Source file src/embed/embed.go
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 // Neither embeds ‘image/dir/.tempfile’. 84 // 85 // If a pattern begins with the prefix ‘all:’, then the rule for walking directories is changed 86 // to include those files beginning with ‘.’ or ‘_’. For example, ‘all:image’ embeds 87 // both ‘image/.tempfile’ and ‘image/dir/.tempfile’. 88 // 89 // The //go:embed directive can be used with both exported and unexported variables, 90 // depending on whether the package wants to make the data available to other packages. 91 // It can only be used with variables at package scope, not with local variables. 92 // 93 // Patterns must not match files outside the package's module, such as ‘.git/*’, symbolic links, 94 // 'vendor/', or any directories containing go.mod (these are separate modules). 95 // Patterns must not match files whose names include the special punctuation characters " * < > ? ` ' | / \ and :. 96 // Matches for empty directories are ignored. After that, each pattern in a //go:embed line 97 // must match at least one file or non-empty directory. 98 // 99 // If any patterns are invalid or have invalid matches, the build will fail. 100 // 101 // # Strings and Bytes 102 // 103 // The //go:embed line for a variable of type string or []byte can have only a single pattern, 104 // and that pattern can match only a single file. The string or []byte is initialized with 105 // the contents of that file. 106 // 107 // The //go:embed directive requires importing "embed", even when using a string or []byte. 108 // In source files that don't refer to [embed.FS], use a blank import (import _ "embed"). 109 // 110 // # File Systems 111 // 112 // For embedding a single file, a variable of type string or []byte is often best. 113 // The [FS] type enables embedding a tree of files, such as a directory of static 114 // web server content, as in the example above. 115 // 116 // FS implements the [io/fs] package's [FS] interface, so it can be used with any package that 117 // understands file systems, including [net/http], [text/template], and [html/template]. 118 // 119 // For example, given the content variable in the example above, we can write: 120 // 121 // http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.FS(content)))) 122 // 123 // template.ParseFS(content, "*.tmpl") 124 // 125 // # Tools 126 // 127 // To support tools that analyze Go packages, the patterns found in //go:embed lines 128 // are available in “go list” output. See the EmbedPatterns, TestEmbedPatterns, 129 // and XTestEmbedPatterns fields in the “go help list” output. 130 package embed 131 132 import ( 133 "errors" 134 "internal/bytealg" 135 "internal/stringslite" 136 "io" 137 "io/fs" 138 "time" 139 ) 140 141 // An FS is a read-only collection of files, usually initialized with a //go:embed directive. 142 // When declared without a //go:embed directive, an FS is an empty file system. 143 // 144 // An FS is a read-only value, so it is safe to use from multiple goroutines 145 // simultaneously and also safe to assign values of type FS to each other. 146 // 147 // FS implements fs.FS, so it can be used with any package that understands 148 // file system interfaces, including net/http, text/template, and html/template. 149 // 150 // See the package documentation for more details about initializing an FS. 151 type FS struct { 152 // The compiler knows the layout of this struct. 153 // See cmd/compile/internal/staticdata's WriteEmbed. 154 // 155 // The files list is sorted by name but not by simple string comparison. 156 // Instead, each file's name takes the form "dir/elem" or "dir/elem/". 157 // The optional trailing slash indicates that the file is itself a directory. 158 // The files list is sorted first by dir (if dir is missing, it is taken to be ".") 