1 // Copyright 2020 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 // Package embed provides access to files embedded in the running Go program. 6 // 7 // Go source files that import "embed" can use the //go:embed directive 8 // to initialize a variable of type string, []byte, or FS with the contents of 9 // files read from the package directory or subdirectories at compile time. 10 // 11 // For example, here are three ways to embed a file named hello.txt 12 // and then print its contents at run time. 13 // 14 // Embedding one file into a string: 15 // 16 // import _ "embed" 17 // 18 // //go:embed hello.txt 19 // var s string 20 // print(s) 21 // 22 // Embedding one file into a slice of bytes: 23 // 24 // import _ "embed" 25 // 26 // //go:embed hello.txt 27 // var b []byte 28 // print(string(b)) 29 // 30 // Embedded one or more files into a file system: 31 // 32 // import "embed" 33 // 34 // //go:embed hello.txt 35 // var f embed.FS 36 // data, _ := f.ReadFile("hello.txt") 37 // print(string(data)) 38 // 39 // Directives 40 // 41 // A //go:embed directive above a variable declaration specifies which files to embed, 42 // using one or more path.Match patterns. 43 // 44 // The directive must immediately precede a line containing the declaration of a single variable. 45 // Only blank lines and ‘//’ line comments are permitted between the directive and the declaration. 46 // 47 // The type of the variable must be a string type, or a slice of a byte type, 48 // or FS (or an alias of FS). 49 // 50 // For example: 51 // 52 // package server 53 // 54 // import "embed" 55 // 56 // // content holds our static web server content. 57 // //go:embed image/* template/* 58 // //go:embed html/index.html 59 // var content embed.FS 60 // 61 // The Go build system will recognize the directives and arrange for the declared variable 62 // (in the example above, content) to be populated with the matching files from the file system. 63 // 64 // The //go:embed directive accepts multiple space-separated patterns for 65 // brevity, but it can also be repeated, to avoid very long lines when there are 66 // many patterns. The patterns are interpreted relative to the package directory 67 // containing the source file. The path separator is a forward slash, even on 68 // Windows systems. Patterns may not contain ‘.’ or ‘..’ or empty path elements, 69 // nor may they begin or end with a slash. To match everything in the current 70 // directory, use ‘*’ instead of ‘.’. To allow for naming files with spaces in 71 // their names, patterns can be written as Go double-quoted or back-quoted 72 // string literals. 73 // 74 // If a pattern names a directory, all files in the subtree rooted at that directory are 75 // embedded (recursively), except that files with names beginning with ‘.’ or ‘_’ 76 // are excluded. So the variable in the above example is almost equivalent to: 77 // 78 // // content is our static web server content. 79 // //go:embed image template html/index.html 80 // var content embed.FS 81 // 82 // The difference is that ‘image/*’ embeds ‘image/.tempfile’ while ‘image’ does not. 83 // 84 // The //go:embed directive can be used with both exported and unexported variables, 85 // depending on whether the package wants to make the data available to other packages. 86 // It can only be used with global variables at package scope, 87 // not with local variables. 88 // 89 // Patterns must not match files outside the package's module, such as ‘.git/*’ or symbolic links. 90 // Matches for empty directories are ignored. After that, each pattern in a //go:embed line 91 // must match at least one file or non-empty directory. 92 // 93 // If any patterns are invalid or have invalid matches, the build will fail. 94 // 95 // Strings and Bytes 96 // 97 // The //go:embed line for a variable of type string or []byte can have only a single pattern, 98 // and that pattern can match only a single file. The string or []byte is initialized with 99 // the contents of that file. 100 // 101 // The //go:embed directive requires importing "embed", even when using a string or []byte. 102 // In source files that don't refer to embed.FS, use a blank import (import _ "embed"). 103 // 104 // File Systems 105 // 106 // For embedding a single file, a variable of type string or []byte is often best. 107 // The FS type enables embedding a tree of files, such as a directory of static 108 // web server content, as in the example above. 109 // 110 // FS implements the io/fs package's FS interface, so it can be used with any package that 111 // understands file systems, including net/http, text/template, and html/template. 