
	 353  	// ETag is either W/"text" or "text".
	 354  	// See RFC 7232 2.3.
	 355  	for i := start + 1; i < len(s); i++ {
	 356  		c := s[i]
	 357  		switch {
	 358  		// Character values allowed in ETags.
	 359  		case c == 0x21 || c >= 0x23 && c <= 0x7E || c >= 0x80:
	 360  		case c == '"':
	 361  			return s[:i+1], s[i+1:]
	 362  		default:
	 363  			return "", ""
	 364  		}
	 365  	}
	 366  	return "", ""
	 367  }
	 368  
	 369  // etagStrongMatch reports whether a and b match using strong ETag comparison.
	 370  // Assumes a and b are valid ETags.
	 371  func etagStrongMatch(a, b string) bool {
	 372  	return a == b && a != "" && a[0] == '"'
	 373  }
	 374  
	 375  // etagWeakMatch reports whether a and b match using weak ETag comparison.
	 376  // Assumes a and b are valid ETags.
	 377  func etagWeakMatch(a, b string) bool {
	 378  	return strings.TrimPrefix(a, "W/") == strings.TrimPrefix(b, "W/")
	 379  }
	 380  
	 381  // condResult is the result of an HTTP request precondition check.
	 382  // See https://tools.ietf.org/html/rfc7232 section 3.
	 383  type condResult int
	 384  
	 385  const (
	 386  	condNone condResult = iota
	 387  	condTrue
	 388  	condFalse
	 389  )
	 390  
	 391  func checkIfMatch(w ResponseWriter, r *Request) condResult {
	 392  	im := r.Header.Get("If-Match")
	 393  	if im == "" {
	 394  		return condNone
	 395  	}
	 396  	for {
	 397  		im = textproto.TrimString(im)
	 398  		if len(im) == 0 {
	 399  			break
	 400  		}
	 401  		if im[0] == ',' {
	 402  			im = im[1:]
	 403  			continue
	 404  		}
	 405  		if im[0] == '*' {
	 406  			return condTrue
	 407  		}
	 408  		etag, remain := scanETag(im)
	 409  		if etag == "" {
	 410  			break
	 411  		}
	 412  		if etagStrongMatch(etag, w.Header().get("Etag")) {
	 413  			return condTrue
	 414  		}
	 415  		im = remain
	 416  	}
	 417  
	 418  	return condFalse
	 419  }
	 420  
	 421  func checkIfUnmodifiedSince(r *Request, modtime time.Time) condResult {
	 422  	ius := r.Header.Get("If-Unmodified-Since")
	 423  	if ius == "" || isZeroTime(modtime) {
	 424  		return condNone
	 425  	}
	 426  	t, err := ParseTime(ius)
	 427  	if err != nil {
	 428  		return condNone
	 429  	}
	 430  
	 431  	// The Last-Modified header truncates sub-second precision so
	 432  	// the modtime needs to be truncated too.
	 433  	modtime = modtime.Truncate(time.Second)
	 434  	if modtime.Before(t) || modtime.Equal(t) {
	 435  		return condTrue
	 436  	}
	 437  	return condFalse
	 438  }
	 439  
	 440  func checkIfNoneMatch(w ResponseWriter, r *Request) condResult {
	 441  	inm := r.Header.get("If-None-Match")
	 442  	if inm == "" {
	 443  		return condNone
	 444  	}
	 445  	buf := inm
	 446  	for {
	 447  		buf = textproto.TrimString(buf)
	 448  		if len(buf) == 0 {
	 449  			break
	 450  		}
	 451  		if buf[0] == ',' {
	 452  			buf = buf[1:]
	 453  			continue
	 454  		}
	 455  		if buf[0] == '*' {
	 456  			return condFalse
	 457  		}
	 458  		etag, remain := scanETag(buf)
	 459  		if etag == "" {
	 460  			break
	 461  		}
	 462  		if etagWeakMatch(etag, w.Header().get("Etag")) {
	 463  			return condFalse
	 464  		}
	 465  		buf = remain
	 466  	}
	 467  	return condTrue
	 468  }
	 469  
	 470  func checkIfModifiedSince(r *Request, modtime time.Time) condResult {
	 471  	if r.Method != "GET" && r.Method != "HEAD" {
	 472  		return condNone
	 473  	}
	 474  	ims := r.Header.Get("If-Modified-Since")
	 475  	if ims == "" || isZeroTime(modtime) {
	 476  		return condNone
	 477  	}
	 478  	t, err := ParseTime(ims)
	 479  	if err != nil {
	 480  		return condNone
	 481  	}
	 482  	// The Last-Modified header truncates sub-second precision so
	 483  	// the modtime needs to be truncated too.
