codekingpro/portable-devtools

1// look up the realpath, but cache stats to minimize overhead
2// If the parent folder is in  the realpath cache, then we just
3// lstat the child, since there's no need to do a full realpath
4// This is not a separate module, and is much simpler than Node's
5// built-in fs.realpath, because we only care about symbolic links,
6// so we can handle many fewer edge cases.
7
8const { lstat, readlink } = require('node:fs/promises')
9const { resolve, basename, dirname } = require('node:path')
10
11const realpathCached = (path, rpcache, stcache, depth) => {
12  // just a safety against extremely deep eloops
13  /* istanbul ignore next */
14  if (depth > 2000) {
15    throw eloop(path)
16  }
17
18  path = resolve(path)
19  if (rpcache.has(path)) {
20    return Promise.resolve(rpcache.get(path))
21  }
22
23  const dir = dirname(path)
24  const base = basename(path)
25
26  if (base && rpcache.has(dir)) {
27    return realpathChild(dir, base, rpcache, stcache, depth)
28  }
29
30  // if it's the root, then we know it's real
31  if (!base) {
32    rpcache.set(dir, dir)
33    return Promise.resolve(dir)
34  }
35
36  // the parent, what is that?
37  // find out, and then come back.
38  return realpathCached(dir, rpcache, stcache, depth + 1).then(() =>
39    realpathCached(path, rpcache, stcache, depth + 1))
40}
41
42const lstatCached = (path, stcache) => {
43  if (stcache.has(path)) {
44    return Promise.resolve(stcache.get(path))
45  }
46
47  const p = lstat(path).then(st => {
48    stcache.set(path, st)
49    return st
50  })
51  stcache.set(path, p)
52  return p
53}
54
55// This is a slight fib, as it doesn't actually occur during a stat syscall.
56// But file systems are giant piles of lies, so whatever.
57const eloop = path =>
58  Object.assign(new Error(
59    `ELOOP: too many symbolic links encountered, stat '${path}'`), {
60    errno: -62,
61    syscall: 'stat',
62    code: 'ELOOP',
63    path: path,
64  })
65
66const realpathChild = (dir, base, rpcache, stcache, depth) => {
67  const realdir = rpcache.get(dir)
68  // that unpossible
69  /* istanbul ignore next */
70  if (typeof realdir === 'undefined') {
71    throw new Error('in realpathChild without parent being in realpath cache')
72  }
73
74  const realish = resolve(realdir, base)
75  return lstatCached(realish, stcache).then(st => {
76    if (!st.isSymbolicLink()) {
77      rpcache.set(resolve(dir, base), realish)
78      return realish
79    }
80
81    return readlink(realish).then(target => {
82      const resolved = resolve(realdir, target)
83      if (realish === resolved) {
84        throw eloop(realish)
85      }
86
87      return realpathCached(resolved, rpcache, stcache, depth + 1)
88    }).then(real => {
89      rpcache.set(resolve(dir, base), real)
90      return real
91    })
92  })
93}
94
95module.exports = realpathCached
96