终于想通了：
有两个问题：
1.流指针位置
在客户端代码中，改变这个：
await file.CopyToAsync(stream);
到那个：
await file.CopyToAsync(stream);
stream.Position = 0;
问题是请求中的文件被复制到流中并且指针的左侧位置位于流的末尾。这就是为什么从客户端发送的请求具有适当长度的流，但实际上当它开始读取它时，它不能（读取 0 个字节）。
2。服务器上处理请求的方式错误。
我使用来自dotnetcoretutorials.com的代码
下面的工作代码：
客户端：
[HttpPost("UploadFiles")]
public async Task<IActionResult> Post(IFormFile file)
{
var filePath = Path.GetTempFileName();
using (var stream = new FileStream(filePath, FileMode.Create, FileAccess.ReadWrite))
{
await file.CopyToAsync(stream);
stream.Position = 0;
using (var formDataContent = new MultipartFormDataContent())
{
using (var httpClient = new HttpClient())
{
formDataContent.Add(CreateFileContent(stream, "myfile.test", "application/octet-stream"));
var response = await httpClient.PostAsync(
"http://localhost:56595/home/upload",
formDataContent);
return Json(response);
}
}
}
}
internal static StreamContent CreateFileContent(Stream stream, string fileName, string contentType)
{
var fileContent = new StreamContent(stream);
fileContent.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("form-data")
{
Name = "\"file\"",
FileName = "\"" + fileName + "\"",
};
fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);
return fileContent;
}
服务器端：
控制器：
[HttpPost]
[DisableFormValueModelBinding]
public async Task<IActionResult> Upload()
{
var viewModel = new MyViewModel();
try
{
FormValueProvider formModel;
using (var stream = System.IO.File.Create("c:\\temp\\myfile.temp"))
{
formModel = await Request.StreamFile(stream);
}
var bindingSuccessful = await TryUpdateModelAsync(viewModel, prefix: "",
valueProvider: formModel);
if (!bindingSuccessful)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
}
}
catch(Exception exception)
{
throw;
}
return Ok(viewModel);
}
来自控制器的方法的帮助类：
public static class MultipartRequestHelper
{
// Content-Type: multipart/form-data; boundary="----WebKitFormBoundarymx2fSWqWSd0OxQqq"
// The spec says 70 characters is a reasonable limit.
public static string GetBoundary(MediaTypeHeaderValue contentType, int lengthLimit)
{
var boundary = HeaderUtilities.RemoveQuotes(contentType.Boundary);
if (string.IsNullOrWhiteSpace(boundary.ToString()))
{
throw new InvalidDataException("Missing content-type boundary.");
}
if (boundary.Length > lengthLimit)
{
throw new InvalidDataException(
$"Multipart boundary length limit {lengthLimit} exceeded.");
}
return boundary.ToString();
}
public static bool IsMultipartContentType(string contentType)
{
return !string.IsNullOrEmpty(contentType)
&& contentType.IndexOf("multipart/", StringComparison.OrdinalIgnoreCase) >= 0;
}
public static bool HasFormDataContentDisposition(ContentDispositionHeaderValue contentDisposition)
{
// Content-Disposition: form-data; name="key";
return contentDisposition != null
&& contentDisposition.DispositionType.Equals("form-data")
&& string.IsNullOrEmpty(contentDisposition.FileName.ToString())
&& string.IsNullOrEmpty(contentDisposition.FileNameStar.ToString());
}
public static bool HasFileContentDisposition(ContentDispositionHeaderValue contentDisposition)
{
// Content-Disposition: form-data; name="myfile1"; filename="Misc 002.jpg"
return contentDisposition != null
&& contentDisposition.DispositionType.Equals("form-data")
&& (!string.IsNullOrEmpty(contentDisposition.FileName.ToString())
|| !string.IsNullOrEmpty(contentDisposition.FileNameStar.ToString()));
}
}
public static class FileStreamingHelper
{
private static readonly FormOptions _defaultFormOptions = new FormOptions();
public static async Task<FormValueProvider> StreamFile(this HttpRequest request, Stream targetStream)
{
if (!MultipartRequestHelper.IsMultipartContentType(request.ContentType))
{
throw new Exception($"Expected a multipart request, but got {request.ContentType}");
}
// Used to accumulate all the form url encoded key value pairs in the
// request.
