* first action!

node_modules/cacache/lib/util/move-file.js

@@ -0,0 +1,51 @@
+'use strict'
+
+const fs = require('graceful-fs')
+const BB = require('bluebird')
+const chmod = BB.promisify(fs.chmod)
+const unlink = BB.promisify(fs.unlink)
+let move
+let pinflight
+
+module.exports = moveFile
+function moveFile (src, dest) {
+  // This isn't quite an fs.rename -- the assumption is that
+  // if `dest` already exists, and we get certain errors while
+  // trying to move it, we should just not bother.
+  //
+  // In the case of cache corruption, users will receive an
+  // EINTEGRITY error elsewhere, and can remove the offending
+  // content their own way.
+  //
+  // Note that, as the name suggests, this strictly only supports file moves.
+  return BB.fromNode(cb => {
+    fs.link(src, dest, err => {
+      if (err) {
+        if (err.code === 'EEXIST' || err.code === 'EBUSY') {
+          // file already exists, so whatever
+        } else if (err.code === 'EPERM' && process.platform === 'win32') {
+          // file handle stayed open even past graceful-fs limits
+        } else {
+          return cb(err)
+        }
+      }
+      return cb()
+    })
+  }).then(() => {
+    // content should never change for any reason, so make it read-only
+    return BB.join(unlink(src), process.platform !== 'win32' && chmod(dest, '0444'))
+  }).catch(() => {
+    if (!pinflight) { pinflight = require('promise-inflight') }
+    return pinflight('cacache-move-file:' + dest, () => {
+      return BB.promisify(fs.stat)(dest).catch(err => {
+        if (err.code !== 'ENOENT') {
+          // Something else is wrong here. Bail bail bail
+          throw err
+        }
+        // file doesn't already exist! let's try a rename -> copy fallback
+        if (!move) { move = require('move-concurrently') }
+        return move(src, dest, { BB, fs })
+      })
+    })
+  })
+}