src/embed/embed.go - go - Git at Google

 // Copyright 2020 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.

 // Package embed provides access to files embedded in the running Go program.
 //
 // Go source files that import "embed" can use the //go:embed directive
 // to initialize a variable of type string, []byte, or FS with the contents of
 // files read from the package directory or subdirectories at compile time.
 //
 // For example, here are three ways to embed a file named hello.txt
 // and then print its contents at run time.
 //
 // Embedding one file into a string:
 //
 //	import _ "embed"
 //
 //	//go:embed hello.txt
 //	var s string
 //	print(s)
 //
 // Embedding one file into a slice of bytes:
 //
 //	import _ "embed"
 //
 //	//go:embed hello.txt
 //	var b []byte
 //	print(string(b))
 //
 // Embedded one or more files into a file system:
 //
 //	import "embed"
 //
 //	//go:embed hello.txt
 //	var f embed.FS
 //	data, _ := f.ReadFile("hello.txt")
 //	print(string(data))
 //
 // Directives
 //
 // A //go:embed directive above a variable declaration specifies which files to embed,
 // using one or more path.Match patterns.
 //
 // The directive must immediately precede a line containing the declaration of a single variable.
 // Only blank lines and ‘//’ line comments are permitted between the directive and the declaration.
 //
 // The type of the variable must be a string type, or a slice of a byte type,
 // or FS (or an alias of FS).
 //
 // For example:
 //
 //	package server
 //
 //	import "embed"
 //
 //	// content holds our static web server content.
 //	//go:embed image/* template/*
 //	//go:embed html/index.html
 //	var content embed.FS
 //
 // The Go build system will recognize the directives and arrange for the declared variable
 // (in the example above, content) to be populated with the matching files from the file system.
 //
 // The //go:embed directive accepts multiple space-separated patterns for
 // brevity, but it can also be repeated, to avoid very long lines when there are
 // many patterns. The patterns are interpreted relative to the package directory
 // containing the source file. The path separator is a forward slash, even on
 // Windows systems. Patterns may not contain ‘.’ or ‘..’ or empty path elements,
 // nor may they begin or end with a slash. To match everything in the current
 // directory, use ‘*’ instead of ‘.’. To allow for naming files with spaces in
 // their names, patterns can be written as Go double-quoted or back-quoted
 // string literals.
 //
 // If a pattern names a directory, all files in the subtree rooted at that directory are
 // embedded (recursively), except that files with names beginning with ‘.’ or ‘_’
 // are excluded. So the variable in the above example is almost equivalent to:
 //
 //	// content is our static web server content.
 //	//go:embed image template html/index.html
 //	var content embed.FS
 //
 // The difference is that ‘image/*’ embeds ‘image/.tempfile’ while ‘image’ does not.
 //
 // The //go:embed directive can be used with both exported and unexported variables,
 // depending on whether the package wants to make the data available to other packages.
 // It can only be used with variables at package scope, not with local variables.
 //
 // Patterns must not match files outside the package's module, such as ‘.git/*’ or symbolic links.
 // Matches for empty directories are ignored. After that, each pattern in a //go:embed line
 // must match at least one file or non-empty directory.
 //
 // If any patterns are invalid or have invalid matches, the build will fail.
 //
 // Strings and Bytes
 //
 // The //go:embed line for a variable of type string or []byte can have only a single pattern,
 // and that pattern can match only a single file. The string or []byte is initialized with
 // the contents of that file.
 //
 // The //go:embed directive requires importing "embed", even when using a string or []byte.
 // In source files that don't refer to embed.FS, use a blank import (import _ "embed").
 //
 // File Systems
 //
 // For embedding a single file, a variable of type string or []byte is often best.
 // The FS type enables embedding a tree of files, such as a directory of static
 // web server content, as in the example above.
 //
 // FS implements the io/fs package's FS interface, so it can be used with any package that
 // understands file systems, including net/http, text/template, and html/template.
 //
 // For example, given the content variable in the example above, we can write:
 //
 //	http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.FS(content))))
 //
 //	template.ParseFS(content, "*.tmpl")
 //
 // Tools
 //
 // To support tools that analyze Go packages, the patterns found in //go:embed lines
 // are available in “go list” output. See the EmbedPatterns, TestEmbedPatterns,
 // and XTestEmbedPatterns fields in the “go help list” output.
 //
 package embed

 import (
 	"errors"
 	"io"
 	"io/fs"
 	"time"
 )

 // An FS is a read-only collection of files, usually initialized with a //go:embed directive.
 // When declared without a //go:embed directive, an FS is an empty file system.
 //
 // An FS is a read-only value, so it is safe to use from multiple goroutines
 // simultaneously and also safe to assign values of type FS to each other.
 //
 // FS implements fs.FS, so it can be used with any package that understands
 // file system interfaces, including net/http, text/template, and html/template.
 //
 // See the package documentation for more details about initializing an FS.
 type FS struct {
 	// The compiler knows the layout of this struct.
 	// See cmd/compile/internal/staticdata's WriteEmbed.
 	//
 	// The files list is sorted by name but not by simple string comparison.
 	// Instead, each file's name takes the form "dir/elem" or "dir/elem/".
 	// The optional trailing slash indicates that the file is itself a directory.
 	// The files list is sorted first by dir (if dir is missing, it is taken to be ".")
 	// and then by base, so this list of files:
 	//
 	//	p
 	//	q/
 	//	q/r
 	//	q/s/
 	//	q/s/t
 	//	q/s/u
 	//	q/v
 	//	w
 	//
 	// is actually sorted as:
 	//
 	//	p       # dir=.    elem=p
 	//	q/      # dir=.    elem=q
 	//	w/      # dir=.    elem=w
 	//	q/r     # dir=q    elem=r
 	//	q/s/    # dir=q    elem=s
 	//	q/v     # dir=q    elem=v
 	//	q/s/t   # dir=q/s  elem=t
 	//	q/s/u   # dir=q/s  elem=u
 	//
 	// This order brings directory contents together in contiguous sections
 	// of the list, allowing a directory read to use binary search to find
 	// the relevant sequence of entries.
 	files *[]file
 }

 // split splits the name into dir and elem as described in the
 // comment in the FS struct above. isDir reports whether the
 // final trailing slash was present, indicating that name is a directory.
 func split(name string) (dir, elem string, isDir bool) {
 	if name[len(name)-1] == '/' {
 		isDir = true
 		name = name[:len(name)-1]
 	}
 	i := len(name) - 1
 	for i >= 0 && name[i] != '/' {
 		i--
 	}
 	if i < 0 {
 		return ".", name, isDir
 	}
 	return name[:i], name[i+1:], isDir
 }

 // trimSlash trims a trailing slash from name, if present,
 // returning the possibly shortened name.
 func trimSlash(name string) string {
 	if len(name) > 0 && name[len(name)-1] == '/' {
 		return name[:len(name)-1]
 	}
 	return name
 }

 var (
 	_ fs.ReadDirFS  = FS{}
 	_ fs.ReadFileFS = FS{}
 )

 // A file is a single file in the FS.
 // It implements fs.FileInfo and fs.DirEntry.
 type file struct {
 	// The compiler knows the layout of this struct.
 	// See cmd/compile/internal/staticdata's WriteEmbed.
 	name string
 	data string
 	hash [16]byte // truncated SHA256 hash
 }

 var (
 	_ fs.FileInfo = (*file)(nil)
 	_ fs.DirEntry = (*file)(nil)
 )

 func (f *file) Name() string               { _, elem, _ := split(f.name); return elem }
 func (f *file) Size() int64                { return int64(len(f.data)) }
 func (f *file) ModTime() time.Time         { return time.Time{} }
 func (f *file) IsDir() bool                { _, _, isDir := split(f.name); return isDir }
 func (f *file) Sys() interface{}           { return nil }
 func (f *file) Type() fs.FileMode          { return f.Mode().Type() }
 func (f *file) Info() (fs.FileInfo, error) { return f, nil }

 func (f *file) Mode() fs.FileMode {
 	if f.IsDir() {
 		return fs.ModeDir | 0555
 	}
 	return 0444
 }

 // dotFile is a file for the root directory,
 // which is omitted from the files list in a FS.
 var dotFile = &file{name: "./"}

 // lookup returns the named file, or nil if it is not present.
 func (f FS) lookup(name string) *file {
 	if !fs.ValidPath(name) {
 		// The compiler should never emit a file with an invalid name,
 		// so this check is not strictly necessary (if name is invalid,
 		// we shouldn't find a match below), but it's a good backstop anyway.
 		return nil
 	}
 	if name == "." {
 		return dotFile
 	}
 	if f.files == nil {
 		return nil
 	}

