代理中间件

stringsvc3没有完全按照官网中stringsvc3的写法，而是在stringsvc2的基础上增加了proxy.go
主要就是给uppercase增加了代理中间件，主要步骤分三步：
1）向特定地址代理服务器发送请求的client的编码和解码函数。
2）生成向特定地址代理服务器发送请求的client。
3）用client配合load balancer构建代理服务器中间件。

package main

import (
    "bytes"
    "context"
    "encoding/json"
    "errors"
    "fmt"
    "net/http"
    "net/url"
    "strings"
    "time"

    "github.com/go-kit/kit/sd/lb"

    "golang.org/x/time/rate"

    "github.com/go-kit/kit/endpoint"
    "github.com/go-kit/kit/ratelimit"
    "github.com/sony/gobreaker"

    "io/ioutil"

    "github.com/go-kit/kit/circuitbreaker"

    "github.com/go-kit/kit/log"
    "github.com/go-kit/kit/sd"
    httptransport "github.com/go-kit/kit/transport/http"
)

定义所需类型

type ServiceMiddleware func(StringService) StringService

获取用户指定的代理服务器地址列表,本样例中，用户输入多个代理服务器用”,”分割

func split(s string) []string {
    a := strings.Split(s, ",")
    for i := range a {
        a[i] = strings.TrimSpace(a[i])
    }

    return a
}

根据httptransport.NewClient的参数需要，需要一个将client的request编码的函数（如下encodeRequest），以及将代理服务器返回的数据转为response的函数（如下：decodeUppercaseResponse）

往代理服务发送请求时，将request转为io.ReaderCloser

func encodeRequest(_ context.Context, r *http.Request, request interface{}) error {
    var buf bytes.Buffer
    if err := json.NewEncoder(&buf).Encode(request); err != nil {
        return err
    }
    r.Body = ioutil.NopCloser(&buf)
    return nil

}

func decodeUppercaseResponse(_ context.Context, r *http.Response) (interface{}, error) {
    var response uppercaseResponse
    if err := json.NewDecoder(r.Body).Decode(&response); err != nil {
        return nil, err
    }
    return response, nil
}

创建到特定地址代理服务器的client

func makeUppercaseProxy(ctc context.Context, instance string) endpoint.Endpoint {
    if !strings.HasPrefix(instance, "http") {
        instance = "http://" + instance
    }

    u, err := url.Parse(instance)
    if err != nil {
        panic(err)
    }
    if u.Path == "" {
        u.Path = "/uppercase"
    }

    return httptransport.NewClient(
        "GET",
        u,
        encodeRequest,
        decodeUppercaseResponse,
    ).Endpoint()
}

定义使用了代理机制的新服务

type proxymw struct {
    next      StringService //用于处理Count请求
    uppercase endpoint.Endpoint //load balance处理uppercase
}

//直接用当前服务处理Count请求
func (mw proxymw) Count(ctx context.Context, s string) int {
    return mw.next.Count(ctx, s)
}

//将uppercase请求发往各个代理服务器中(后面会讲到通过Load balancer实现）
func (mw proxymw) Uppercase(ctx context.Context, s string) (string, error) {
    response, err := mw.uppercase(ctx, uppercaseRequest{S: s})
    if err != nil {
        return "", err
    }

    resp := response.(uppercaseResponse)
    if resp.Err != "" {
        return resp.V, errors.New(resp.Err)
    }

    return resp.V, nil
}

根据用户输入的代理服务器地址生成对应的代理服务器中间件

//根据用户输入的多个地址，创建到多个服务器的代理
func proxyMiddleware(ctx context.Context, instances string, logger log.Logger) ServiceMiddleware {
    if instances == "" {
        logger.Log("proxy_to", "none")
        return func(next StringService) StringService { return next }
    }

    var (
        qps         = 100                    //请求频率超过多少会返回错误
        maxAttempts = 3                      //请求在放弃前重试多少次，用于 load balancer
        maxTime     = 250 * time.Millisecond // 请求在放弃前的超时时间，用于 load balancer
    )

    var (
        instanceList = split(instances)
        endpointer   sd.FixedEndpointer
    )
    logger.Log("proxy_to", fmt.Sprint(instanceList))
    for _, instance := range instanceList {
        var e endpoint.Endpoint
        e = makeUppercaseProxy(ctx, instance) //创建client
        e = circuitbreaker.Gobreaker(gobreaker.NewCircuitBreaker(gobreaker.Settings{}))(e) //添加breader
        e = ratelimit.NewErroringLimiter(rate.NewLimiter(rate.Every(time.Second), qps))(e) //添加limiter
        endpointer = append(endpointer, e)
    }
    balancer := lb.NewRoundRobin(endpointer) //添加load balancer

