Java tutorial
package be.milieuinfo.core.proxy.controller; /** * Copyright MITRE * * 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. */ import java.io.Closeable; import java.io.IOException; import java.io.OutputStream; import java.net.URI; import java.util.BitSet; import java.util.Enumeration; import java.util.Formatter; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.http.Header; import org.apache.http.HttpEntity; import org.apache.http.HttpEntityEnclosingRequest; import org.apache.http.HttpHeaders; import org.apache.http.HttpHost; import org.apache.http.HttpRequest; import org.apache.http.HttpResponse; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.AbortableHttpRequest; import org.apache.http.client.params.ClientPNames; import org.apache.http.client.utils.URIUtils; import org.apache.http.entity.InputStreamEntity; import org.apache.http.impl.client.DefaultHttpClient; import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager; import org.apache.http.message.BasicHeader; import org.apache.http.message.BasicHttpEntityEnclosingRequest; import org.apache.http.message.BasicHttpRequest; import org.apache.http.message.HeaderGroup; import org.apache.http.params.BasicHttpParams; import org.apache.http.params.HttpParams; import org.apache.http.util.EntityUtils; /** * An HTTP reverse proxy/gateway servlet. It is designed to be extended for customization * if desired. Most of the work is handled by * <a href="http://hc.apache.org/httpcomponents-client-ga/">Apache HttpClient</a>. * <p> * There are alternatives to a servlet based proxy such as Apache mod_proxy if that is available to you. However * this servlet is easily customizable by Java, secure-able by your web application's security (e.g. spring-security), * portable across servlet engines, and is embeddable into another web application. * </p> * <p> * Inspiration: http://httpd.apache.org/docs/2.0/mod/mod_proxy.html * </p> * * @author David Smiley dsmiley@mitre.org> */ public class ProxyServlet extends HttpServlet { /* INIT PARAMETER NAME CONSTANTS */ private static final long serialVersionUID = 6994808711038236579L; /** A boolean parameter then when enabled will log input and target URLs to the servlet log. */ public static final String P_LOG = "log"; /* MISC */ protected boolean doLog = false; protected URI targetUri; protected HttpClient proxyClient; @Override public String getServletInfo() { return "A proxy servlet by David Smiley, dsmiley@mitre.org"; } @Override public void init(ServletConfig servletConfig) throws ServletException { super.init(servletConfig); String doLogStr = servletConfig.getInitParameter(P_LOG); if (doLogStr != null) { this.doLog = Boolean.parseBoolean(doLogStr); } try { targetUri = new URI(servletConfig.getInitParameter("targetUri")); } catch (Exception e) { throw new RuntimeException("Trying to process targetUri init parameter: " + e, e); } HttpParams hcParams = new BasicHttpParams(); readConfigParam(hcParams, ClientPNames.HANDLE_REDIRECTS, Boolean.class); proxyClient = createHttpClient(hcParams); } /** Called from {@link #init(javax.servlet.ServletConfig)}. HttpClient offers many opportunities for customization. * @param hcParams*/ protected HttpClient createHttpClient(HttpParams hcParams) { return new DefaultHttpClient(new ThreadSafeClientConnManager(), hcParams); } private void readConfigParam(HttpParams hcParams, String hcParamName, Class<?> type) { String val_str = getServletConfig().getInitParameter(hcParamName); if (val_str == null) return; Object val_obj; if (type == String.class) { val_obj = val_str; } else { try { val_obj = type.getMethod("valueOf", String.class).invoke(type, val_str); } catch (Exception e) { throw new RuntimeException(e); } } hcParams.setParameter(hcParamName, val_obj); } @Override public void destroy() { //shutdown() must be called according to documentation. if (proxyClient != null) proxyClient.getConnectionManager().shutdown(); super.destroy(); } @SuppressWarnings("deprecation") @Override protected void service(HttpServletRequest servletRequest, HttpServletResponse servletResponse) throws ServletException, IOException { // Make the Request //note: we won't transfer the protocol version because I'm not sure it would truly be compatible String method = servletRequest.getMethod(); String proxyRequestUri = rewriteUrlFromRequest(servletRequest); HttpRequest proxyRequest; //spec: RFC 2616, sec 4.3: either these two headers signal that there is a message body. if (servletRequest.getHeader(HttpHeaders.CONTENT_LENGTH) != null || servletRequest.getHeader(HttpHeaders.TRANSFER_ENCODING) != null) { HttpEntityEnclosingRequest eProxyRequest = new BasicHttpEntityEnclosingRequest(method, proxyRequestUri); // Add the input entity (streamed) // note: we don't bother ensuring we close the servletInputStream since the container handles it eProxyRequest.setEntity( new InputStreamEntity(servletRequest.getInputStream(), servletRequest.getContentLength())); proxyRequest = eProxyRequest; } else proxyRequest = new BasicHttpRequest(method, proxyRequestUri); copyRequestHeaders(servletRequest, proxyRequest); try { // Execute the request if (doLog) { log("proxy " + method + " uri: " + servletRequest.getRequestURI() + " -- " + proxyRequest.getRequestLine().getUri()); } HttpResponse proxyResponse = proxyClient.execute(URIUtils.extractHost(targetUri), proxyRequest); // Process the response int statusCode = proxyResponse.getStatusLine().getStatusCode(); if (doResponseRedirectOrNotModifiedLogic(servletRequest, servletResponse, proxyResponse, statusCode)) { //just to be sure, but is probably a no-op EntityUtils.consume(proxyResponse.getEntity()); return; } // Pass the response code. This method with the "reason phrase" is deprecated but it's the only way to pass the // reason along too. //noinspection deprecation servletResponse.setStatus(statusCode, proxyResponse.getStatusLine().getReasonPhrase()); copyResponseHeaders(proxyResponse, servletResponse); // Send the content to the client copyResponseEntity(proxyResponse, servletResponse); } catch (Exception e) { //abort request, according to best practice with HttpClient if (proxyRequest instanceof AbortableHttpRequest) { AbortableHttpRequest abortableHttpRequest = (AbortableHttpRequest) proxyRequest; abortableHttpRequest.abort(); } if (e instanceof RuntimeException) throw (RuntimeException) e; if (e instanceof ServletException) throw (ServletException) e; if (e instanceof IOException) throw (IOException) e; throw new RuntimeException(e); } } private boolean doResponseRedirectOrNotModifiedLogic(HttpServletRequest servletRequest, HttpServletResponse servletResponse, HttpResponse proxyResponse, int statusCode) throws ServletException, IOException { // Check if the proxy response is a redirect // The following code is adapted from org.tigris.noodle.filters.CheckForRedirect if (statusCode >= HttpServletResponse.SC_MULTIPLE_CHOICES /* 300 */ && statusCode < HttpServletResponse.SC_NOT_MODIFIED /* 304 */) { Header locationHeader = proxyResponse.getLastHeader(HttpHeaders.LOCATION); if (locationHeader == null) { throw new ServletException("Received status code: " + statusCode + " but no " + HttpHeaders.LOCATION + " header was found in the response"); } // Modify the redirect to go to this proxy servlet rather that the proxied host String locStr = rewriteUrlFromResponse(servletRequest, locationHeader.getValue()); servletResponse.sendRedirect(locStr); return true; } // 304 needs special handling. See: // http://www.ics.uci.edu/pub/ietf/http/rfc1945.html#Code304 // We get a 304 whenever passed an 'If-Modified-Since' // header and the data on disk has not changed; server // responds w/ a 304 saying I'm not going to send the // body because the file has not changed. if (statusCode == HttpServletResponse.SC_NOT_MODIFIED) { servletResponse.setIntHeader(HttpHeaders.CONTENT_LENGTH, 0); servletResponse.setStatus(HttpServletResponse.SC_NOT_MODIFIED); return true; } return false; } protected void closeQuietly(Closeable closeable) { try { closeable.close(); } catch (IOException e) { log(e.getMessage(), e); } } /** These are the "hop-by-hop" headers that should not be copied. * http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html * I use an HttpClient HeaderGroup class instead of Set<String> because this * approach does case insensitive lookup faster. */ private static final HeaderGroup hopByHopHeaders; static { hopByHopHeaders = new HeaderGroup(); String[] headers = new String[] { "Connection", "Keep-Alive", "Proxy-Authenticate", "Proxy-Authorization", "TE", "Trailers", "Transfer-Encoding", "Upgrade" }; for (String header : headers) { hopByHopHeaders.addHeader(new BasicHeader(header, null)); } } /** Copy request headers from the servlet client to the proxy request. */ protected void copyRequestHeaders(HttpServletRequest servletRequest, HttpRequest proxyRequest) { // Get an Enumeration of all of the header names sent by the client Enumeration enumerationOfHeaderNames = servletRequest.getHeaderNames(); while (enumerationOfHeaderNames.hasMoreElements()) { String headerName = (String) enumerationOfHeaderNames.nextElement(); //Instead the content-length is effectively set via InputStreamEntity if (headerName.equalsIgnoreCase(HttpHeaders.CONTENT_LENGTH)) continue; if (hopByHopHeaders.containsHeader(headerName)) continue; // As per the Java Servlet API 2.5 documentation: // Some headers, such as Accept-Language can be sent by clients // as several headers each with