如何在 go 中为 lambda 中间件创建泛型类型

问题内容

我正在 aws lambda 中使用 go 并寻找通用的中间件解决方案。我有以下代码：

func wshandler(ctx context.context, event events.apigatewaywebsocketproxyrequest) (events.apigatewayproxyresponse, error) {
}

type handlerfunc func(context.context, events.apigatewaywebsocketproxyrequest) (events.apigatewayproxyresponse, error)

func logmiddleware(next handlerfunc) handlerfunc {
    return handlerfunc(func(ctx context.context, event events.apigatewaywebsocketproxyrequest) (events.apigatewayproxyresponse, error) {
        
        return next(ctx, event)
    })
}

lambda.start(logmiddleware(wshandler))

中间件函数有一个参数 events.apigatewaywebsocketproxyrequest 因为目标处理程序 wshandler 使用此类型。

我有另一个处理程序，它采用参数 event events.apigatewayproxyrequest ，如下所示。由于参数不匹配，因此无法使用此中间件。

graphqlquerymutationhandler(ctx context.context, event events.apigatewayproxyrequest){
...
}

我尝试将中间件句柄更改为 interface{}，但不起作用。 go 抱怨这种类型。

type HandlerFunc func(context.Context, interface{}) (interface{}, error)

有没有办法让中间件适用于任何处理程序类型？

正确答案

让我分享我能够在我的系统上复制的工作解决方案。首先给大家分享一下我使用的项目布局：

events/
  http_event.json
  sqs_event.json
hello-world/
  main.go
sqs/
  main.go
middlewares/
  middlewares.go

现在，让我们关注代码。

middlewares/middlewares.go

代码如下：

package middlewares

import (
    "context"
    "fmt"

    "github.com/aws/aws-lambda-go/events"
)

type record struct {
    events.apigatewayproxyrequest `json:",omitempty"`
    events.sqsevent               `json:",omitempty"`
}

type event struct {
    records []record `json:"records"`
}

type handlerfunc func(ctx context.context, event event) (string, error)

func logmiddleware(ctx context.context, next handlerfunc) handlerfunc {
    return handlerfunc(func(ctx context.context, event event) (string, error) {
        fmt.println("log from middleware!")
        return next(ctx, event)
    })
}

让我们总结一下基本概念：

• 我们定义 event 结构体，它将成为我们的通用事件。它是 record 结构的包装器。
• record 结构使用结构嵌入来嵌入我们要处理的所有事件（例如 event.apigatewayproxyrequest 和 sqsevent）。
• 我们依靠中间件签名中的这一点来尽可能通用。

events/http_event.json

{
    "records": [
        {
            "body": "{\"message\": \"hello world\"}",
            "resource": "/hello",
            "path": "/hello",
            "httpmethod": "get",
            "isbase64encoded": false,
            "querystringparameters": {
                "foo": "bar"
            },
            "pathparameters": {
                "proxy": "/path/to/resource"
            },
            "stagevariables": {
                "baz": "qux"
            },
            "headers": {
                "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
                "accept-encoding": "gzip, deflate, sdch",
                "accept-language": "en-us,en;q=0.8",
                "cache-control": "max-age=0",
                "cloudfront-forwarded-proto": "https",
                "cloudfront-is-desktop-viewer": "true",
                "cloudfront-is-mobile-viewer": "false",
                "cloudfront-is-smarttv-viewer": "false",
                "cloudfront-is-tablet-viewer": "false",
                "cloudfront-viewer-country": "us",
                "host": "1234567890.execute-api.us-east-1.amazonaws.com",
                "upgrade-insecure-requests": "1",
                "user-agent": "custom user agent string",
                "via": "1.1 08f323deadbeefa7af34d5feb414ce27.cloudfront.net (cloudfront)",
                "x-amz-cf-id": "cdehvqoznx43vyqb9j2-nvch-9z396uhbp027y2jvkcpnlmgjhqlaa==",
                "x-forwarded-for": "127.0.0.1, 127.0.0.2",
                "x-forwarded-port": "443",
                "x-forwarded-proto": "https"
            },
            "requestcontext": {
                "accountid": "123456789012",
                "resourceid": "123456",
                "stage": "prod",
                "requestid": "c6af9ac6-7b61-11e6-9a41-93e8deadbeef",
                "requesttime": "09/apr/2015:12:34:56 +0000",
                "requesttimeepoch": 1428582896000,
                "identity": {
                    "cognitoidentitypoolid": null,
                    "accountid": null,
                    "cognitoidentityid": null,
                    "caller": null,
                    "accesskey": null,
                    "sourceip": "127.0.0.1",
                    "cognitoauthenticationtype": null,
                    "cognitoauthenticationprovider": null,
                    "userarn": null,
                    "useragent": "custom user agent string",
                    "user": null
                },
                "path": "/prod/hello",
                "resourcepath": "/hello",
                "httpmethod": "get",
                "apiid": "1234567890",
                "protocol": "http/1.1"
            }
        }
    ]
}

这里没什么可说的。

events/sqs_event.json

{
    "records": [
        {
            "records": [
                {
                    "messageid": "19dd0b57-b21e-4ac1-bd88-01bbb068cb78",
                    "receipthandle": "messagereceipthandle",
                    "body": "my own event payload!",
                    "attributes": {
                        "approximatereceivecount": "1",
                        "senttimestamp": "1523232000000",
                        "senderid": "123456789012",
                        "approximatefirstreceivetimestamp": "1523232000001"
                    },
                    "messageattributes": {},
                    "md5ofbody": "4d1d0024b51659ad8c3725f9ba7e2471",
                    "eventsource": "aws:sqs",
                    "eventsourcearn": "arn:aws:sqs:us-east-1:123456789012:myqueue",
                    "awsregion": "us-east-1"
                }
            ]
        }
    ]
}

这同样适用于这里。

hello-world/main.go

package main

import (
    "context"
    "fmt"

    "httplambda/middlewares"

    "github.com/aws/aws-lambda-go/lambda"
)

func lambdahandler(ctx context.context, event middlewares.event) (string, error) {
    _ = ctx
    fmt.println("path:", event.records[0].apigatewayproxyrequest.path)

    fmt.println("hi from http-triggered lambda!")

    return "", nil
}

func main() {
    // start the lambda handler
    lambda.start(middlewares.logmiddleware(context.background(), lambdahandler))
}

请注意我们如何获取活动信息。

sqs/main.go

package main

import (
    "context"
    "fmt"

    "httplambda/middlewares"

    "github.com/aws/aws-lambda-go/lambda"
)

func lambdaHandler(ctx context.Context, event middlewares.Event) (string, error) {
    _ = ctx
    fmt.Println("Queue name:", event.Records[0].SQSEvent.Records[0].EventSourceARN)
    fmt.Println("Hi from SQS-triggered lambda!")
    return "", nil
}

func main() {
    lambda.Start(middlewares.LogMiddleware(context.Background(), lambdaHandler))
}

决赛

有几个注意事项需要考虑：

1. 在遵循此解决方案之前，我尝试使用类型参数，但没有成功。中间件的签名中似乎不允许使用它们。
2. 代码过于简化，且尚未做好生产准备。

如果这有帮助或者您需要其他任何东西，请告诉我，谢谢！

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