In my original response I had totally misread the question and thought the poster was asking how to read the Request.Body But he had asked how to read the Response.Body. I’m leaving my original answer to preserve history but also updating it to show how I would answer the question once reading it correctly.
Original Answer
If you want a buffered stream that supports reading multiple times you need to set
context.Request.EnableRewind()
Ideally do this early in the middleware before anything needs to read the body.
So for example you could place the following code in the beginning of the Configure method of the Startup.cs file:
app.Use(async (context, next) => {
context.Request.EnableRewind();
await next();
});
Prior to enabling Rewind the stream associated with the Request.Body is a forward only stream that doesn’t support seeking or reading the stream a second time. This was done to make the default configuration of request handling as lightweight and performant as possible. But once you enable rewind the stream is upgrade to a stream that supports seeking and reading multiple times. You can observe this “upgrade” by setting a breakpoint just before and just after the call to EnableRewind and observing the Request.Body properties. So for example Request.Body.CanSeek will change from false to true.
update: Starting in ASP.NET Core 2.1 Request.EnableBuffering() is available which upgrades the Request.Body to a FileBufferingReadStream just like Request.EnableRewind() and since Request.EnableBuffering() is in a public namespace rather than an internal one it should be preferred over EnableRewind(). (Thanks to @ArjanEinbu for pointing out)
Then to read the body stream you could for example do this:
string bodyContent = new StreamReader(Request.Body).ReadToEnd();
Don’t wrap the StreamReader creation in a using statement though or it will close the underlying body stream at the conclusion of the using block and code later in the request lifecycle wont be able to read the body.
Also just to be safe, it might be a good idea to follow the above line of code that reads the body content with this line of code to reset the body’s stream position back to 0.
request.Body.Position = 0;
That way any code later in the request lifecycle will find the request.Body in a state just like it hasn’t been read yet.
Updated Answer
Sorry I originally misread your question. The concept of upgrading the associated stream to be a buffered stream still applies. However you do have to do it manually, I’m unaware of any built in .Net Core functionality that lets you read the response stream once written in the way that EnableRewind() lets a developer reread the request stream after it’s been read.
Your “hacky” approach is likely totally appropriate. You are basically converting a stream that can’t seek to one that can. At the end of the day the Response.Body stream has to get swapped out with a stream that is buffered and supports seeking. Here is another take on middleware to do that but you will notice it’s quite similar to your approach. I did however choose to use a finally block as added protection for putting the original stream back on the Response.Body and I used the Position property of the stream rather than the Seek method since the syntax is a bit simpler but the effect is no different than your approach.
public class ResponseRewindMiddleware
{
private readonly RequestDelegate next;
public ResponseRewindMiddleware(RequestDelegate next) {
this.next = next;
}
public async Task Invoke(HttpContext context) {
Stream originalBody = context.Response.Body;
try {
using (var memStream = new MemoryStream()) {
context.Response.Body = memStream;
await next(context);
memStream.Position = 0;
string responseBody = new StreamReader(memStream).ReadToEnd();
memStream.Position = 0;
await memStream.CopyToAsync(originalBody);
}
} finally {
context.Response.Body = originalBody;
}
}
}