Properly handle an empty array of keys for prefetch/getMany, #151

Author: kriszyp

package.json

@@ -1,7 +1,7 @@
 {
   "name": "lmdb",
   "author": "Kris Zyp",
-  "version": "2.2.5",
+  "version": "2.2.6",
   "description": "Simple, efficient, scalable, high-performance LMDB interface",
   "license": "MIT",
   "repository": {

read.js

@@ -417,14 +417,15 @@ export function addReadMethods(LMDBStore, {
 			// allowing a separate to absorb the potentially largest cost: hard page faults (and disk I/O).
 			// And then we just do standard sync gets (to deserialized data) to fulfil the callback/promise
 			// once the prefetch occurs
+			let promise = callback ? undefined : new Promise(resolve => callback = (error, results) => resolve(results));
 			this.prefetch(keys, () => {
 				let results = new Array(keys.length);
 				for (let i = 0, l = keys.length; i < l; i++) {
 					results[i] = get.call(this, keys[i]);
 				}
 				callback(null, results);
 			});
-			return callback ? undefined : new Promise(resolve => callback = (error, results) => resolve(results));
+			return promise;
 		},
 		getSharedBufferForGet(id) {
 			let txn = (env.writeTxn || (readTxnRenewed ? readTxn : renewReadTxn()));
@@ -451,6 +452,15 @@ export function addReadMethods(LMDBStore, {
 			return buffer.slice(lastOffset, lastOffset + this.lastSize);/*Uint8ArraySlice.call(buffer, lastOffset, lastOffset + this.lastSize)*/
 		},
 		prefetch(keys, callback) {
+			if (!keys)
+				throw new Error('An array of keys must be provided');
+			if (!keys.length) {
+				if (callback) {
+					callback(null);
+					return;
+				} else
+					return Promise.resolve();
+			}
 			let buffers = [];
 			let startPosition;
 			let bufferHolder = {};

test/index.test.js

@@ -668,6 +668,8 @@ describe('lmdb-js', function() {
       let values = await db.getMany(keys);
       should.equal(values.length, 20);
       should.equal(values[3], value);
+      values = await db.getMany([]);
+      should.equal(values.length, 0);
     });
 
     it('invalid key', async function() {