summaryrefslogtreecommitdiff
path: root/modules/caddyhttp/fileserver/staticfiles.go
blob: 761dfc3cbfdd9f727c5e9eac633657e431cac1d6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package fileserver

import (
	"fmt"
	"html/template"
	weakrand "math/rand"
	"mime"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/caddyserver/caddy/v2"
	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
)

func init() {
	weakrand.Seed(time.Now().UnixNano())

	caddy.RegisterModule(caddy.Module{
		Name: "http.handlers.file_server",
		New:  func() interface{} { return new(FileServer) },
	})
}

// FileServer implements a static file server responder for Caddy.
type FileServer struct {
	Root       string   `json:"root,omitempty"` // default is current directory
	Hide       []string `json:"hide,omitempty"`
	IndexNames []string `json:"index_names,omitempty"`
	Browse     *Browse  `json:"browse,omitempty"`
	// TODO: Content negotiation
}

// Provision sets up the static files responder.
func (fsrv *FileServer) Provision(ctx caddy.Context) error {
	if fsrv.IndexNames == nil {
		fsrv.IndexNames = defaultIndexNames
	}

	if fsrv.Browse != nil {
		var tpl *template.Template
		var err error
		if fsrv.Browse.TemplateFile != "" {
			tpl, err = template.ParseFiles(fsrv.Browse.TemplateFile)
			if err != nil {
				return fmt.Errorf("parsing browse template file: %v", err)
			}
		} else {
			tpl, err = template.New("default_listing").Parse(defaultBrowseTemplate)
			if err != nil {
				return fmt.Errorf("parsing default browse template: %v", err)
			}
		}
		fsrv.Browse.template = tpl
	}

	return nil
}

func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, _ caddyhttp.Handler) error {
	repl := r.Context().Value(caddy.ReplacerCtxKey).(caddy.Replacer)

	filesToHide := fsrv.transformHidePaths(repl)

	root := repl.ReplaceAll(fsrv.Root, "")
	suffix := repl.ReplaceAll(r.URL.Path, "")
	filename := sanitizedPathJoin(root, suffix)

	// get information about the file
	info, err := os.Stat(filename)
	if err != nil {
		err = mapDirOpenError(err, filename)
		if os.IsNotExist(err) {
			return caddyhttp.Error(http.StatusNotFound, err)
		} else if os.IsPermission(err) {
			return caddyhttp.Error(http.StatusForbidden, err)
		}
		// TODO: treat this as resource exhaustion like with os.Open? Or unnecessary here?
		return caddyhttp.Error(http.StatusInternalServerError, err)
	}

	// if the request mapped to a directory, see if
	// there is an index file we can serve
	if info.IsDir() && len(fsrv.IndexNames) > 0 {
		for _, indexPage := range fsrv.IndexNames {
			indexPath := sanitizedPathJoin(filename, indexPage)
			if fileHidden(indexPath, filesToHide) {
				// pretend this file doesn't exist
				continue
			}

			indexInfo, err := os.Stat(indexPath)
			if err != nil {
				continue
			}

			// we found an index file that might work,
			// so rewrite the request path
			r.URL.Path = path.Join(r.URL.Path, indexPage)

			info = indexInfo
			filename = indexPath
			break
		}
	}

	// if still referencing a directory, delegate
	// to browse or return an error
	if info.IsDir() {
		if fsrv.Browse != nil && !fileHidden(filename, filesToHide) {
			return fsrv.serveBrowse(filename, w, r)
		}
		return caddyhttp.Error(http.StatusNotFound, nil)
	}

	// TODO: content negotiation (brotli sidecar files, etc...)

	// one last check to ensure the file isn't hidden (we might
	// have changed the filename from when we last checked)
	if fileHidden(filename, filesToHide) {
		return caddyhttp.Error(http.StatusNotFound, nil)
	}

	// open the file
	file, err := fsrv.openFile(filename, w)
	if err != nil {
		return err
	}
	defer file.Close()

	// set the ETag - note that a conditional If-None-Match request is handled
	// by http.ServeContent below, which checks against this ETag value
	w.Header().Set("ETag", calculateEtag(info))

	if w.Header().Get("Content-Type") == "" {
		mtyp := mime.TypeByExtension(filepath.Ext(filename))
		if mtyp == "" {
			// do not allow Go to sniff the content-type; see
			// https://www.youtube.com/watch?v=8t8JYpt0egE
			// TODO: Consider writing a default mime type of application/octet-stream - this is secure but violates spec
			w.Header()["Content-Type"] = nil
		} else {
			w.Header().Set("Content-Type", mtyp)
		}
	}

	// let the standard library do what it does best; note, however,
	// that errors generated by ServeContent are written immediately
	// to the response, so we cannot handle them (but errors there
	// are rare)
	http.ServeContent(w, r, info.Name(), info.ModTime(), file)

	return nil
}

// openFile opens the file at the given filename. If there was an error,
// the response is configured to inform the client how to best handle it
// and a well-described handler error is returned (do not wrap the
// returned error value).
func (fsrv *FileServer) openFile(filename string, w http.ResponseWriter) (*os.File, error) {
	file, err := os.Open(filename)
	if err != nil {
		err = mapDirOpenError(err, filename)
		if os.IsNotExist(err) {
			return nil, caddyhttp.Error(http.StatusNotFound, err)
		} else if os.IsPermission(err) {
			return nil, caddyhttp.Error(http.StatusForbidden, err)
		}
		// maybe the server is under load and ran out of file descriptors?
		// have client wait arbitrary seconds to help prevent a stampede
		backoff := weakrand.Intn(maxBackoff-minBackoff) + minBackoff
		w.Header().Set("Retry-After", strconv.Itoa(backoff))
		return nil, caddyhttp.Error(http.StatusServiceUnavailable, err)
	}
	return file, nil
}

// 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 golang/go#18984.
// Adapted from the Go standard library; originally written by Nathaniel Caza.
// https://go-review.googlesource.com/c/go/+/36635/
// https://go-review.googlesource.com/c/go/+/36804/
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
}

// transformHidePaths performs replacements for all the elements of
// fsrv.Hide and returns a new list of the transformed values.
func (fsrv *FileServer) transformHidePaths(repl caddy.Replacer) []string {
	hide := make([]string, len(fsrv.Hide))
	for i := range fsrv.Hide {
		hide[i] = repl.ReplaceAll(fsrv.Hide[i], "")
	}
	return hide
}

// sanitizedPathJoin performs filepath.Join(root, reqPath) that
// is safe against directory traversal attacks. It uses logic
// similar to that in the Go standard library, specifically
// in the implementation of http.Dir. The root is assumed to
// be a trusted path, but reqPath is not.
func sanitizedPathJoin(root, reqPath string) string {
	// TODO: Caddy 1 uses this:
	// prevent absolute path access on Windows, e.g. http://localhost:5000/C:\Windows\notepad.exe
	// if runtime.GOOS == "windows" && len(reqPath) > 0 && filepath.IsAbs(reqPath[1:]) {
	// TODO.
	// }

	// TODO: whereas std lib's http.Dir.Open() uses this:
	// if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
	// 	return nil, errors.New("http: invalid character in file path")
	// }

	// TODO: see https://play.golang.org/p/oh77BiVQFti for another thing to consider

	if root == "" {
		root = "."
	}
	return filepath.Join(root, filepath.FromSlash(path.Clean("/"+reqPath)))
}

// fileHidden returns true if filename is hidden
// according to the hide list.
func fileHidden(filename string, hide []string) bool {
	nameOnly := filepath.Base(filename)
	sep := string(filepath.Separator)

	for _, h := range hide {
		// assuming h is a glob/shell-like pattern,
		// use it to compare the whole file path;
		// but if there is no separator in h, then
		// just compare against the file's name
		compare := filename
		if !strings.Contains(h, sep) {
			compare = nameOnly
		}

		hidden, err := filepath.Match(h, compare)
		if err != nil {
			// malformed pattern; fallback by checking prefix
			if strings.HasPrefix(filename, h) {
				return true
			}
		}
		if hidden {
			// file name or path matches hide pattern
			return true
		}
	}

	return false
}

// calculateEtag produces a strong etag by default, although, for
// efficiency reasons, it does not actually consume the contents
// of the file to make a hash of all the bytes. ¯\_(ツ)_/¯
// Prefix the etag with "W/" to convert it into a weak etag.
// See: https://tools.ietf.org/html/rfc7232#section-2.3
func calculateEtag(d os.FileInfo) string {
	t := strconv.FormatInt(d.ModTime().Unix(), 36)
	s := strconv.FormatInt(d.Size(), 36)
	return `"` + t + s + `"`
}

var defaultIndexNames = []string{"index.html"}

const minBackoff, maxBackoff = 2, 5

// Interface guards
var (
	_ caddy.Provisioner           = (*FileServer)(nil)
	_ caddyhttp.MiddlewareHandler = (*FileServer)(nil)
)