112 // 113 // For example, given the content variable in the example above, we can write: 114 // 115 // http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.FS(content)))) 116 // 117 // template.ParseFS(content, "*.tmpl") 118 // 119 // Tools 120 // 121 // To support tools that analyze Go packages, the patterns found in //go:embed lines 122 // are available in “go list” output. See the EmbedPatterns, TestEmbedPatterns, 123 // and XTestEmbedPatterns fields in the “go help list” output. 124 // 125 package embed 126 127 import ( 128 "errors" 129 "io" 130 "io/fs" 131 "time" 132 ) 133 134 // An FS is a read-only collection of files, usually initialized with a //go:embed directive. 135 // When declared without a //go:embed directive, an FS is an empty file system. 136 // 137 // An FS is a read-only value, so it is safe to use from multiple goroutines 138 // simultaneously and also safe to assign values of type FS to each other. 139 // 140 // FS implements fs.FS, so it can be used with any package that understands 141 // file system interfaces, including net/http, text/template, and html/template. 142 // 143 // See the package documentation for more details about initializing an FS. 144 type FS struct { 145 // The compiler knows the layout of this struct. 146 // See cmd/compile/internal/staticdata's WriteEmbed. 147 // 148 // The files list is sorted by name but not by simple string comparison. 149 // Instead, each file's name takes the form "dir/elem" or "dir/elem/". 150 // The optional trailing slash indicates that the file is itself a directory. 151 // The files list is sorted first by dir (if dir is missing, it is taken to be ".") 152 // and then by base, so this list of files: 153 // 154 // p 155 // q/ 156 // q/r 157 // q/s/ 158 // q/s/t 159 // q/s/u 160 // q/v 161 // w 162 // 163 // is actually sorted as: 164 // 165 // p # dir=. elem=p 166 // q/ # dir=. elem=q 167 // w/ # dir=. elem=w 168 // q/r # dir=q elem=r 169 // q/s/ # dir=q elem=s 170 // q/v # dir=q elem=v 171 // q/s/t # dir=q/s elem=t 172 // q/s/u # dir=q/s elem=u 173 // 174 // This order brings directory contents together in contiguous sections 175 // of the list, allowing a directory read to use binary search to find 176 // the relevant sequence of entries. 177 files *[]file 178 } 179 180 // split splits the name into dir and elem as described in the 181 // comment in the FS struct above. isDir reports whether the 182 // final trailing slash was present, indicating that name is a directory. 183 func split(name string) (dir, elem string, isDir bool) { 184 if name[len(name)-1] == '/' { 185 isDir = true 186 name = name[:len(name)-1] 187 } 188 i := len(name) - 1 189 for i >= 0 && name[i] != '/' { 190 i-- 191 } 192 if i < 0 { 193 return ".", name, isDir 194 } 195 return name[:i], name[i+1:], isDir 196 } 197 198 // trimSlash trims a trailing slash from name, if present, 199 // returning the possibly shortened name. 200 func trimSlash(name string) string { 201 if len(name) > 0 && name[len(name)-1] == '/' { 202 return name[:len(name)-1] 203 } 204 return name 205 } 206 207 var ( 208 _ fs.ReadDirFS = FS{} 209 _ fs.ReadFileFS = FS{} 210 ) 211 212 // A file is a single file in the FS. 213 // It implements fs.FileInfo and fs.DirEntry. 214 type file struct { 215 // The compiler knows the layout of this struct. 216 // See cmd/compile/internal/staticdata's WriteEmbed. 217 name string 218 data string 219 hash [16]byte // truncated SHA256 hash 220 } 221 222 var ( 223 _ fs.FileInfo = (*file)(nil) 224 _ fs.DirEntry = (*file)(nil) 225 ) 226 227 func (f *file) Name() string { _, elem, _ := split(f.name); return elem } 228 func (f *file) Size() int64 { return int64(len(f.data)) } 229 func (f *file) ModTime() time.Time { return time.Time{} } 230 func (f *file) IsDir() bool { _, _, isDir := split(f.name); return isDir } 231 func (f *file) Sys() interface{} { return nil } 232 func (f *file) Type() fs.FileMode { return f.Mode().Type() } 233 func (f *file) Info() (fs.FileInfo, error) { return f, nil } 234 235 func (f *file) Mode() fs.FileMode { 236 if f.IsDir() { 237 return fs.ModeDir | 0555 238 } 239 return 0444 240 } 241 242 // dotFile is a file for the root directory, 243 // which is omitted from the files list in a FS. 244 var dotFile = &file{name: "./"} 245 246 // lookup returns the named file, or nil if it is not present. 247 func (f FS) lookup(name string) *file { 248 if !fs.ValidPath(name) { 249 // The compiler should never emit a file with an invalid name, 250 // so this check is not strictly necessary (if name is invalid, 251 // we shouldn't find a match below), but it's a good backstop anyway. 