Add duplicate function to duplicate the current client instance

Fixes #919

README.md

@@ -572,6 +572,10 @@ the second word as first parameter:
     client.multi().script('load', 'return 1').exec(...);
     client.multi([['script', 'load', 'return 1']]).exec(...);
 
+## client.duplicate([options])
+
+Duplicate all current options and return a new redisClient instance. All options passed to the duplicate function are going to replace the original option.
+
 ## client.send_command(command_name[, [args][, callback]])
 
 Used internally to send commands to Redis. Nearly all Redis commands have been added to the `client` object.

index.js

@@ -135,6 +135,15 @@ RedisClient.prototype.create_stream = function () {
 RedisClient.prototype.cork = noop;
 RedisClient.prototype.uncork = noop;
 
+RedisClient.prototype.duplicate = function (options) {
+    var existing_options = clone(this.options);
+    options = clone(options);
+    for (var elem in options) { // jshint ignore: line
+        existing_options[elem] = options[elem];
+    }
+    return new RedisClient(existing_options);
+};
+
 RedisClient.prototype.initialize_retry_vars = function () {
     this.retry_timer = null;
     this.retry_totaltime = 0;

test/node_redis.spec.js

@@ -42,6 +42,45 @@ describe("The node_redis client", function () {
                     });
                 });
 
+                describe('duplicate', function () {
+                    it('check if all options got copied properly', function(done) {
+                        var client2 = client.duplicate();
+                        assert(client.connected);
+                        assert(!client2.connected);
+                        for (var elem in client.options) {
+                            if (client.options.hasOwnProperty(elem)) {
+                                assert.strictEqual(client2.options[elem], client.options[elem]);
+                            }
+                        }
+                        client2.on('ready', function () {
+                            client2.end(true);
+                            done();
+                        });
+                    });
+
+                    it('check if all new options replaced the old ones', function(done) {
+                        var client2 = client.duplicate({
+                            no_ready_check: true
+                        });
+                        assert(client.connected);
+                        assert(!client2.connected);
+                        assert.strictEqual(client.options.no_ready_check, undefined);
+                        assert.strictEqual(client2.options.no_ready_check, true);
+                        assert.notDeepEqual(client.options, client2.options);
+                        for (var elem in client.options) {
+                            if (client.options.hasOwnProperty(elem)) {
+                                if (elem !== 'no_ready_check') {
+                                    assert.strictEqual(client2.options[elem], client.options[elem]);
+                                }
+                            }
+                        }
+                        client2.on('ready', function () {
+                            client2.end(true);
+                            done();
+                        });
+                    });
+                });
+
                 describe('big data', function () {
 
                     // Check if the fast mode for big strings is working correct