如何正确实现 MediaTypeFormatter 来处理“多部分/混合"类型的请求? [英] How does one correctly implement a MediaTypeFormatter to handle requests of type 'multipart/mixed'?
问题描述
考虑一个用 ASP.NET Web API 编写的 Web 服务，以接受任意数量的文件作为多部分/混合"请求.辅助方法 mat 如下所示(假设 _client 是 System.Net.Http.HttpClient 的一个实例):
Consider a web service written in ASP.NET Web API to accept any number files as a 'multipart/mixed' request. The helper method mat look as follows (assuming _client is an instance of System.Net.Http.HttpClient):
public T Post<T>(string requestUri, T value, params Stream[] streams)
{
var requestMessage = new HttpRequestMessage();
var objectContent = requestMessage.CreateContent(
value,
MediaTypeHeaderValue.Parse("application/json"),
new MediaTypeFormatter[] {new JsonMediaTypeFormatter()},
new FormatterSelector());
var content = new MultipartContent();
content.Add(objectContent);
foreach (var stream in streams)
{
var streamContent = new StreamContent(stream);
streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
streamContent.Headers.ContentDisposition =
new ContentDispositionHeaderValue("form-data")
{
Name = "file",
FileName = "mystream.doc"
};
content.Add(streamContent);
}
return _httpClient.PostAsync(requestUri, content)
.ContinueWith(t => t.Result.Content.ReadAsAsync<T>()).Unwrap().Result;
}
ApiController的子类中接受请求的方法有如下签名:
The method that accepts the request in the subclass of ApiController has a signature as follows:
public HttpResponseMessage Post(HttpRequestMessage request)
{
/* parse request using MultipartFormDataStreamProvider */
}
理想情况下，我想这样定义它，其中根据Content-Disposition"标头的name"属性从multipart/mixed"内容中提取联系人、源和目标.
Ideally, I'd like to define it like this, where contact, source and target are extracted from the 'multipart/mixed' content based on the 'name' property of the 'Content-Disposition' header.
public HttpResponseMessage Post(Contact contact, Stream source, Stream target)
{
// process contact, source and target
}
但是，使用我现有的签名，将数据发布到服务器会导致 InvalidOperationException 错误消息:
However, with my existing signature, posting the data to the server results in an InvalidOperationException with an error message of:
没有MediaTypeFormatter"可用于读取类型的对象媒体类型为multipart/mixed"的HttpRequestMessage".
No 'MediaTypeFormatter' is available to read an object of type 'HttpRequestMessage' with the media type 'multipart/mixed'.
Internet 上有许多示例，说明如何使用 ASP.NET Web API 和 HttpClient 发送和接收文件.但是，我还没有找到任何显示如何处理此问题的方法.
There are a number of examples on the internet how to send and receive files using the ASP.NET Web API and HttpClient. However, I have not found any that show how to deal with this problem.
我开始考虑实现自定义 MediaTypeFormatter 并将其注册到全局配置中.然而，虽然在自定义 MediaTypeFormatter 中处理序列化 XML 和 JSON 很容易，但不清楚如何处理几乎可以是任何东西的多部分/混合"请求.
I started looking at implementing a custom MediaTypeFormatter and register it with the global configuration. However, while it is easy to deal with serializing XML and JSON in a custom MediaTypeFormatter, it is unclear how to deal with 'multipart/mixed' requests which can pretty much be anything.
推荐答案
看看这个论坛:http://forums.asp.net/t/1777847.aspx/1?MVC4+Beta+Web+API+and+multipart+form+数据
以下是一段代码(由 imran_ku07 发布)，可以帮助您实现自定义格式化程序来处理 multipart/form-data:
Here is a snippet of code (posted by imran_ku07) that might help you implement a custom formatter to handle the multipart/form-data:
public class MultiFormDataMediaTypeFormatter : FormUrlEncodedMediaTypeFormatter
{
public MultiFormDataMediaTypeFormatter() : base()
{
this.SupportedMediaTypes.Add(new MediaTypeHeaderValue("multipart/form-data"));
}
protected override bool CanReadType(Type type)
{
return true;
}
protected override bool CanWriteType(Type type)
{
return false;
}
protected override Task<object> OnReadFromStreamAsync(Type type, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext)
{
var contents = formatterContext.Request.Content.ReadAsMultipartAsync().Result;
return Task.Factory.StartNew<object>(() =>
{
return new MultiFormKeyValueModel(contents);
});
}
class MultiFormKeyValueModel : IKeyValueModel
{
IEnumerable<HttpContent> _contents;
public MultiFormKeyValueModel(IEnumerable<HttpContent> contents)
{
_contents = contents;
}
public IEnumerable<string> Keys
{
get
{
return _contents.Cast<string>();
}
}
public bool TryGetValue(string key, out object value)
{
value = _contents.FirstDispositionNameOrDefault(key).ReadAsStringAsync().Result;
return true;
}
}
}
然后您需要将此格式化程序添加到您的应用程序中.如果进行自托管，您可以简单地添加:
You then need to add this formatter to your application. If doing self-host you can simply add it by including:
config.Formatters.Insert(0, new MultiFormDataMediaTypeFormatter());
在实例化 HttpSelfHostServer 类之前.
before instantiating the HttpSelfHostServer class.
-- 编辑 --
要解析二进制流，您需要另一个格式化程序.这是我在我的一个工作项目中用来解析图像的一个.
To parse binary streams you'll need another formatter. Here is one that I am using to parse images in one of my work projects.
class JpegFormatter : MediaTypeFormatter
{
protected override bool CanReadType(Type type)
{
return (type == typeof(Binary));
}
protected override bool CanWriteType(Type type)
{
return false;
}
public JpegFormatter()
{
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/jpeg"));
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/jpg"));
SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/png"));
}
protected override Task<object> OnReadFromStreamAsync(Type type, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext)
{
return Task.Factory.StartNew(() =>
{
byte[] fileBytes = new byte[stream.Length];
stream.Read(fileBytes, 0, (int)fileBytes.Length);
return (object)new Binary(fileBytes);
});
}
protected override Task OnWriteToStreamAsync(Type type, object value, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext, TransportContext transportContext)
{
throw new NotImplementedException();
}
}
在您的控制器/动作中，您需要执行以下操作:
In your controller/action you'll want to do something along the lines of:
public HttpResponseMessage UploadImage(Binary File) {
//do something with your file
}
这篇关于如何正确实现 MediaTypeFormatter 来处理“多部分/混合"类型的请求?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
