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