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namespace.go
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namespace.go
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// Copyright 2011 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 vfs
import (
"fmt"
"io"
"os"
pathpkg "path"
"sort"
"strings"
"time"
)
// Setting debugNS = true will enable debugging prints about
// name space translations.
const debugNS = false
// A NameSpace is a file system made up of other file systems
// mounted at specific locations in the name space.
//
// The representation is a map from mount point locations
// to the list of file systems mounted at that location. A traditional
// Unix mount table would use a single file system per mount point,
// but we want to be able to mount multiple file systems on a single
// mount point and have the system behave as if the union of those
// file systems were present at the mount point.
// For example, if the OS file system has a Go installation in
// c:\Go and additional Go path trees in d:\Work1 and d:\Work2, then
// this name space creates the view we want for the godoc server:
//
// NameSpace{
// "/": {
// {old: "/", fs: OS(`c:\Go`), new: "/"},
// },
// "/src/pkg": {
// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
// },
// }
//
// This is created by executing:
//
// ns := NameSpace{}
// ns.Bind("/", OS(`c:\Go`), "/", BindReplace)
// ns.Bind("/src/pkg", OS(`d:\Work1`), "/src", BindAfter)
// ns.Bind("/src/pkg", OS(`d:\Work2`), "/src", BindAfter)
//
// A particular mount point entry is a triple (old, fs, new), meaning that to
// operate on a path beginning with old, replace that prefix (old) with new
// and then pass that path to the FileSystem implementation fs.
//
// Given this name space, a ReadDir of /src/pkg/code will check each prefix
// of the path for a mount point (first /src/pkg/code, then /src/pkg, then /src,
// then /), stopping when it finds one. For the above example, /src/pkg/code
// will find the mount point at /src/pkg:
//
// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
//
// ReadDir will when execute these three calls and merge the results:
//
// OS(`c:\Go`).ReadDir("/src/pkg/code")
// OS(`d:\Work1').ReadDir("/src/code")
// OS(`d:\Work2').ReadDir("/src/code")
//
// Note that the "/src/pkg" in "/src/pkg/code" has been replaced by
// just "/src" in the final two calls.
//
// OS is itself an implementation of a file system: it implements
// OS(`c:\Go`).ReadDir("/src/pkg/code") as ioutil.ReadDir(`c:\Go\src\pkg\code`).
//
// Because the new path is evaluated by fs (here OS(root)), another way
// to read the mount table is to mentally combine fs+new, so that this table:
//
// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
//
// reads as:
//
// "/src/pkg" -> c:\Go\src\pkg
// "/src/pkg" -> d:\Work1\src
// "/src/pkg" -> d:\Work2\src
//
// An invariant (a redundancy) of the name space representation is that
// ns[mtpt][i].old is always equal to mtpt (in the example, ns["/src/pkg"]'s
// mount table entries always have old == "/src/pkg"). The 'old' field is
// useful to callers, because they receive just a []mountedFS and not any
// other indication of which mount point was found.
//
type NameSpace map[string][]mountedFS
// A mountedFS handles requests for path by replacing
// a prefix 'old' with 'new' and then calling the fs methods.
type mountedFS struct {
old string
fs FileSystem
new string
}
// hasPathPrefix returns true if x == y or x == y + "/" + more
func hasPathPrefix(x, y string) bool {
return x == y || strings.HasPrefix(x, y) && (strings.HasSuffix(y, "/") || strings.HasPrefix(x[len(y):], "/"))
}
// translate translates path for use in m, replacing old with new.
//
// mountedFS{"/src/pkg", fs, "/src"}.translate("/src/pkg/code") == "/src/code".
func (m mountedFS) translate(path string) string {
path = pathpkg.Clean("/" + path)
if !hasPathPrefix(path, m.old) {
panic("translate " + path + " but old=" + m.old)
}
return pathpkg.Join(m.new, path[len(m.old):])
}
func (NameSpace) String() string {
return "ns"
}
// Fprint writes a text representation of the name space to w.
func (ns NameSpace) Fprint(w io.Writer) {
fmt.Fprint(w, "name space {\n")
var all []string
for mtpt := range ns {
all = append(all, mtpt)
}
sort.Strings(all)
for _, mtpt := range all {
fmt.Fprintf(w, "\t%s:\n", mtpt)
for _, m := range ns[mtpt] {
fmt.Fprintf(w, "\t\t%s %s\n", m.fs, m.new)
}
}
fmt.Fprint(w, "}\n")
}
// clean returns a cleaned, rooted path for evaluation.
// It canonicalizes the path so that we can use string operations
// to analyze it.
func (NameSpace) clean(path string) string {
return pathpkg.Clean("/" + path)
}
type BindMode int
const (
BindReplace BindMode = iota
BindBefore
BindAfter
)
// Bind causes references to old to redirect to the path new in newfs.
// If mode is BindReplace, old redirections are discarded.
// If mode is BindBefore, this redirection takes priority over existing ones,
// but earlier ones are still consulted for paths that do not exist in newfs.
// If mode is BindAfter, this redirection happens only after existing ones
// have been tried and failed.
func (ns NameSpace) Bind(old string, newfs FileSystem, new string, mode BindMode) {
old = ns.clean(old)
new = ns.clean(new)
m := mountedFS{old, newfs, new}
var mtpt []mountedFS
switch mode {
case BindReplace:
mtpt = append(mtpt, m)
case BindAfter:
mtpt = append(mtpt, ns.resolve(old)...)
mtpt = append(mtpt, m)
case BindBefore:
mtpt = append(mtpt, m)
mtpt = append(mtpt, ns.resolve(old)...)
