perf: try to unpack tarball immediatly instead of exist check

package.json

@@ -75,7 +75,7 @@
     "ssri": "^4.1.3",
     "symlink-dir": "^1.0.3",
     "thenify": "^3.3.0",
-    "unpack-stream": "^2.0.0-beta.1",
+    "unpack-stream": "^2.0.0",
     "write-json-file": "^2.0.0",
     "write-pkg": "^3.1.0",
     "write-yaml-file": "^1.0.0"

shrinkwrap.yaml

@@ -59,7 +59,7 @@ dependencies:
   ssri: 4.1.6
   symlink-dir: 1.0.3
   thenify: 3.3.0
-  unpack-stream: 2.0.0-beta.1
+  unpack-stream: 2.0.0
   write-json-file: 2.2.0
   write-pkg: 3.1.0
   write-yaml-file: 1.0.0
@@ -2069,14 +2069,14 @@ packages:
       through: 2.3.8
     resolution:
       integrity: sha1-jITITVtMwo/B+fV3IDu9PLhgoWo=
-  /unpack-stream/2.0.0-beta.1:
+  /unpack-stream/2.0.0:
     dependencies:
       '@types/node': 7.0.33
       decompress-maybe: 1.0.0
       ssri: 4.1.6
       tar-fs: 1.15.3
     resolution:
-      integrity: sha1-mJt0iwP06FuGy0pvmP8RGu0mCmM=
+      integrity: sha1-PFpevB3voZ3LiyzkPqdJPyBOWG4=
   /unquote/1.1.0:
     dev: true
     resolution:
@@ -2246,7 +2246,7 @@ specifiers:
   thenify: ^3.3.0
   tslint: ^5.4.2
   typescript: ^2.4.1
-  unpack-stream: ^2.0.0-beta.1
+  unpack-stream: ^2.0.0
   validate-commit-msg: ^2.7.0
   write-json-file: ^2.0.0
   write-pkg: ^3.1.0

src/install/fetchResolution.ts

@@ -4,7 +4,6 @@ import path = require('path')
 import execa = require('execa')
 import {IncomingMessage} from 'http'
 import * as unpackStream from 'unpack-stream'
-import existsFile = require('path-exists')
 import dint = require('dint')
 import {Resolution} from '../resolve'
 import {Got} from '../network/got'
@@ -90,7 +89,16 @@ export function fetchFromTarball (dir: string, dist: PackageDist, opts: FetchOpt
 
 export async function fetchFromRemoteTarball (dir: string, dist: PackageDist, opts: FetchOptions) {
   const localTarballPath = path.join(opts.storePath, opts.pkgId, 'packed.tgz')
-  if (!await existsFile(localTarballPath)) {
+  try {
+    const index = await fetchFromLocalTarball(dir, {
+      integrity: dist.integrity,
+      tarball: localTarballPath,
+    })
+    fetchLogger.debug(`finish ${dist.integrity} ${dist.tarball}`)
+    return index
+  } catch (err) {
+    if (err['code'] !== 'ENOENT') throw err
+
     if (opts.offline) {
       throw new PnpmError('NO_OFFLINE_TARBALL', `Could not find ${localTarballPath} in local registry mirror ${opts.storePath}`)
     }
@@ -101,12 +109,6 @@ export async function fetchFromRemoteTarball (dir: string, dist: PackageDist, op
       onStart: () => logStatus({status: 'fetching', pkgId: opts.pkgId}),
     })
   }
-  const index = await fetchFromLocalTarball(dir, {
-    integrity: dist.integrity,
-    tarball: localTarballPath,
-  })
-  fetchLogger.debug(`finish ${dist.integrity} ${dist.tarball}`)
-  return index
 }
 
 async function fetchFromLocalTarball (