a different value rather than // sending the header as a comma separated list. // Thus, we get an Enumeration of the header values sent by the client Enumeration headers = servletRequest.getHeaders(headerName); while (headers.hasMoreElements()) { String headerValue = (String) headers.nextElement(); // In case the proxy host is running multiple virtual servers, // rewrite the Host header to ensure that we get content from // the correct virtual server if (headerName.equalsIgnoreCase(HttpHeaders.HOST)) { HttpHost host = URIUtils.extractHost(this.targetUri); headerValue = host.getHostName(); if (host.getPort() != -1) headerValue += ":" + host.getPort(); } proxyRequest.addHeader(headerName, headerValue); } } } /** Copy proxied response headers back to the servlet client. */ protected void copyResponseHeaders(HttpResponse proxyResponse, HttpServletResponse servletResponse) { for (Header header : proxyResponse.getAllHeaders()) { if (hopByHopHeaders.containsHeader(header.getName())) continue; servletResponse.addHeader(header.getName(), header.getValue()); } } /** Copy response body data (the entity) from the proxy to the servlet client. */ private void copyResponseEntity(HttpResponse proxyResponse, HttpServletResponse servletResponse) throws IOException { HttpEntity entity = proxyResponse.getEntity(); if (entity != null) { OutputStream servletOutputStream = servletResponse.getOutputStream(); try { entity.writeTo(servletOutputStream); } finally { closeQuietly(servletOutputStream); } } } private String rewriteUrlFromRequest(HttpServletRequest servletRequest) { StringBuilder uri = new StringBuilder(500); uri.append(this.targetUri.toString()); // Handle the path given to the servlet if (servletRequest.getPathInfo() != null) {//ex: /my/path.html uri.append(servletRequest.getPathInfo()); } // Handle the query string String queryString = servletRequest.getQueryString();//ex:(following '?'): name=value&foo=bar#fragment if (queryString != null && queryString.length() > 0) { uri.append('?'); int fragIdx = queryString.indexOf('#'); String queryNoFrag = (fragIdx < 0 ? queryString : queryString.substring(0, fragIdx)); uri.append(encodeUriQuery(queryNoFrag)); if (fragIdx >= 0) { uri.append('#'); uri.append(encodeUriQuery(queryString.substring(fragIdx + 1))); } } return uri.toString(); } private String rewriteUrlFromResponse(HttpServletRequest servletRequest, String theUrl) { //TODO document example paths if (theUrl.startsWith(this.targetUri.toString())) { String curUrl = servletRequest.getRequestURL().toString();//no query String pathInfo = servletRequest.getPathInfo(); if (pathInfo != null) { assert curUrl.endsWith(pathInfo); curUrl = curUrl.substring(0, curUrl.length() - pathInfo.length());//take pathInfo off } theUrl = curUrl + theUrl.substring(this.targetUri.toString().length()); } return theUrl; } /** * <p>Encodes characters in the query or fragment part of the URI. * * <p>Unfortunately, an incoming URI sometimes has characters disallowed by the spec. HttpClient * insists that the outgoing proxied request has a valid URI because it uses Java's {@link URI}. To be more * forgiving, we must escape the problematic characters. See the URI class for the spec. * * @param in example: name=value&foo=bar#fragment */ static CharSequence encodeUriQuery(CharSequence in) { //Note that I can't simply use URI.java to encode because it will escape pre-existing escaped things. StringBuilder outBuf = null; Formatter formatter = null; for (int i = 0; i < in.length(); i++) { char c = in.charAt(i); boolean escape = true; if (c < 128) { if (asciiQueryChars.get((int) c)) { escape = false; } } else if (!Character.isISOControl(c) && !Character.isSpaceChar(c)) {//not-ascii escape = false; } if (!escape) { if (outBuf != null) outBuf.append(c); } else { //escape if (outBuf == null) { outBuf = new StringBuilder(in.length() + 5 * 3); outBuf.append(in, 0, i); formatter = new Formatter(outBuf); } //leading %, 0 padded, width 2, capital hex formatter.format("%%%02X", (int) c);//TODO } } return outBuf != null ? outBuf : in; } static final BitSet asciiQueryChars; static { char[] c_unreserved = "_-!.~'()*".toCharArray();//plus alphanum char[] c_punct = ",;:$&+=".toCharArray(); char[] c_reserved = "?/[]@".toCharArray();//plus punct asciiQueryChars = new BitSet(128); for (char c = 'a'; c <= 'z'; c++) asciiQueryChars.set((int) c); for (char c = 'A'; c <= 'Z'; c++) asciiQueryChars.set((int) c); for (char c = '0'; c <= '9'; c++) asciiQueryChars.set((int) c); for (char c : c_unreserved) asciiQueryChars.set((int) c); for (char c : c_punct) asciiQueryChars.set((int) c); for (char c : c_reserved) asciiQueryChars.set((int) c); asciiQueryChars.set((int) '%');//leave existing percent escapes in place } }