[英]How can I safely intercept the Response stream in a custom Owin Middleware
我正在嘗試編寫一個簡單的OWIN中間件,以攔截響應流。 我要做的是用自定義的基於Stream的類替換原始流,在那里我將能夠攔截對響應流的寫入。
但是,我遇到了一些問題,因為我無法知道響應是否已被鏈中的內部中間件組件完全寫入。 永遠不會調用Stream的Dispose
重寫。 所以我不知道什么時候進行我的處理,這應該發生在響應流的末尾。
這是一個示例代碼:
public sealed class CustomMiddleware: OwinMiddleware
{
public CustomMiddleware(OwinMiddleware next)
: base(next)
{
}
public override async Task Invoke(IOwinContext context)
{
var request = context.Request;
var response = context.Response;
// capture response stream
var vr = new MemoryStream();
var responseStream = new ResponseStream(vr, response.Body);
response.OnSendingHeaders(state =>
{
var resp = (state as IOwinContext).Response;
var contentLength = resp.Headers.ContentLength;
// contentLength == null for Chunked responses
}, context);
// invoke the next middleware in the pipeline
await Next.Invoke(context);
}
}
public sealed class ResponseStream : Stream
{
private readonly Stream stream_; // MemoryStream
private readonly Stream output_; // Owin response
private long writtenBytes_ = 0L;
public ResponseStream(Stream stream, Stream output)
{
stream_ = stream;
output_ = output;
}
... // System.IO.Stream implementation
public override void Write(byte[] buffer, int offset, int count)
{
// capture writes to the response stream in our local stream
stream_.Write(buffer, offset, count);
// write to the real output stream
output_.Write(buffer, offset, count);
// update the number of bytes written
writtenBytes_ += count;
// how do we know the response is complete ?
// we could check that the number of bytes written
// is equal to the content length, but content length
// is not available for Chunked responses.
}
protected override void Dispose(bool disposing)
{
// we could perform our processing
// when the stream is disposed of.
// however, this method is never called by
// the OWIN/Katana infrastructure.
}
}
正如我在上面代碼的評論中提到的那樣,我可以想到兩種策略來檢測響應是否完整。
a)我可以記錄寫入響應流的字節數,並將其與預期的響應長度相關聯。 但是,在使用Chunked Transfer Encoding的響應的情況下,長度是未知的。
b)在響應流上調用Dispose
時,我可以決定響應流是否完整。 但是,OWIN / Katana基礎結構從不在已替換的流上調用Dispose。
我一直在研究Opaque Streaming ,以便了解操縱底層HTTP協議是否是一種可行的方法,但我似乎沒有發現Katana是否支持Opaque Streaming。
有沒有辦法實現我想要的?
我不認為你需要一個子類流,但接下來就是你如何閱讀響應。 確保這個中間件是OWIN管道中的第一個,這樣它就是最后一個檢查響應的中間件。
using AppFunc = Func<IDictionary<string, object>, Task>;
public class CustomMiddleware
{
private readonly AppFunc next;
public CustomMiddleware(AppFunc next)
{
this.next = next;
}
public async Task Invoke(IDictionary<string, object> env)
{
IOwinContext context = new OwinContext(env);
// Buffer the response
var stream = context.Response.Body;
var buffer = new MemoryStream();
context.Response.Body = buffer;
await this.next(env);
buffer.Seek(0, SeekOrigin.Begin);
var reader = new StreamReader(buffer);
string responseBody = await reader.ReadToEndAsync();
// Now, you can access response body.
Debug.WriteLine(responseBody);
// You need to do this so that the response we buffered
// is flushed out to the client application.
buffer.Seek(0, SeekOrigin.Begin);
await buffer.CopyToAsync(stream);
}
}
據我所知,BTW源自OwinMiddleware
並不是一個好習慣,因為OwinMiddleware
是專門針對Katana的。 但是,它與你的問題無關。
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