c# - 如何将 azure blob 存储文件作为 FileStreamResult 返回？

Question

我正在开发用于处理文件的 Web API。我正在尝试从 azure blob 存储下载文件并将其作为响应返回。对于开发 API，我使用 FastEndpoints。

在 Stack Overflow 上，我发现最好的选择是使用 FileStreamResult，但我收到错误:

System.NotSupportedException: Deserialization of types without aparameterless constructor

我该如何解决这个问题以及为什么我会遇到这个问题？

端点

public class Endpoint : Endpoint<DownloadFileRequest, FileStreamResult>
{
    private readonly DatabaseContext _context;
    private readonly ILogger _logger;
    private readonly IConfiguration _configuration;

    public Endpoint(DatabaseContext context, ILogger<Endpoint> logger, IConfiguration configuration)
    {
        _context = context;
        _logger = logger;
        _configuration = configuration;
    }

    public override void Configure()
    {
        Get("/file/{id}/download");
        Roles(Role.Administrator, Role.ProjectManager, Role.GraphicDesigner, Role.Accountant);
        Description(b => b.WithName("DownloadFile"));
    }

    public override async Task HandleAsync(DownloadFileRequest r, CancellationToken c)
    {
        var file = await Data.GetTriadaFileAsync(_context, r.Id, c); // gets file to 
                                                                     // download

        if (file == null)
        {
            await SendNotFoundAsync(c);
            return;
        }
           
        var result = await Data.DownloadBlobAsync(file.AzureName, r, c, _configuration);

        if (result != null)
        {
            Response.FileStream = result.FileStream;
        }
    }
}

数据

public static class Data
{
    public static async Task<TriadaFile?> GetTriadaFileAsync(DatabaseContext context, Guid id, CancellationToken c)
    {
        return await context.Files
            .FirstOrDefaultAsync(x => x.Id == id, c);
    }
    public static async Task<FileStreamResult?> DownloadBlobAsync(string blobFileName, DownloadFileRequest r, CancellationToken c, IConfiguration _configuration)
    {
        string connectionString = _configuration.GetSection("Azure").GetValue<string>("BlobConnectionString")!;
        string containerName = _configuration.GetSection("Azure").GetValue<string>("BlobContainerName")!;

        BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);
        BlobContainerClient containerClient = blobServiceClient.GetBlobContainerClient(containerName);

        BlobClient blobClient = containerClient.GetBlobClient(blobFileName);

        using (var stream = new MemoryStream())
        {
            await blobClient.DownloadToAsync(stream);
            stream.Position = 0;
            var contentType = (await blobClient.GetPropertiesAsync()).Value.ContentType;

            var fileStreamResult = new FileStreamResult(stream, "application/octet-stream");

            fileStreamResult.FileDownloadName = blobFileName;

            return fileStreamResult;
        }
    }


}

模型

public class DownloadFileRequest
{
    public Guid Id{ get; set; }
}

public class Validator : Validator<DownloadFileRequest>
{
    public Validator()
    {
        RuleFor(x => x.Id)
            .NotEmpty();
    }
}

public class DownloadFileResponse
{
   

}

Question that helped me with me

Answer 1

问题是无论内容类型是什么，它总是将对象序列化为 JSON。所以我在 Program.cs 中像这样修复了它:

app.UseFastEndpoints(c =>
{
    var options = new JsonSerializerOptions(JsonSerializerDefaults.Web);

    c.Serializer.ResponseSerializer = (rsp, dto, cType, jCtx, ct) =>
    {
        // this condition allows any content type
        if (dto is FileStreamResult fsr)
        {
            rsp.ContentType = fsr.ContentType;
            rsp.Body = fsr.FileStream;

            return rsp.SendStreamAsync(rsp.Body, fsr.FileDownloadName, null, fsr.ContentType); ;
        }

        rsp.ContentType = cType;
        return rsp.WriteAsync(JsonSerializer.Serialize(dto, options), ct);
    };
    c.Serializer.RequestDeserializer = async (req, tDto, jCtx, ct) =>
    {       
        using var reader = new StreamReader(req.Body);
        return JsonSerializer.Deserialize(await reader.ReadToEndAsync(), tDto, options);              
    };
});

数据

public static async Task<FileStreamResult?> DownloadBlobAsync(string blobFileName , IConfiguration configuration)
    {
        string connectionString = configuration.GetSection("Azure").GetValue<string>("BlobConnectionString")!;
        string containerName = configuration.GetSection("Azure").GetValue<string>("BlobContainerName")!;

        BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);
        BlobContainerClient containerClient = blobServiceClient.GetBlobContainerClient(containerName);

        BlobClient blobClient = containerClient.GetBlobClient(blobFileName);

        BlobDownloadInfo download = await blobClient.DownloadAsync();
        Stream stream = download.Content;

        var contentType = download.ContentType;
      
        return new FileStreamResult(stream, contentType)
        {
            FileDownloadName = blobFileName
        };
    }
}