 	// Binary search to find where name would be in the list,
 	// and then check if name is at that position.
 	dir, elem, _ := split(name)
 	files := *f.files
 	i := sortSearch(len(files), func(i int) bool {
 		idir, ielem, _ := split(files[i].name)
 		return idir > dir || idir == dir && ielem >= elem
 	})
 	if i < len(files) && trimSlash(files[i].name) == name {
 		return &files[i]
 	}
 	return nil
 }

 // readDir returns the list of files corresponding to the directory dir.
 func (f FS) readDir(dir string) []file {
 	if f.files == nil {
 		return nil
 	}
 	// Binary search to find where dir starts and ends in the list
 	// and then return that slice of the list.
 	files := *f.files
 	i := sortSearch(len(files), func(i int) bool {
 		idir, _, _ := split(files[i].name)
 		return idir >= dir
 	})
 	j := sortSearch(len(files), func(j int) bool {
 		jdir, _, _ := split(files[j].name)
 		return jdir > dir
 	})
 	return files[i:j]
 }

 // Open opens the named file for reading and returns it as an fs.File.
 //
 // The returned file implements io.Seeker when the file is not a directory.
 func (f FS) Open(name string) (fs.File, error) {
 	file := f.lookup(name)
 	if file == nil {
 		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
 	}
 	if file.IsDir() {
 		return &openDir{file, f.readDir(name), 0}, nil
 	}
 	return &openFile{file, 0}, nil
 }

 // ReadDir reads and returns the entire named directory.
 func (f FS) ReadDir(name string) ([]fs.DirEntry, error) {
 	file, err := f.Open(name)
 	if err != nil {
 		return nil, err
 	}
 	dir, ok := file.(*openDir)
 	if !ok {
 		return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("not a directory")}
 	}
 	list := make([]fs.DirEntry, len(dir.files))
 	for i := range list {
 		list[i] = &dir.files[i]
 	}
 	return list, nil
 }

 // ReadFile reads and returns the content of the named file.
 func (f FS) ReadFile(name string) ([]byte, error) {
 	file, err := f.Open(name)
 	if err != nil {
 		return nil, err
 	}
 	ofile, ok := file.(*openFile)
 	if !ok {
 		return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("is a directory")}
 	}
 	return []byte(ofile.f.data), nil
 }

 // An openFile is a regular file open for reading.
 type openFile struct {
 	f      *file // the file itself
 	offset int64 // current read offset
 }

 var (
 	_ io.Seeker = (*openFile)(nil)
 )

 func (f *openFile) Close() error               { return nil }
 func (f *openFile) Stat() (fs.FileInfo, error) { return f.f, nil }

 func (f *openFile) Read(b []byte) (int, error) {
 	if f.offset >= int64(len(f.f.data)) {
 		return 0, io.EOF
 	}
 	if f.offset < 0 {
 		return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid}
 	}
 	n := copy(b, f.f.data[f.offset:])
 	f.offset += int64(n)
 	return n, nil
 }

 func (f *openFile) Seek(offset int64, whence int) (int64, error) {
 	switch whence {
 	case 0:
 		// offset += 0
 	case 1:
 		offset += f.offset
 	case 2:
 		offset += int64(len(f.f.data))
 	}
 	if offset < 0 || offset > int64(len(f.f.data)) {
 		return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
 	}
 	f.offset = offset
 	return offset, nil
 }

 // An openDir is a directory open for reading.
 type openDir struct {
 	f      *file  // the directory file itself
 	files  []file // the directory contents
 	offset int    // the read offset, an index into the files slice
 }

 func (d *openDir) Close() error               { return nil }
 func (d *openDir) Stat() (fs.FileInfo, error) { return d.f, nil }

 func (d *openDir) Read([]byte) (int, error) {
 	return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")}
 }

 func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
 	n := len(d.files) - d.offset
 	if n == 0 {
 		if count <= 0 {
 			return nil, nil
 		}
 		return nil, io.EOF
 	}
 	if count > 0 && n > count {
 		n = count
 	}
 	list := make([]fs.DirEntry, n)
 	for i := range list {
 		list[i] = &d.files[d.offset+i]
 	}
 	d.offset += n
 	return list, nil
 }

 // sortSearch is like sort.Search, avoiding an import.
 func sortSearch(n int, f func(int) bool) int {
 	// Define f(-1) == false and f(n) == true.
 	// Invariant: f(i-1) == false, f(j) == true.
 	i, j := 0, n
 	for i < j {
 		h := int(uint(i+j) >> 1) // avoid overflow when computing h
 		// i ≤ h < j
 		if !f(h) {
 			i = h + 1 // preserves f(i-1) == false
 		} else {
 			j = h // preserves f(j) == true
 		}
 	}
 	// i == j, f(i-1) == false, and f(j) (= f(i)) == true  =>  answer is i.
 	return i
 }
	// Copyright 2020 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.