	 484  	modtime = modtime.Truncate(time.Second)
	 485  	if modtime.Before(t) || modtime.Equal(t) {
	 486  		return condFalse
	 487  	}
	 488  	return condTrue
	 489  }
	 490  
	 491  func checkIfRange(w ResponseWriter, r *Request, modtime time.Time) condResult {
	 492  	if r.Method != "GET" && r.Method != "HEAD" {
	 493  		return condNone
	 494  	}
	 495  	ir := r.Header.get("If-Range")
	 496  	if ir == "" {
	 497  		return condNone
	 498  	}
	 499  	etag, _ := scanETag(ir)
	 500  	if etag != "" {
	 501  		if etagStrongMatch(etag, w.Header().Get("Etag")) {
	 502  			return condTrue
	 503  		} else {
	 504  			return condFalse
	 505  		}
	 506  	}
	 507  	// The If-Range value is typically the ETag value, but it may also be
	 508  	// the modtime date. See golang.org/issue/8367.
	 509  	if modtime.IsZero() {
	 510  		return condFalse
	 511  	}
	 512  	t, err := ParseTime(ir)
	 513  	if err != nil {
	 514  		return condFalse
	 515  	}
	 516  	if t.Unix() == modtime.Unix() {
	 517  		return condTrue
	 518  	}
	 519  	return condFalse
	 520  }
	 521  
	 522  var unixEpochTime = time.Unix(0, 0)
	 523  
	 524  // isZeroTime reports whether t is obviously unspecified (either zero or Unix()=0).
	 525  func isZeroTime(t time.Time) bool {
	 526  	return t.IsZero() || t.Equal(unixEpochTime)
	 527  }
	 528  
	 529  func setLastModified(w ResponseWriter, modtime time.Time) {
	 530  	if !isZeroTime(modtime) {
	 531  		w.Header().Set("Last-Modified", modtime.UTC().Format(TimeFormat))
	 532  	}
	 533  }
	 534  
	 535  func writeNotModified(w ResponseWriter) {
	 536  	// RFC 7232 section 4.1:
	 537  	// a sender SHOULD NOT generate representation metadata other than the
	 538  	// above listed fields unless said metadata exists for the purpose of
	 539  	// guiding cache updates (e.g., Last-Modified might be useful if the
	 540  	// response does not have an ETag field).
	 541  	h := w.Header()
	 542  	delete(h, "Content-Type")
	 543  	delete(h, "Content-Length")
	 544  	if h.Get("Etag") != "" {
	 545  		delete(h, "Last-Modified")
	 546  	}
	 547  	w.WriteHeader(StatusNotModified)
	 548  }
	 549  
	 550  // checkPreconditions evaluates request preconditions and reports whether a precondition
	 551  // resulted in sending StatusNotModified or StatusPreconditionFailed.
	 552  func checkPreconditions(w ResponseWriter, r *Request, modtime time.Time) (done bool, rangeHeader string) {
	 553  	// This function carefully follows RFC 7232 section 6.
