如何使用 .Net 4.0 中包含的 HttpClient 类将文件上传到在 IIS Express 中运行的 Asp.Net MVC 4.0 操作

问题描述

我有一个 C/S 应用程序.我用 Asp.Net MVC 4.0 实现了服务器，而客户端在 .Net 4.5 上运行.

I have a C/S application. I implemented the server with Asp.Net MVC 4.0, and the client runs on .Net 4.5.

我在服务器端有一个控制器动作如下所示:

I have a Controller Action in the server side looks like this:

public JsonResult Upload(string arg1, int arg2)
{
    //do something about arg1 and arg2 here
    ...

    var files = Request.Files;
    if (files.Count > 0)
    {
        foreach(var file in files)
        {
            var ms = new MemoryStream();
            file.InputStream.CopyTo(ms);
            //save it to somewhere
            ...
        }
    }

    ...
}

我创建了一个测试 html 页面以在浏览器中对其进行测试.它按预期工作.

I created a test html page to test it in browser. It worked as expected.

在客户端，我使用 HttpClient 类，它在不涉及文件上传的情况下完美运行.然而，经过几天的研究，我仍然没有运气在我运行 IIS Express 的调试机器中解决这个问题.发现所有的线索都指向MultipartFormDataContent，但是还是不行，即使我复制了那些示例代码，服务器端还是拿不到东西，所有的args都为空，并且Request.Files 中没有文件.我曾经拥有基于 HttpWebRequest，它适用于文件上传，但我更喜欢在这个新项目中使用 HttpClient.

In the client side, I use HttpClient class and it worked perfectly where no file uploading involved. However after days of researching I still have no luck to resolve this in my debug machine which runs IIS Express. I found that all clues leads to MultipartFormDataContent, but still can't get it work, even if I copy those sample codes, the server side still can't get a thing, all args are empty, and no files is there in the Request.Files. I used to have my own http helper class based on HttpWebRequest, which works for file uploading, but I prefer to use HttpClient in this new project.

那么，如何使用 HttpClient 将文件上传到服务器?

So, How do I upload files to the server with HttpClient?

推荐答案

用 Fiddler 调试后，对比了原始的 http 消息和 WinMerge，我发现了 Firefox 和我的程序的区别:

After debugging with Fiddler, comparing raw http message with WinMerge, I found the differences between Firefox and my program:

Firefox(删除了一些标题以使事情变得简单):

POST http://localhost:53400/Input/Upload HTTP/1.1
Host: localhost:53400
Content-Type: multipart/form-data; boundary=---------------------------1590871622043
Content-Length: ****

-----------------------------1590871622043
Content-Disposition: form-data; name="arg1"

abc
-----------------------------1590871622043
Content-Disposition: form-data; name="arg2"

3
-----------------------------1590871622043
Content-Disposition: form-data; name="uploadfile"; filename="wave.wav"
Content-Type: audio/wav

//file data here
-----------------------------1590871622043--

我的带有 MultipartFormDataContent 的程序:

My Program with MultipartFormDataContent:

POST http://localhost:53400/Input/Save HTTP/1.1
Content-Type: multipart/form-data; boundary="caac5ea7-8ab4-4682-be40-ecb3ddf3e70a"
Host: localhost:53400
Content-Length: ****

--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=arg1

abc
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=arg2

3
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a
Content-Disposition: form-data; name=uploadfile; filename=wave.wav; filename*=utf-8''wave.wav

//file data here
--caac5ea7-8ab4-4682-be40-ecb3ddf3e70a--

我注意到的最后一件事是，在这些 Content-Disposition 行中，Firefox 引用了所有值，但我的程序没有引用.人们很容易认为这无关紧要，但最终我发现这才是真正的原因.

The last thing I would notice is that in these Content-Disposition lines, Firefox quotes all values, but my program does not. One could easily assume that it would not matter, but in the end, I found that is the exact cause.

现在我知道原因了，下面是有效的代码，就像引用名称一样简单:

Now that I know the reason, here comes the code that works, as easy as quoting the names:

var multipart = new MultipartFormDataContent();
multipart.Add(new StringContent("abc"), '"' + "arg1" + '"');
multipart.Add(new StringContent("3"), '"' + "arg2" + '"');

// byte[] fileData;
multipart.Add(new ByteArrayContent(fileData), '"' + "uploadfile"+ '"', '"' + "wave.wav" + '"');
//HttpClient http; string url;
var response = await http.PostAsync(url, multipart);
response.EnsureSuccessStatusCode();
//...

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