159 // and then by base, so this list of files: 160 // 161 // p 162 // q/ 163 // q/r 164 // q/s/ 165 // q/s/t 166 // q/s/u 167 // q/v 168 // w 169 // 170 // is actually sorted as: 171 // 172 // p # dir=. elem=p 173 // q/ # dir=. elem=q 174 // w # dir=. elem=w 175 // q/r # dir=q elem=r 176 // q/s/ # dir=q elem=s 177 // q/v # dir=q elem=v 178 // q/s/t # dir=q/s elem=t 179 // q/s/u # dir=q/s elem=u 180 // 181 // This order brings directory contents together in contiguous sections 182 // of the list, allowing a directory read to use binary search to find 183 // the relevant sequence of entries. 184 files *[]file 185 } 186 187 // split splits the name into dir and elem as described in the 188 // comment in the FS struct above. isDir reports whether the 189 // final trailing slash was present, indicating that name is a directory. 190 func split(name string) (dir, elem string, isDir bool) { 191 name, isDir = stringslite.CutSuffix(name, "/") 192 i := bytealg.LastIndexByteString(name, '/') 193 if i < 0 { 194 return ".", name, isDir 195 } 196 return name[:i], name[i+1:], isDir 197 } 198 199 var ( 200 _ fs.ReadDirFS = FS{} 201 _ fs.ReadFileFS = FS{} 202 ) 203 204 // A file is a single file in the FS. 205 // It implements fs.FileInfo and fs.DirEntry. 206 type file struct { 207 // The compiler knows the layout of this struct. 208 // See cmd/compile/internal/staticdata's WriteEmbed. 209 name string 210 data string 211 hash [16]byte // truncated SHA256 hash 212 } 213 214 var ( 215 _ fs.FileInfo = (*file)(nil) 216 _ fs.DirEntry = (*file)(nil) 217 ) 218 219 func (f *file) Name() string { _, elem, _ := split(f.name); return elem } 220 func (f *file) Size() int64 { return int64(len(f.data)) } 221 func (f *file) ModTime() time.Time { return time.Time{} } 222 func (f *file) IsDir() bool { _, _, isDir := split(f.name); return isDir } 223 func (f *file) Sys() any { return nil } 224 func (f *file) Type() fs.FileMode { return f.Mode().Type() } 225 func (f *file) Info() (fs.FileInfo, error) { return f, nil } 226 227 func (f *file) Mode() fs.FileMode { 228 if f.IsDir() { 229 return fs.ModeDir | 0555 230 } 231 return 0444 232 } 233 234 func (f *file) String() string { 235 return fs.FormatFileInfo(f) 236 } 237 238 // dotFile is a file for the root directory, 239 // which is omitted from the files list in a FS. 240 var dotFile = &file{name: "./"} 241 242 // lookup returns the named file, or nil if it is not present. 243 func (f FS) lookup(name string) *file { 244 if !fs.ValidPath(name) { 245 // The compiler should never emit a file with an invalid name, 246 // so this check is not strictly necessary (if name is invalid, 247 // we shouldn't find a match below), but it's a good backstop anyway. 248 return nil 249 } 250 if name == "." { 251 return dotFile 252 } 253 if f.files == nil { 254 return nil 255 } 256 257 // Binary search to find where name would be in the list, 258 // and then check if name is at that position. 259 dir, elem, _ := split(name) 260 files := *f.files 261 i := sortSearch(len(files), func(i int) bool { 262 idir, ielem, _ := split(files[i].name) 263 return idir > dir || idir == dir && ielem >= elem 264 }) 265 if i < len(files) && stringslite.TrimSuffix(files[i].name, "/") == name { 266 return &files[i] 267 } 268 return nil 269 } 270 271 // readDir returns the list of files corresponding to the directory dir. 272 func (f FS) readDir(dir string) []file { 273 if f.files == nil { 274 return nil 275 } 276 // Binary search to find where dir starts and ends in the list 277 // and then return that slice of the list. 278 files := *f.files 279 i := sortSearch(len(files), func(i int) bool { 280 idir, _, _ := split(files[i].name) 281 return idir >= dir 282 }) 283 j := sortSearch(len(files), func(j int) bool { 284 jdir, _, _ := split(files[j].name) 285 return jdir > dir 286 }) 287 return files[i:j] 288 } 289 290 // Open opens the named file for reading and returns it as an [fs.File]. 291 // 292 // The returned file implements [io.Seeker] and [io.ReaderAt] when the file is not a directory. 