在 ASP.Net Core 中压缩之前记录响应正文

Question

I have a seemingly simple thing that I need to do; log the response body from middleware AFTER it has been fully formed by controllers but BEFORE compression is applied.

The problem here is that I am only able to read a response after awaiting next() from the logging middleware, which also compresses the response body.

My logging implementation is based on this article; https://elanderson.net/2019/12/log-requests-and-responses-in-asp-net-core-3/?unapproved=220252&moderation-hash=337bbb1489547696340e7506459779ba#comment-220252

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
...
    app.UseMiddleware<RequestResponseLoggingMiddleware>();

    app.UseRouting();

    //compression
    app.UseResponseCompression();

    app.UseAuthentication();
    app.UseAuthorization();

    app.UseEndpoints(endpoints => {
        endpoints.MapControllers();
    });

    ConfigurePSTZone();
...
}

RequestResponseLoggingMiddleware middleware;

    var originalBodyStream = context.Response.Body;
    await using var responseBody = _recyclableMemoryStreamManager.GetStream();
    context.Response.Body = responseBody;
    await _next(context); 
    context.Response.Body.Seek(0, SeekOrigin.Begin);
    var responseBody = await new StreamReader(context.Response.Body).ReadToEndAsync();

If you call await _next(context); then responseBody will be filled with the compressed response after. If you dont call it, responseBody will be empty. Even if you move the UseMiddleware(); to the very end of Configure.

Not sure there is actually a solution for this currently in .Net 5, but hey maybe someone has figured it out.

Thanks

ADDED NOTE: This seems to only be a problem when using Asp.Net with kestrel (linux based). On windows you dont need response compression middleware.. so I guess not a lot of people have switched to Linux yet which is why nobody has asked this question before. Jeepers

Answer 1

Middlewares are executed in order ( link ).
You can move app.UseMiddleware<RequestResponseLoggingMiddleware>(); call after app.UseResponseCompression();

Answer 2

I had faced the same issue while using the .net core inbuilt ResponseCompression, but was able to use the inspiration from CompressionMiddleware.cs to create a custom compression middleware

And Configure in Startup.cs is as follows

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IServiceProvider serviceProvider)
    {
        app.UseCompression();
        
        app.UseMiddleware<RequestResponseLogger>();