}
// Extend m.old, m.new in inherited mount point entries.
for i := range mtpt {
m := &mtpt[i]
if m.old != old {
if !hasPathPrefix(old, m.old) {
// This should not happen. If it does, panic so
// that we can see the call trace that led to it.
panic(fmt.Sprintf("invalid Bind: old=%q m={%q, %s, %q}", old, m.old, m.fs.String(), m.new))
}
suffix := old[len(m.old):]
m.old = pathpkg.Join(m.old, suffix)
m.new = pathpkg.Join(m.new, suffix)
}
}
ns[old] = mtpt
}
// resolve resolves a path to the list of mountedFS to use for path.
func (ns NameSpace) resolve(path string) []mountedFS {
path = ns.clean(path)
for {
if m := ns[path]; m != nil {
if debugNS {
fmt.Printf("resolve %s: %v\n", path, m)
}
return m
}
if path == "/" {
break
}
path = pathpkg.Dir(path)
}
return nil
}
// Open implements the FileSystem Open method.
func (ns NameSpace) Open(path string) (ReadSeekCloser, error) {
var err error
for _, m := range ns.resolve(path) {
if debugNS {
fmt.Printf("tx %s: %v\n", path, m.translate(path))
}
r, err1 := m.fs.Open(m.translate(path))
if err1 == nil {
return r, nil
}
if err == nil {
err = err1
}
}
if err == nil {
err = &os.PathError{Op: "open", Path: path, Err: os.ErrNotExist}
}
return nil, err
}
// stat implements the FileSystem Stat and Lstat methods.
func (ns NameSpace) stat(path string, f func(FileSystem, string) (os.FileInfo, error)) (os.FileInfo, error) {
var err error
for _, m := range ns.resolve(path) {
fi, err1 := f(m.fs, m.translate(path))
if err1 == nil {
return fi, nil
}
if err == nil {
err = err1
}
}
if err == nil {
err = &os.PathError{Op: "stat", Path: path, Err: os.ErrNotExist}
}
return nil, err
}
func (ns NameSpace) Stat(path string) (os.FileInfo, error) {
return ns.stat(path, FileSystem.Stat)
}
func (ns NameSpace) Lstat(path string) (os.FileInfo, error) {
return ns.stat(path, FileSystem.Lstat)
}
// dirInfo is a trivial implementation of os.FileInfo for a directory.
type dirInfo string
func (d dirInfo) Name() string { return string(d) }
func (d dirInfo) Size() int64 { return 0 }
func (d dirInfo) Mode() os.FileMode { return os.ModeDir | 0555 }
func (d dirInfo) ModTime() time.Time { return startTime }
func (d dirInfo) IsDir() bool { return true }
func (d dirInfo) Sys() interface{} { return nil }
var startTime = time.Now()
// ReadDir implements the FileSystem ReadDir method. It's where most of the magic is.
// (The rest is in resolve.)
//
// Logically, ReadDir must return the union of all the directories that are named
// by path. In order to avoid misinterpreting Go packages, of all the directories
// that contain Go source code, we only include the files from the first,
// but we include subdirectories from all.
//
// ReadDir must also return directory entries needed to reach mount points.
// If the name space looks like the example in the type NameSpace comment,
// but c:\Go does not have a src/pkg subdirectory, we still want to be able
// to find that subdirectory, because we've mounted d:\Work1 and d:\Work2
// there. So if we don't see "src" in the directory listing for c:\Go, we add an
// entry for it before returning.
//
func (ns NameSpace) ReadDir(path string) ([]os.FileInfo, error) {
path = ns.clean(path)
var (
haveGo = false
haveName = map[string]bool{}
all []os.FileInfo
err error
first []os.FileInfo
)
for _, m := range ns.resolve(path) {
dir, err1 := m.fs.ReadDir(m.translate(path))
if err1 != nil {
if err == nil {
err = err1
}
continue
}
if dir == nil {
dir = []os.FileInfo{}
}
if first == nil {
first = dir
}
// If we don't yet have Go files in 'all' and this directory
// has some, add all the files from this directory.
// Otherwise, only add subdirectories.
useFiles := false
if !haveGo {
for _, d := range dir {
if strings.HasSuffix(d.Name(), ".go") {
useFiles = true
haveGo = true
break
}
}
}
for _, d := range dir {
name := d.Name()
if (d.IsDir() || useFiles) && !haveName[name] {
haveName[name] = true
all = append(all, d)
}
}
}
// We didn't find any directories containing Go files.
// If some directory returned successfully, use that.
if !haveGo {
for _, d := range first {
if !haveName[d.Name()] {
haveName[d.Name()] = true
all = append(all, d)
}
}
}
// Built union. Add any missing directories needed to reach mount points.
for old := range ns {
if hasPathPrefix(old, path) && old != path {
// Find next element after path in old.
elem := old[len(path):]
elem = strings.TrimPrefix(elem, "/")
if i := strings.Index(elem, "/"); i >= 0 {
elem = elem[:i]
}
if !haveName[elem] {
haveName[elem] = true
all = append(all, dirInfo(elem))
}
}
}
if len(all) == 0 {
return nil, err
}
sort.Sort(byName(all))
return all, nil
}
// byName implements sort.Interface.
type byName []os.FileInfo
func (f byName) Len() int { return len(f) }
func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
func (f byName) Swap(i, j int) { f[i], f[j] = f[j], f[i] }