// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// HTTP file system request handler
package http
import (
"errors"
"fmt"
"io"
"mime"
"mime/multipart"
"net/textproto"
"net/url"
"os"
"path"
"path/filepath"
"sort"
"strconv"
"strings"
"time"
)
// A Dir implements FileSystem using the native file system restricted to a
// specific directory tree.
//
// While the FileSystem.Open method takes '/'-separated paths, a Dir's string
// value is a filename on the native file system, not a URL, so it is separated
// by filepath.Separator, which isn't necessarily '/'.
//
// Note that Dir will allow access to files and directories starting with a
// period, which could expose sensitive directories like a .git directory or
// sensitive files like .htpasswd. To exclude files with a leading period,
// remove the files/directories from the server or create a custom FileSystem
// implementation.
//
// An empty Dir is treated as ".".
type Dir string
// mapDirOpenError maps the provided non-nil error from opening name
// to a possibly better non-nil error. In particular, it turns OS-specific errors
// about opening files in non-directories into os.ErrNotExist. See Issue 18984.
func mapDirOpenError(originalErr error, name string) error {
if os.IsNotExist(originalErr) || os.IsPermission(originalErr) {
return originalErr
}
parts := strings.Split(name, string(filepath.Separator))
for i := range parts {
if parts[i] == "" {
continue
}
fi, err := os.Stat(strings.Join(parts[:i+1], string(filepath.Separator)))
if err != nil {
return originalErr
}
if !fi.IsDir() {
return os.ErrNotExist
}
}
return originalErr
}
// Open implements FileSystem using os.Open, opening files for reading rooted
// and relative to the directory d.
func (d Dir) Open(name string) (File, error) {
if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
return nil, errors.New("http: invalid character in file path")
}
dir := string(d)
if dir == "" {
dir = "."
}
fullName := filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name)))
f, err := os.Open(fullName)
if err != nil {
return nil, mapDirOpenError(err, fullName)
}
return f, nil
}
// A FileSystem implements access to a collection of named files.
// The elements in a file path are separated by slash ('/', U+002F)
// characters, regardless of host operating system convention.
type FileSystem interface {
Open(name string) (File, error)
}
// A File is returned by a FileSystem's Open method and can be
// served by the FileServer implementation.
//
// The methods should behave the same as those on an *os.File.
type File interface {
io.Closer
io.Reader
io.Seeker
Readdir(count int) ([]os.FileInfo, error)
Stat() (os.FileInfo, error)
}
func dirList(w ResponseWriter, r *Request, f File) {
dirs, err := f.Readdir(-1)
if err != nil {
logf(r, "http: error reading directory: %v", err)
Error(w, "Error reading directory", StatusInternalServerError)
return
}
sort.Slice(dirs, func(i, j int) bool { return dirs[i].Name() < dirs[j].Name() })
w.Header().Set("Content-Type", "text/html; charset=utf-8")
fmt.Fprintf(w, "<pre>\n")
for _, d := range dirs {
name := d.Name()
if d.IsDir() {
name += "/"
}
// name may contain '?' or '#', which must be escaped to remain
// part of the URL path, and not indicate the start of a query
// string or fragment.
url := url.URL{Path: name}
fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
}
fmt.Fprintf(w, "</pre>\n")
}
// ServeContent replies to the request using the content in the
// provided ReadSeeker. The main benefit of ServeContent over io.Copy
// is that it handles Range requests properly, sets the MIME type, and
// handles If-Match, If-Unmodified-Since, If-None-Match, If-Modified-Since,
// and If-Range requests.
//
// If the response's Content-Type header is not set, ServeContent
// first tries to deduce the type from name's file extension and,
// if that fails, falls back to reading the first block of the content
// and passing it to DetectContentType.
// The name is otherwise unused; in particular it can be empty and is
// never sent in the response.
//
// If modtime is not the zero time or Unix epoch, ServeContent
// includes it in a Last-Modified header in the response. If the
// request includes an If-Modified-Since header, ServeContent uses
// modtime to decide whether the content needs to be sent at all.
//
// The content's Seek method must work: ServeContent uses
// a seek to the end of the content to determine its size.
//
// If the caller has set w's ETag header formatted per RFC 7232, section 2.3,
// ServeContent uses it to handle requests using If-Match, If-None-Match, or If-Range.
