SendGridのWebAPIを使ってメールを送信するためのLambdaアプリケーション

main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

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

type systemManagerResponse struct {
	Parameter systemManagerResponseParameter `json:"Parameter"`
}

type systemManagerResponseParameter struct {
	Arn              string      `json:"ARN"`
	DataType         string      `json:"DataType"`
	LastModifiedDate time.Time   `json:"LastModifiedDate"`
	Name             string      `json:"Name"`
	Selector         interface{} `json:"Selector"`
	SourceResult     interface{} `json:"SourceResult"`
	Type             string      `json:"Type"`
	Value            string      `json:"Value"`
	Version          int         `json:"Version"`
}

/**
SystemManager parameter storeからAPI_KEYを取得する
@see https://docs.aws.amazon.com/systems-manager/latest/userguide/ps-integration-lambda-extensions.html
*/
func getAPIKey() (*string, error) {
	url := fmt.Sprintf("http://localhost:2773/systemsmanager/parameters/get?name=%s&withDecryption=true", os.Getenv("API_KEY_PATH"))
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		log.Printf("ERROR: %v", err)
		return nil, err
	}
	req.Header.Set("X-Aws-Parameters-Secrets-Token", os.Getenv("AWS_SESSION_TOKEN"))

	client := http.Client{
		Timeout: 5 * time.Second,
	}
	res, err := client.Do(req)
	if err != nil {
		log.Printf("ERROR: %v", err)
		return nil, err
	}

	defer res.Body.Close()
	var smr systemManagerResponse
	json.NewDecoder(res.Body).Decode(&smr)
	if err != nil {
		log.Printf("ERROR: %v", err)
		return nil, err
	}

	return &smr.Parameter.Value, nil
}

func sendMail(messageBody string) error {
	apiKey, err := getAPIKey()
	if err != nil {
		log.Printf("ERROR: %v", err)
		return err
	}

	// SQSのキュー情報をそのままメール送信APIに渡すだけ
	req := sendgrid.GetRequest(*apiKey, "/v3/mail/send", "https://api.sendgrid.com")
	req.Method = "POST"
	req.Body = []byte(messageBody)
	ctx := context.Background()
	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	res, err := sendgrid.MakeRequestWithContext(ctx, req)

	// @see https://sendgrid.kke.co.jp/docs/API_Reference/Web_API_v3/Mail/errors.html
	if err != nil || res.StatusCode != 202 {
		log.Printf("ERROR: %v", err)
		log.Printf("StatusCode: %v", res.StatusCode)
		log.Printf("Response Headers: %v", res.Headers)
		log.Printf("Response Body: %v", res.Body)
		return fmt.Errorf("%s", "failed to send email.")
	}

	return nil
}

func handler(ctx context.Context, sqsEvent events.SQSEvent) error {
	for _, message := range sqsEvent.Records {
		err := sendMail(message.Body)
		if err != nil {
			log.Printf("ERROR: %v", err.Error())
			// 関数を異常終了させてキューを戻す
			os.Exit(1)
		}
	}
	return nil
}

func init() {
	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
}

func main() {
	lambda.Start(handler)
}