	 554  	ch := checkIfMatch(w, r)
	 555  	if ch == condNone {
	 556  		ch = checkIfUnmodifiedSince(r, modtime)
	 557  	}
	 558  	if ch == condFalse {
	 559  		w.WriteHeader(StatusPreconditionFailed)
	 560  		return true, ""
	 561  	}
	 562  	switch checkIfNoneMatch(w, r) {
	 563  	case condFalse:
	 564  		if r.Method == "GET" || r.Method == "HEAD" {
	 565  			writeNotModified(w)
	 566  			return true, ""
	 567  		} else {
	 568  			w.WriteHeader(StatusPreconditionFailed)
	 569  			return true, ""
	 570  		}
	 571  	case condNone:
	 572  		if checkIfModifiedSince(r, modtime) == condFalse {
	 573  			writeNotModified(w)
	 574  			return true, ""
	 575  		}
	 576  	}
	 577  
	 578  	rangeHeader = r.Header.get("Range")
	 579  	if rangeHeader != "" && checkIfRange(w, r, modtime) == condFalse {
	 580  		rangeHeader = ""
	 581  	}
	 582  	return false, rangeHeader
	 583  }
	 584  
	 585  // name is '/'-separated, not filepath.Separator.
	 586  func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirect bool) {
	 587  	const indexPage = "/index.html"
	 588  
	 589  	// redirect .../index.html to .../
	 590  	// can't use Redirect() because that would make the path absolute,
	 591  	// which would be a problem running under StripPrefix
	 592  	if strings.HasSuffix(r.URL.Path, indexPage) {
	 593  		localRedirect(w, r, "./")
	 594  		return
	 595  	}
	 596  
	 597  	f, err := fs.Open(name)
	 598  	if err != nil {
	 599  		msg, code := toHTTPError(err)
	 600  		Error(w, msg, code)
	 601  		return
	 602  	}
	 603  	defer f.Close()
	 604  
	 605  	d, err := f.Stat()
	 606  	if err != nil {
	 607  		msg, code := toHTTPError(err)
	 608  		Error(w, msg, code)
	 609  		return
	 610  	}
	 611  
	 612  	if redirect {
	 613  		// redirect to canonical path: / at end of directory url
	 614  		// r.URL.Path always begins with /
	 615  		url := r.URL.Path
	 616  		if d.IsDir() {
	 617  			if url[len(url)-1] != '/' {
	 618  				localRedirect(w, r, path.Base(url)+"/")
	 619  				return
	 620  			}
	 621  		} else {
	 622  			if url[len(url)-1] == '/' {
	 623  				localRedirect(w, r, "../"+path.Base(url))
	 624  				return
	 625  			}
	 626  		}
	 627  	}
	 628  
	 629  	if d.IsDir() {
	 630  		url := r.URL.Path
	 631  		// redirect if the directory name doesn't end in a slash
	 632  		if url == "" || url[len(url)-1] != '/' {
	 633  			localRedirect(w, r, path.Base(url)+"/")
	 634  			return
	 635  		}
	 636  
	 637  		// use contents of index.html for directory, if present
	 638  		index := strings.TrimSuffix(name, "/") + indexPage
	 639  		ff, err := fs.Open(index)
	 640  		if err == nil {
	 641  			defer ff.Close()
	 642  			dd, err := ff.Stat()
	 643  			if err == nil {
	 644  				name = index
	 645  				d = dd
	 646  				f = ff
	 647  			}
	 648  		}
	 649  	}
	 650  
	 651  	// Still a directory? (we didn't find an index.html file)
	 652  	if d.IsDir() {
	 653  		if checkIfModifiedSince(r, d.ModTime()) == condFalse {
	 654  			writeNotModified(w)
	 655  			return
	 656  		}
	 657  		setLastModified(w, d.ModTime())
	 658  		dirList(w, r, f)
	 659  		return
	 660  	}
	 661  
	 662  	// serveContent will check modification time
	 663  	sizeFunc := func() (int64, error) { return d.Size(), nil }
	 664  	serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, f)
	 665  }
	 666  
	 667  // toHTTPError returns a non-specific HTTP error message and status code
	 668  // for a given non-nil error value. It's important that toHTTPError does not
	 669  // actually return err.Error(), since msg and httpStatus are returned to users,
	 670  // and historically Go's ServeContent always returned just "404 Not Found" for
	 671  // all errors. We don't want to start leaking information in error messages.
