Go言語によるAmazon S3実装ガイド

{
    "Version": "2012-10-17",
    "Id": "Policy1741260717481",
    "Statement": [
        {
            "Sid": "Stmt1741260713124",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::047719652545:user/cli-user"
            },
            "Action": [
                "s3:PutObject",
                "s3:PutObjectAcl"
            ],
            "Resource": [
                "arn:aws:s3:::trouble-storage-bucket",
                "arn:aws:s3:::trouble-storage-bucket/*"
            ],
            "Condition": {
                "StringEquals": {
                    "s3:x-amz-acl": "public-read"
                }
            }
        }
    ]
}

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package main

import (
 "context"
 "fmt"
 "log"
 "mime/multipart"
 "net/http"
 "os"
 "time"

 "github.com/aws/aws-sdk-go-v2/aws"
 "github.com/aws/aws-sdk-go-v2/config"
 "github.com/aws/aws-sdk-go-v2/credentials"
 "github.com/aws/aws-sdk-go-v2/feature/s3/manager"
 "github.com/aws/aws-sdk-go-v2/service/s3"
)

const (
 BucketName = "storagebucket"
 Region     = "region"
 AccessKey  = "Access_key"
 SecretKey  = "Secret Key"
)

var uploader *manager.Uploader
var client *s3.Client

func init() {
 cfg, err := config.LoadDefaultConfig(context.TODO(),
  config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(
   AccessKey,
   SecretKey,
   "",
  )),
  config.WithRegion(Region),
 )
 if err != nil {
  log.Fatalf("Failed to load AWS SDK config: %v", err)
 }

 // Create S3 client and uploader gloabally so it can be used.
 client = s3.NewFromConfig(cfg)
 uploader = manager.NewUploader(client)
}

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func uploadFileToS3(file multipart.File, fileHeader *multipart.FileHeader) (string, error) {
 // Upload input
 uploadInput := &s3.PutObjectInput{
  Bucket:      aws.String(BucketName),
  Key:         aws.String(fileHeader.Filename),
  Body:        file,
  ContentType: aws.String(fileHeader.Header.Get("Content-Type")),
 }

 // Upload file
 result, err := uploader.Upload(context.TODO(), uploadInput)
 if err != nil {
  return "", fmt.Errorf("failed to upload file to S3: %w", err)
 }

 // getsigned url
 fmt.Println("result.Location ::", *result.Key)
 url, err := GetPresignedURL(fileHeader.Filename)
 return url, nil
}

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func GetPresignedURL(fileName string) (string, error) {
 presigner := s3.NewPresignClient(client)
 // Generate a pre-signed URL for PUT (upload)
 presignedReq, err := presigner.PresignGetObject(context.TODO(), &s3.GetObjectInput{
  Bucket: aws.String(BucketName),
  Key:    aws.String(fileName),
 }, s3.WithPresignExpires(15*time.Minute)) // URL expires in 15 minutes

 if err != nil {
  return "", fmt.Errorf("failed to create presigned URL: %w", err)
 }
 fmt.Println("presignedURL ::", presignedReq.URL)

 return presignedReq.URL, nil
}

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func main() {
 http.HandleFunc("/upload", UploadHandler)

 port := os.Getenv("PORT")
 if port == "" {
  port = "8080"
 }
 log.Println("Server running on port:", port)
 log.Fatal(http.ListenAndServe(":"+port, nil))
}

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// UploadHandler handles file upload to S3
func UploadHandler(w http.ResponseWriter, r *http.Request) {
 if r.Method != http.MethodPost {
  http.Error(w, "Invalid request method", http.StatusMethodNotAllowed)
  return
 }

 // Parse the multipart form
 err := r.ParseMultipartForm(10 << 20) // 10 MB max file size
 if err != nil {
  http.Error(w, "Failed to parse form", http.StatusBadRequest)
  return
 }

 // Retrieve the file
 file, fileHeader, err := r.FormFile("file")
 if err != nil {
  http.Error(w, "Failed to get file", http.StatusBadRequest)
  return
 }
 defer file.Close()

 // Upload file to S3
 fileURL, err := uploadFileToS3(file, fileHeader)
 if err != nil {
  fmt.Println("Error ::", err.Error())
  http.Error(w, "Failed to upload file to S3", http.StatusInternalServerError)
  return
 }

 // Return the file URL
 w.WriteHeader(http.StatusOK)
 fmt.Fprintf(w, `{"message": "File uploaded successfully", "url": "%s"}`, fileURL)
}

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