//
// Note that *os.File implements the io.ReadSeeker interface.
func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time, content io.ReadSeeker) {
sizeFunc := func() (int64, error) {
size, err := content.Seek(0, io.SeekEnd)
if err != nil {
return 0, errSeeker
}
_, err = content.Seek(0, io.SeekStart)
if err != nil {
return 0, errSeeker
}
return size, nil
}
serveContent(w, req, name, modtime, sizeFunc, content)
}
// errSeeker is returned by ServeContent's sizeFunc when the content
// doesn't seek properly. The underlying Seeker's error text isn't
// included in the sizeFunc reply so it's not sent over HTTP to end
// users.
var errSeeker = errors.New("seeker can't seek")
// errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
// all of the byte-range-spec values is greater than the content size.
var errNoOverlap = errors.New("invalid range: failed to overlap")
// if name is empty, filename is unknown. (used for mime type, before sniffing)
// if modtime.IsZero(), modtime is unknown.
// content must be seeked to the beginning of the file.
// The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
func serveContent(w ResponseWriter, r *Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
setLastModified(w, modtime)
done, rangeReq := checkPreconditions(w, r, modtime)
if done {
return
}
code := StatusOK
// If Content-Type isn't set, use the file's extension to find it, but
// if the Content-Type is unset explicitly, do not sniff the type.
ctypes, haveType := w.Header()["Content-Type"]
var ctype string
if !haveType {
ctype = mime.TypeByExtension(filepath.Ext(name))
if ctype == "" {
// read a chunk to decide between utf-8 text and binary
var buf [sniffLen]byte
n, _ := io.ReadFull(content, buf[:])
ctype = DetectContentType(buf[:n])
_, err := content.Seek(0, io.SeekStart) // rewind to output whole file
if err != nil {
Error(w, "seeker can't seek", StatusInternalServerError)
return
}
}
w.Header().Set("Content-Type", ctype)
} else if len(ctypes) > 0 {
ctype = ctypes[0]
}
size, err := sizeFunc()
if err != nil {
Error(w, err.Error(), StatusInternalServerError)
return
}
// handle Content-Range header.
sendSize := size
var sendContent io.Reader = content
if size >= 0 {
ranges, err := parseRange(rangeReq, size)
if err != nil {
if err == errNoOverlap {
w.Header().Set("Content-Range", fmt.Sprintf("bytes */%d", size))
}
Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
return
}
if sumRangesSize(ranges) > size {
// The total number of bytes in all the ranges
// is larger than the size of the file by
// itself, so this is probably an attack, or a
// dumb client. Ignore the range request.
ranges = nil
}
switch {
case len(ranges) == 1:
// RFC 7233, Section 4.1:
// "If a single part is being transferred, the server
// generating the 206 response MUST generate a
// Content-Range header field, describing what range
// of the selected representation is enclosed, and a
// payload consisting of the range.
// ...
// A server MUST NOT generate a multipart response to
// a request for a single range, since a client that
// does not request multiple parts might not support
// multipart responses."
ra := ranges[0]
if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
return
}
sendSize = ra.length
code = StatusPartialContent
w.Header().Set("Content-Range", ra.contentRange(size))
case len(ranges) > 1:
sendSize = rangesMIMESize(ranges, ctype, size)
code = StatusPartialContent
pr, pw := io.Pipe()
mw := multipart.NewWriter(pw)
w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
sendContent = pr
defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
go func() {
for _, ra := range ranges {
part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
if err != nil {
pw.CloseWithError(err)
return
}
if _, err := content.Seek(ra.start, io.SeekStart); err != nil {
pw.CloseWithError(err)
return
}
if _, err := io.CopyN(part, content, ra.length); err != nil {
pw.CloseWithError(err)
return
}
}
mw.Close()
pw.Close()
}()
}
w.Header().Set("Accept-Ranges", "bytes")
if w.Header().Get("Content-Encoding") == "" {
w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
}
}
w.WriteHeader(code)
if r.Method != "HEAD" {
io.CopyN(w, sendContent, sendSize)
}
}
// scanETag determines if a syntactically valid ETag is present at s. If so,
// the ETag and remaining text after consuming ETag is returned. Otherwise,
// it returns "", "".
func scanETag(s string) (etag string, remain string) {
s = textproto.TrimString(s)
start := 0
if strings.HasPrefix(s, "W/") {
start = 2
}
if len(s[start:]) < 2 || s[start] != '"' {
return "", ""
}
// ETag is either W/"text" or "text".
// See RFC 7232 2.3.
for i := start + 1; i < len(s); i++ {
c := s[i]
switch {
// Character values allowed in ETags.
case c == 0x21 || c >= 0x23 && c <= 0x7E || c >= 0x80:
case c == '"':
return s[:i+1], s[i+1:]
default:
return "", ""
}
}
return "", ""
}
// etagStrongMatch reports whether a and b match using strong ETag comparison.