	 672  func toHTTPError(err error) (msg string, httpStatus int) {
	 673  	if errors.Is(err, fs.ErrNotExist) {
	 674  		return "404 page not found", StatusNotFound
	 675  	}
	 676  	if errors.Is(err, fs.ErrPermission) {
	 677  		return "403 Forbidden", StatusForbidden
	 678  	}
	 679  	// Default:
	 680  	return "500 Internal Server Error", StatusInternalServerError
	 681  }
	 682  
	 683  // localRedirect gives a Moved Permanently response.
	 684  // It does not convert relative paths to absolute paths like Redirect does.
	 685  func localRedirect(w ResponseWriter, r *Request, newPath string) {
	 686  	if q := r.URL.RawQuery; q != "" {
	 687  		newPath += "?" + q
	 688  	}
	 689  	w.Header().Set("Location", newPath)
	 690  	w.WriteHeader(StatusMovedPermanently)
	 691  }
	 692  
	 693  // ServeFile replies to the request with the contents of the named
	 694  // file or directory.
	 695  //
	 696  // If the provided file or directory name is a relative path, it is
	 697  // interpreted relative to the current directory and may ascend to
	 698  // parent directories. If the provided name is constructed from user
	 699  // input, it should be sanitized before calling ServeFile.
	 700  //
	 701  // As a precaution, ServeFile will reject requests where r.URL.Path
	 702  // contains a ".." path element; this protects against callers who
	 703  // might unsafely use filepath.Join on r.URL.Path without sanitizing
	 704  // it and then use that filepath.Join result as the name argument.
	 705  //
	 706  // As another special case, ServeFile redirects any request where r.URL.Path
	 707  // ends in "/index.html" to the same path, without the final
	 708  // "index.html". To avoid such redirects either modify the path or
	 709  // use ServeContent.
	 710  //
	 711  // Outside of those two special cases, ServeFile does not use
	 712  // r.URL.Path for selecting the file or directory to serve; only the
	 713  // file or directory provided in the name argument is used.
	 714  func ServeFile(w ResponseWriter, r *Request, name string) {
	 715  	if containsDotDot(r.URL.Path) {
	 716  		// Too many programs use r.URL.Path to construct the argument to
	 717  		// serveFile. Reject the request under the assumption that happened
	 718  		// here and ".." may not be wanted.
	 719  		// Note that name might not contain "..", for example if code (still
	 720  		// incorrectly) used filepath.Join(myDir, r.URL.Path).
	 721  		Error(w, "invalid URL path", StatusBadRequest)
	 722  		return
	 723  	}
	 724  	dir, file := filepath.Split(name)
	 725  	serveFile(w, r, Dir(dir), file, false)
	 726  }
	 727  
	 728  func containsDotDot(v string) bool {
	 729  	if !strings.Contains(v, "..") {
	 730  		return false
	 731  	}
	 732  	for _, ent := range strings.FieldsFunc(v, isSlashRune) {
	 733  		if ent == ".." {
	 734  			return true
	 735  		}
	 736  	}
	 737  	return false
	 738  }
	 739  
	 740  func isSlashRune(r rune) bool { return r == '/' || r == '\\' }
	 741  
	 742  type fileHandler struct {
	 743  	root FileSystem
	 744  }
	 745  
	 746  type ioFS struct {
	 747  	fsys fs.FS
	 748  }
	 749  
	 750  type ioFile struct {
	 751  	file fs.File
	 752  }
	 753  
	 754  func (f ioFS) Open(name string) (File, error) {
	 755  	if name == "/" {
	 756  		name = "."
