go 1.8 插件使用自定义接口(interface)

Question

我想使用基于 go 插件的自定义接口(interface)，但我发现它不支持。

filter.Filter的定义

package filter

import (
    "net/http"

    "github.com/valyala/fasthttp"
)

// Context filter context
type Context interface {
    SetStartAt(startAt int64)
    SetEndAt(endAt int64)
    GetStartAt() int64
    GetEndAt() int64

    GetProxyServerAddr() string
    GetProxyOuterRequest() *fasthttp.Request
    GetProxyResponse() *fasthttp.Response
    NeedMerge() bool

    GetOriginRequestCtx() *fasthttp.RequestCtx

    GetMaxQPS() int

    ValidateProxyOuterRequest() bool

    InBlacklist(ip string) bool
    InWhitelist(ip string) bool

    IsCircuitOpen() bool
    IsCircuitHalf() bool

    GetOpenToCloseFailureRate() int
    GetHalfTrafficRate() int
    GetHalfToOpenSucceedRate() int
    GetOpenToCloseCollectSeconds() int

    ChangeCircuitStatusToClose()
    ChangeCircuitStatusToOpen()

    RecordMetricsForRequest()
    RecordMetricsForResponse()
    RecordMetricsForFailure()
    RecordMetricsForReject()

    GetRecentlyRequestSuccessedCount(sec int) int
    GetRecentlyRequestCount(sec int) int
    GetRecentlyRequestFailureCount(sec int) int
}

// Filter filter interface
type Filter interface {
    Name() string

    Pre(c Context) (statusCode int, err error)
    Post(c Context) (statusCode int, err error)
    PostErr(c Context)
}

// BaseFilter base filter support default implemention
type BaseFilter struct{}

// Pre execute before proxy
func (f BaseFilter) Pre(c Context) (statusCode int, err error) {
    return http.StatusOK, nil
}

// Post execute after proxy
func (f BaseFilter) Post(c Context) (statusCode int, err error) {
    return http.StatusOK, nil
}

// PostErr execute proxy has errors
func (f BaseFilter) PostErr(c Context) {

}

这个 pkg 在我的 go app 项目中。

加载插件文件

package proxy

import (
    "errors"
    "plugin"
    "strings"

    "github.com/fagongzi/gateway/pkg/conf"
    "github.com/fagongzi/gateway/pkg/filter"
)

var (
    // ErrKnownFilter known filter error
    ErrKnownFilter = errors.New("unknow filter")
)

const (
    // FilterHTTPAccess access log filter
    FilterHTTPAccess = "HTTP-ACCESS"
    // FilterHeader header filter
    FilterHeader = "HEAD" // process header fiter
    // FilterXForward xforward fiter
    FilterXForward = "XFORWARD"
    // FilterBlackList blacklist filter
    FilterBlackList = "BLACKLIST"
    // FilterWhiteList whitelist filter
    FilterWhiteList = "WHITELIST"
    // FilterAnalysis analysis filter
    FilterAnalysis = "ANALYSIS"
    // FilterRateLimiting limit filter
    FilterRateLimiting = "RATE-LIMITING"
    // FilterCircuitBreake circuit breake filter
    FilterCircuitBreake = "CIRCUIT-BREAKE"
    // FilterValidation validation request filter
    FilterValidation = "VALIDATION"
)

func newFilter(filterSpec *conf.FilterSpec) (filter.Filter, error) {
    if filterSpec.External {
        return newExternalFilter(filterSpec)
    }

    input := strings.ToUpper(filterSpec.Name)

    switch input {
    case FilterHTTPAccess:
        return newAccessFilter(), nil
    case FilterHeader:
        return newHeadersFilter(), nil
    case FilterXForward:
        return newXForwardForFilter(), nil
    case FilterAnalysis:
        return newAnalysisFilter(), nil
    case FilterBlackList:
        return newBlackListFilter(), nil
    case FilterWhiteList:
        return newWhiteListFilter(), nil
    case FilterRateLimiting:
        return newRateLimitingFilter(), nil
    case FilterCircuitBreake:
        return newCircuitBreakeFilter(), nil
    case FilterValidation:
        return newValidationFilter(), nil
    default:
        return nil, ErrKnownFilter
    }
}

func newExternalFilter(filterSpec *conf.FilterSpec) (filter.Filter, error) {
    p, err := plugin.Open(filterSpec.ExternalPluginFile)
    if err != nil {
        return nil, err
    }

    s, err := p.Lookup("NewExternalFilter")
    if err != nil {
        return nil, err
    }

    sf := s.(func() (filter.Filter, error))
    return sf()
}

这是我的go app项目中加载插件的代码

package main

import (
    "C"
    "strings"
    "time"

    "github.com/CodisLabs/codis/pkg/utils/log"
    "github.com/fagongzi/gateway/pkg/filter"
    "github.com/valyala/fasthttp"
)

// AccessFilter record the http access log
// log format: $remoteip "$method $path" $code "$agent" $svr $cost
type AccessFilter struct {
}

// NewExternalFilter create a External filter
func NewExternalFilter() (filter.Filter, error) {
    return &AccessFilter{}, nil
}