252 return nil 253 } 254 if name == "." { 255 return dotFile 256 } 257 if f.files == nil { 258 return nil 259 } 260 261 // Binary search to find where name would be in the list, 262 // and then check if name is at that position. 263 dir, elem, _ := split(name) 264 files := *f.files 265 i := sortSearch(len(files), func(i int) bool { 266 idir, ielem, _ := split(files[i].name) 267 return idir > dir || idir == dir && ielem >= elem 268 }) 269 if i < len(files) && trimSlash(files[i].name) == name { 270 return &files[i] 271 } 272 return nil 273 } 274 275 // readDir returns the list of files corresponding to the directory dir. 276 func (f FS) readDir(dir string) []file { 277 if f.files == nil { 278 return nil 279 } 280 // Binary search to find where dir starts and ends in the list 281 // and then return that slice of the list. 282 files := *f.files 283 i := sortSearch(len(files), func(i int) bool { 284 idir, _, _ := split(files[i].name) 285 return idir >= dir 286 }) 287 j := sortSearch(len(files), func(j int) bool { 288 jdir, _, _ := split(files[j].name) 289 return jdir > dir 290 }) 291 return files[i:j] 292 } 293 294 // Open opens the named file for reading and returns it as an fs.File. 295 func (f FS) Open(name string) (fs.File, error) { 296 file := f.lookup(name) 297 if file == nil { 298 return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist} 299 } 300 if file.IsDir() { 301 return &openDir{file, f.readDir(name), 0}, nil 302 } 303 return &openFile{file, 0}, nil 304 } 305 306 // ReadDir reads and returns the entire named directory. 307 func (f FS) ReadDir(name string) ([]fs.DirEntry, error) { 308 file, err := f.Open(name) 309 if err != nil { 310 return nil, err 311 } 312 dir, ok := file.(*openDir) 313 if !ok { 314 return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("not a directory")} 315 } 316 list := make([]fs.DirEntry, len(dir.files)) 317 for i := range list { 318 list[i] = &dir.files[i] 319 } 320 return list, nil 321 } 322 323 // ReadFile reads and returns the content of the named file. 324 func (f FS) ReadFile(name string) ([]byte, error) { 325 file, err := f.Open(name) 326 if err != nil { 327 return nil, err 328 } 329 ofile, ok := file.(*openFile) 330 if !ok { 331 return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("is a directory")} 332 } 333 return []byte(ofile.f.data), nil 334 } 335 336 // An openFile is a regular file open for reading. 337 type openFile struct { 338 f *file // the file itself 339 offset int64 // current read offset 340 } 341 342 func (f *openFile) Close() error { return nil } 343 func (f *openFile) Stat() (fs.FileInfo, error) { return f.f, nil } 344 345 func (f *openFile) Read(b []byte) (int, error) { 346 if f.offset >= int64(len(f.f.data)) { 347 return 0, io.EOF 348 } 349 if f.offset < 0 { 350 return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid} 351 } 352 n := copy(b, f.f.data[f.offset:]) 353 f.offset += int64(n) 354 return n, nil 355 } 356 357 func (f *openFile) Seek(offset int64, whence int) (int64, error) { 358 switch whence { 359 case 0: 360 // offset += 0 361 case 1: 362 offset += f.offset 363 case 2: 364 offset += int64(len(f.f.data)) 365 } 366 if offset < 0 || offset > int64(len(f.f.data)) { 367 return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid} 368 } 369 f.offset = offset 370 return offset, nil 371 } 372 373 // An openDir is a directory open for reading. 374 type openDir struct { 375 f *file // the directory file itself 376 files []file // the directory contents 377 offset int // the read offset, an index into the files slice 378 } 379 380 func (d *openDir) Close() error { return nil } 381 func (d *openDir) Stat() (fs.FileInfo, error) { return d.f, nil } 382 383 func (d *openDir) Read([]byte) (int, error) { 384 return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")} 385 } 386 387 func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) { 388 n := len(d.files) - d.offset 389 if n == 0 { 390 if count <= 0 { 391 return nil, nil 392 } 393 return nil, io.EOF 394 } 395 if count > 0 && n > count { 396 n = count 397 } 398 list := make([]fs.DirEntry, n) 399 for i := range list { 400 list[i] = &d.files[d.offset+i] 401 } 402 d.offset += n 403 return list, nil 404 } 405 406 // sortSearch is like sort.Search, avoiding an import. 407 func sortSearch(n int, f func(int) bool) int { 408 // Define f(-1) == false and f(n) == true. 409 // Invariant: f(i-1) == false, f(j) == true. 410 i, j := 0, n 411 for i < j { 412 h := int(uint(i+j) >> 1) // avoid overflow when computing h 413 // i ≤ h < j 414 if !f(h) { 415 i = h + 1 // preserves f(i-1) == false 416 } else { 417 j = h // preserves f(j) == true 418 } 419 } 420 // i == j, f(i-1) == false, and f(j) (= f(i)) == true => answer is i. 421 return i 422 } 423