部署到AWS Lambda后图片上传无法显示问题求助

本地运行代码时，上传至AWS S3的图片可通过浏览器链接正常显示；但将代码部署到AWS Lambda后，上传的图片无法显示。已添加S3相关IAM权限但问题仍未解决。

func UploadFile(uploader *manager.Uploader, key string, file multipart.File, fileHeader *multipart.FileHeader) (string, error) {

    if file == nil {
        return "", errors.New("file is nil")
    }

    contentType := fileHeader.Header.Get("Content-Type")
    if contentType == "" {
        contentType = "application/octet-stream" // Default to binary if content type is not provided
    }

    fileStat, err := fileHeader.Open()
    if err != nil {
        return "", fmt.Errorf("failed to open file for debugging: %w", err)
    }
    defer fileStat.Close()

    if _, err := file.Seek(0, 0); err != nil {
        return "", errors.New("failed to reset file cursor: " + err.Error())
    }

    result, err := uploader.Upload(context.TODO(), &s3.PutObjectInput{
        Bucket:      aws.String("unleap-bucket"),
        Key:         aws.String("uneleap/" + key),
        Body:        file,
        ContentType: aws.String(contentType),
        ACL:         types.ObjectCannedACLPublicRead,
    })

    if err != nil {
        return "", err
    }
    // Ensure the result is not nil and return the location of the uploaded file
    if result == nil || result.Location == "" {
        return "", errors.New("failed to get the uploaded file location")
    }
    return result.Location, err
}

service: uneleap-api-client

frameworkVersion: ">=4.1.19"


provider:
  name: aws
  region: eu-north-1
  runtime: go1.x
  stage: ${opt:stage}
  iam:
    role:
      statements:
        - Effect: "Allow"
          Action:
            - "s3:PutObject"
            - "s3:GetObject"
            - "s3:PutObjectAcl"
          Resource: "arn:aws:s3:::u-bucket/*"

custom:
  hooks:
    'package:initialize': ./scripts/generate_swagger.sh

package:
  patterns:
    - '!*/**'
    - bin/main

functions:
  api:
    handler: bin/main
    events:
      - http:
          path: /{proxy+}
          method: ANY
          cors: true

iam:
        role:
          statements:
            - Effect: "Allow"
              Action:
                - "s3:PutObject"
                - "s3:GetObject"
                - "s3:PutObjectAcl"
              Resource: "arn:aws:s3:::u-bucket/*"

• Bucket名称不匹配：代码中指定的Bucket是unleap-bucket，但IAM权限配置的Resource是u-bucket，两者不一致，导致权限无法覆盖实际使用的Bucket，这是核心问题之一。
• 文件指针重置有效性：代码中打开了fileStat但未使用，反而对file执行Seek(0,0)，需确认file的指针位置是否正确，若上传前文件指针已到末尾，会导致上传空文件。
• S3 Bucket公开访问限制：检查Bucket的「Block Public Access」设置，若开启了阻止公开访问，即使设置PublicRead ACL也无法让对象公开可访问。
• IAM权限范围修正：将IAM角色的Resource修改为arn:aws:s3:::unleap-bucket/*，确保权限覆盖实际使用的Bucket及对象路径。
• 上传内容完整性验证：查看Lambda日志，对比本地和Lambda环境下上传的文件大小，确认是否完整上传。
• Content-Type正确性检查：验证Lambda环境下是否正确获取到文件的Content-Type，若Content-Type错误（如默认成application/octet-stream），浏览器可能无法正确解析图片。

内容的提问来源于stack exchange，提问作者Gbenga B Ayannuga