RabbitMQ镜像队列初始化连接时的“优化”

之前发过一篇帖子 应用.Net+Consul维护RabbitMq的高可用性，然后最近老大问我当初我这么搞是抽的什么想法- -然后顺便贴了两行C#代码：

　　　　　　　　　var factory = new ConnectionFactory()
                {
                    UserName = "username",
                    Password = "password",
                    AutomaticRecoveryEnabled = true,
                    TopologyRecoveryEnabled = true
                };
                Connection = factory.CreateConnection(new string[3] { "ip1", "ip2", "ip3" });

AutomaticRecoveryEnabled的作用就是断线重连，假如当前的连接断开了，连接不会释放

TopologyRecoveryEnabled 重连后恢复当前的工作进程，比如channel、queue、发布的消息进度等。

看上去其实却是比较方便的，为了狡辩我当场列出了我设计的方案的主要优点:

1.rabbitmq网关设计的时候一方面是为了让客户端能够保证建立与master节点的连接，直连master性能较高。

2.通过配置队列名+VirthHost可以获取队列信息，Consul可以起到配置中心的作用，可配置性高一些(其实此处是狡辩。。)

3.RabbitMQ与Master队列建立的连接在发生故障时会第一时间查询网关获取新的Mater队列信息进行重连（当然代码内部也有重试机制，不会随便就更换连接的），相比于AutomaticRecoveryEnabled效率更高一些。

4.客户端SDK内部实现定时更新队列连接，发现Master节点更换时重新建立连接

看上去我设计的方案还是有点意义的（其实是真懒得改代码）

不过此处有个问题就是既然创建连接时的参数可以提供多个IP的集合，假如RabbitMQ提供的客户端SDK内部实现的更好，那我狡辩什么不也完戏了吗。。。于是假装下载了下客户端sdk代码扫了扫，此处以C#代码为例，代码还是比较简单的。github地址

直接定位ConnectionFactory类找CreateConnection()方法

       /// <summary>
        /// Create a connection using a list of hostnames using the configured port.
        /// By default each hostname is tried in a random order until a successful connection is
        /// found or the list is exhausted using the DefaultEndpointResolver.
        /// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
        /// </summary>
        /// <param name="hostnames">
        /// List of hostnames to use for the initial
        /// connection and recovery.
        /// </param>
        /// <returns>Open connection</returns>
        /// <exception cref="BrokerUnreachableException">
        /// When no hostname was reachable.
        /// </exception>
        public IConnection CreateConnection(IList<string> hostnames)
        {
            return CreateConnection(hostnames, null);
        }

        /// <summary>
        /// Create a connection using a list of hostnames using the configured port.
        /// By default each endpoint is tried in a random order until a successful connection is
        /// found or the list is exhausted.
        /// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
        /// </summary>
        /// <param name="hostnames">
        /// List of hostnames to use for the initial
        /// connection and recovery.
        /// </param>
        /// <param name="clientProvidedName">
        /// Application-specific connection name, will be displayed in the management UI
        /// if RabbitMQ server supports it. This value doesn't have to be unique and cannot
        /// be used as a connection identifier, e.g. in HTTP API requests.
        /// This value is supposed to be human-readable.
        /// </param>
        /// <returns>Open connection</returns>
        /// <exception cref="BrokerUnreachableException">
        /// When no hostname was reachable.
        /// </exception>
        public IConnection CreateConnection(IList<string> hostnames, String clientProvidedName)
        {
            var endpoints = hostnames.Select(h => new AmqpTcpEndpoint(h, this.Port, this.Ssl));
            return CreateConnection(new DefaultEndpointResolver(endpoints), clientProvidedName);
        }

        /// <summary>
        /// Create a connection using a list of endpoints. By default each endpoint will be tried
        /// in a random order until a successful connection is found or the list is exhausted.
        /// The selection behaviour can be overriden by configuring the EndpointResolverFactory.
        /// </summary>
        /// <param name="endpoints">
        /// List of endpoints to use for the initial
        /// connection and recovery.
        /// </param>
        /// <returns>Open connection</returns>
        /// <exception cref="BrokerUnreachableException">
        /// When no hostname was reachable.
        /// </exception>
        public IConnection CreateConnection(IList<AmqpTcpEndpoint> endpoints)
        {
            return CreateConnection(new DefaultEndpointResolver(endpoints), null);
        }

