我正在尝试使用一些自定义的 Owin 中间件来修改(在这种情况下,完全替换)特定情况下的响应流。
每当我发出一个触发我的中间件来替换响应的调用时,一切都会正常工作。仅当我拨打我的中间件未对其进行更改时才会出现此问题。此外,我只能在未被替换的 API 调用返回手动创建的 HttpResponseMessage 对象时发生错误。
例如调用这个 API:
public class testController : ApiController
{
public HttpResponseMessage Get()
{
return Request.CreateResponse(HttpStatusCode.OK,new { message = "It worked." });
}
}
工作正常,但这个类:
public class testController : ApiController
{
public HttpResponseMessage Get()
{
HttpResponseMessage m = Request.CreateResponse();
m.StatusCode = HttpStatusCode.OK;
m.Content = new StringContent("It worked.", System.Text.Encoding.UTF8, "text/plain");
return m;
}
}
导致错误发生。(在这两种情况下,http://localhost:<port>/test
都被调用。)
该错误会导致以下任一情况:
- 导致 iisexpress.exe(或 w3wp.exe,如果在实际 IIS 中运行)因访问冲突而崩溃。
抛出一个
AccessViolationException
Visual Studio 捕获但无法执行任何操作的事件,因为它出现在外部代码中。当 Visual Studio 确实捕获异常时,我看到:An unhandled exception of type 'System.AccessViolationException' occurred in System.Web.dll Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
显然,如果我不启用我的中间件,我根本就没有问题。此外,我只能在手动创建和返回 HttpResponseMessage 对象时导致问题发生,如第二类所示。
这是我的中间件类。它目前设置为在有人请求端点时简单地替换整个响应流,/replace
无论管道中是否有其他任何东西对其进行了任何操作。
using Microsoft.Owin;
using Owin;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Net;
using System.Threading.Tasks;
using Newtonsoft.Json;
using AppFunc = System.Func<
System.Collections.Generic.IDictionary<string, object>,
System.Threading.Tasks.Task
>;
namespace TestOwinAPI
{
public class ResponseChangeMiddleware
{
AppFunc _next;
public ResponseChangeMiddleware(AppFunc next, ResponseChangeMiddlewareOptions opts)
{
_next = next;
}
public async Task Invoke(IDictionary<string,object> env)
{
var ctx = new OwinContext(env);
// create a new memory stream which will replace the default output stream
using (var ms = new MemoryStream())
{
// hold on to a reference to the actual output stream for later use
var outStream = ctx.Response.Body;
// reassign the context's output stream to be our memory stream
ctx.Response.Body = ms;
Debug.WriteLine(" <- " + ctx.Request.Path);
// allow the rest of the middleware to do its job
await _next(env);
// Now the request is on the way out.
if (ctx.Request.Path.ToString() == "/replace")
{
// Now write new response.
string json = JsonConvert.SerializeObject(new { response = "true", message = "This response will replace anything that the rest of the API might have created!" });
byte[] jsonBytes = System.Text.Encoding.UTF8.GetBytes(json);
// clear everything else that anything might have put in the output stream
ms.SetLength(0);
// write the new data
ms.Write(jsonBytes, 0, jsonBytes.Length);
// set parameters on the response object
ctx.Response.StatusCode = 200;
ctx.Response.ContentLength = jsonBytes.Length;
ctx.Response.ContentType = "application/json";
}
// In all cases finally write the memory stream's contents back to the actual response stream
ms.Seek(0, SeekOrigin.Begin);
await ms.CopyToAsync(outStream);
}
}
}
public static class AppBuilderExtender
{
public static void UseResponseChangeMiddleware(this IAppBuilder app, ResponseChangeMiddlewareOptions options = null )
{
if (options == null)
options = new ResponseChangeMiddlewareOptions();
app.Use<ResponseChangeMiddleware>(options);
}
}
public class ResponseChangeMiddlewareOptions
{
}
}
我已经做了很明显的事情——一整夜的 RAM 测试(一切都很好),并在另一个系统上尝试(它也发生在那里)。
此外,错误并不一致 - 它发生的时间大约有一半。换句话说,通常我可以通过一两个成功的请求,但最终还是会发生错误。
最后,如果我在我的中间件内存流复制之前在我的程序中设置一个断点,然后慢慢地单步执行代码,则永远不会发生错误。这向我表明我必须遇到某种竞争条件,并且它必须与我正在玩 MemoryStreams 的事实有关。
有任何想法吗?