multiGet breaking test and fix

Summary:
the flush + optimized multiGet result in an obscure bug that results when two multiGet requests with overlapping key sets get issued. The result array for both requests ends up bigger than the key array (because it has duplicates)
Closes https://github.com/facebook/react-native/pull/5514

Reviewed By: svcscm

Differential Revision: D2908264

Pulled By: nicklockwood

fb-gh-sync-id: 60be1bce4acfc47083e4ae28bb8b63f9dfa56039

IntegrationTests/AsyncStorageTest.js

@@ -142,12 +142,30 @@ function testMerge() {
         expectAsyncNoError('testMerge/setItem', err3);
         expectEqual(JSON.parse(result), VAL_MERGE_EXPECT, 'testMerge');
         updateMessage('objects deeply merged\nDone!');
+        runTestCase('multi set and get', testOptimizedMultiGet);
+      });
+    });
+  });
+}
+
+function testOptimizedMultiGet() {
+  let batch = [[KEY_1, VAL_1], [KEY_2, VAL_2]];
+  let keys = batch.map(([key, value]) => key);
+  AsyncStorage.multiSet(batch, (err1) => {
+    // yes, twice on purpose
+    ;[1, 2].forEach((i) => {
+      expectAsyncNoError(`${i} testOptimizedMultiGet/multiSet`, err1);
+      AsyncStorage.multiGet(keys, (err2, result) => {
+        expectAsyncNoError(`${i} testOptimizedMultiGet/multiGet`, err2);
+        expectEqual(result, batch, `${i} testOptimizedMultiGet multiGet`);
+        updateMessage('multiGet([key_1, key_2]) correctly returned ' + JSON.stringify(result));
         done();
       });
     });
   });
 }
 
+
 var AsyncStorageTest = React.createClass({
   getInitialState() {
     return {

Libraries/Storage/AsyncStorage.js

@@ -180,14 +180,16 @@ var AsyncStorage = {
       // Even though the runtime complexity of this is theoretically worse vs if we used a map,
       // it's much, much faster in practice for the data sets we deal with (we avoid
       // allocating result pair arrays). This was heavily benchmarked.
+      //
+      // Is there a way to avoid using the map but fix the bug in this breaking test?
+      // https://github.com/facebook/react-native/commit/8dd8ad76579d7feef34c014d387bf02065692264
+      let map = {};
+      result.forEach(([key, value]) => map[key] = value);
       const reqLength = getRequests.length;
       for (let i = 0; i < reqLength; i++) {
         const request = getRequests[i];
         const requestKeys = request.keys;
-        var requestResult = result.filter(function(resultPair) {
+        let requestResult = requestKeys.map(key => [key, map[key]]);
-          return requestKeys.indexOf(resultPair[0]) !== -1;
-        });
-
         request.callback && request.callback(null, requestResult);
         request.resolve && request.resolve(requestResult);
       }
@@ -214,6 +216,7 @@ var AsyncStorage = {
     var getRequest = {
       keys: keys,
       callback: callback,
+      // do we need this?
       keyIndex: this._getKeys.length,
       resolve: null,
       reject: null,
@@ -225,7 +228,12 @@ var AsyncStorage = {
     });
 
     this._getRequests.push(getRequest);
-    this._getKeys.push.apply(this._getKeys, keys);
+    // avoid fetching duplicates
+    keys.forEach(key => {
+      if (this._getKeys.indexOf(key) === -1) {
+        this._getKeys.push(key);
+      }
+    });
 
     return promiseResult;
   },