// Name return name of this filter
func (f *AccessFilter) Name() string {
    return "HTTP-ACCESS"
}

// Pre pre process
func (f *AccessFilter) Pre(c filter.Context) (statusCode int, err error) {
    return 200, nil
}

// Post execute after proxy
func (f *AccessFilter) Post(c filter.Context) (statusCode int, err error) {
    cost := (c.GetStartAt() - c.GetEndAt())

    log.Infof("%s %s \"%s\" %d \"%s\" %s %s",
        GetRealClientIP(c.GetOriginRequestCtx()),
        c.GetOriginRequestCtx().Method(),
        c.GetProxyOuterRequest().RequestURI(),
        c.GetProxyResponse().StatusCode(),
        c.GetOriginRequestCtx().UserAgent(),
        c.GetProxyServerAddr(),
        time.Duration(cost))

    return 200, nil
}

// PostErr post error process
func (f *AccessFilter) PostErr(c filter.Context) {

}

// GetRealClientIP get read client ip
func GetRealClientIP(ctx *fasthttp.RequestCtx) string {
    xforward := ctx.Request.Header.Peek("X-Forwarded-For")
    if nil == xforward {
        return strings.SplitN(ctx.RemoteAddr().String(), ":", 2)[0]
    }

    return strings.SplitN(string(xforward), ",", 2)[0]
}

这是插件的定义，在我的插件项目中。 plugin项目和go app项目是不同的项目。

我发现错误:

panic: interface conversion: plugin.Symbol is func() (filter.Filter, error), not func() (filter.Filter, error)

你可以在这个项目中找到代码https://github.com/fagongzi/gateway/tree/go18-plugin-support。

1. filter.Filter 在 pkg/filter 包中。
2. 加载插件文件 in proxy/factory.go
3. plugin go file 在另一个项目中。

Answer 1

自定义界面工作得很好。

但是一件重要的事情:你只能type assert从在插件的外部 定义的插件查找的值中的类型(您不能引用插件中定义的类型)。这也适用于“复合类型”的每个组件，例如，您只能键入断言其参数和结果类型也在插件外部定义的函数类型。

1。在插件之外使用通用包

一种解决方案是在插件外部的包中定义接口(interface)，插件和您的应用程序都可以导入和引用它。

在filter包中定义:

package filter

type Filter interface {
    Name() string
    Age() int
}

插件在pq包中，导入filter包:

package main

import (
    "fmt"
    "filter"
)

type plgFilter struct{}

func (plgFilter) Name() string { return "Bob" }
func (plgFilter) Age() int     { return 23 }

func GetFilter() (f filter.Filter, err error) {
    f = plgFilter{}
    fmt.Printf("[plugin GetFilter] Returning filter: %T %v\n", f, f)
    return
}

主应用程序也导入(相同的)包 filter，加载插件，查找 GetFilter()，调用它并使用返回的 过滤器:

package main

import (
    "fmt"
    "filter"
    "plugin"
)

func main() {
    p, err := plugin.Open("pg/pg.so")
    if err != nil {
        panic(err)
    }

    GetFilter, err := p.Lookup("GetFilter")
    if err != nil {
        panic(err)
    }
    filter, err := GetFilter.(func() (filter.Filter, error))()
    fmt.Printf("GetFilter result: %T %v %v\n", filter, filter, err)
    fmt.Println("\tName:", filter.Name())
    fmt.Println("\tAge:", filter.Age())
}

输出:

[plugin GetFilter] Returning filter: main.plgFilter {}
GetFilter result: main.plgFilter {} <nil>
        Name: Bob
        Age: 23

2。插件返回 interface{}，并在主应用中定义接口(interface)

另一种解决方案是让插件函数返回类型为 interface{} 的值。您的主应用可以定义它期望的接口(interface)，并且可以对插件返回的 interface{} 值使用类型断言。

这次没有filter包。

插件在pq包中:

package main

import (
    "fmt"
)

type plgFilter struct{}

func (plgFilter) Name() string { return "Bob" }
func (plgFilter) Age() int     { return 23 }

func GetFilterIface() (f interface{}, err error) {
    f = plgFilter{}
    fmt.Printf("[plugin GetFilterIface] Returning filter: %T %v\n", f, f)
    return
}

和主应用程序:

package main

import (
    "fmt"
    "plugin"
)

func main() {
    p, err := plugin.Open("pg/pg.so")
    if err != nil {
        panic(err)
    }

    GetFilterIface, err := p.Lookup("GetFilterIface")
    if err != nil {
        panic(err)
    }
    filterIface, err := GetFilterIface.(func() (interface{}, error))()
    fmt.Printf("GetFilterIface result: %T %v %v\n", filterIface, filterIface, err)
    myfilter := filterIface.(MyFilter)
    fmt.Println("\tName:", myfilter.Name())
    fmt.Println("\tAge:", myfilter.Age())
}

type MyFilter interface {
    Name() string
    Age() int
}

输出:

[plugin GetFilterIface] Returning filter: main.plgFilter {}
GetFilterIface result: main.plgFilter {} <nil>
        Name: Bob
        Age: 23

另见相关问题:How do Go plugin dependencies work?