// Assumes a and b are valid ETags.
func etagStrongMatch(a, b string) bool {
return a == b && a != "" && a[0] == '"'
}
// etagWeakMatch reports whether a and b match using weak ETag comparison.
// Assumes a and b are valid ETags.
func etagWeakMatch(a, b string) bool {
return strings.TrimPrefix(a, "W/") == strings.TrimPrefix(b, "W/")
}
// condResult is the result of an HTTP request precondition check.
// See https://tools.ietf.org/html/rfc7232 section 3.
type condResult int
const (
condNone condResult = iota
condTrue
condFalse
)
func checkIfMatch(w ResponseWriter, r *Request) condResult {
im := r.Header.Get("If-Match")
if im == "" {
return condNone
}
for {
im = textproto.TrimString(im)
if len(im) == 0 {
break
}
if im[0] == ',' {
im = im[1:]
continue
}
if im[0] == '*' {
return condTrue
}
etag, remain := scanETag(im)
if etag == "" {
break
}
if etagStrongMatch(etag, w.Header().get("Etag")) {
return condTrue
}
im = remain
}
return condFalse
}
func checkIfUnmodifiedSince(r *Request, modtime time.Time) condResult {
ius := r.Header.Get("If-Unmodified-Since")
if ius == "" || isZeroTime(modtime) {
return condNone
}
if t, err := ParseTime(ius); err == nil {
// The Date-Modified header truncates sub-second precision, so
// use mtime < t+1s instead of mtime <= t to check for unmodified.
if modtime.Before(t.Add(1 * time.Second)) {
return condTrue
}
return condFalse
}
return condNone
}
func checkIfNoneMatch(w ResponseWriter, r *Request) condResult {
inm := r.Header.get("If-None-Match")
if inm == "" {
return condNone
}
buf := inm
for {
buf = textproto.TrimString(buf)
if len(buf) == 0 {
break
}
if buf[0] == ',' {
buf = buf[1:]
}
if buf[0] == '*' {
return condFalse
}
etag, remain := scanETag(buf)
if etag == "" {
break
}
if etagWeakMatch(etag, w.Header().get("Etag")) {
return condFalse
}
buf = remain
}
return condTrue
}
func checkIfModifiedSince(r *Request, modtime time.Time) condResult {
if r.Method != "GET" && r.Method != "HEAD" {
return condNone
}
ims := r.Header.Get("If-Modified-Since")
if ims == "" || isZeroTime(modtime) {
return condNone
}
t, err := ParseTime(ims)
if err != nil {
return condNone
}
// The Date-Modified header truncates sub-second precision, so
// use mtime < t+1s instead of mtime <= t to check for unmodified.
if modtime.Before(t.Add(1 * time.Second)) {
return condFalse
}
return condTrue
}
func checkIfRange(w ResponseWriter, r *Request, modtime time.Time) condResult {
if r.Method != "GET" && r.Method != "HEAD" {
return condNone
}
ir := r.Header.get("If-Range")
if ir == "" {
return condNone
}
etag, _ := scanETag(ir)
if etag != "" {
if etagStrongMatch(etag, w.Header().Get("Etag")) {
return condTrue
} else {
return condFalse
}
}
// The If-Range value is typically the ETag value, but it may also be
// the modtime date. See golang.org/issue/8367.
if modtime.IsZero() {
return condFalse
}
t, err := ParseTime(ir)
if err != nil {
return condFalse
}
if t.Unix() == modtime.Unix() {
return condTrue
}
return condFalse
}
var unixEpochTime = time.Unix(0, 0)
// isZeroTime reports whether t is obviously unspecified (either zero or Unix()=0).
func isZeroTime(t time.Time) bool {
return t.IsZero() || t.Equal(unixEpochTime)
}
func setLastModified(w ResponseWriter, modtime time.Time) {
if !isZeroTime(modtime) {
w.Header().Set("Last-Modified", modtime.UTC().Format(TimeFormat))
}
}
func writeNotModified(w ResponseWriter) {
// RFC 7232 section 4.1:
// a sender SHOULD NOT generate representation metadata other than the
// above listed fields unless said metadata exists for the purpose of
// guiding cache updates (e.g., Last-Modified might be useful if the
// response does not have an ETag field).
h := w.Header()
delete(h, "Content-Type")
delete(h, "Content-Length")
if h.Get("Etag") != "" {
delete(h, "Last-Modified")
}
w.WriteHeader(StatusNotModified)
}
// checkPreconditions evaluates request preconditions and reports whether a precondition
// resulted in sending StatusNotModified or StatusPreconditionFailed.