	 757  	} else {
	 758  		name = strings.TrimPrefix(name, "/")
	 759  	}
	 760  	file, err := f.fsys.Open(name)
	 761  	if err != nil {
	 762  		return nil, err
	 763  	}
	 764  	return ioFile{file}, nil
	 765  }
	 766  
	 767  func (f ioFile) Close() error							 { return f.file.Close() }
	 768  func (f ioFile) Read(b []byte) (int, error) { return f.file.Read(b) }
	 769  func (f ioFile) Stat() (fs.FileInfo, error) { return f.file.Stat() }
	 770  
	 771  var errMissingSeek = errors.New("io.File missing Seek method")
	 772  var errMissingReadDir = errors.New("io.File directory missing ReadDir method")
	 773  
	 774  func (f ioFile) Seek(offset int64, whence int) (int64, error) {
	 775  	s, ok := f.file.(io.Seeker)
	 776  	if !ok {
	 777  		return 0, errMissingSeek
	 778  	}
	 779  	return s.Seek(offset, whence)
	 780  }
	 781  
	 782  func (f ioFile) ReadDir(count int) ([]fs.DirEntry, error) {
	 783  	d, ok := f.file.(fs.ReadDirFile)
	 784  	if !ok {
	 785  		return nil, errMissingReadDir
	 786  	}
	 787  	return d.ReadDir(count)
	 788  }
	 789  
	 790  func (f ioFile) Readdir(count int) ([]fs.FileInfo, error) {
	 791  	d, ok := f.file.(fs.ReadDirFile)
	 792  	if !ok {
	 793  		return nil, errMissingReadDir
	 794  	}
	 795  	var list []fs.FileInfo
	 796  	for {
	 797  		dirs, err := d.ReadDir(count - len(list))
	 798  		for _, dir := range dirs {
	 799  			info, err := dir.Info()
	 800  			if err != nil {
	 801  				// Pretend it doesn't exist, like (*os.File).Readdir does.
	 802  				continue
	 803  			}
	 804  			list = append(list, info)
	 805  		}
	 806  		if err != nil {
	 807  			return list, err
	 808  		}
	 809  		if count < 0 || len(list) >= count {
	 810  			break
	 811  		}
	 812  	}
	 813  	return list, nil
	 814  }
	 815  
	 816  // FS converts fsys to a FileSystem implementation,
	 817  // for use with FileServer and NewFileTransport.
	 818  func FS(fsys fs.FS) FileSystem {
	 819  	return ioFS{fsys}
	 820  }
	 821  
	 822  // FileServer returns a handler that serves HTTP requests
	 823  // with the contents of the file system rooted at root.
	 824  //
	 825  // As a special case, the returned file server redirects any request
	 826  // ending in "/index.html" to the same path, without the final
	 827  // "index.html".
	 828  //
	 829  // To use the operating system's file system implementation,
	 830  // use http.Dir:
	 831  //
	 832  //		 http.Handle("/", http.FileServer(http.Dir("/tmp")))
	 833  //
	 834  // To use an fs.FS implementation, use http.FS to convert it:
	 835  //
	 836  //	http.Handle("/", http.FileServer(http.FS(fsys)))
	 837  //
	 838  func FileServer(root FileSystem) Handler {
	 839  	return &fileHandler{root}
	 840  }
	 841  
	 842  func (f *fileHandler) ServeHTTP(w ResponseWriter, r *Request) {
	 843  	upath := r.URL.Path
	 844  	if !strings.HasPrefix(upath, "/") {
	 845  		upath = "/" + upath
	 846  		r.URL.Path = upath
	 847  	}
	 848  	serveFile(w, r, f.root, path.Clean(upath), true)
	 849  }
	 850  
	 851  // httpRange specifies the byte range to be sent to the client.
	 852  type httpRange struct {
	 853  	start, length int64
	 854  }
	 855  
	 856  func (r httpRange) contentRange(size int64) string {
	 857  	return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
	 858  }
	 859  
	 860  func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
	 861  	return textproto.MIMEHeader{
	 862  		"Content-Range": {r.contentRange(size)},
	 863  		"Content-Type":	{contentType},
	 864  	}
	 865  }
	 866  
	 867  // parseRange parses a Range header string as per RFC 7233.
	 868  // errNoOverlap is returned if none of the ranges overlap.
	 869  func parseRange(s string, size int64) ([]httpRange, error) {
	 870  	if s == "" {
	 871  		return nil, nil // header not present
	 872  	}
	 873  	const b = "bytes="
	 874  	if !strings.HasPrefix(s, b) {
	 875  		return nil, errors.New("invalid range")
	 876  	}
	 877  	var ranges []httpRange
	 878  	noOverlap := false
	 879  	for _, ra := range strings.Split(s[len(b):], ",") {
	 880  		ra = textproto.TrimString(ra)
	 881  		if ra == "" {
	 882  			continue
	 883  		}
	 884  		i := strings.Index(ra, "-")
	 885  		if i < 0 {
	 886  			return nil, errors.New("invalid range")
	 887  		}
	 888  		start, end := textproto.TrimString(ra[:i]), textproto.TrimString(ra[i+1:])
	 889  		var r httpRange
	 890  		if start == "" {
	 891  			// If no start is specified, end specifies the
	 892  			// range start relative to the end of the file,
	 893  			// and we are dealing with <suffix-length>
	 894  			// which has to be a non-negative integer as per
	 895  			// RFC 7233 Section 2.1 "Byte-Ranges".
	 896  			if end == "" || end[0] == '-' {
	 897  				return nil, errors.New("invalid range")
	 898  			}
	 899  			i, err := strconv.ParseInt(end, 10, 64)
	 900  			if i < 0 || err != nil {
	 901  				return nil, errors.New("invalid range")
	 902  			}
	 903  			if i > size {
	 904  				i = size
	 905  			}
	 906  			r.start = size - i
	 907  			r.length = size - r.start
	 908  		} else {
	 909  			i, err := strconv.ParseInt(start, 10, 64)
	 910  			if err != nil || i < 0 {
	 911  				return nil, errors.New("invalid range")
	 912  			}
	 913  			if i >= size {
	 914  				// If the range begins after the size of the content,
	 915  				// then it does not overlap.
	 916  				noOverlap = true
	 917  				continue
	 918  			}
	 919  			r.start = i
	 920  			if end == "" {
	 921  				// If no end is specified, range extends to end of the file.
	 922  				r.length = size - r.start
	 923  			} else {
	 924  				i, err := strconv.ParseInt(end, 10, 64)
	 925  				if err != nil || r.start > i {
	 926  					return nil, errors.New("invalid range")
	 927  				}
	 928  				if i >= size {
	 929  					i = size - 1
	 930  				}
	 931  				r.length = i - r.start + 1
	 932  			}
	 933  		}
	 934  		ranges = append(ranges, r)
	 935  	}
	 936  	if noOverlap && len(ranges) == 0 {
	 937  		// The specified ranges did not overlap with the content.
	 938  		return nil, errNoOverlap
	 939  	}
	 940  	return ranges, nil
	 941  }
	 942  
	 943  // countingWriter counts how many bytes have been written to it.
	 944  type countingWriter int64
	 945  
	 946  func (w *countingWriter) Write(p []byte) (n int, err error) {
	 947  	*w += countingWriter(len(p))
	 948  	return len(p), nil
	 949  }
	 950  
	 951  // rangesMIMESize returns the number of bytes it takes to encode the
	 952  // provided ranges as a multipart response.
	 953  func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
	 954  	var w countingWriter
	 955  	mw := multipart.NewWriter(&w)
	 956  	for _, ra := range ranges {
	 957  		mw.CreatePart(ra.mimeHeader(contentType, contentSize))
	 958  		encSize += ra.length
	 959  	}
	 960  	mw.Close()
	 961  	encSize += int64(w)
	 962  	return
	 963  }
	 964  
	 965  func sumRangesSize(ranges []httpRange) (size int64) {
	 966  	for _, ra := range ranges {
	 967  		size += ra.length
	 968  	}
	 969  	return
	 970  }
	 971  

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