WebFilter is not able to modify response when running with quarkus:dev

[38leinaD]

Describe the bug
I have written a @webfilter (using HttpServletResponseWrapper) that wants to modify/rewrite a response (see code at end of issue description). The implementation works fine when quarkus is running "normally"; it is not working when running via "quarkus:dev".
It is not possible to modify the the contentLength, contentType or body. The browser receives the original headers but no body; so, just waits to load the body endlessly. It seems the response is already commited/sent to the client.

Expected behavior
The Filter should be able to modify the headers and body.
E.g. for index.html return body "hello world" and content-type "text/plain".

Actual behavior
Headers sent to the client are the ones of the orginal response as set by
filterChain.doFilter(request, wrappedResp);
It see the response is already commited and has started to be sent to the client.

To Reproduce
Steps to reproduce the behavior:

1. Set up a simple quarkus project containing a dependency to quarkus-undertow
2. Add the attached code.
3. Run with mvn compile quarkus:dev
4. Try to open localhost:8080/index.html

Instead of showing the index.html, "hello world" should be printed as text/plain.

Configuration

# empty

Screenshots

Environment (please complete the following information):

• Output of uname -a or ver: Linux hedgehog 4.9.0-12-amd64 Switch to the Maven distributed copy of the SubstrateVM annotations #1 SMP Debian 4.9.210-1 (2020-01-20) x86_64 GNU/Linux
• Output of java -version: openjdk version "13" 2019-09-17
  OpenJDK Runtime Environment (build 13+33)
  OpenJDK 64-Bit Server VM (build 13+33, mixed mode, sharing)
• GraalVM version (if different from Java):
• Quarkus version or git rev: 1.3.2.Final
• Build tool (ie. output of mvnw --version or gradlew --version): Apache Maven 3.6.3 (cecedd343002696d0abb50b32b541b8a6ba2883f)
  Maven home: /home/daniel/.m2/wrapper/dists/apache-maven-3.6.3-bin/1iopthnavndlasol9gbrbg6bf2/apache-maven-3.6.3
  Java version: 13, vendor: Oracle Corporation, runtime: /home/daniel/.sdkman/candidates/java/13.0.0-open
  Default locale: en_US, platform encoding: UTF-8
  OS name: "linux", version: "4.9.0-12-amd64", arch: "amd64", family: "unix"

Additional context
The Filter implementation:

package org.acme;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.WriteListener;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

import io.undertow.servlet.spec.HttpServletRequestImpl;

class ServletResponseWrapper extends HttpServletResponseWrapper {

    private final ByteArrayOutputStream capture;
    private ServletOutputStream output;
    private PrintWriter writer;

    public ServletResponseWrapper(HttpServletResponse response) throws IOException {
        super(response);
        capture = new ByteArrayOutputStream(response.getBufferSize());
    }

    @Override
    public ServletOutputStream getOutputStream() {
        if (writer != null) {
            throw new IllegalStateException("getWriter() has already been called on this response.");
        }

        if (output == null) {
            output = new ServletOutputStream() {
                @Override
                public void write(int b) throws IOException {
                    capture.write(b);
                }

                @Override
                public void write(byte b[]) throws IOException {
                    capture.write(b);
                }
                
                @Override
                public void write(byte b[], int off, int len) throws IOException {
                    capture.write(b, off, len);
                }
                
                @Override
                public void flush() throws IOException {
                    capture.flush();
                }

                @Override
                public void close() throws IOException {
                    capture.close();
                }

                @Override
                public boolean isReady() {
                    return false;
                }

                @Override
                public void setWriteListener(WriteListener arg0) {
                }
            };
        }

        return output;
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        if (output != null) {
            throw new IllegalStateException("getOutputStream() has already been called on this response.");
        }

        if (writer == null) {
            writer = new PrintWriter(new OutputStreamWriter(capture, getCharacterEncoding()));
        }

        return writer;
    }

    public void close() throws IOException {
        if (writer != null) {
            writer.close();
        }
        if (output != null) {
            output.close();
        }
    }
    
    @Override
    public void flushBuffer() throws IOException {
        System.out.println("-- flush buffer");
        if (writer != null) {
            writer.flush();
        } else if (output != null) {
            output.flush();
        }
    }

    public byte[] getResponseData() throws IOException {
        if (writer != null) {
            writer.close();
        } else if (output != null) {
            output.close();
        }
        return capture.toByteArray();
    }
    
    @Override
    public String toString() {
        try {
            return new String(getResponseData());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

@WebFilter("/*")
public class WebResourceFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {

        System.out.println("Filtering " + request);

        if (request instanceof HttpServletRequestImpl) {
            String url = ((HttpServletRequestImpl) request).getRequestURL().toString();

            if (url.endsWith("/index.html")) {

                ServletResponseWrapper wrappedResp = new ServletResponseWrapper((HttpServletResponse) response);

                filterChain.doFilter(request, wrappedResp);

                String respBody = wrappedResp.toString();
                
                if (wrappedResp.getContentType().contains("text/html")) {
                    System.out.println("-- committed? " + response.isCommitted());

 
                    String msg = "hello world";
                    response.setContentType("text/plain");
                    response.setContentLength(msg.length());
                    response.getWriter().write(msg);
                }
                else {
                    System.out.println("-- Just return original resonse");
                    response.setContentType(wrappedResp.getContentType());
                    response.setContentLength(respBody.length());
                    response.getWriter().append(respBody);
                }
                return;
            }
        }
        filterChain.doFilter(request, response);
    }
    
    public void destroy() {
    }
}