2.1/user/src/com/google/gwt/user/server/rpc/RPCServletUtils.java - gwt - Git at Google

 /*
  * Copyright 2008 Google Inc.
  *
  * 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 com.google.gwt.user.server.rpc;

 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.reflect.Method;
 import java.util.zip.GZIPOutputStream;

 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 /**
  * Utility class containing helper methods used by servlets that integrate with
  * the RPC system.
  */
 public class RPCServletUtils {
   /**
    * Package protected for use in tests.
    */
   static final int BUFFER_SIZE = 4096;

   private static final String ACCEPT_ENCODING = "Accept-Encoding";

   private static final String ATTACHMENT = "attachment";

   /**
    * Used both as expected request charset and encoded response charset.
    */
   private static final String CHARSET_UTF8 = "UTF-8";

   private static final String CONTENT_DISPOSITION = "Content-Disposition";

   private static final String CONTENT_ENCODING = "Content-Encoding";

   private static final String CONTENT_ENCODING_GZIP = "gzip";

   private static final String CONTENT_TYPE_APPLICATION_JSON_UTF8 = "application/json; charset=utf-8";

   private static final String GENERIC_FAILURE_MSG = "The call failed on the server; see server log for details";

   private static final String GWT_RPC_CONTENT_TYPE = "text/x-gwt-rpc";

   /**
    * Controls the compression threshold at and below which no compression will
    * take place.
    */
   private static final int UNCOMPRESSED_BYTE_SIZE_LIMIT = 256;

   /**
    * Returns <code>true</code> if the {@link HttpServletRequest} accepts Gzip
    * encoding. This is done by checking that the accept-encoding header
    * specifies gzip as a supported encoding.
    *
    * @param request the request instance to test for gzip encoding acceptance
    * @return <code>true</code> if the {@link HttpServletRequest} accepts Gzip
    *         encoding
    */
   public static boolean acceptsGzipEncoding(HttpServletRequest request) {
     assert (request != null);

     String acceptEncoding = request.getHeader(ACCEPT_ENCODING);
     if (null == acceptEncoding) {
       return false;
     }

     return (acceptEncoding.indexOf(CONTENT_ENCODING_GZIP) != -1);
   }

   /**
    * Returns <code>true</code> if the response content's estimated UTF-8 byte
    * length exceeds 256 bytes.
    *
    * @param content the contents of the response
    * @return <code>true</code> if the response content's estimated UTF-8 byte
    *         length exceeds 256 bytes
    */
   public static boolean exceedsUncompressedContentLengthLimit(String content) {
     return (content.length() * 2) > UNCOMPRESSED_BYTE_SIZE_LIMIT;
   }

   /**
    * Returns true if the {@link java.lang.reflect.Method Method} definition on
    * the service is specified to throw the exception contained in the
    * InvocationTargetException or false otherwise. NOTE we do not check that the
    * type is serializable here. We assume that it must be otherwise the
    * application would never have been allowed to run.
    *
    * @param serviceIntfMethod the method from the RPC request
    * @param cause the exception that the method threw
    * @return true if the exception's type is in the method's signature
    */
   public static boolean isExpectedException(Method serviceIntfMethod,
       Throwable cause) {
     assert (serviceIntfMethod != null);
     assert (cause != null);

     Class<?>[] exceptionsThrown = serviceIntfMethod.getExceptionTypes();
     if (exceptionsThrown.length <= 0) {
       // The method is not specified to throw any exceptions
       //
       return false;
     }

     Class<? extends Throwable> causeType = cause.getClass();

     for (Class<?> exceptionThrown : exceptionsThrown) {
       assert (exceptionThrown != null);

       if (exceptionThrown.isAssignableFrom(causeType)) {
         return true;
       }
     }

     return false;
   }

   /**
    * Returns the content of an {@link HttpServletRequest} by decoding it using
    * <code>expectedCharSet</code>, or <code>UTF-8</code> if
    * <code>expectedCharSet</code> is <code>null</null>.
    *
    * @param request the servlet request whose content we want to read
    * @param expectedContentType the expected content (i.e. 'type/subtype' only)
    *          in the Content-Type request header, or <code>null</code> if no
    *          validation is to be performed, and you are willing to allow for
    *          some types of cross type security attacks
    * @param expectedCharSet the expected request charset, or <code>null</code>
    *          if no charset validation is to be performed and <code>UTF-8</code>
    *          should be assumed
    * @return the content of an {@link HttpServletRequest} by decoding it using
    *         <code>expectedCharSet</code>, or <code>UTF-8</code> if
    *         <code>expectedCharSet</code> is <code>null</null>
    * @throws IOException if the request's input stream cannot be accessed, read
    *         from or closed
    * @throws ServletException if the request's content type does not
    *         equal the supplied <code>expectedContentType</code> or
    *         <code>expectedCharSet</code>
    */
   public static String readContent(HttpServletRequest request,
       String expectedContentType, String expectedCharSet)
       throws IOException, ServletException {
     if (expectedContentType != null) {
       checkContentTypeIgnoreCase(request, expectedContentType);
     }
     if (expectedCharSet != null) {
       checkCharacterEncodingIgnoreCase(request, expectedCharSet);
     }

