getFriendsThatPlay(appID, callback) {
		return StdLib.Promises.timeoutCallbackPromise(10000, null, callback, (resolve, reject) => {
			let buf = ByteBuffer.allocate(8, ByteBuffer.LITTLE_ENDIAN);
			buf.writeUint64(appID);
			this._send(EMsg.ClientGetFriendsWhoPlayGame, buf.flip(), (body) => {
				let eresult = body.readUint32();
				let err = Helpers.eresultError(eresult);
				if (err) {
					return reject(err);
				}

				let steamIds = [];
				let responseAppid = body.readUint64().toString();
				let countFriends = body.readUint32().toString();

				if (responseAppid != appID) {
					return reject(new Error('AppID in response does not match request'));
				}

				for (let i = 0; i < countFriends; i++) {
					steamIds.push(new SteamID(body.readUint64().toString()));
				}

				return resolve({friends: steamIds});
			});
		});
	}
Get a list of friends that play a specific app.
@param {int} appID
@param {function} [callback]
@returns {Promise}