	// Package embed provides access to files embedded in the running Go program.
	//
	// Go source files that import "embed" can use the //go:embed directive
	// to initialize a variable of type string, []byte, or FS with the contents of
	// files read from the package directory or subdirectories at compile time.
	//
	// For example, here are three ways to embed a file named hello.txt
	// and then print its contents at run time.
	//
	// Embedding one file into a string:
	//
	// import _ "embed"
	//
	// //go:embed hello.txt
	// var s string
	// print(s)
	//
	// Embedding one file into a slice of bytes:
	//
	// import _ "embed"
	//
	// //go:embed hello.txt
	// var b []byte
	// print(string(b))
	//
	// Embedded one or more files into a file system:
	//
	// import "embed"
	//
	// //go:embed hello.txt
	// var f embed.FS
	// data, _ := f.ReadFile("hello.txt")
	// print(string(data))
	//
	// Directives
	//
	// A //go:embed directive above a variable declaration specifies which files to embed,
	// using one or more path.Match patterns.
	//
	// The directive must immediately precede a line containing the declaration of a single variable.
	// Only blank lines and ‘//’ line comments are permitted between the directive and the declaration.
	//
	// The type of the variable must be a string type, or a slice of a byte type,
	// or FS (or an alias of FS).
	//
	// For example:
	//
	// package server
	//
	// import "embed"
	//
	// // content holds our static web server content.
	// //go:embed image/* template/*
	// //go:embed html/index.html
	// var content embed.FS
	//
	// The Go build system will recognize the directives and arrange for the declared variable
	// (in the example above, content) to be populated with the matching files from the file system.
	//
	// The //go:embed directive accepts multiple space-separated patterns for
	// brevity, but it can also be repeated, to avoid very long lines when there are
	// many patterns. The patterns are interpreted relative to the package directory
	// containing the source file. The path separator is a forward slash, even on
	// Windows systems. Patterns may not contain ‘.’ or ‘..’ or empty path elements,
	// nor may they begin or end with a slash. To match everything in the current
	// directory, use ‘*’ instead of ‘.’. To allow for naming files with spaces in
	// their names, patterns can be written as Go double-quoted or back-quoted
	// string literals.
	//
	// If a pattern names a directory, all files in the subtree rooted at that directory are
	// embedded (recursively), except that files with names beginning with ‘.’ or ‘_’
	// are excluded. So the variable in the above example is almost equivalent to:
	//
	// // content is our static web server content.
	// //go:embed image template html/index.html
	// var content embed.FS
	//
	// The difference is that ‘image/*’ embeds ‘image/.tempfile’ while ‘image’ does not.
	//
	// The //go:embed directive can be used with both exported and unexported variables,
	// depending on whether the package wants to make the data available to other packages.
	// It can only be used with variables at package scope, not with local variables.
	//
	// Patterns must not match files outside the package's module, such as ‘.git/*’ or symbolic links.
	// Matches for empty directories are ignored. After that, each pattern in a //go:embed line
	// must match at least one file or non-empty directory.
	//
	// If any patterns are invalid or have invalid matches, the build will fail.
	//
	// Strings and Bytes
	//
	// The //go:embed line for a variable of type string or []byte can have only a single pattern,
	// and that pattern can match only a single file. The string or []byte is initialized with
	// the contents of that file.
	//
	// The //go:embed directive requires importing "embed", even when using a string or []byte.
	// In source files that don't refer to embed.FS, use a blank import (import _ "embed").
	//
	// File Systems
	//
	// For embedding a single file, a variable of type string or []byte is often best.
	// The FS type enables embedding a tree of files, such as a directory of static
	// web server content, as in the example above.
	//
	// FS implements the io/fs package's FS interface, so it can be used with any package that
	// understands file systems, including net/http, text/template, and html/template.
	//
	// For example, given the content variable in the example above, we can write:
	//
	// http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.FS(content))))
	//
	// template.ParseFS(content, "*.tmpl")
	//
	// Tools
	//
	// To support tools that analyze Go packages, the patterns found in //go:embed lines
	// are available in “go list” output. See the EmbedPatterns, TestEmbedPatterns,
	// and XTestEmbedPatterns fields in the “go help list” output.
	//
	package embed

	import (
	"errors"
	"io"
	"io/fs"
	"time"
	)