293 func (f FS) Open(name string) (fs.File, error) { 294 file := f.lookup(name) 295 if file == nil { 296 return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist} 297 } 298 if file.IsDir() { 299 return &openDir{file, f.readDir(name), 0}, nil 300 } 301 return &openFile{file, 0}, nil 302 } 303 304 // ReadDir reads and returns the entire named directory. 305 func (f FS) ReadDir(name string) ([]fs.DirEntry, error) { 306 file, err := f.Open(name) 307 if err != nil { 308 return nil, err 309 } 310 dir, ok := file.(*openDir) 311 if !ok { 312 return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("not a directory")} 313 } 314 list := make([]fs.DirEntry, len(dir.files)) 315 for i := range list { 316 list[i] = &dir.files[i] 317 } 318 return list, nil 319 } 320 321 // ReadFile reads and returns the content of the named file. 322 func (f FS) ReadFile(name string) ([]byte, error) { 323 file, err := f.Open(name) 324 if err != nil { 325 return nil, err 326 } 327 ofile, ok := file.(*openFile) 328 if !ok { 329 return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("is a directory")} 330 } 331 return []byte(ofile.f.data), nil 332 } 333 334 // An openFile is a regular file open for reading. 335 type openFile struct { 336 f *file // the file itself 337 offset int64 // current read offset 338 } 339 340 var ( 341 _ io.Seeker = (*openFile)(nil) 342 _ io.ReaderAt = (*openFile)(nil) 343 ) 344 345 func (f *openFile) Close() error { return nil } 346 func (f *openFile) Stat() (fs.FileInfo, error) { return f.f, nil } 347 348 func (f *openFile) Read(b []byte) (int, error) { 349 if f.offset >= int64(len(f.f.data)) { 350 return 0, io.EOF 351 } 352 if f.offset < 0 { 353 return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid} 354 } 355 n := copy(b, f.f.data[f.offset:]) 356 f.offset += int64(n) 357 return n, nil 358 } 359 360 func (f *openFile) Seek(offset int64, whence int) (int64, error) { 361 switch whence { 362 case 0: 363 // offset += 0 364 case 1: 365 offset += f.offset 366 case 2: 367 offset += int64(len(f.f.data)) 368 } 369 if offset < 0 || offset > int64(len(f.f.data)) { 370 return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid} 371 } 372 f.offset = offset 373 return offset, nil 374 } 375 376 func (f *openFile) ReadAt(b []byte, offset int64) (int, error) { 377 if offset < 0 || offset > int64(len(f.f.data)) { 378 return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid} 379 } 380 n := copy(b, f.f.data[offset:]) 381 if n < len(b) { 382 return n, io.EOF 383 } 384 return n, nil 385 } 386 387 // An openDir is a directory open for reading. 388 type openDir struct { 389 f *file // the directory file itself 390 files []file // the directory contents 391 offset int // the read offset, an index into the files slice 392 } 393 394 func (d *openDir) Close() error { return nil } 395 func (d *openDir) Stat() (fs.FileInfo, error) { return d.f, nil } 396 397 func (d *openDir) Read([]byte) (int, error) { 398 return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")} 399 } 400 401 func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) { 402 n := len(d.files) - d.offset 403 if n == 0 { 404 if count <= 0 { 405 return nil, nil 406 } 407 return nil, io.EOF 408 } 409 if count > 0 && n > count { 410 n = count 411 } 412 list := make([]fs.DirEntry, n) 413 for i := range list { 414 list[i] = &d.files[d.offset+i] 415 } 416 d.offset += n 417 return list, nil 418 } 419 420 // sortSearch is like sort.Search, avoiding an import. 421 func sortSearch(n int, f func(int) bool) int { 422 // Define f(-1) == false and f(n) == true. 423 // Invariant: f(i-1) == false, f(j) == true. 424 i, j := 0, n 425 for i < j { 426 h := int(uint(i+j) >> 1) // avoid overflow when computing h 427 // i ≤ h < j 428 if !f(h) { 429 i = h + 1 // preserves f(i-1) == false 430 } else { 431 j = h // preserves f(j) == true 432 } 433 } 434 // i == j, f(i-1) == false, and f(j) (= f(i)) == true => answer is i. 435 return i 436 } 437