最近手上有点时间,打算继续了解下go-micro的发布订阅(消息),看了micro的examples后,有个疑问,go-micro在提供发布订阅的插件Broker(以及几种实现)的同时,go-micro本身还实现了Publish(Client)以及Subscribe(Server)功能,于是翻了下源码,做个记录。

Broker

Broker是go-micro定义的一个异步消息的接口,同时使用插件的形式,可随意在不同的实现(http,nats,rabbitmq)之间无缝切换。

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// Broker is an interface used for asynchronous messaging.
type Broker interface {
   Init(...Option) error
   Options() Options
   Address() string
   Connect() error
   Disconnect() error
   Publish(topic string, m *Message, opts ...PublishOption) error
   Subscribe(topic string, h Handler, opts ...SubscribeOption) (Subscriber, error)
   String() string
}

从上面的接口可以看出,使用Broker来完成发布订阅只需要以下几步:

  1. 初始化一个Broker(Init)
  2. 连接Broker(Connect)
  3. 使用准备好的Broker发布/订阅(Publish/Subscribe)
  4. 关闭Broker(Disconnect)

go-micro中默认的broker实现

go-micro默认有基于http的Broker实现,可以直接使用。micro有给出具体的example,具体看下source code中的实现。

下面是go-micro中broer.go中对DefaultBroker的相关code:

var (
 DefaultBroker Broker = NewBroker()
)

func Init(opts ...Option) error {
 return DefaultBroker.Init(opts...)
}

func Connect() error {
 return DefaultBroker.Connect()
}

func Disconnect() error {
 return DefaultBroker.Disconnect()
}

func Publish(topic string, msg *Message, opts ...PublishOption) error {
 return DefaultBroker.Publish(topic, msg, opts...)
}

func Subscribe(topic string, handler Handler, opts ...SubscribeOption) (Subscriber, error) {
 return DefaultBroker.Subscribe(topic, handler, opts...)
}

func String() string {
 return DefaultBroker.String()
}

可以看到都是基于NewBroker()返回的broker实例来做的公用方法封装,我们进一步看看。

// NewBroker returns a new http broker
func NewBroker(opts ...Option) Broker {
 return newHttpBroker(opts...)
}

这里是直接返回了一个http实现的broker(和上面提到的默认是基于http实现的匹配),继续跟newHttpBroker

这里这列出部分code,详细的可直接参考go-micro下的http.go

h := &httpBroker{
    id:          uuid.New().String(),
    address:     addr,
    opts:        options,
    r:           options.Registry,
    c:           &http.Client{Transport: newTransport(options.TLSConfig)},
    subscribers: make(map[string][]*httpSubscriber),
    exit:        make(chan chan error),
    mux:         http.NewServeMux(),
    inbox:       make(map[string][][]byte),
  }

这里的核心是new了一个httpBroker,做为Broker接口的实现,在具体的实现就不在这里说了,下来我们看看上面提到接口的实现。

Init

func (h *httpBroker) Init(opts ...Option) error {
  h.RLock()
  if h.running {
    h.RUnlock()
    return errors.New("cannot init while connected")
  }
  h.RUnlock()
  h.Lock()
  defer h.Unlock()
  for _, o := range opts {
    o(&h.opts)
  }
  if len(h.opts.Addrs) > 0 && len(h.opts.Addrs[0]) > 0 {
    h.address = h.opts.Addrs[0]
  }
  if len(h.id) == 0 {
    h.id = "go.micro.http.broker-" + uuid.New().String()
  }
  // get registry
  reg := h.opts.Registry
  if reg == nil {
    reg = registry.DefaultRegistry
  }
  // get cache
  if rc, ok := h.r.(cache.Cache); ok {
    rc.Stop()
  }
  // set registry
  h.r = cache.New(reg)
  // reconfigure tls config
  if c := h.opts.TLSConfig; c != nil {
    h.c = &http.Client{
      Transport: newTransport(c),
    }
  }
  return nil
}