	// An FS is a read-only collection of files, usually initialized with a //go:embed directive.
	// When declared without a //go:embed directive, an FS is an empty file system.
	//
	// An FS is a read-only value, so it is safe to use from multiple goroutines
	// simultaneously and also safe to assign values of type FS to each other.
	//
	// FS implements fs.FS, so it can be used with any package that understands
	// file system interfaces, including net/http, text/template, and html/template.
	//
	// See the package documentation for more details about initializing an FS.
	type FS struct {
	// The compiler knows the layout of this struct.
	// See cmd/compile/internal/staticdata's WriteEmbed.
	//
	// The files list is sorted by name but not by simple string comparison.
	// Instead, each file's name takes the form "dir/elem" or "dir/elem/".
	// The optional trailing slash indicates that the file is itself a directory.
	// The files list is sorted first by dir (if dir is missing, it is taken to be ".")
	// and then by base, so this list of files:
	//
	// p
	// q/
	// q/r
	// q/s/
	// q/s/t
	// q/s/u
	// q/v
	// w
	//
	// is actually sorted as:
	//
	// p # dir=. elem=p
	// q/ # dir=. elem=q
	// w/ # dir=. elem=w
	// q/r # dir=q elem=r
	// q/s/ # dir=q elem=s
	// q/v # dir=q elem=v
	// q/s/t # dir=q/s elem=t
	// q/s/u # dir=q/s elem=u
	//
	// This order brings directory contents together in contiguous sections
	// of the list, allowing a directory read to use binary search to find
	// the relevant sequence of entries.
	files *[]file
	}

	// split splits the name into dir and elem as described in the
	// comment in the FS struct above. isDir reports whether the
	// final trailing slash was present, indicating that name is a directory.
	func split(name string) (dir, elem string, isDir bool) {
	if name[len(name)-1] == '/' {
	isDir = true
	name = name[:len(name)-1]
	}
	i := len(name) - 1
	for i >= 0 && name[i] != '/' {
	i--
	}
	if i < 0 {
	return ".", name, isDir
	}
	return name[:i], name[i+1:], isDir
	}

	// trimSlash trims a trailing slash from name, if present,
	// returning the possibly shortened name.
	func trimSlash(name string) string {
	if len(name) > 0 && name[len(name)-1] == '/' {
	return name[:len(name)-1]
	}
	return name
	}

	var (
	_ fs.ReadDirFS = FS{}
	_ fs.ReadFileFS = FS{}
	)

	// A file is a single file in the FS.
	// It implements fs.FileInfo and fs.DirEntry.
	type file struct {
	// The compiler knows the layout of this struct.
	// See cmd/compile/internal/staticdata's WriteEmbed.
	name string
	data string
	hash [16]byte // truncated SHA256 hash
	}

	var (
	_ fs.FileInfo = (*file)(nil)
	_ fs.DirEntry = (*file)(nil)
	)

	func (f *file) Name() string { _, elem, _ := split(f.name); return elem }
	func (f *file) Size() int64 { return int64(len(f.data)) }
	func (f *file) ModTime() time.Time { return time.Time{} }
	func (f *file) IsDir() bool { _, _, isDir := split(f.name); return isDir }
	func (f *file) Sys() interface{} { return nil }
	func (f *file) Type() fs.FileMode { return f.Mode().Type() }
	func (f *file) Info() (fs.FileInfo, error) { return f, nil }

	func (f *file) Mode() fs.FileMode {
	if f.IsDir() {
	return fs.ModeDir \| 0555
	}
	return 0444
	}

	// dotFile is a file for the root directory,
	// which is omitted from the files list in a FS.
	var dotFile = &file{name: "./"}

	// lookup returns the named file, or nil if it is not present.
	func (f FS) lookup(name string) *file {
	if !fs.ValidPath(name) {
	// The compiler should never emit a file with an invalid name,
	// so this check is not strictly necessary (if name is invalid,
	// we shouldn't find a match below), but it's a good backstop anyway.
	return nil
	}
	if name == "." {
	return dotFile
	}
	if f.files == nil {
	return nil
	}

	// Binary search to find where name would be in the list,
	// and then check if name is at that position.
	dir, elem, _ := split(name)
	files := *f.files
	i := sortSearch(len(files), func(i int) bool {
	idir, ielem, _ := split(files[i].name)
	return idir > dir \|\| idir == dir && ielem >= elem
	})
	if i < len(files) && trimSlash(files[i].name) == name {
	return &files[i]
	}
	return nil
	}

