Question

我正在尝试创建.Net标准“客户端”类，以将文件（有时非常大）上载到Controller。我想通过将文件分成多个块并一次上传一个文件来实现。目的是让其他应用程序使用此功能，而不是直接与Web Api通信。

我已经让Controller工作了。我已验证它是否可以使用支持大块节省的Kendo-ui控件正常工作。

我遇到的问题是，从客户端类发布时，控制器的IEnumerable<IFormFile> files参数始终为空

控制器

[Route("api/Upload")]
public ActionResult ChunkSave(IEnumerable<IFormFile> files, string metaData, Guid id)
{
    MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(metaData));
    var serializer = new DataContractJsonSerializer(typeof(ChunkMetaData));
    ChunkMetaData somemetaData = serializer.ReadObject(ms) as ChunkMetaData;

    // The Name of the Upload component is "files"
    if (files != null)
    {
        // If this is the first chunk, try to delete the file so that we don't accidently
        // and up appending new bytes to the old file.
        if (somemetaData.ChunkIndex == 0)
        {
            _io.DeleteFile(id, Path.GetFileName(somemetaData.FileName));
        }

        foreach (var file in files)
        {
            // Some browsers send file names with full path. This needs to be stripped.
             _io.AppendToFile(id, Path.GetFileName(somemetaData.FileName), file.OpenReadStream());
        }
    }

    FileResult fileBlob = new FileResult();
    fileBlob.uploaded = somemetaData.TotalChunks - 1 <= somemetaData.ChunkIndex;
    fileBlob.fileUid = somemetaData.UploadUid;
    return new JsonResult(fileBlob);
}

客户：

public class FileTransferClient
{
    HttpClient Client { get; set; } 

    public FileTransferClient(Uri apiUrl)
    {
        this.Client = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true })
        {
            BaseAddress = apiUrl
        };
        this.Client.DefaultRequestHeaders.Accept.Add(
            new MediaTypeWithQualityHeaderValue("application/json"));
    }

    public async Task<bool> UploadFile(Guid id, Stream file, string name, string contentType)
    {
        bool ret = true;
        int chunckSize = 2097152; //2MB
        int totalChunks = (int)(file.Length / chunckSize);
        if (file.Length % chunckSize != 0)
        {
            totalChunks++;
        }

        for (int i = 0; i < totalChunks; i++)
        {
            long position = (i * (long)chunckSize);
            int toRead = (int)Math.Min(file.Length - position + 1, chunckSize);
            byte[] buffer = new byte[toRead];
            await file.ReadAsync(buffer, 0, toRead);

            MultipartFormDataContent content = new MultipartFormDataContent();
            content.Add(new StringContent(id.ToString()), "id");
            var meta = JsonConvert.SerializeObject(new ChunkMetaData
            {
                UploadUid = id.ToString(),
                FileName = name,
                ChunkIndex = i,
                TotalChunks = totalChunks,
                TotalFileSize = file.Length,
                ContentType = contentType
            });
            content.Add(new StringContent(meta), "metaData");
            using (var ms = new MemoryStream(buffer))
            {
                content.Add(new StreamContent(ms),"files");
                var response = await Client.PostAsync("/api/Upload", content).ConfigureAwait(false);
                if (!response.IsSuccessStatusCode)
                {
                    ret = false;
                    break;
                }
            }
        }
        return ret;
    }
}

Answer 1

您的参数为空，因为您不是发送文件数组，而是发送一个文件。因此，绑定失败，并且您将获得null。分块的行为（实际上甚至没有做）不等于IEnumerable<IFormFile>；仍然只是IFormFile。

虽然由于要同时发送文件上传和其他一些帖子数据而需要以multipart/form-data的形式发送，但我认为您误会了它的实际作用。它只是意味着请求主体包含多个不同的mime类型，而不是意味着它正在将文件上传为多个部分，这似乎就是您在想的那样。

流传输上载的实际行为发生在服务器端。它与服务器选择如何处理要上传的文件有关，而与用户如何上传无关。更具体地说，任何类型的模型绑定，尤其是对IFormFile的模型绑定，都将导致文件先被后台处理到磁盘，然后传递到您的操作中。换句话说，如果您接受IFormFile，则说明您已经输掉了这场战斗。它已经从客户端完全转移到您的服务器。

ASP.NET Core docs向您展示了如何实际流式传输上传内容，毫不奇怪的是，其中涉及到很多代码，您目前还没有。基本上，您必须完全在操作上关闭模型绑定，并自己手动解析请求主体，请小心地对来自流的读取进行实际分块，而不要执行将所有内容立即强制进入内存的操作。

Answer 2

问题是我使用StreamContent而不是ByteArrayContent来代表我的文件块。这就是我最终得到的：

public async Task<FileData> UploadFileAsync(Guid id, string name, Stream file)
{
    Guid uid = Guid.NewGuid();
    int chunckSize = 2097152; //2MB
    int totalChunks = (int)(file.Length / chunckSize);
    if (file.Length % chunckSize != 0)
    {
        totalChunks++;
    }

    for (int i = 0; i < totalChunks; i++)
    {
        long position = (i * (long)chunckSize);
        int toRead = (int)Math.Min(file.Length - position + 1, chunckSize);
        byte[] buffer = new byte[toRead];
        await file.ReadAsync(buffer, 0, buffer.Length);

        using (MultipartFormDataContent form = new MultipartFormDataContent())
        {
            form.Add(new ByteArrayContent(buffer), "files", name);
            form.Add(new StringContent(id.ToString()), "id");
            var meta = JsonConvert.SerializeObject(new ChunkMetaData
            {
                UploadUid = id.ToString(),
                FileName = name,
                ChunkIndex = i,
                TotalChunks = totalChunks,
                TotalFileSize = file.Length,
                ContentType = "application/unknown"
            });
            form.Add(new StringContent(meta), "metaData");
            var response = await Client.PostAsync("/api/Upload", form).ConfigureAwait(false);
            return response.IsSuccessStatusCode;
        }
    }
    return true;
}

使用HttpClient将大文件分块上传到Controller，IFormFile始终为空

2 个答案: