PLWL/src/symlinks.js

'use strict'

// Symlink and permission healing, shared by wine builds, prefixes, game
// imports and LAN sync.
//
// Two things break when a tree is copied between machines (or the launcher is
// just moved):
//  - symlinks stored ABSOLUTE keep pointing at the path they had on the
//    machine that wrote them. A Proton prefix is full of them (fonts, built-in
//    program stubs, dlls, all pointing into its build), and a wine build's
//    bundled default prefix has the same problem.
//  - the executable bit is dropped by every content-piping copy
//    (createWriteStream, fs.copyFile), which makes an imported `proton` or
//    `wine` binary unrunnable - the launcher then cannot start that build at
//    all.
//
// Everything here rewires a link to a RELATIVE path when the file it points at
// can be found locally, so the tree stays relocatable forever, and restores
// the executable bit on the binaries a wine/proton build needs.

const fsp = require('fs').promises
const fs = require('fs')
const path = require('path')

function exists(p) {
  try {
    fs.accessSync(p)
    return true
  } catch {
    return false
  }
}

// dosdevices/ holds the prefix's drive mappings (c:, z:, d:, com1 ...). They
// are *supposed* to point outside the prefix - at the filesystem root, a
// mounted CD or a serial port - and wine rewrites them itself, so they are
// never touched.
const SKIP_DIRS = new Set(['dosdevices'])

async function collectSymlinks(dir, out) {
  let entries
  try {
    entries = await fsp.readdir(dir, { withFileTypes: true })
  } catch {
    return
  }
  for (const entry of entries) {
    const full = path.join(dir, entry.name)
    if (entry.isSymbolicLink()) out.push(full)
    else if (entry.isDirectory() && !SKIP_DIRS.has(entry.name)) await collectSymlinks(full, out)
  }
}

// A target that does not exist here YET can only be something PLWL itself
// creates later: Proton links files/data/fake-steam/appcache into its prefix,
// a prefix links into files/wines/<build>/... (see the fallback pass below).
// Restricting the fallback to these trees keeps an unrelated /usr/lib/... link
// from being mistaken for a wine build's own files/lib/ directory.
const ANCHOR_DIRS = new Set(['wines', 'wineprefixes', 'apps', 'data', 'translations'])

// True when `candidate` sits under `root` and its deepest EXISTING parent is at
// least two components inside it. `files/data/fake-steam/appcache` passes even
// before appcache is created, because files/data/fake-steam is already there;
// `files/bin/<x>` does not, because a single-component parent is no evidence
// that the link really belongs to the launcher.
function anchoredInside(root, candidate) {
  let p = candidate
  while (p.length > root.length + 1) {
    p = path.dirname(p)
    if (p === root || !p.startsWith(root + path.sep)) return false
    if (exists(p)) return path.relative(root, p).split(path.sep).length >= 2
  }
  return false
}

// The new target for an absolute link: the same file, reached from the link's
// own directory. `roots` are the trees the target may live in - the tree being
// healed first, then (for a prefix linking into its build) the launcher's
// files/ root. When the target is not directly inside one of them, the longest
// suffix that exists here is used instead, which is what makes a link written
// on another machine work on this one.
function relativeTarget(link, target, roots) {
  const dir = path.dirname(link)
  for (const root of roots) {
    if (!root) continue
    if (target.startsWith(root + path.sep)) {
      const rel = path.relative(dir, target)
      if (rel && !path.isAbsolute(rel)) return rel
    }
  }
  // Second chance for links whose file is not here yet (or whose parent chain
  // only partially exists): the relative path is still the right one, and
  // writing it now beats leaving a link that can never resolve.
  for (const requireLeaf of [true, false]) {
    for (const root of roots) {
      if (!root) continue
      let i = target.indexOf(path.sep, 1)
      while (i !== -1) {
        const rest = target.slice(i + 1)
        if (rest && !rest.split(path.sep).includes('..')) {
          const candidate = path.join(root, rest)
          if (candidate.startsWith(root + path.sep)) {
            const ok = requireLeaf
              ? exists(candidate)
              : ANCHOR_DIRS.has(rest.replace(/\\/g, '/').split('/')[0]) && anchoredInside(root, candidate)
            if (ok) {
              const rel = path.relative(dir, candidate)
              if (rel && !path.isAbsolute(rel)) return rel
            }
          }
        }
        i = target.indexOf(path.sep, i + 1)
      }
    }
  }
  return null
}

// Rewire every absolute symlink under `root` that can be expressed relative to
// `roots` (usually [root, DIRS.FILES]). Returns how many links changed. A link
// may only become rewirable once another link it chains through has been
// fixed, so the pass repeats until nothing changes.
async function rewireSymlinks(root, roots = []) {
  if (!root) return 0
  const candidates = [root, ...roots.filter(r => r && r !== root)]
  const links = []
  await collectSymlinks(root, links)
  let fixed = 0
  for (let pass = 0; pass < 5; pass++) {
    let changed = 0
    for (const link of links) {
      let target
      try {
        target = await fsp.readlink(link)
      } catch {
        continue
      }
      if (!path.isAbsolute(target)) continue // already relocatable
      const next = relativeTarget(link, path.normalize(target), candidates)
      if (!next || next === target) continue
      try {
        await fsp.unlink(link)
        await fsp.symlink(next, link)
        fixed++
        changed++
      } catch {}
    }
    if (!changed) break
  }
  return fixed
}

// Binaries a wine/proton build has to be able to execute. A copy that pipes
// file contents (the LAN sync, fs.copyFile) drops the bit, and without it
// `spawn` fails with EACCES and the build can never run. Windows .exe files
// are NOT in here on purpose: wine starts those itself, they need no bit.
const EXEC_NAMES = new Set(['proton', 'wine', 'wine64', 'wine-preloader', 'wine64-preloader', 'wineserver', 'winetricks', 'wineboot'])

// Give the exec bit back to a build's binaries (and anything in a bin/ dir).
// Used after a sync or an import - and to repair a build that was synced
// before the sync knew about permissions, without re-copying it.
async function restoreExecutableBits(root) {
  if (!root) return 0
  let fixed = 0
  const walk = async dir => {
    let entries
    try {
      entries = await fsp.readdir(dir, { withFileTypes: true })
    } catch {
      return
    }
    for (const entry of entries) {
      const full = path.join(dir, entry.name)
      if (entry.isSymbolicLink()) continue
      if (entry.isDirectory()) {
        await walk(full)
        continue
      }
      if (!entry.isFile()) continue
      const inBin = path.basename(dir) === 'bin'
      if (!inBin && !EXEC_NAMES.has(entry.name) && !entry.name.endsWith('.sh')) continue
      try {
        const st = await fsp.stat(full)
        if (st.mode & 0o111) continue
        await fsp.chmod(full, (st.mode & 0o777) | 0o755)
        fixed++
      } catch {}
    }
  }
  await walk(root)
  return fixed
}

module.exports = { rewireSymlinks, restoreExecutableBits, collectSymlinks, relativeTarget, EXEC_NAMES }