    //Retry封装一个service load balancer，返回面向特定service method的load balancer。到这个endpoint的请求会自动通过
    //load balancer进行分配到各个代理服务器中。返回失败的请求会自动retry直到成功或者到达最大失败次数或者超时。
    retry := lb.Retry(maxAttempts, maxTime, balancer)//添加retry机制
    return func(next StringService) StringService {
        return proxymw{next, retry}
    }
}

func main() {
    var (
        listen = flag.String("listen", ":8080", "http lisetern address")
        proxy  = flag.String("proxy", "", "optional ")
    )
    flag.Parse()
    logger := log.NewLogfmtLogger(os.Stderr)
    logger = log.With(logger, "listern", *listen, "caller", log.DefaultCaller)
    //注意这里的 filedkeys要和 methodField 中的一致，不然会报错
    //fieldKeys := []string{"metod", "error"}
    //2017/10/19 18:09:28 http: panic serving [::1]:55246: label name "metod" missing in label map
    fieldKeys := []string{"method", "error"}
    requestCount := kitprometheus.NewCounterFrom(stdprometheus.CounterOpts{
        Namespace: "my_gropu",
        Subsystem: "string_service",
        Name:      "request_count",
        Help:      "Number of requests received.",
    }, fieldKeys)

    requestLatency := kitprometheus.NewSummaryFrom(stdprometheus.SummaryOpts{
        Namespace: "my_gropu",
        Subsystem: "string_service",
        Name:      "request_latence_microseconds",
        Help:      "Number of requests in misroseconds.",
    }, fieldKeys)

    countResult := kitprometheus.NewSummaryFrom(stdprometheus.SummaryOpts{
        Namespace: "my_gropu",
        Subsystem: "string_service",
        Name:      "count_result",
        Help:      "The result of each count method.",
    }, []string{})

    //svc := stringService{}
    //cannot use logMiddleware literal (type logMiddleware) as type stringService in assignment

    var svc StringService
    svc = stringService{}
    svc = proxyMiddleware(context.Background(), *proxy, logger)(svc)
    svc = logMiddleware{logger, svc}
    svc = instrumentingMiddleware{requestCount, requestLatency, countResult, svc}

    uppercaseHandler := httptransport.NewServer(
        makeUppercaseEndpoint(svc),
        decodeUpperCaseRequest,
        encodeResponse,
    )

    countHandler := httptransport.NewServer(
        makeCountEndpoint(svc),
        decodeCountRequest,
        encodeResponse,
    )
    http.Handle("/uppercase", uppercaseHandler)
    http.Handle("/count", countHandler)
    http.Handle("/metrics", promhttp.Handler())
    logger.Log("msg", "HTTP", "addr", *listen)
    logger.Log("err", http.ListenAndServe(*listen, nil))
}

相对于stringsvc2.md，就增加了

    svc = proxyMiddleware(context.Background(), *proxy, logger)(svc)

可以看到，利用gokit的middlerware方式书写代码，增加功能非常简单。

Sean-MacBook-Air:stringsrv3 kes$ ./main -listen=:8001
listern=:8001 caller=proxy.go:109 proxy_to=none
listern=:8001 caller=main.go:329 msg=HTTP addr=:8001
listern=:8001 caller=main.go:186 logmethod=uppercase input=foo output=FOO err=null took=1.883µs


Sean-MacBook-Air:stringsrv3 kes$ ./main -listen=:8082
listern=:8082 caller=proxy.go:109 proxy_to=none
listern=:8082 caller=main.go:329 msg=HTTP addr=:8082
listern=:8082 caller=main.go:186 logmethod=uppercase input=bar output=BAR err=null took=1.993µs


Sean-MacBook-Air:stringsrv3 kes$ ./main -listen=:8080 -proxy=localhost:8001,localhost:8082
listern=:8080 caller=proxy.go:123 proxy_to="[localhost:8001 localhost:8082]"
listern=:8080 caller=main.go:329 msg=HTTP addr=:8080
listern=:8080 caller=main.go:186 logmethod=uppercase input=foo output=FOO err=null took=4.496073ms
listern=:8080 caller=main.go:186 logmethod=uppercase input=bar output=BAR err=null took=1.983719ms

Sean-MacBook-Air:goproject kes$ for s in foo bar ;do curl -d"{\"s\":\"$s\"}" localhost:8080/uppercase;done
{"v":"FOO"}
{"v":"BAR"}

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