     /*
      * Need to support 'Transfer-Encoding: chunked', so do not rely on
      * presence of a 'Content-Length' request header.
      */
     InputStream in = request.getInputStream();
     byte[] buffer = new byte[BUFFER_SIZE];
     ByteArrayOutputStream out = new  ByteArrayOutputStream(BUFFER_SIZE);
     try {
       while (true) {
         int byteCount = in.read(buffer);
         if (byteCount == -1) {
           break;
         }
         out.write(buffer, 0, byteCount);
       }
       String contentCharSet = expectedCharSet != null
           ? expectedCharSet : CHARSET_UTF8;
       return out.toString(contentCharSet);
     } finally {
       if (in != null) {
         in.close();
       }
     }
   }

   /**
    * Returns the content of an {@link HttpServletRequest}, after verifying a
    * <code>gwt/x-gwt-rpc; charset=utf-8</code> content type.
    *
    * @param request the servlet request whose content we want to read
    * @return the content of an {@link HttpServletRequest} by decoding it using
    *         <code>UTF-8</code>
    * @throws IOException if the request's input stream cannot be accessed, read
    *         from or closed
    * @throws ServletException if the request's content type is not
    *         <code>gwt/x-gwt-rpc; charset=utf-8</code>, ignoring case
    */
   public static String readContentAsGwtRpc(HttpServletRequest request)
       throws IOException, ServletException {
       return readContent(request, GWT_RPC_CONTENT_TYPE, CHARSET_UTF8);
   }

  /**
    * Returns the content of an {@link HttpServletRequest} by decoding it using
    * the UTF-8 charset.
    *
    * @param request the servlet request whose content we want to read
    * @return the content of an {@link HttpServletRequest} by decoding it using
    *         the UTF-8 charset
    * @throws IOException if the requests input stream cannot be accessed, read
    *           from or closed
    * @throws ServletException if the content length of the request is not
    *           specified of if the request's content type is not
    *           'text/x-gwt-rpc' and 'charset=utf-8'
    * @deprecated Use {@link readContent} instead.
    */
   @Deprecated
   public static String readContentAsUtf8(HttpServletRequest request)
       throws IOException, ServletException {
     return readContent(request, null, null);
   }

   /**
    * Returns the content of an {@link HttpServletRequest} by decoding it using
    * the UTF-8 charset.
    *
    * @param request the servlet request whose content we want to read
    * @param checkHeaders Specify 'true' to check the Content-Type header to see
    *          that it matches the expected value 'text/x-gwt-rpc' and the
    *          content encoding is UTF-8. Disabling this check may allow some
    *          types of cross type security attacks.
    * @return the content of an {@link HttpServletRequest} by decoding it using
    *         the UTF-8 charset
    * @throws IOException if the requests input stream cannot be accessed, read
    *           from or closed
    * @throws ServletException if the content length of the request is not
    *           specified of if the request's content type is not
    *           'text/x-gwt-rpc' and 'charset=utf-8'
    * @deprecated Use {@link readContent} instead.
    */
   @Deprecated
   public static String readContentAsUtf8(HttpServletRequest request,
       boolean checkHeaders) throws IOException, ServletException {
     return readContent(request, GWT_RPC_CONTENT_TYPE, CHARSET_UTF8);
   }

   /**
    * Sets the correct header to indicate that a response is gzipped.
    */
   public static void setGzipEncodingHeader(HttpServletResponse response) {
     response.setHeader(CONTENT_ENCODING, CONTENT_ENCODING_GZIP);
   }

   /**
    * Returns <code>true</code> if the request accepts gzip encoding and the the
    * response content's estimated UTF-8 byte length exceeds 256 bytes.
    *
    * @param request the request associated with the response content
    * @param responseContent a string that will be
    * @return <code>true</code> if the request accepts gzip encoding and the the
    *         response content's estimated UTF-8 byte length exceeds 256 bytes
    */
   public static boolean shouldGzipResponseContent(HttpServletRequest request,
       String responseContent) {
     return acceptsGzipEncoding(request)
         && exceedsUncompressedContentLengthLimit(responseContent);
   }

   /**
    * