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  	"internal/safefilepath"
    13  	"io"
    14  	"io/fs"
    15  	"mime"
    16  	"mime/multipart"
    17  	"net/textproto"
    18  	"net/url"
    19  	"os"
    20  	"path"
    21  	"path/filepath"
    22  	"sort"
    23  	"strconv"
    24  	"strings"
    25  	"time"
    26  )
    27  
    28  // A Dir implements [FileSystem] using the native file system restricted to a
    29  // specific directory tree.
    30  //
    31  // While the [FileSystem.Open] method takes '/'-separated paths, a Dir's string
    32  // value is a filename on the native file system, not a URL, so it is separated
    33  // by [filepath.Separator], which isn't necessarily '/'.
    34  //
    35  // Note that Dir could expose sensitive files and directories. Dir will follow
    36  // symlinks pointing out of the directory tree, which can be especially dangerous
    37  // if serving from a directory in which users are able to create arbitrary symlinks.
    38  // Dir will also allow access to files and directories starting with a period,
    39  // which could expose sensitive directories like .git or sensitive files like
    40  // .htpasswd. To exclude files with a leading period, remove the files/directories
    41  // from the server or create a custom FileSystem implementation.
    42  //
    43  // An empty Dir is treated as ".".
    44  type Dir string
    45  
    46  // mapOpenError maps the provided non-nil error from opening name
    47  // to a possibly better non-nil error. In particular, it turns OS-specific errors
    48  // about opening files in non-directories into fs.ErrNotExist. See Issues 18984 and 49552.
    49  func mapOpenError(originalErr error, name string, sep rune, stat func(string) (fs.FileInfo, error)) error {
    50  	if errors.Is(originalErr, fs.ErrNotExist) || errors.Is(originalErr, fs.ErrPermission) {
    51  		return originalErr
    52  	}
    53  
    54  	parts := strings.Split(name, string(sep))
    55  	for i := range parts {
    56  		if parts[i] == "" {
    57  			continue
    58  		}
    59  		fi, err := stat(strings.Join(parts[:i+1], string(sep)))
    60  		if err != nil {
    61  			return originalErr
    62  		}
    63  		if !fi.IsDir() {
    64  			return fs.ErrNotExist
    65  		}
    66  	}
    67  	return originalErr
    68  }
    69  
    70  // Open implements [FileSystem] using [os.Open], opening files for reading rooted
    71  // and relative to the directory d.
    72  func (d Dir) Open(name string) (File, error) {
    73  	path, err := safefilepath.FromFS(path.Clean("/" + name))
    74  	if err != nil {
    75  		return nil, errors.New("http: invalid or unsafe file path")
    76  	}
    77  	dir := string(d)
    78  	if dir == "" {
    79  		dir = "."
    80  	}
    81  	fullName := filepath.Join(dir, path)
    82  	f, err := os.Open(fullName)
    83  	if err != nil {
    84  		return nil, mapOpenError(err, fullName, filepath.Separator, os.Stat)
    85  	}
    86  	return f, nil
    87  }
    88  
    89  // A FileSystem implements access to a collection of named files.
    90  // The elements in a file path are separated by slash ('/', U+002F)
    91  // characters, regardless of host operating system convention.
    92  // See the [FileServer] function to convert a FileSystem to a [Handler].
    93  //
    94  // This interface predates the [fs.FS] interface, which can be used instead:
    95  // the [FS] adapter function converts an fs.FS to a FileSystem.
    96  type FileSystem interface {
    97  	Open(name string) (File, error)
    98  }
    99  
   100  // A File is returned by a [FileSystem]'s Open method and can be
   101  // served by the [FileServer] implementation.
   102  //
   103  // The methods should behave the same as those on an [*os.File].
   104  type File interface {
   105  	io.Closer
   106  	io.Reader
   107  	io.Seeker
   108  	Readdir(count int) ([]fs.FileInfo, error)
   109  	Stat() (fs.FileInfo, error)
   110  }
   111  
   112  type anyDirs interface {
   113  	len() int
   114  	name(i int) string
   115  	isDir(i int) bool
   116  }
   117  
   118  type fileInfoDirs []fs.FileInfo
   119  
   120  func (d fileInfoDirs) len() int          { return len(d) }
   121  func (d fileInfoDirs) isDir(i int) bool  { return d[i].IsDir() }
   122  func (d fileInfoDirs) name(i int) string { return d[i].Name() }
   123  
   124  type dirEntryDirs []fs.DirEntry
   125  
   126  func (d dirEntryDirs) len() int          { return len(d) }
   127  func (d dirEntryDirs) isDir(i int) bool  { return d[i].IsDir() }
   128  func (d dirEntryDirs) name(i int) string { return d[i].Name() }
   129  
   130  func dirList(w ResponseWriter, r *Request, f File) {
   131  	// Prefer to use ReadDir instead of Readdir,
   132  	// because the former doesn't require calling
   133  	// Stat on every entry of a directory on Unix.
   134  	var dirs anyDirs
   135  	var err error
   136  	if d, ok := f.(fs.ReadDirFile); ok {
   137  		var list dirEntryDirs
   138  		list, err = d.ReadDir(-1)
   139  		dirs = list
   140  	} else {
   141  		var list fileInfoDirs
   142  		list, err = f.Readdir(-1)
   143  		dirs = list
   144  	}
   145  
   146  	if err != nil {
   147  		logf(r, "http: error reading directory: %v", err)
   148  		Error(w, "Error reading directory", StatusInternalServerError)
   149  		return
   150  	}
   151  	sort.Slice(dirs, func(i, j int) bool { return dirs.name(i) < dirs.name(j) })
   152  
   153  	w.Header().Set("Content-Type", "text/html; charset=utf-8")
   154  	fmt.Fprintf(w, "<pre>\n")
   155  	for i, n := 0, dirs.len(); i < n; i++ {
   156  		name := dirs.name(i)
   157  		if dirs.isDir(i) {
   158  			name += "/"
   159  		}
   160  		// name may contain '?' or '#', which must be escaped to remain
   161  		// part of the URL path, and not indicate the start of a query
   162  		// string or fragment.
   163  		url := url.URL{Path: name}
   164  		fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
   165  	}
   166  	fmt.Fprintf(w, "</pre>\n")
   167  }
   168  
   169  // ServeContent replies to the request using the content in the
   170  // provided ReadSeeker. The main benefit of ServeContent over [io.Copy]
   171  // is that it handles Range requests properly, sets the MIME type, and
   172  // handles If-Match, If-Unmodified-Since, If-None-Match, If-Modified-Since,
   173  // and If-Range requests.
   174  //
   175  // If the response's Content-Type header is not set, ServeContent
   176  // first tries to deduce the type from name's file extension and,
   177  // if that fails, falls back to reading the first block of the content
   178  // and passing it to [DetectContentType].
   179  // The name is otherwise unused; in particular it can be empty and is
   180  // never sent in the response.
   181  //
   182  // If modtime is not the zero time or Unix epoch, ServeContent
   183  // includes it in a Last-Modified header in the response. If the
   184  // request includes an If-Modified-Since header, ServeContent uses
   185  // modtime to decide whether the content needs to be sent at all.
   186  //
   187  // The content's Seek method must work: ServeContent uses
   188  // a seek to the end of the content to determine its size.
   189  //
   190  // If the caller has set w's ETag header formatted per RFC 7232, section 2.3,
   191  // ServeContent uses it to handle requests using If-Match, If-None-Match, or If-Range.
   192  //
   193  // Note that [*os.File] implements the [io.ReadSeeker] interface.
   194  func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, content io.ReadSeeker) {
   195  	sizeFunc := func() (int64, error) {
   196  		size, err := content.Seek(0, io.SeekEnd)
   197  		if err != nil {
   198  			return 0, errSeeker
   199  		}
   200  		_, err = content.Seek(0, io.SeekStart)
   201  		if err != nil {
   202  			return 0, errSeeker
   203  		}
   204  		return size, nil
   205  	}
   206  	serveContent(w, req, name, modtime, sizeFunc, content)
   207  }
   208  
   209  // errSeeker is returned by ServeContent's sizeFunc when the content
   210  // doesn't seek properly. The underlying Seeker's error text isn't
   211  // included in the sizeFunc reply so it's not sent over HTTP to end
   212  // users.
   213  var errSeeker = errors.New("seeker can't seek")
   214  
   215  // errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
   216  // all of the byte-range-spec values is greater than the content size.
   217  var errNoOverlap = errors.New("invalid range: failed to overlap")
   218  
   219  // if name is empty, filename is unknown. (used for mime type, before sniffing)
   220  // if modtime.IsZero(), modtime is unknown.
   221  // content must be seeked to the beginning of the file.
   222  // The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
   223  func serveContent(w ResponseWriter, r *Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
   224  	setLastModified(w, modtime)
   225  	done, rangeReq := checkPreconditions(w, r, modtime)
   226  	if done {
   227  		return
   228  	}
   229  
   230  	code := StatusOK
   231  
   232  	// If Content-Type isn't set, use the file's extension to find it, but
   233  	// if the Content-Type is unset explicitly, do not sniff the type.
   234  	ctypes, haveType := w.Header()["Content-Type"]
   235  	var ctype string
   236  	if !haveType {
   237  		ctype = mime.TypeByExtension(filepath.Ext(name))
   238  		if ctype == "" {
   239  			// read a chunk to decide between utf-8 text and binary
   240  			var buf [sniffLen]byte
   241  			n, _ := io.ReadFull(content, buf[:])
   242  			ctype = DetectContentType(buf[:n])
   243  			_, err := content.Seek(0, io.SeekStart) // rewind to output whole file
   244  			if err != nil {
   245  				Error(w, "seeker can't seek", StatusInternalServerError)
   246  				return
   247  			}
   248  		}
   249  		w.Header().Set("Content-Type", ctype)
   250  	} else if len(ctypes) > 0 {
   251  		ctype = ctypes[0]
   252  	}
   253  
   254  	size, err := sizeFunc()
   255  	if err != nil {
   256  		Error(w, err.Error(), StatusInternalServerError)
   257  		return
   258  	}
   259  	if size < 0 {
   260  		// Should never happen but just to be sure
   261  		Error(w, "negative content size computed", StatusInternalServerError)
   262  		return
   263  	}
   264  
   265  	// handle Content-Range header.
   266  	sendSize := size
   267  	var sendContent io.Reader = content
   268  	ranges, err := parseRange(rangeReq, size)
   269  	switch err {
   270  	case nil:
   271  	case errNoOverlap:
   272  		if size == 0 {
   273  			// Some clients add a Range header to all requests to
   274  			// limit the size of the response. If the file is empty,
   275  			// ignore the range header and respond with a 200 rather
   276  			// than a 416.
   277  			ranges = nil
   278  			break
   279  		}
   280  		w.Header().Set("Content-Range", fmt.Sprintf("bytes */%d", size))
   281  		fallthrough
   282  	default:
   283  		Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
   284  		return
   285  	}
   286  
   287  	if sumRangesSize(ranges) > size {
   288  		// The total number of bytes in all the ranges
   289  		// is larger than the size of the file by
   290  		// itself, so this is probably an attack, or a
   291  		// dumb client. Ignore the range request.
   292  		ranges = nil
   293  	}
   294  	switch {
   295  	case len(ranges) == 1:
   296  		// RFC 7233, Section 4.1:
   297  		// "If a single part is being transferred, the server
   298  		// generating the 206 response MUST generate a
   299  		// Content-Range header field, describing what range
   300  		// of the selected representation is enclosed, and a
   301  		// payload consisting of the range.
   302  		// ...
   303  		// A server MUST NOT generate a multipart response to
   304  		// a request for a single range, since a client that
   305  		// does not request multiple parts might not support
   306  		// multipart responses."
   307  		ra := ranges[0]
   308  		if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
   309  			Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
   310  			return
   311  		}
   312  		sendSize = ra.length
   313  		code = StatusPartialContent
   314  		w.Header().Set("Content-Range", ra.contentRange(size))
   315  	case len(ranges) > 1:
   316  		sendSize = rangesMIMESize(ranges, ctype, size)
   317  		code = StatusPartialContent
   318  
   319  		pr, pw := io.Pipe()
   320  		mw := multipart.NewWriter(pw)
   321  		w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
   322  		sendContent = pr
   323  		defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
   324  		go func() {
   325  			for _, ra := range ranges {
   326  				part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
   327  				if err != nil {
   328  					pw.CloseWithError(err)
   329  					return
   330  				}
   331  				if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
   332  					pw.CloseWithError(err)
   333  					return
   334  				}
   335  				if _, err := io.CopyN(part, content, ra.length); err != nil {
   336  					pw.CloseWithError(err)
   337  					return
   338  				}
   339  			}
   340  			mw.Close()
   341  			pw.Close()
   342  		}()
   343  	}
   344  
   345  	w.Header().Set("Accept-Ranges", "bytes")
   346  
   347  	// We should be able to unconditionally set the Content-Length here.
   348  	//
   349  	// However, there is a pattern observed in the wild that this breaks:
   350  	// The user wraps the ResponseWriter in one which gzips data written to it,
   351  	// and sets "Content-Encoding: gzip".
   352  	//
   353  	// The user shouldn't be doing this; the serveContent path here depends
   354  	// on serving seekable data with a known length. If you want to compress
   355  	// on the fly, then you shouldn't be using ServeFile/ServeContent, or
   356  	// you should compress the entire file up-front and provide a seekable
   357  	// view of the compressed data.
   358  	//
   359  	// However, since we've observed this pattern in the wild, and since
   360  	// setting Content-Length here breaks code that mostly-works today,
   361  	// skip setting Content-Length if the user set Content-Encoding.
   362  	//
   363  	// If this is a range request, always set Content-Length.
   364  	// If the user isn't changing the bytes sent in the ResponseWrite,
   365  	// the Content-Length will be correct.
   366  	// If the user is changing the bytes sent, then the range request wasn't
   367  	// going to work properly anyway and we aren't worse off.
   368  	//
   369  	// A possible future improvement on this might be to look at the type
   370  	// of the ResponseWriter, and always set Content-Length if it's one
   371  	// that we recognize.
   372  	if len(ranges) > 0 || w.Header().Get("Content-Encoding") == "" {
   373  		w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
   374  	}
   375  	w.WriteHeader(code)
   376  
   377  	if r.Method != "HEAD" {
   378  		io.CopyN(w, sendContent, sendSize)
   379  	}
   380  }
   381  
   382  // scanETag determines if a syntactically valid ETag is present at s. If so,
   383  // the ETag and remaining text after consuming ETag is returned. Otherwise,
   384  // it returns "", "".
   385  func scanETag(s string) (etag string, remain string) {
   386  	s = textproto.TrimString(s)
   387  	start := 0
   388  	if strings.HasPrefix(s, "W/") {
   389  		start = 2
   390  	}
   391  	if len(s[start:]) < 2 || s[start] != '"' {
   392  		return "", ""
   393  	}
   394  	// ETag is either W/"text" or "text".
   395  	// See RFC 7232 2.3.
   396  	for i := start + 1; i < len(s); i++ {
   397  		c := s[i]
   398  		switch {
   399  		// Character values allowed in ETags.
   400  		case c == 0x21 || c >= 0x23 && c <= 0x7E || c >= 0x80:
   401  		case c == '"':
   402  			return s[:i+1], s[i+1:]
   403  		default:
   404  			return "", ""
   405  		}
   406  	}
   407  	return "", ""
   408  }
   409  
   410  // etagStrongMatch reports whether a and b match using strong ETag comparison.
   411  // Assumes a and b are valid ETags.
   412  func etagStrongMatch(a, b string) bool {
   413  	return a == b && a != "" && a[0] == '"'
   414  }
   415  
   416  // etagWeakMatch reports whether a and b match using weak ETag comparison.
   417  // Assumes a and b are valid ETags.
   418  func etagWeakMatch(a, b string) bool {
   419  	return strings.TrimPrefix(a, "W/") == strings.TrimPrefix(b, "W/")
   420  }
   421  
   422  // condResult is the result of an HTTP request precondition check.
   423  // See https://tools.ietf.org/html/rfc7232 section 3.
   424  type condResult int
   425  
   426  const (
   427  	condNone condResult = iota
   428  	condTrue
   429  	condFalse
   430  )
   431  
   432  func checkIfMatch(w ResponseWriter, r *Request) condResult {
   433  	im := r.Header.Get("If-Match")
   434  	if im == "" {
   435  		return condNone
   436  	}
   437  	for {
   438  		im = textproto.TrimString(im)
   439  		if len(im) == 0 {
   440  			break
   441  		}
   442  		if im[0] == ',' {
   443  			im = im[1:]
   444  			continue
   445  		}
   446  		if im[0] == '*' {
   447  			return condTrue
   448  		}
   449  		etag, remain := scanETag(im)
   450  		if etag == "" {
   451  			break
   452  		}
   453  		if etagStrongMatch(etag, w.Header().get("Etag")) {
   454  			return condTrue
   455  		}
   456  		im = remain
   457  	}
   458  
   459  	return condFalse
   460  }
   461  
   462  func checkIfUnmodifiedSince(r *Request, modtime time.Time) condResult {
   463  	ius := r.Header.Get("If-Unmodified-Since")
   464  	if ius == "" || isZeroTime(modtime) {
   465  		return condNone
   466  	}
   467  	t, err := ParseTime(ius)
   468  	if err != nil {
   469  		return condNone
   470  	}
   471  
   472  	// The Last-Modified header truncates sub-second precision so
   473  	// the modtime needs to be truncated too.
   474  	modtime = modtime.Truncate(time.Second)
   475  	if ret := modtime.Compare(t); ret <= 0 {
   476  		return condTrue
   477  	}
   478  	return condFalse
   479  }
   480  
   481  func checkIfNoneMatch(w ResponseWriter, r *Request) condResult {
   482  	inm := r.Header.get("If-None-Match")
   483  	if inm == "" {
   484  		return condNone
   485  	}
   486  	buf := inm
   487  	for {
   488  		buf = textproto.TrimString(buf)
   489  		if len(buf) == 0 {
   490  			break
   491  		}
   492  		if buf[0] == ',' {
   493  			buf = buf[1:]
   494  			continue
   495  		}
   496  		if buf[0] == '*' {
   497  			return condFalse
   498  		}
   499  		etag, remain := scanETag(buf)
   500  		if etag == "" {
   501  			break
   502  		}
   503  		if etagWeakMatch(etag, w.Header().get("Etag")) {
   504  			return condFalse
   505  		}
   506  		buf = remain
   507  	}
   508  	return condTrue
   509  }
   510  
   511  func checkIfModifiedSince(r *Request, modtime time.Time) condResult {
   512  	if r.Method != "GET" && r.Method != "HEAD" {
   513  		return condNone
   514  	}
   515  	ims := r.Header.Get("If-Modified-Since")
   516  	if ims == "" || isZeroTime(modtime) {
   517  		return condNone
   518  	}
   519  	t, err := ParseTime(ims)
   520  	if err != nil {
   521  		return condNone
   522  	}
   523  	// The Last-Modified header truncates sub-second precision so
   524  	// the modtime needs to be truncated too.
   525  	modtime = modtime.Truncate(time.Second)
   526  	if ret := modtime.Compare(t); ret <= 0 {
   527  		return condFalse
   528  	}
   529  	return condTrue
   530  }
   531  
   532  func checkIfRange(w ResponseWriter, r *Request, modtime time.Time) condResult {
   533  	if r.Method != "GET" && r.Method != "HEAD" {
   534  		return condNone
   535  	}
   536  	ir := r.Header.get("If-Range")
   537  	if ir == "" {
   538  		return condNone
   539  	}
   540  	etag, _ := scanETag(ir)
   541  	if etag != "" {
   542  		if etagStrongMatch(etag, w.Header().Get("Etag")) {
   543  			return condTrue
   544  		} else {
   545  			return condFalse
   546  		}
   547  	}
   548  	// The If-Range value is typically the ETag value, but it may also be
   549  	// the modtime date. See golang.org/issue/8367.
   550  	if modtime.IsZero() {
   551  		return condFalse
   552  	}
   553  	t, err := ParseTime(ir)
   554  	if err != nil {
   555  		return condFalse
   556  	}
   557  	if t.Unix() == modtime.Unix() {
   558  		return condTrue
   559  	}
   560  	return condFalse
   561  }
   562  
   563  var unixEpochTime = time.Unix(0, 0)
   564  
   565  // isZeroTime reports whether t is obviously unspecified (either zero or Unix()=0).
   566  func isZeroTime(t time.Time) bool {
   567  	return t.IsZero() || t.Equal(unixEpochTime)
   568  }
   569  
   570  func setLastModified(w ResponseWriter, modtime time.Time) {
   571  	if !isZeroTime(modtime) {
   572  		w.Header().Set("Last-Modified", modtime.UTC().Format(TimeFormat))
   573  	}
   574  }
   575  
   576  func writeNotModified(w ResponseWriter) {
   577  	// RFC 7232 section 4.1:
   578  	// a sender SHOULD NOT generate representation metadata other than the
   579  	// above listed fields unless said metadata exists for the purpose of
   580  	// guiding cache updates (e.g., Last-Modified might be useful if the
   581  	// response does not have an ETag field).
   582  	h := w.Header()
   583  	delete(h, "Content-Type")
   584  	delete(h, "Content-Length")
   585  	delete(h, "Content-Encoding")
   586  	if h.Get("Etag") != "" {
   587  		delete(h, "Last-Modified")
   588  	}
   589  	w.WriteHeader(StatusNotModified)
   590  }
   591  
   592  // checkPreconditions evaluates request preconditions and reports whether a precondition
   593  // resulted in sending StatusNotModified or StatusPreconditionFailed.
   594  func checkPreconditions(w ResponseWriter, r *Request, modtime time.Time) (done bool, rangeHeader string) {
   595  	// This function carefully follows RFC 7232 section 6.
   596  	ch := checkIfMatch(w, r)
   597  	if ch == condNone {
   598  		ch = checkIfUnmodifiedSince(r, modtime)
   599  	}
   600  	if ch == condFalse {
   601  		w.WriteHeader(StatusPreconditionFailed)
   602  		return true, ""
   603  	}
   604  	switch checkIfNoneMatch(w, r) {
   605  	case condFalse:
   606  		if r.Method == "GET" || r.Method == "HEAD" {
   607  			writeNotModified(w)
   608  			return true, ""
   609  		} else {
   610  			w.WriteHeader(StatusPreconditionFailed)
   611  			return true, ""
   612  		}
   613  	case condNone:
   614  		if checkIfModifiedSince(r, modtime) == condFalse {
   615  			writeNotModified(w)
   616  			return true, ""
   617  		}
   618  	}
   619  
   620  	rangeHeader = r.Header.get("Range")
   621  	if rangeHeader != "" && checkIfRange(w, r, modtime) == condFalse {
   622  		rangeHeader = ""
   623  	}
   624  	return false, rangeHeader
   625  }
   626  
   627  // name is '/'-separated, not filepath.Separator.
   628  func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirect bool) {
   629  	const indexPage = "/index.html"
   630  
   631  	// redirect .../index.html to .../
   632  	// can't use Redirect() because that would make the path absolute,
   633  	// which would be a problem running under StripPrefix
   634  	if strings.HasSuffix(r.URL.Path, indexPage) {
   635  		localRedirect(w, r, "./")
   636  		return
   637  	}
   638  
   639  	f, err := fs.Open(name)
   640  	if err != nil {
   641  		msg, code := toHTTPError(err)
   642  		Error(w, msg, code)
   643  		return
   644  	}
   645  	defer f.Close()
   646  
   647  	d, err := f.Stat()
   648  	if err != nil {
   649  		msg, code := toHTTPError(err)
   650  		Error(w, msg, code)
   651  		return
   652  	}
   653  
   654  	if redirect {
   655  		// redirect to canonical path: / at end of directory url
   656  		// r.URL.Path always begins with /
   657  		url := r.URL.Path
   658  		if d.IsDir() {
   659  			if url[len(url)-1] != '/' {
   660  				localRedirect(w, r, path.Base(url)+"/")
   661  				return
   662  			}
   663  		} else {
   664  			if url[len(url)-1] == '/' {
   665  				localRedirect(w, r, "../"+path.Base(url))
   666  				return
   667  			}
   668  		}
   669  	}
   670  
   671  	if d.IsDir() {
   672  		url := r.URL.Path
   673  		// redirect if the directory name doesn't end in a slash
   674  		if url == "" || url[len(url)-1] != '/' {
   675  			localRedirect(w, r, path.Base(url)+"/")
   676  			return
   677  		}
   678  
   679  		// use contents of index.html for directory, if present
   680  		index := strings.TrimSuffix(name, "/") + indexPage
   681  		ff, err := fs.Open(index)
   682  		if err == nil {
   683  			defer ff.Close()
   684  			dd, err := ff.Stat()
   685  			if err == nil {
   686  				d = dd
   687  				f = ff
   688  			}
   689  		}
   690  	}
   691  
   692  	// Still a directory? (we didn't find an index.html file)
   693  	if d.IsDir() {
   694  		if checkIfModifiedSince(r, d.ModTime()) == condFalse {
   695  			writeNotModified(w)
   696  			return
   697  		}
   698  		setLastModified(w, d.ModTime())
   699  		dirList(w, r, f)
   700  		return
   701  	}
   702  
   703  	// serveContent will check modification time
   704  	sizeFunc := func() (int64, error) { return d.Size(), nil }
   705  	serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, f)
   706  }
   707  
   708  // toHTTPError returns a non-specific HTTP error message and status code
   709  // for a given non-nil error value. It's important that toHTTPError does not
   710  // actually return err.Error(), since msg and httpStatus are returned to users,
   711  // and historically Go's ServeContent always returned just "404 Not Found" for
   712  // all errors. We don't want to start leaking information in error messages.
   713  func toHTTPError(err error) (msg string, httpStatus int) {
   714  	if errors.Is(err, fs.ErrNotExist) {
   715  		return "404 page not found", StatusNotFound
   716  	}
   717  	if errors.Is(err, fs.ErrPermission) {
   718  		return "403 Forbidden", StatusForbidden
   719  	}
   720  	// Default:
   721  	return "500 Internal Server Error", StatusInternalServerError
   722  }
   723  
   724  // localRedirect gives a Moved Permanently response.
   725  // It does not convert relative paths to absolute paths like Redirect does.
   726  func localRedirect(w ResponseWriter, r *Request, newPath string) {
   727  	if q := r.URL.RawQuery; q != "" {
   728  		newPath += "?" + q
   729  	}
   730  	w.Header().Set("Location", newPath)
   731  	w.WriteHeader(StatusMovedPermanently)
   732  }
   733  
   734  // ServeFile replies to the request with the contents of the named
   735  // file or directory.
   736  //
   737  // If the provided file or directory name is a relative path, it is
   738  // interpreted relative to the current directory and may ascend to
   739  // parent directories. If the provided name is constructed from user
   740  // input, it should be sanitized before calling ServeFile.
   741  //
   742  // As a precaution, ServeFile will reject requests where r.URL.Path
   743  // contains a ".." path element; this protects against callers who
   744  // might unsafely use [filepath.Join] on r.URL.Path without sanitizing
   745  // it and then use that filepath.Join result as the name argument.
   746  //
   747  // As another special case, ServeFile redirects any request where r.URL.Path
   748  // ends in "/index.html" to the same path, without the final
   749  // "index.html". To avoid such redirects either modify the path or
   750  // use [ServeContent].
   751  //
   752  // Outside of those two special cases, ServeFile does not use
   753  // r.URL.Path for selecting the file or directory to serve; only the
   754  // file or directory provided in the name argument is used.
   755  func ServeFile(w ResponseWriter, r *Request, name string) {
   756  	if containsDotDot(r.URL.Path) {
   757  		// Too many programs use r.URL.Path to construct the argument to
   758  		// serveFile. Reject the request under the assumption that happened
   759  		// here and ".." may not be wanted.
   760  		// Note that name might not contain "..", for example if code (still
   761  		// incorrectly) used filepath.Join(myDir, r.URL.Path).
   762  		Error(w, "invalid URL path", StatusBadRequest)
   763  		return
   764  	}
   765  	dir, file := filepath.Split(name)
   766  	serveFile(w, r, Dir(dir), file, false)
   767  }
   768  
   769  // ServeFileFS replies to the request with the contents
   770  // of the named file or directory from the file system fsys.
   771  //
   772  // If the provided file or directory name is a relative path, it is
   773  // interpreted relative to the current directory and may ascend to
   774  // parent directories. If the provided name is constructed from user
   775  // input, it should be sanitized before calling [ServeFile].
   776  //
   777  // As a precaution, ServeFile will reject requests where r.URL.Path
   778  // contains a ".." path element; this protects against callers who
   779  // might unsafely use [filepath.Join] on r.URL.Path without sanitizing
   780  // it and then use that filepath.Join result as the name argument.
   781  //
   782  // As another special case, ServeFile redirects any request where r.URL.Path
   783  // ends in "/index.html" to the same path, without the final
   784  // "index.html". To avoid such redirects either modify the path or
   785  // use ServeContent.