var formAccumulator = new KeyValueAccumulator();
string targetFilePath = null;
var boundary = MultipartRequestHelper.GetBoundary(
MediaTypeHeaderValue.Parse(request.ContentType),
_defaultFormOptions.MultipartBoundaryLengthLimit);
var reader = new MultipartReader(boundary, request.Body);
var section = await reader.ReadNextSectionAsync();
while (section != null)
{
ContentDispositionHeaderValue contentDisposition;
var hasContentDispositionHeader = ContentDispositionHeaderValue.TryParse(section.ContentDisposition, out contentDisposition);
if (hasContentDispositionHeader)
{
if (MultipartRequestHelper.HasFileContentDisposition(contentDisposition))
{
await section.Body.CopyToAsync(targetStream);
}
else if (MultipartRequestHelper.HasFormDataContentDisposition(contentDisposition))
{
// Content-Disposition: form-data; name="key"
//
// value
// Do not limit the key name length here because the
// multipart headers length limit is already in effect.
var key = HeaderUtilities.RemoveQuotes(contentDisposition.Name);
var encoding = GetEncoding(section);
using (var streamReader = new StreamReader(
section.Body,
encoding,
detectEncodingFromByteOrderMarks: true,
bufferSize: 1024,
leaveOpen: true))
{
// The value length limit is enforced by MultipartBodyLengthLimit
var value = await streamReader.ReadToEndAsync();
if (String.Equals(value, "undefined", StringComparison.OrdinalIgnoreCase))
{
value = String.Empty;
}
formAccumulator.Append(key.ToString(), value);
if (formAccumulator.ValueCount > _defaultFormOptions.ValueCountLimit)
{
throw new InvalidDataException($"Form key count limit {_defaultFormOptions.ValueCountLimit} exceeded.");
}
}
}
}
// Drains any remaining section body that has not been consumed and
// reads the headers for the next section.
section = await reader.ReadNextSectionAsync();
}
// Bind form data to a model
var formValueProvider = new FormValueProvider(
BindingSource.Form,
new FormCollection(formAccumulator.GetResults()),
CultureInfo.CurrentCulture);
return formValueProvider;
}
private static Encoding GetEncoding(MultipartSection section)
{
MediaTypeHeaderValue mediaType;
var hasMediaTypeHeader = MediaTypeHeaderValue.TryParse(section.ContentType, out mediaType);
// UTF-7 is insecure and should not be honored. UTF-8 will succeed in
// most cases.
if (!hasMediaTypeHeader || Encoding.UTF7.Equals(mediaType.Encoding))
{
return Encoding.UTF8;
}
return mediaType.Encoding;
}
}
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class DisableFormValueModelBindingAttribute : Attribute, IResourceFilter
{
public void OnResourceExecuting(ResourceExecutingContext context)
{
var formValueProviderFactory = context.ValueProviderFactories
.OfType<FormValueProviderFactory>()
.FirstOrDefault();
if (formValueProviderFactory != null)
{
context.ValueProviderFactories.Remove(formValueProviderFactory);
}
var jqueryFormValueProviderFactory = context.ValueProviderFactories
.OfType<JQueryFormValueProviderFactory>()
.FirstOrDefault();
if (jqueryFormValueProviderFactory != null)
{
context.ValueProviderFactories.Remove(jqueryFormValueProviderFactory);
}
}
public void OnResourceExecuted(ResourceExecutedContext context)
{
}
}
其他想法：
不需要发送文件。
-
（在客户端）当 MediaTypeHeaderValue 是以下之一时发送文件：
应用程序/x-msdownload
应用程序/json
应用程序/八位字节流
（在服务器端）要在服务器端使用带有contentDisposition.FileNameStar 的行，您需要将它们更改为contentDisposition.FileNameStar.ToString()
（在服务器端）用于服务器端的代码将适用于较小的文件（Mb），但要发送 GB 文件，我们需要粘贴在答案中的代码。
部分代码取自aspnet core docs