func checkPreconditions(w ResponseWriter, r *Request, modtime time.Time) (done bool, rangeHeader string) {
// This function carefully follows RFC 7232 section 6.
ch := checkIfMatch(w, r)
if ch == condNone {
ch = checkIfUnmodifiedSince(r, modtime)
}
if ch == condFalse {
w.WriteHeader(StatusPreconditionFailed)
return true, ""
}
switch checkIfNoneMatch(w, r) {
case condFalse:
if r.Method == "GET" || r.Method == "HEAD" {
writeNotModified(w)
return true, ""
} else {
w.WriteHeader(StatusPreconditionFailed)
return true, ""
}
case condNone:
if checkIfModifiedSince(r, modtime) == condFalse {
writeNotModified(w)
return true, ""
}
}
rangeHeader = r.Header.get("Range")
if rangeHeader != "" && checkIfRange(w, r, modtime) == condFalse {
rangeHeader = ""
}
return false, rangeHeader
}
// name is '/'-separated, not filepath.Separator.
func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirect bool) {
const indexPage = "/index.html"
// redirect .../index.html to .../
// can't use Redirect() because that would make the path absolute,
// which would be a problem running under StripPrefix
if strings.HasSuffix(r.URL.Path, indexPage) {
localRedirect(w, r, "./")
return
}
f, err := fs.Open(name)
if err != nil {
msg, code := toHTTPError(err)
Error(w, msg, code)
return
}
defer f.Close()
d, err := f.Stat()
if err != nil {
msg, code := toHTTPError(err)
Error(w, msg, code)
return
}
if redirect {
// redirect to canonical path: / at end of directory url
// r.URL.Path always begins with /
url := r.URL.Path
if d.IsDir() {
if url[len(url)-1] != '/' {
localRedirect(w, r, path.Base(url)+"/")
return
}
} else {
if url[len(url)-1] == '/' {
localRedirect(w, r, "../"+path.Base(url))
return
}
}
}
// redirect if the directory name doesn't end in a slash
if d.IsDir() {
url := r.URL.Path
if url[len(url)-1] != '/' {
localRedirect(w, r, path.Base(url)+"/")
return
}
}
// use contents of index.html for directory, if present
if d.IsDir() {
index := strings.TrimSuffix(name, "/") + indexPage
ff, err := fs.Open(index)
if err == nil {
defer ff.Close()
dd, err := ff.Stat()
if err == nil {
name = index
d = dd
f = ff
}
}
}
// Still a directory? (we didn't find an index.html file)
if d.IsDir() {
if checkIfModifiedSince(r, d.ModTime()) == condFalse {
writeNotModified(w)
return
}
w.Header().Set("Last-Modified", d.ModTime().UTC().Format(TimeFormat))
dirList(w, r, f)
return
}
// serveContent will check modification time
sizeFunc := func() (int64, error) { return d.Size(), nil }
serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, f)
}
// toHTTPError returns a non-specific HTTP error message and status code
// for a given non-nil error value. It's important that toHTTPError does not
// actually return err.Error(), since msg and httpStatus are returned to users,
// and historically Go's ServeContent always returned just "404 Not Found" for
// all errors. We don't want to start leaking information in error messages.
func toHTTPError(err error) (msg string, httpStatus int) {
if os.IsNotExist(err) {
return "404 page not found", StatusNotFound
}
if os.IsPermission(err) {
return "403 Forbidden", StatusForbidden
}
// Default:
return "500 Internal Server Error", StatusInternalServerError
}
// localRedirect gives a Moved Permanently response.
// It does not convert relative paths to absolute paths like Redirect does.
func localRedirect(w ResponseWriter, r *Request, newPath string) {
if q := r.URL.RawQuery; q != "" {
newPath += "?" + q
}
w.Header().Set("Location", newPath)
w.WriteHeader(StatusMovedPermanently)
}
// ServeFile replies to the request with the contents of the named
// file or directory.
//
// If the provided file or directory name is a relative path, it is
// interpreted relative to the current directory and may ascend to
// parent directories. If the provided name is constructed from user
// input, it should be sanitized before calling ServeFile.
//
// As a precaution, ServeFile will reject requests where r.URL.Path
// contains a ".." path element; this protects against callers who
// might unsafely use filepath.Join on r.URL.Path without sanitizing
// it and then use that filepath.Join result as the name argument.
//
// As another special case, ServeFile redirects any request where r.URL.Path
// ends in "/index.html" to the same path, without the final
// "index.html". To avoid such redirects either modify the path or
// use ServeContent.
