关于micro:go-micro-wrapper-中间件

go micro wrapper 中间件

本篇不波及中间件底层是如何运作的，如有趣味请见 [micro server] 篇

在 options.go 中有如下定义

// WrapClient is a convenience method for wrapping a Client with
// some middleware component. A list of wrappers can be provided.
// Wrappers are applied in reverse order so the last is executed first.
func WrapClient(w ...client.Wrapper) Option {return func(o *Options) {
        // apply in reverse
        for i := len(w); i > 0; i-- {o.Client = w[i-1](o.Client)
        }
    }
}

// WrapCall is a convenience method for wrapping a Client CallFunc
func WrapCall(w ...client.CallWrapper) Option {return func(o *Options) {o.Client.Init(client.WrapCall(w...))
    }
}

// WrapHandler adds a handler Wrapper to a list of options passed into the server
func WrapHandler(w ...server.HandlerWrapper) Option {return func(o *Options) {var wrappers []server.Option

        for _, wrap := range w {wrappers = append(wrappers, server.WrapHandler(wrap))
        }

        // Init once
        o.Server.Init(wrappers...)
    }
}

// WrapSubscriber adds a subscriber Wrapper to a list of options passed into the server
func WrapSubscriber(w ...server.SubscriberWrapper) Option {return func(o *Options) {var wrappers []server.Option

        for _, wrap := range w {wrappers = append(wrappers, server.WrapSubscriber(wrap))
        }

        // Init once
        o.Server.Init(wrappers...)
    }
}

这些参数设置用于 micro.NewService() 参数

有以下几种类型

1. WrapClient() 用于用一些中间件组件包装 Client, 包装器以相同的程序利用，因而最初一个先执行。
2. WrapCall() 用于不便包装 Client CallFunc
3. WrapHandler() 将一系列 handler 中间件传给 server，并初始化
4. WrapSubscriber() 将一系列 subscriber 中间件传给 server，并初始化

在 server/wrapper.go 中，定义了 wrapper

// HandlerFunc represents a single method of a handler. It's used primarily
// for the wrappers. What's handed to the actual method is the concrete
// request and response types.
type HandlerFunc func(ctx context.Context, req Request, rsp interface{}) error

// SubscriberFunc represents a single method of a subscriber. It's used primarily
// for the wrappers. What's handed to the actual method is the concrete
// publication message.
type SubscriberFunc func(ctx context.Context, msg Message) error

// HandlerWrapper wraps the HandlerFunc and returns the equivalent
type HandlerWrapper func(HandlerFunc) HandlerFunc

// SubscriberWrapper wraps the SubscriberFunc and returns the equivalent
type SubscriberWrapper func(SubscriberFunc) SubscriberFunc

// StreamWrapper wraps a Stream interface and returns the equivalent.
// Because streams exist for the lifetime of a method invocation this
// is a convenient way to wrap a Stream as its in use for trace, monitoring,
// metrics, etc.
type StreamWrapper func(Stream) Stream

服务端次要是

1. HandlerWrapper() 用于 handler 处理器的中间件
2. SubscriberWrapper() 用于订阅的中间件
3. StreamWrapper() 用于流的中间件

在 client/wrapper.go 中，定义了 client 的中间件

// CallFunc represents the individual call func
type CallFunc func(ctx context.Context, node *registry.Node, req Request, rsp interface{}, opts CallOptions) error

// CallWrapper is a low level wrapper for the CallFunc
type CallWrapper func(CallFunc) CallFunc

// Wrapper wraps a client and returns a client
type Wrapper func(Client) Client

// StreamWrapper wraps a Stream and returns the equivalent
type StreamWrapper func(Stream) Stream

客户端次要是

1. CallWrapper() client call 中间件
2. Wrapper() client 中间件
3. StreamWrapper() 流中间件

上面是一个 client 中间件 Wrapper 的例子

type logWrapper struct {client.Client}

func (l *logWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {md, _ := metadata.FromContext(ctx)
    fmt.Printf("[Log Wrapper] ctx: %v service: %s method: %s\n", md, req.Service(), req.Endpoint())
    return l.Client.Call(ctx, req, rsp)
}

func NewLogWrapper(c client.Client) client.Client {return &logWrapper{c}
}

NewLogWrapper()实现了type Wrapper func(Client) Client

上面是一个 handler wrapper 的例子

func NewLogWrapper(fn server.HandlerFunc) server.HandlerFunc {return func(ctx context.Context, req server.Request, rsp interface{}) error {log.Printf("[Log Wrapper] Before serving request method: %v", req.Endpoint())
        err := fn(ctx, req, rsp)
        log.Printf("[Log Wrapper] After serving request")
        return err
    }
}

NewLogWrapper()实现了type HandlerWrapper func(HandlerFunc) HandlerFunc

HandlerFunc定义是type HandlerFunc func(ctx context.Context, req Request, rsp interface{}) error

所以咱们看到中间件都是函数里 return 的写法

具体实例能够参考官网 plugins 中的 opentracing wrapper 写法

https://github.com/micro/go-p…

这里包含

1. client.Client 定义
2. NewClientWrapper
3. NewCallWrapper
4. NewHandlerWrapper
5. NewSubscriberWrapper

如果你想要实现本人的中间件，这里的官网实现是个不错的参考

Service Wrapper

很多时候须要从处理程序外部拜访服务。Service Wrapper 就是形式之一。它将服务嵌入到 ctx 中，这样就能够在 handler 中应用它。

srv := micro.NewService(micro.Name("com.example.srv.foo"),
)

srv.Init(micro.WrapClient(service.NewClientWrapper(srv))
    micro.WrapHandler(service.NewHandlerWrapper(srv)),
)

在 srv.Init()中增加 wrapper

在 handler 中能够这样应用 service

func (e *Example) Handler(ctx context.Context, req *example.Request, rsp *example.Response) error {service, ok := micro.FromContext(ctx)
    if !ok {return errors.InternalServerError("com.example.srv.foo", "Could not retrieve service")
    }

    // do something with the service
    fmt.Println("Got service", service)
    return nil
}

在 client wrapper 中也能够应用

type myWrapper struct {client.Client}

func (m *myWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {service, ok = micro.FromContext(ctx)
    if !ok {return errors.InternalServerError("com.example.srv.foo.mywrapper", "Could not retrieve service")
    }

    // do something with the service
    fmt.Println("Got service", service)

    // now do some call
    return c.Client.Call(ctx, req, rsp, opts...)
}

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go micro config
go micro store
go micro registry
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go micro runtime
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go micro 链路追踪
go micro 熔断与限流
go micro wrapper 中间件
go micro metrics 接入 Prometheus、Grafana