CompressionMiddleware.cs

using System;
using System.IO;
using System.IO.Compression;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

namespace Middlewares
{
    /// <summary>
    /// Experimental compression middleware for self-hosted web app
    /// </summary>
    public class CompressionMiddleware
    {
        private readonly RequestDelegate _next;
        private const long MinimumLength = 2700;

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

        public async Task Invoke(HttpContext context)
        {
            var acceptEncoding = context.Request.Headers["Accept-Encoding"];
            if (acceptEncoding.ToString().IndexOf("gzip", StringComparison.CurrentCultureIgnoreCase) < 0)
            {
                await _next(context);
                return;
            }

            using (var buffer = new MemoryStream())
            {
                var body = context.Response.Body;
                context.Response.Body = buffer;
                try
                {
                    await _next(context);

                    if (buffer.Length >= MinimumLength)
                    {
                        using (var compressed = new MemoryStream())
                        {
                            using (var gzip = new GZipStream(compressed, CompressionLevel.Optimal, leaveOpen: true))
                            {
                                buffer.Seek(0, SeekOrigin.Begin);
                                await buffer.CopyToAsync(gzip);
                            }

                            if (compressed.Length < buffer.Length)
                            {
                                // write compressed data to response
                                context.Response.Headers.Add("Content-Encoding", new[] { "gzip" });
                                if (context.Response.Headers["Content-Length"].Count > 0)
                                {
                                    context.Response.Headers["Content-Length"] = compressed.Length.ToString();
                                }

                                compressed.Seek(0, SeekOrigin.Begin);
                                await compressed.CopyToAsync(body);
                                return;
                            }
                        }
                    }

                    // write uncompressed data to response
                    buffer.Seek(0, SeekOrigin.Begin);
                    await buffer.CopyToAsync(body);
                }
                finally
                {
                    context.Response.Body = body;
                }
            }
        }
    }
}

hi Andri,
I found compression middleware while searching over for custom middleware implementation, thanks for sharing. When i tried to use the same middle ware , i don't see content-encoding is not present in response header ? Is that i am missing anything here,
thanks
Vimal