        /// <summary>
        /// Create a connection using an IEndpointResolver.
        /// </summary>
        /// <param name="endpointResolver">
        /// The endpointResolver that returns the endpoints to use for the connection attempt.
        /// </param>
        /// <param name="clientProvidedName">
        /// Application-specific connection name, will be displayed in the management UI
        /// if RabbitMQ server supports it. This value doesn't have to be unique and cannot
        /// be used as a connection identifier, e.g. in HTTP API requests.
        /// This value is supposed to be human-readable.
        /// </param>
        /// <returns>Open connection</returns>
        /// <exception cref="BrokerUnreachableException">
        /// When no hostname was reachable.
        /// </exception>
        public IConnection CreateConnection(IEndpointResolver endpointResolver, String clientProvidedName)
        {
            IConnection conn;
            try
            {
                if (AutomaticRecoveryEnabled)
                {
                    var autorecoveringConnection = new AutorecoveringConnection(this, clientProvidedName);
                    autorecoveringConnection.Init(endpointResolver);
                    conn = autorecoveringConnection;
                }
                else
                {
                    IProtocol protocol = Protocols.DefaultProtocol;
                    conn = protocol.CreateConnection(this, false, endpointResolver.SelectOne(this.CreateFrameHandler), clientProvidedName);
                }
            }
            catch (Exception e)
            {
                throw new BrokerUnreachableException(e);
            }

            return conn;
        }

代码比较直观，第二个方法的时候把传入的字符串集合转换成了AmqpTcpEndpoint集合，AmqpTcpEndpoint里包含队列绑定信息，包含默认ip,端口,SSL配置信息，RabbitMQ的Amqp协议信息，初始化Socket连接的协议类型（一个AddressFamily枚举），当然都是可配置的（除了ip貌似都喜欢使用默认的）。

然后就倒主要部分了。

               if (AutomaticRecoveryEnabled)
                {
                    var autorecoveringConnection = new AutorecoveringConnection(this, clientProvidedName);
                    autorecoveringConnection.Init(endpointResolver);
                    conn = autorecoveringConnection;
                }
                else
                {
                    IProtocol protocol = Protocols.DefaultProtocol;
                    conn = protocol.CreateConnection(this, false, endpointResolver.SelectOne(this.CreateFrameHandler), clientProvidedName);
                }             

由于主要想看看传入多个连接是不是可以智能的选择master连接，所以此处直接看else里的代码就行了。。。（其实一样。。）

protocol.CreateConnection方法调用时传入的第三个参数endpointResolver.SelectOne(this.CreateFrameHandler)作用其实就是选择连接然后扔到CreateFrameHandler委托里作为参数进行Socket初始化的。看一下SelectOne这个扩展方法即可。。看了两行终于可以继续狡辩了。。

         public static T SelectOne<T>(this IEndpointResolver resolver, Func<AmqpTcpEndpoint, T> selector)
        {
            var t = default(T);
            Exception exception = null;
            foreach(var ep in resolver.All())
            {
                try
                {
                    t = selector(ep);
                    if(t.Equals(default(T)) == false)
                    {
                        return t;
                    }
                }
                catch (Exception e)
                {
                    exception = e;
                }
            }

            if(Object.Equals(t, default(T)) && exception != null)
            {
                throw exception;
            }

            return t;
        }

这个foreach还是“比较好的”，能够建立一个Socket连接就愉快的返回了!，不过这个resolver.All()里是不是还有玄机呢！看了一眼。。终于放心了。。

     public class DefaultEndpointResolver : IEndpointResolver
    {
        private List<AmqpTcpEndpoint> endpoints;
        private Random rnd = new Random();

        public DefaultEndpointResolver (IEnumerable<AmqpTcpEndpoint> tcpEndpoints)
        {
           this.endpoints = tcpEndpoints.ToList();
        }

        public IEnumerable<AmqpTcpEndpoint> All()
        {
            return endpoints.OrderBy(item => rnd.Next());
        }

就是随机排序一下。。不过这么看自己实现下IEndpointResolver接口改个选择master队列的策略也是不错的。