main.go

package main

import (
	"bytes"
	"context"
	"encoding/base64"
	"fmt"
	"log"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/s3/s3manager"
	"golang.org/x/sync/errgroup"
	"golang.org/x/sync/semaphore"
)

// 100並行までのセマフォを作る
var s *semaphore.Weighted = semaphore.NewWeighted(100)

func main() {
	// base64の文字列の配列
	images := []string{}

	sess := session.Must(session.NewSession())
	uploader := s3manager.NewUploader(sess)

	ctx := context.Background()

	// エラーがあった場合、処理を中断するため errogroup.Group を使う
	var eg errgroup.Group
	for i := range images {
		// シャドーイングを回避
		image := images[i]

		eg.Go(func() error {
			// 重みを追加
			s.Acquire(ctx, 1)
			// 重みをリリース
			defer s.Release(1)

			b, err := base64.StdEncoding.DecodeString(image)
			if err != nil {
				return fmt.Errorf("failed to decode image from base64 string: %w", err)
			}
			// make object key
			key := ""

			// upload to s3
			_, err = uploader.Upload(&s3manager.UploadInput{
				Bucket: aws.String("bucket"),
				Key:    aws.String(key),
				Body:   bytes.NewBuffer(b),
			})
			if err != nil {
				return fmt.Errorf("failed to upload s3: %w", err)
			}
			return nil
		})
	}
	if err := eg.Wait(); err != nil {
		log.Fatalf("faield to convert or upload image: %s", err)
	}
}