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/*
* Copyright © 2016-2018 European Support Limited
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.onap.workflow.web;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import org.eclipse.jetty.proxy.ProxyServlet;
/**
* <p>A naive implementation of transparent proxy based on
* <a href="https://www.eclipse.org/jetty/documentation/9.4.x/proxy-servlet.html">Jetty proxy servlet</a>.
* The only difference is that the <code>proxyTo</code> configuration parameter is taken from a JVM argument (and can
* be therefore injected via an environment variable), instead of an <code>init-param</code> in <i>web.xml</i>.</p>
* <p>Example: <code>java -DproxyTo=http://172.17.0.9:8080 -jar $JETTY_HOME/start.jar</code></p>
* <p>If you get a <i>502 Bad Gateway</i> error:</p>
* <ul>
* <ol>
* Make sure that Jetty 'proxy' module
* <a href="https://www.eclipse.org/jetty/documentation/9.4.x/startup-modules.html">is not enabled</a>.
* </ol>
* <ol>
* Check the value of <code>proxyTo</code>. Make sure it does not redirect to the proxy server itself.
* </ol>
* <ol>
* Make sure there is no proxy (e.g. in a corporate environment) between the servlet and <code>proxyTo</code>.
* </ol>
* </ul>
*
* @author evitaliy
* @since 16 Jul 2018
*/
public class TransparentProxy extends ProxyServlet.Transparent {
@Override
public void init(ServletConfig config) throws ServletException {
super.init(new ServletConfigWrapper(config));
}
private class ServletConfigWrapper implements ServletConfig {
private static final String PROXY_TO = "proxyTo";
private final String proxyTo;
private final ServletConfig config;
ServletConfigWrapper(ServletConfig config) throws ServletException {
this.proxyTo = System.getProperty(PROXY_TO);
if (this.proxyTo == null) {
throw new ServletException("-D" + PROXY_TO + " must be specified");
}
this.config = config;
}
@Override
public String getServletName() {
return config.getServletName();
}
@Override
public ServletContext getServletContext() {
return config.getServletContext();
}
@Override
public String getInitParameter(String s) {
return PROXY_TO.equals(s) ? this.proxyTo : config.getInitParameter(s);
}
@Override
public Enumeration<String> getInitParameterNames() {
ArrayList<String> params = Collections.list(config.getInitParameterNames());
params.add(PROXY_TO);
return Collections.enumeration(params);
}
}
}
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