fix(prefetch): fall back to the _integrity in the manifest if none ca…

…lculated

prefetch.js

@@ -50,6 +50,11 @@ function prefetchByManifest (start, spec, opts) {
     return finished(stream)
   }).then(() => {
     opts.log.verbose('prefetch', `${spec} done in ${Date.now() - start}ms`)
-    return {manifest, spec, integrity, byDigest: false}
+    return {
+      manifest,
+      spec,
+      integrity: integrity || manifest._integrity,
+      byDigest: false
+    }
   })
 }

test/prefetch.js

@@ -69,7 +69,7 @@ test('prefetch by manifest if no integrity hash', t => {
       t.equal(srv.isDone(), true)
       t.deepEqual(info, {
         byDigest: false,
-        integrity: null, // not previously cached, so no integrity
+        integrity: BASE._integrity,
         manifest: BASE,
         spec: 'foo@1.0.0'
       }, 'fresh fetch info returned')
@@ -127,7 +127,7 @@ test('prefetch by manifest if digest provided but no cache content found', t =>
     return prefetch('foo@1.0.0', OPTS).then(info => {
       t.deepEqual(info, {
         byDigest: false,
-        integrity: null, // not already cached, so no integrity
+        integrity: BASE._integrity,
         manifest: BASE,
         spec: 'foo@1.0.0'
       }, 'fresh fetch info returned')