Flutter/Dart：自动将上传到 S3 Bucket 的图像设置为“image/jpeg”？

Question

每当我从 Flutter 应用程序将图像文件上传到我的存储桶时，该对象会自动在元数据中显示为“binary/octet-stream”，而不是我需要的“image/jpeg”类别。

我使用的代码是这样的；

String filename}) async {
    final endpoint = 'https://$bucket.s3-$region.amazonaws.com ';
    final uploadDest = '$destDir/${filename ?? path.basename(file.path)}';

    final stream = http.ByteStream(Stream.castFrom(file.openRead()));
    
    final length = await file.length();

    final uri = Uri.parse(endpoint);
    final req = http.MultipartRequest("POST", uri);
    final multipartFile = http.MultipartFile('file', stream, length,
        filename: path.basename(file.path)
        );

    final policy = Policy.fromS3PresignedPost(uploadDest, bucket, accessKey, 15, length, region: region);
    final key = SigV4.calculateSigningKey(secretKey, policy.datetime, region, 's3');
    final signature = SigV4.calculateSignature(key, policy.encode());

    req.files.add(multipartFile);
    req.fields['key'] = policy.key;
    req.fields['acl'] = 'public-read';
    req.fields['X-Amz-Credential'] = policy.credential;
    req.fields['X-Amz-Algorithm'] = 'AWS4-HMAC-SHA256';
    req.fields['X-Amz-Date'] = policy.datetime;
    req.fields['Policy'] = policy.encode();
    req.fields['X-Amz-Signature'] = signature;

如何将照片自动上传为“image/jpeg”，以便可以在浏览器中查看而不是下载到我的桌​​面？

Answer 1

您可以附加一个媒体 contentType: new MediaType('image', 'jpeg') 类型，如下所示

new http.MultipartFile.fromBytes('file', await File.fromUri("<path/to/file>").readAsBytes(), contentType: new MediaType('image', 'jpeg'))

别忘了导入 import 'package:http_parser/http_parser.dart';