Strategy and how to create Request and Response pipes in .net core 3.0 middleware

Question

I am developing a .net core middle-ware (api) and thinking to use pipes with following flow, Can someone tell me is this is a good approach and comply best practices or should i use different strategy.

1. Request comes to api
2. Authorization pipe validates the request.
3. Request pipe logs the request into db.
4. Request goes to api and perform action and return a result.
5. Response pipe gets the response and logs into db and return the result to client.

I know that we can read stream only time (point 3) but i figured this out already and after reading i have attach it to request stream again.

So, confusion is where to write the response? In api? or in separate pipe.

If i do it in separate pipe then i am handling my response two time (one is creating response in api, second is reading response in separate pipe) which is a performance hit.

Can i pass the data from point number 4 to 5 like from api to my pipe and from there that response should added into response stream and if it is correct then how can i pass the data from api to pipe?

Answer 1

Yes, response stream can only be read once. You can use the MemoryStream to load the response , reference article :

• First, read the request and format it into a string.

• Next, create a dummy MemoryStream to load the new response into.

• Then, wait for the server to return a response.

• Finally, copy the dummy MemoryStream (containing the actual response) into the original stream, which gets returned to the client.

Code sample :

public class RequestResponseLoggingMiddleware
{
    private readonly RequestDelegate _next;

    public RequestResponseLoggingMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        //First, get the incoming request
        var request = await FormatRequest(context.Request);

        //Copy a pointer to the original response body stream
        var originalBodyStream = context.Response.Body;

        //Create a new memory stream...
        using (var responseBody = new MemoryStream())
        {
            //...and use that for the temporary response body
            context.Response.Body = responseBody;

            //Continue down the Middleware pipeline, eventually returning to this class
            await _next(context);

            //Format the response from the server
            var response = await FormatResponse(context.Response);

            //TODO: Save log to chosen datastore

            //Copy the contents of the new memory stream (which contains the response) to the original stream, which is then returned to the client.
            await responseBody.CopyToAsync(originalBodyStream);
        }
    }

    private async Task<string> FormatRequest(HttpRequest request)
    {
        var body = request.Body;

        //This line allows us to set the reader for the request back at the beginning of its stream.
        request.EnableRewind();

        //We now need to read the request stream.  First, we create a new byte[] with the same length as the request stream...
        var buffer = new byte[Convert.ToInt32(request.ContentLength)];

        //...Then we copy the entire request stream into the new buffer.
        await request.Body.ReadAsync(buffer, 0, buffer.Length);

        //We convert the byte[] into a string using UTF8 encoding...
        var bodyAsText = Encoding.UTF8.GetString(buffer);

        //..and finally, assign the read body back to the request body, which is allowed because of EnableRewind()
        request.Body = body;

        return $"{request.Scheme} {request.Host}{request.Path} {request.QueryString} {bodyAsText}";
    }

    private async Task<string> FormatResponse(HttpResponse response)
    {
        //We need to read the response stream from the beginning...
        response.Body.Seek(0, SeekOrigin.Begin);

        //...and copy it into a string
        string text = await new StreamReader(response.Body).ReadToEndAsync();

        //We need to reset the reader for the response so that the client can read it.
        response.Body.Seek(0, SeekOrigin.Begin);

        //Return the string for the response, including the status code (e.g. 200, 404, 401, etc.)
        return $"{response.StatusCode}: {text}";
    }
}

And register the middleware :

app.UseMiddleware<RequestResponseLoggingMiddleware>();