Support listing out npm cache

lib/cache.js

@@ -22,18 +22,21 @@ cache.usage = 'npm cache add <tarball file>' +
               '\nnpm cache add <git url>' +
               '\nnpm cache add <name>@<version>' +
               '\nnpm cache clean' +
+              '\nnpm cache list [--json]' +
               '\nnpm cache verify'
 
 cache.completion = function (opts, cb) {
   var argv = opts.conf.argv.remain
   if (argv.length === 2) {
-    return cb(null, ['add', 'clean'])
+    return cb(null, ['add', 'clean', 'list', 'verify'])
   }
 
   // TODO - eventually...
   switch (argv[2]) {
     case 'clean':
     case 'add':
+    case 'list':
+    case 'verify':
       return cb(null, [])
   }
 }
@@ -52,6 +55,9 @@ function cache (args, cb) {
     case 'verify': case 'check':
       result = verify()
       break
+    case 'list': case 'ls':
+      result = list()
+      break
     default: return cb('Usage: ' + cache.usage)
   }
   if (!result || !result.then) {
@@ -135,3 +141,49 @@ function unpack (pkg, ver, unpackTarget, dmode, fmode, uid, gid) {
     return pacote.extract(npa.resolve(pkg, ver), unpackTarget, opts)
   })
 }
+
+cache.list = list
+function list () {
+  const json = npm.config.get('json')
+  const cache = path.join(npm.config.get('cache'), '_cacache')
+  let writer
+  if (json) {
+    writer = {
+      item: undefined,
+      handleElement: function (item) {
+        if (this.item === undefined) {
+          output('[')
+        } else {
+          output('  ' + JSON.stringify(this.item) + ',')
+        }
+        this.item = item
+      },
+      done: function () {
+        if (this.item === undefined) {
+          output(JSON.stringify([]))
+        } else {
+          output('  ' + JSON.stringify(this.item))
+          output(']')
+        }
+      }
+    }
+  } else {
+    writer = {
+      handleElement: function (item) {
+        output(item.key)
+        output('  url = ' + (item.metadata === undefined ? 'undefined' : item.metadata.url))
+        output('  path = ' + item.path)
+        output('  size = ' + item.size)
+        output('  time = ' + item.time)
+      },
+      done: () => {}
+    }
+  }
+
+  return new BB((resolve, reject) => {
+    const stream = cacache.ls.stream(cache)
+    stream.on('data', (item) => writer.handleElement(item))
+    stream.on('error', error => { reject(error) })
+    stream.on('end', () => { writer.done(); resolve('done') })
+  })
+}