从上面的code中可以看到,Init的作用就是初始化各种配置,如果Option参数有提供,就是用参数提供的,如果没有就在这里设置一个,这里有2个点我们需要额外关注下:

  • Registry

    Registry是注册中心,如果option中没有提供registry,就会使用go-micro默认实现的(msdn)

  • TLSConfig

    TLSConfig是针对https的配置,默认是http

Connect

func (h *httpBroker) Connect() error {
  h.RLock()
  if h.running {
    h.RUnlock()
    return nil
  }
  h.RUnlock()
  
  h.Lock()
  defer h.Unlock()
  
  var l net.Listener
  var err error
  
  if h.opts.Secure || h.opts.TLSConfig != nil {
    config := h.opts.TLSConfig
  
    fn := func(addr string) (net.Listener, error) {
      if config == nil {
        hosts := []string{addr}

        // check if its a valid host:port
        if host, _, err := net.SplitHostPort(addr); err == nil {
          if len(host) == 0 {
            hosts = maddr.IPs()
          } else {
            hosts = []string{host}
          }
        }

        // generate a certificate
        cert, err := mls.Certificate(hosts...)
        if err != nil {
          return nil, err
        }
        config = &tls.Config{Certificates: []tls.Certificate{cert}}
      }
      return tls.Listen("tcp", addr, config)
    }

    l, err = mnet.Listen(h.address, fn)
  } else {
    fn := func(addr string) (net.Listener, error) {
      return net.Listen("tcp", addr)
    }
  
    l, err = mnet.Listen(h.address, fn)
  }
  
  if err != nil {
    return err
  }
  
  addr := h.address
  h.address = l.Addr().String()
  
  go http.Serve(l, h.mux)
  go func() {
    h.run(l)
    h.Lock()
    h.opts.Addrs = []string{addr}
    h.address = addr
    h.Unlock()
  }()
  
  // get registry
  reg := h.opts.Registry
  if reg == nil {
    reg = registry.DefaultRegistry
  }
  // set cache
  h.r = cache.New(reg)
  
  // set running
  h.running = true
  return nil
}

Connect方法的主要作用是创建一个Htto Server用来接收Publish时发送的消息

Subscribe

func (h *httpBroker) Subscribe(topic string, handler Handler, opts ...SubscribeOption) (Subscriber, error) {
  var err error
  var host, port string
  options := NewSubscribeOptions(opts...)
  
  // parse address for host, port
  host, port, err = net.SplitHostPort(h.Address())
  if err != nil {
    return nil, err
  }
  
  addr, err := maddr.Extract(host)
  if err != nil {
    return nil, err
  }
  
  var secure bool
  
  if h.opts.Secure || h.opts.TLSConfig != nil {
    secure = true
  }
  
  // register service
  node := &registry.Node{
    Id:      topic + "-" + h.id,
    Address: mnet.HostPort(addr, port),
    Metadata: map[string]string{
      "secure": fmt.Sprintf("%t", secure),
      "broker": "http",
      "topic":  topic,
    },
  }
  
  // check for queue group or broadcast queue
  version := options.Queue
  if len(version) == 0 {
    version = broadcastVersion
  }
  
  service := &registry.Service{
    Name:    serviceName,
    Version: version,
    Nodes:   []*registry.Node{node},
  }
  
  // generate subscriber
  subscriber := &httpSubscriber{
    opts:  options,
    hb:    h,
    id:    node.Id,
    topic: topic,
    fn:    handler,
    svc:   service,
  }
  
  // subscribe now
  if err := h.subscribe(subscriber); err != nil {
    return nil, err
  }
  
  // return the subscriber
  return subscriber, nil
}

这部分代码的核心功能就是创建用于订阅的server,一个topic创建一个server并收集(注册)到httpSubscriber的svc列表中(发布消息时使用topic在subscriber的svc列表中查询到对应的server给他发送消息)。