//
// Outside of those two special cases, ServeFile does not use
// r.URL.Path for selecting the file or directory to serve; only the
// file or directory provided in the name argument is used.
func ServeFile(w ResponseWriter, r *Request, name string) {
if containsDotDot(r.URL.Path) {
// Too many programs use r.URL.Path to construct the argument to
// serveFile. Reject the request under the assumption that happened
// here and ".." may not be wanted.
// Note that name might not contain "..", for example if code (still
// incorrectly) used filepath.Join(myDir, r.URL.Path).
Error(w, "invalid URL path", StatusBadRequest)
return
}
dir, file := filepath.Split(name)
serveFile(w, r, Dir(dir), file, false)
}
func containsDotDot(v string) bool {
if !strings.Contains(v, "..") {
return false
}
for _, ent := range strings.FieldsFunc(v, isSlashRune) {
if ent == ".." {
return true
}
}
return false
}
func isSlashRune(r rune) bool { return r == '/' || r == '\\' }
type fileHandler struct {
root FileSystem
}
// FileServer returns a handler that serves HTTP requests
// with the contents of the file system rooted at root.
//
// To use the operating system's file system implementation,
// use http.Dir:
//
// http.Handle("/", http.FileServer(http.Dir("/tmp")))
//
// As a special case, the returned file server redirects any request
// ending in "/index.html" to the same path, without the final
// "index.html".
func FileServer(root FileSystem) Handler {
return &fileHandler{root}
}
func (f *fileHandler) ServeHTTP(w ResponseWriter, r *Request) {
upath := r.URL.Path
if !strings.HasPrefix(upath, "/") {
upath = "/" + upath
r.URL.Path = upath
}
serveFile(w, r, f.root, path.Clean(upath), true)
}
// httpRange specifies the byte range to be sent to the client.
type httpRange struct {
start, length int64
}
func (r httpRange) contentRange(size int64) string {
return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
}
func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
return textproto.MIMEHeader{
"Content-Range": {r.contentRange(size)},
"Content-Type": {contentType},
}
}
// parseRange parses a Range header string as per RFC 7233.
// errNoOverlap is returned if none of the ranges overlap.
func parseRange(s string, size int64) ([]httpRange, error) {
if s == "" {
return nil, nil // header not present
}
const b = "bytes="
if !strings.HasPrefix(s, b) {
return nil, errors.New("invalid range")
}
var ranges []httpRange
noOverlap := false
for _, ra := range strings.Split(s[len(b):], ",") {
ra = strings.TrimSpace(ra)
if ra == "" {
continue
}
i := strings.Index(ra, "-")
if i < 0 {
return nil, errors.New("invalid range")
}
start, end := strings.TrimSpace(ra[:i]), strings.TrimSpace(ra[i+1:])
var r httpRange
if start == "" {
// If no start is specified, end specifies the
// range start relative to the end of the file.
i, err := strconv.ParseInt(end, 10, 64)
if err != nil {
return nil, errors.New("invalid range")
}
if i > size {
i = size
}
r.start = size - i
r.length = size - r.start
} else {
i, err := strconv.ParseInt(start, 10, 64)
if err != nil || i < 0 {
return nil, errors.New("invalid range")
}
if i >= size {
// If the range begins after the size of the content,
// then it does not overlap.
noOverlap = true
continue
}
r.start = i
if end == "" {
// If no end is specified, range extends to end of the file.
r.length = size - r.start
} else {
i, err := strconv.ParseInt(end, 10, 64)
if err != nil || r.start > i {
return nil, errors.New("invalid range")
}
if i >= size {
i = size - 1
}
r.length = i - r.start + 1
}
}
ranges = append(ranges, r)
}
if noOverlap && len(ranges) == 0 {
// The specified ranges did not overlap with the content.
return nil, errNoOverlap
}
return ranges, nil
}
// countingWriter counts how many bytes have been written to it.
type countingWriter int64
func (w *countingWriter) Write(p []byte) (n int, err error) {
*w += countingWriter(len(p))
return len(p), nil
}
// rangesMIMESize returns the number of bytes it takes to encode the
// provided ranges as a multipart response.
func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
var w countingWriter
mw := multipart.NewWriter(&w)
for _, ra := range ranges {
mw.CreatePart(ra.mimeHeader(contentType, contentSize))
encSize += ra.length
}
mw.Close()
encSize += int64(w)
return
}
func sumRangesSize(ranges []httpRange) (size int64) {
for _, ra := range ranges {
size += ra.length
}
return
}
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