fix(read): skip reading the filesystem if our integrity hash is singl…

…e-entry

lib/content/read.js

@@ -52,7 +52,7 @@ function readStream (cache, integrity, opts) {
 module.exports.hasContent = hasContent
 function hasContent (cache, integrity) {
   if (!integrity) { return BB.resolve(false) }
-  return pickContentSri(cache, integrity)
+  return pickContentSri(cache, integrity, true)
   .catch({code: 'ENOENT'}, () => false)
   .catch({code: 'EPERM'}, err => {
     if (process.platform !== 'win32') {
@@ -64,18 +64,22 @@ function hasContent (cache, integrity) {
 }
 
 module.exports._pickContentSri = pickContentSri
-function pickContentSri (cache, integrity) {
+function pickContentSri (cache, integrity, checkFs) {
   const sri = ssri.parse(integrity)
   // If `integrity` has multiple entries, pick the first digest
   // with available local data.
   const algo = sri.pickAlgorithm()
   const digests = sri[algo]
   if (digests.length <= 1) {
     const cpath = contentPath(cache, digests[0])
-    return fs.lstatAsync(cpath).then(() => digests[0])
+    if (checkFs) {
+      return fs.lstatAsync(cpath).then(() => digests[0])
+    } else {
+      return BB.resolve(digests[0])
+    }
   } else {
     return BB.any(sri[sri.pickAlgorithm()].map(meta => {
-      return pickContentSri(cache, meta)
+      return pickContentSri(cache, meta, true)
     }))
   }
 }