Publish

func (h *httpBroker) Publish(topic string, msg *Message, opts ...PublishOption) error {
  // create the message first
  m := &Message{
    Header: make(map[string]string),
    Body:   msg.Body,
  }
  
  for k, v := range msg.Header {
    m.Header[k] = v
  }
  
  m.Header["Micro-Topic"] = topic
  
  // encode the message
  b, err := h.opts.Codec.Marshal(m)
  if err != nil {
    return err
  }
  
  // save the message
  h.saveMessage(topic, b)
  
  // now attempt to get the service
  h.RLock()
  s, err := h.r.GetService(serviceName)
  if err != nil {
    h.RUnlock()
    return err
  }
  h.RUnlock()
  
  pub := func(node *registry.Node, t string, b []byte) error {
    scheme := "http"

    // check if secure is added in metadata
    if node.Metadata["secure"] == "true" {
      scheme = "https"
    }

    vals := url.Values{}
    vals.Add("id", node.Id)

    uri := fmt.Sprintf("%s://%s%s?%s", scheme, node.Address, DefaultPath, vals.Encode  ())
    r, err := h.c.Post(uri, "application/json", bytes.NewReader(b))
    if err != nil {
      return err
    }

    // discard response body
    io.Copy(ioutil.Discard, r.Body)
    r.Body.Close()
    return nil
  }
  
  srv := func(s []*registry.Service, b []byte) {
    for _, service := range s {
      var nodes []*registry.Node

      for _, node := range service.Nodes {
        // only use nodes tagged with broker http
        if node.Metadata["broker"] != "http" {
          continue
        }

        // look for nodes for the topic
        if node.Metadata["topic"] != topic {
          continue
        }

        nodes = append(nodes, node)
      }

      // only process if we have nodes
      if len(nodes) == 0 {
        continue
      }

      switch service.Version {
      // broadcast version means broadcast to all nodes
      case broadcastVersion:
        var success bool

        // publish to all nodes
        for _, node := range nodes {
          // publish async
          if err := pub(node, topic, b); err == nil {
            success = true
          }
        }

        // save if it failed to publish at least once
        if !success {
          h.saveMessage(topic, b)
        }
      default:
        // select node to publish to
        node := nodes[rand.Int()%len(nodes)]
        // publish async to one node
        if err := pub(node, topic, b); err != nil {
          // if failed save it
          h.saveMessage(topic, b)
        }
      }
    }
  }
  
  // do the rest async
  go func() {
    // get a third of the backlog
    messages := h.getMessage(topic, 8)
    delay := (len(messages) > 1)

    // publish all the messages
    for _, msg := range messages {
      // serialize here
      srv(s, msg)

      // sending a backlog of messages
      if delay {
        time.Sleep(time.Millisecond * 100)
      }
    }
  }()
  
  return nil

看过了上面的Subscribe实现,这里的Publish就比较简单

  1. 创建消息体并存储在inbox
  2. 根据topic以及broker的标签(这里是固定http)来查找订阅的server(在上面订阅模块创建的)

    上面有可能会查找出多个node(订阅server),所以里面还有一个版本的机制,如果指定了版本就会给所有的匹配节点发送(默认是随机发送一个)

  3. 使用http post的方式(异步)把消息发送出去

Disconnect

func (h *httpBroker) Disconnect() error {
  h.RLock()
  if !h.running {
    h.RUnlock()
    return nil
  }
  h.RUnlock()
  
  h.Lock()
  defer h.Unlock()
  
  // stop cache
  rc, ok := h.r.(cache.Cache)
  if ok {
    rc.Stop()
  }
  
  // exit and return err
  ch := make(chan error)
  h.exit <- ch
  err := <-ch
  
  // set not running
  h.running = false
  return err
}

这部分功能很简单,清空缓存并发送退出的消息,同时停止服务

以上就是go-micro中默认基于http的broker实现。

go-micro中对于broker的包装

在看完broker的http默认实现后,我们对于broker有了一个大体了解,接下来我们在看下go-micro对于broker做的包装部分,应该是为了简化使用(确实只需要一步就可以)。

订阅RegisterSubscriber

func main() {
  // create a service
  service := micro.NewService(
    micro.Name("go.micro.srv.pubsub"),
  )
  // parse command line
  service.Init()
  
  // register subscriber
  micro.RegisterSubscriber("example.topic.pubsub.1", service.Server(), new(Sub))
  
  // register subscriber with queue, each message is delivered to a unique   subscriber
  micro.RegisterSubscriber("example.topic.pubsub.2", service.Server(), subEv,   server.SubscriberQueue("queue.pubsub"))
  
  if err := service.Run(); err != nil {
    log.Fatal(err)
  }
}

发布NewPublisher, Publish

func main() {
  // create a service
  service := micro.NewService(
    micro.Name("go.micro.cli.pubsub"),
  )
  // parse command line
  service.Init()
  
  // create publisher
  pub1 := micro.NewPublisher("example.topic.pubsub.1", service.Client())
  pub2 := micro.NewPublisher("example.topic.pubsub.2", service.Client())
  
  // pub to topic 1
  go sendEv("example.topic.pubsub.1", pub1)
  // pub to topic 2
  go sendEv("example.topic.pubsub.2", pub2)
  
  // block forever
  select {}
}

以上只是代码节选,具体使用方法可以参考example中的pubsub

Subscriber

订阅对比直接用Broker只需要一步RegisterSubscriber,我们看看里面实现

//go-micro/micro.go
// RegisterSubscriber is syntactic sugar for registering a subscriber
func RegisterSubscriber(topic string, s server.Server, h interface{}, opts ...server.SubscriberOption) error {
  return s.Subscribe(s.NewSubscriber(topic, h, opts...))
}

//go-micro/server/rpc_server.go
func (s *rpcServer) NewSubscriber(topic string, sb interface{}, opts ...SubscriberOption) Subscriber {
  return s.router.NewSubscriber(topic, sb, opts...)
}
func (s *rpcServer) Subscribe(sb Subscriber) error {
  s.Lock()
  defer s.Unlock()
  
  if err := s.router.Subscribe(sb); err != nil {
    return err
  }
  
  s.subscribers[sb] = nil
  return nil
}

//go-micro/server/rpc_router.go
// router represents an RPC router.
type router struct {
  .......
  subscribers map[string][]*subscriber
}

//go-micro/server/subscriber.go
type subscriber struct {
  topic      string
  rcvr       reflect.Value
  typ        reflect.Type
  subscriber interface{}
  handlers   []*handler
  endpoints  []*registry.Endpoint
  opts       SubscriberOptions
}

上面的节选code可以看出,在默认server(rpcServer)中的router中定义了个map类型的变量subscribers用来存储订阅的topic和对应处理的subscriber,server在接收到消息后,只需要根据topic去map中找到subscriber,去处理即可。

subscriber中具体的处理,可以从定义中看出来,里面存储对应路由和响应的handler(server本身的功能),有兴趣可以在go-micro/server/subscriber.go看看具体代码实现。

Publisher

发布是在go-micro的默认client实现(rpc_client)里面定义了一个默认的broker(上面有分析过的http实现)

//go-micro/micro.go
// Deprecated: NewPublisher returns a new Publisher
func NewPublisher(topic string, c client.Client) Event {
  return NewEvent(topic, c)
}

// NewEvent creates a new event publisher
func NewEvent(topic string, c client.Client) Event {
  if c == nil {
    c = client.NewClient()
  }
  return &event{c, topic}
}


//go-micro/event.go
type event struct {
  c     client.Client
  topic string
}

func (e *event) Publish(ctx context.Context, msg interface{}, opts ...client.PublishOption) error {
  return e.c.Publish(ctx, e.c.NewMessage(e.topic, msg), opts...)
}

这里可以看到实际上是使用传递进来的client来初始化一个event,并用来发送消息,如果传递的是空,默认创建一个client(rpcClient)。

总结

经过以上过程的追踪,最终总结下来就几点:

  • broker定义了接口,micro提供的插件的形式可无缝替换实现
  • go-micro提供了一个默认的broker实现,是基于http
  • go-micro的基于默认的server、client以及brkoer包装了一套更简单的pub和sub方法
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