   786  //
   787  // Outside of those two special cases, ServeFile does not use
   788  // r.URL.Path for selecting the file or directory to serve; only the
   789  // file or directory provided in the name argument is used.
   790  func ServeFileFS(w ResponseWriter, r *Request, fsys fs.FS, name string) {
   791  	if containsDotDot(r.URL.Path) {
   792  		// Too many programs use r.URL.Path to construct the argument to
   793  		// serveFile. Reject the request under the assumption that happened
   794  		// here and ".." may not be wanted.
   795  		// Note that name might not contain "..", for example if code (still
   796  		// incorrectly) used filepath.Join(myDir, r.URL.Path).
   797  		Error(w, "invalid URL path", StatusBadRequest)
   798  		return
   799  	}
   800  	serveFile(w, r, FS(fsys), name, false)
   801  }
   802  
   803  func containsDotDot(v string) bool {
   804  	if !strings.Contains(v, "..") {
   805  		return false
   806  	}
   807  	for _, ent := range strings.FieldsFunc(v, isSlashRune) {
   808  		if ent == ".." {
   809  			return true
   810  		}
   811  	}
   812  	return false
   813  }
   814  
   815  func isSlashRune(r rune) bool { return r == '/' || r == '\\' }
   816  
   817  type fileHandler struct {
   818  	root FileSystem
   819  }
   820  
   821  type ioFS struct {
   822  	fsys fs.FS
   823  }
   824  
   825  type ioFile struct {
   826  	file fs.File
   827  }
   828  
   829  func (f ioFS) Open(name string) (File, error) {
   830  	if name == "/" {
   831  		name = "."
   832  	} else {
   833  		name = strings.TrimPrefix(name, "/")
   834  	}
   835  	file, err := f.fsys.Open(name)
   836  	if err != nil {
   837  		return nil, mapOpenError(err, name, '/', func(path string) (fs.FileInfo, error) {
   838  			return fs.Stat(f.fsys, path)
   839  		})
   840  	}
   841  	return ioFile{file}, nil
   842  }
   843  
   844  func (f ioFile) Close() error               { return f.file.Close() }
   845  func (f ioFile) Read(b []byte) (int, error) { return f.file.Read(b) }
   846  func (f ioFile) Stat() (fs.FileInfo, error) { return f.file.Stat() }
   847  
   848  var errMissingSeek = errors.New("io.File missing Seek method")
   849  var errMissingReadDir = errors.New("io.File directory missing ReadDir method")
   850  
   851  func (f ioFile) Seek(offset int64, whence int) (int64, error) {
   852  	s, ok := f.file.(io.Seeker)
   853  	if !ok {
   854  		return 0, errMissingSeek
   855  	}
   856  	return s.Seek(offset, whence)
   857  }
   858  
   859  func (f ioFile) ReadDir(count int) ([]fs.DirEntry, error) {
   860  	d, ok := f.file.(fs.ReadDirFile)
   861  	if !ok {
   862  		return nil, errMissingReadDir
   863  	}
   864  	return d.ReadDir(count)
   865  }
   866  
   867  func (f ioFile) Readdir(count int) ([]fs.FileInfo, error) {
   868  	d, ok := f.file.(fs.ReadDirFile)
   869  	if !ok {
   870  		return nil, errMissingReadDir
   871  	}
   872  	var list []fs.FileInfo
   873  	for {
   874  		dirs, err := d.ReadDir(count - len(list))
   875  		for _, dir := range dirs {
   876  			info, err := dir.Info()
   877  			if err != nil {
   878  				// Pretend it doesn't exist, like (*os.File).Readdir does.
   879  				continue
   880  			}
   881  			list = append(list, info)
   882  		}
   883  		if err != nil {
   884  			return list, err
   885  		}
   886  		if count < 0 || len(list) >= count {
   887  			break
   888  		}
   889  	}
   890  	return list, nil
   891  }
   892  
   893  // FS converts fsys to a [FileSystem] implementation,
   894  // for use with [FileServer] and [NewFileTransport].
   895  // The files provided by fsys must implement [io.Seeker].
   896  func FS(fsys fs.FS) FileSystem {
   897  	return ioFS{fsys}
   898  }
   899  
   900  // FileServer returns a handler that serves HTTP requests
   901  // with the contents of the file system rooted at root.
   902  //
   903  // As a special case, the returned file server redirects any request
   904  // ending in "/index.html" to the same path, without the final
   905  // "index.html".
   906  //
   907  // To use the operating system's file system implementation,
   908  // use [http.Dir]:
   909  //
   910  //	http.Handle("/", http.FileServer(http.Dir("/tmp")))
   911  //
   912  // To use an [fs.FS] implementation, use [http.FileServerFS] instead.
   913  func FileServer(root FileSystem) Handler {
   914  	return &fileHandler{root}
   915  }
   916  
   917  // FileServerFS returns a handler that serves HTTP requests
   918  // with the contents of the file system fsys.
