httpproxy with littleproxy

git clone https://github.com/adamfisk/LittleProxy
cd LittleProxy
./run.bash


To intercept HTTP requests, edit org.littleshoot.proxy.Launcher and insert the line with "withFiltersSource":

System.out.println("About to start...");
bootstrap.withFiltersSource(new MyHttpFiltersSourceAdapter());
bootstrap.start();

package org.littleshoot.proxy.impl;

import org.littleshoot.proxy.HttpFilters;
import org.littleshoot.proxy.HttpFiltersAdapter;
import org.littleshoot.proxy.HttpFiltersSource;

import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.http.HttpObject;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpResponse;
import io.netty.handler.codec.http.DefaultHttpRequest;

public class MyHttpFiltersSourceAdapter implements HttpFiltersSource {
    public HttpFiltersAdapter filterRequest(HttpRequest originalRequest, ChannelHandlerContext ctx) {
        return new HttpFiltersAdapter(originalRequest) {
            @Override
            public HttpResponse clientToProxyRequest(HttpObject httpObject) {
                // TODO: implement your filtering here
             System.out.println("clientToProxyRequest invoked");
             System.out.println(httpObject.toString());
             if (httpObject instanceof DefaultHttpRequest) {
              DefaultHttpRequest request = (DefaultHttpRequest)httpObject;
              System.out.println("it's a DefaultHttpRequest with uri:");
              System.out.println(request.getUri());
              System.out.println(request.toString());
              System.out.println(request.headers());
             }
             System.out.println();
                return null;
            }

            @Override
            public HttpObject serverToProxyResponse(HttpObject httpObject) {
             System.out.println("serverToProxyResponse invoked");
             System.out.println(httpObject.toString());
             System.out.println();
                return httpObject;
            }
        };
    }

 @Override
 public int getMaximumRequestBufferSizeInBytes() {
  // TODO Auto-generated method stub
  return 0;
 }

 @Override
 public int getMaximumResponseBufferSizeInBytes() {
  // TODO Auto-generated method stub
  return 0;
 }
}

This is priceless to analyze what is going on between Nexus repository and Maven central:

make sure your maven uses Nexus as a mirror:

vi /home/centos/apache-maven-3.5.0/conf/settings.xml

<mirror>
<id>nexus</id>
<mirrorOf>*</mirrorOf>
<url>http://localhost:8081/repository/maven-public/</url>
</mirror>

then make sure that Nexus "maven-central" proxy repo (http://localhost:8081/repository/maven-central/) points to http://repo1.maven.org/maven2/ and not to https://repo1.maven.org/maven2/ (it's easier to trace http traffic than https).

then configure Nexus 3.11 (login as admin/admin123, menu System/HTTP, set HTTP proxy to localhost and 8080)

let's prepare a Maven project to compile:

git clone https://github.com/gabrielf/maven-samples
cd maven-samples/
mvn package


to make sure a give jar is missing from the m2 repository, delete it before each build:
rm -rf /home/centos/.m2/repository/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.jar

and remove it also from Nexus (Search/Maven, search for plexus-utils 3.0, Delete component)




What you see in the LittleProxy stdout is:


clientToProxyRequest invoked
DefaultHttpRequest(decodeResult: success, version: HTTP/1.1)
GET http://repo1.maven.org/maven2/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.jar HTTP/1.1
Host: repo1.maven.org
Proxy-Connection: Keep-Alive
User-Agent: Nexus/3.11.0-01 (OSS; Linux; 3.10.0-693.17.1.el7.x86_64; amd64; 1.8.0_141)
Accept-Encoding: gzip,deflate



As you can read in https://github.com/adamfisk/LittleProxy/blob/master/src/main/java/org/littleshoot/proxy/HttpFilters.java for the method clientToProxyRequest, if you return null the request will be further processed; if you return a io.netty.handler.codec.http.HttpResponse, then you effectively break the flow and you can stop the request.