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embed: implement FS

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embed.FS is the implementation of embedded file trees, providing
an fs.FS for each embed.FS variable.

Tests are in a follow-up CL, in the package embed/internal/embedtest.
(They can only be written once the toolchain can initialize one of these,
which requires changes to cmd/compile and cmd/go.)

For #41191.

Change-Id: Ieb0ead1d305cdac3d5d4e11772dca75740a72730
Reviewed-on: https://go-review.googlesource.com/c/go/+/243942
Trust: Russ Cox <rsc@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
This commit is contained in:
Russ Cox 2020-07-18 23:50:48 -04:00
parent 67bce7c1cf
commit 400581b8b0
2 changed files with 409 additions and 6 deletions
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403
src/embed/embed.go Normal file
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@ -0,0 +1,403 @@
// 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:
//
// import "embed"
//
// //go:embed hello.txt
// var s string
// print(s)
//
// //go:embed hello.txt
// var b []byte
// print(string(b))
//
// //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 variable must be of type string, []byte, or FS exactly. Named types or type aliases
// derived from those types are not allowed.
//
// 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.
// 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), so the variable in the above example is equivalent to:
//
// // content is our static web server content.
// //go:embed image template html/index.html
// var content embed.FS
//
// 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.
// Similarly, it can be used with both global and function-local variables,
// depending on what is more convenient in context.
//
// 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.
//
// Patterns must not contain ‘.’ or ‘..’ path elements nor begin with a leading slash.
// To match everything in the current directory, use ‘*’ instead of ‘.’.
//
// 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/gc's initEmbed.
//
// 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/gc's initEmbed.
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
}
// 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 {
// 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.
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
}
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 count > 0 && n > count {
n = count
}
if n == 0 {
if count <= 0 {
return nil, nil
}
return nil, io.EOF
}
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
}

12
src/go/build/read_test.go
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@ -236,23 +236,23 @@ var readEmbedTests = []struct {
nil,
},
{
"package p\nimport \"embed\"\nvar i int\n//go:embed x y z\nvar files embed.Files",
"package p\nimport \"embed\"\nvar i int\n//go:embed x y z\nvar files embed.FS",
[]string{"x", "y", "z"},
},
{
"package p\nimport \"embed\"\nvar i int\n//go:embed x \"\\x79\" `z`\nvar files embed.Files",
"package p\nimport \"embed\"\nvar i int\n//go:embed x \"\\x79\" `z`\nvar files embed.FS",
[]string{"x", "y", "z"},
},
{
"package p\nimport \"embed\"\nvar i int\n//go:embed x y\n//go:embed z\nvar files embed.Files",
"package p\nimport \"embed\"\nvar i int\n//go:embed x y\n//go:embed z\nvar files embed.FS",
[]string{"x", "y", "z"},
},
{
"package p\nimport \"embed\"\nvar i int\n\t //go:embed x y\n\t //go:embed z\n\t var files embed.Files",
"package p\nimport \"embed\"\nvar i int\n\t //go:embed x y\n\t //go:embed z\n\t var files embed.FS",
[]string{"x", "y", "z"},
},
{
"package p\nimport \"embed\"\n//go:embed x y z\nvar files embed.Files",
"package p\nimport \"embed\"\n//go:embed x y z\nvar files embed.FS",
[]string{"x", "y", "z"},
},
{
@ -260,7 +260,7 @@ var readEmbedTests = []struct {
nil,
},
{
"package p\n//go:embed x y z\nvar files embed.Files", // no import, no scan
"package p\n//go:embed x y z\nvar files embed.FS", // no import, no scan
nil,
},
}