   919  //
   920  // As a special case, the returned file server redirects any request
   921  // ending in "/index.html" to the same path, without the final
   922  // "index.html".
   923  //
   924  //	http.Handle("/", http.FileServerFS(fsys))
   925  func FileServerFS(root fs.FS) Handler {
   926  	return FileServer(FS(root))
   927  }
   928  
   929  func (f *fileHandler) ServeHTTP(w ResponseWriter, r *Request) {
   930  	upath := r.URL.Path
   931  	if !strings.HasPrefix(upath, "/") {
   932  		upath = "/" + upath
   933  		r.URL.Path = upath
   934  	}
   935  	serveFile(w, r, f.root, path.Clean(upath), true)
   936  }
   937  
   938  // httpRange specifies the byte range to be sent to the client.
   939  type httpRange struct {
   940  	start, length int64
   941  }
   942  
   943  func (r httpRange) contentRange(size int64) string {
   944  	return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
   945  }
   946  
   947  func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
   948  	return textproto.MIMEHeader{
   949  		"Content-Range": {r.contentRange(size)},
   950  		"Content-Type":  {contentType},
   951  	}
   952  }
   953  
   954  // parseRange parses a Range header string as per RFC 7233.
   955  // errNoOverlap is returned if none of the ranges overlap.
   956  func parseRange(s string, size int64) ([]httpRange, error) {
   957  	if s == "" {
   958  		return nil, nil // header not present
   959  	}
   960  	const b = "bytes="
   961  	if !strings.HasPrefix(s, b) {
   962  		return nil, errors.New("invalid range")
   963  	}
   964  	var ranges []httpRange
   965  	noOverlap := false
   966  	for _, ra := range strings.Split(s[len(b):], ",") {
   967  		ra = textproto.TrimString(ra)
   968  		if ra == "" {
   969  			continue
   970  		}
   971  		start, end, ok := strings.Cut(ra, "-")
   972  		if !ok {
   973  			return nil, errors.New("invalid range")
   974  		}
   975  		start, end = textproto.TrimString(start), textproto.TrimString(end)
   976  		var r httpRange
   977  		if start == "" {
   978  			// If no start is specified, end specifies the
   979  			// range start relative to the end of the file,
   980  			// and we are dealing with <suffix-length>
   981  			// which has to be a non-negative integer as per
   982  			// RFC 7233 Section 2.1 "Byte-Ranges".
   983  			if end == "" || end[0] == '-' {
   984  				return nil, errors.New("invalid range")
   985  			}
   986  			i, err := strconv.ParseInt(end, 10, 64)
   987  			if i < 0 || err != nil {
   988  				return nil, errors.New("invalid range")
   989  			}
   990  			if i > size {
   991  				i = size
   992  			}
   993  			r.start = size - i
   994  			r.length = size - r.start
   995  		} else {
   996  			i, err := strconv.ParseInt(start, 10, 64)
   997  			if err != nil || i < 0 {
   998  				return nil, errors.New("invalid range")
   999  			}
  1000  			if i >= size {
  1001  				// If the range begins after the size of the content,
  1002  				// then it does not overlap.
  1003  				noOverlap = true
  1004  				continue
  1005  			}
  1006  			r.start = i
  1007  			if end == "" {
  1008  				// If no end is specified, range extends to end of the file.
  1009  				r.length = size - r.start
  1010  			} else {
  1011  				i, err := strconv.ParseInt(end, 10, 64)
  1012  				if err != nil || r.start > i {
  1013  					return nil, errors.New("invalid range")
  1014  				}
  1015  				if i >= size {
  1016  					i = size - 1
  1017  				}
  1018  				r.length = i - r.start + 1
  1019  			}
  1020  		}
  1021  		ranges = append(ranges, r)
  1022  	}
  1023  	if noOverlap && len(ranges) == 0 {
  1024  		// The specified ranges did not overlap with the content.
  1025  		return nil, errNoOverlap
  1026  	}
  1027  	return ranges, nil
  1028  }
  1029  
  1030  // countingWriter counts how many bytes have been written to it.
  1031  type countingWriter int64
  1032  
  1033  func (w *countingWriter) Write(p []byte) (n int, err error) {
  1034  	*w += countingWriter(len(p))
  1035  	return len(p), nil
  1036  }
  1037  
  1038  // rangesMIMESize returns the number of bytes it takes to encode the
  1039  // provided ranges as a multipart response.
  1040  func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
  1041  	var w countingWriter
  1042  	mw := multipart.NewWriter(&w)
  1043  	for _, ra := range ranges {
  1044  		mw.CreatePart(ra.mimeHeader(contentType, contentSize))
  1045  		encSize += ra.length
  1046  	}
  1047  	mw.Close()
  1048  	encSize += int64(w)
  1049  	return
  1050  }
  1051  
  1052  func sumRangesSize(ranges []httpRange) (size int64) {
  1053  	for _, ra := range ranges {
  1054  		size += ra.length
  1055  	}
  1056  	return
  1057  }
  1058  

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