	// readDir returns the list of files corresponding to the directory dir.
	func (f FS) readDir(dir string) []file {
	if f.files == nil {
	return nil
	}
	// Binary search to find where dir starts and ends in the list
	// and then return that slice of the list.
	files := *f.files
	i := sortSearch(len(files), func(i int) bool {
	idir, _, _ := split(files[i].name)
	return idir >= dir
	})
	j := sortSearch(len(files), func(j int) bool {
	jdir, _, _ := split(files[j].name)
	return jdir > dir
	})
	return files[i:j]
	}

	// Open opens the named file for reading and returns it as an fs.File.
	//
	// The returned file implements io.Seeker when the file is not a directory.
	func (f FS) Open(name string) (fs.File, error) {
	file := f.lookup(name)
	if file == nil {
	return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
	}
	if file.IsDir() {
	return &openDir{file, f.readDir(name), 0}, nil
	}
	return &openFile{file, 0}, nil
	}

	// ReadDir reads and returns the entire named directory.
	func (f FS) ReadDir(name string) ([]fs.DirEntry, error) {
	file, err := f.Open(name)
	if err != nil {
	return nil, err
	}
	dir, ok := file.(*openDir)
	if !ok {
	return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("not a directory")}
	}
	list := make([]fs.DirEntry, len(dir.files))
	for i := range list {
	list[i] = &dir.files[i]
	}
	return list, nil
	}

	// ReadFile reads and returns the content of the named file.
	func (f FS) ReadFile(name string) ([]byte, error) {
	file, err := f.Open(name)
	if err != nil {
	return nil, err
	}
	ofile, ok := file.(*openFile)
	if !ok {
	return nil, &fs.PathError{Op: "read", Path: name, Err: errors.New("is a directory")}
	}
	return []byte(ofile.f.data), nil
	}

	// An openFile is a regular file open for reading.
	type openFile struct {
	f *file // the file itself
	offset int64 // current read offset
	}

	var (
	_ io.Seeker = (*openFile)(nil)
	)

	func (f *openFile) Close() error { return nil }
	func (f *openFile) Stat() (fs.FileInfo, error) { return f.f, nil }

	func (f *openFile) Read(b []byte) (int, error) {
	if f.offset >= int64(len(f.f.data)) {
	return 0, io.EOF
	}
	if f.offset < 0 {
	return 0, &fs.PathError{Op: "read", Path: f.f.name, Err: fs.ErrInvalid}
	}
	n := copy(b, f.f.data[f.offset:])
	f.offset += int64(n)
	return n, nil
	}

	func (f *openFile) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case 0:
	// offset += 0
	case 1:
	offset += f.offset
	case 2:
	offset += int64(len(f.f.data))
	}
	if offset < 0 \|\| offset > int64(len(f.f.data)) {
	return 0, &fs.PathError{Op: "seek", Path: f.f.name, Err: fs.ErrInvalid}
	}
	f.offset = offset
	return offset, nil
	}

	// An openDir is a directory open for reading.
	type openDir struct {
	f *file // the directory file itself
	files []file // the directory contents
	offset int // the read offset, an index into the files slice
	}

	func (d *openDir) Close() error { return nil }
	func (d *openDir) Stat() (fs.FileInfo, error) { return d.f, nil }

	func (d *openDir) Read([]byte) (int, error) {
	return 0, &fs.PathError{Op: "read", Path: d.f.name, Err: errors.New("is a directory")}
	}

	func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
	n := len(d.files) - d.offset
	if n == 0 {
	if count <= 0 {
	return nil, nil
	}
	return nil, io.EOF
	}
	if count > 0 && n > count {
	n = count
	}
	list := make([]fs.DirEntry, n)
	for i := range list {
	list[i] = &d.files[d.offset+i]
	}
	d.offset += n
	return list, nil
	}

	// sortSearch is like sort.Search, avoiding an import.
	func sortSearch(n int, f func(int) bool) int {
	// Define f(-1) == false and f(n) == true.
	// Invariant: f(i-1) == false, f(j) == true.
	i, j := 0, n
	for i < j {
	h := int(uint(i+j) >> 1) // avoid overflow when computing h
	// i ≤ h < j
	if !f(h) {
	i = h + 1 // preserves f(i-1) == false
	} else {
	j = h // preserves f(j) == true
	}
	}
	// i == j, f(i-1) == false, and f(j) (= f(i)) == true => answer is i.
	return i
	}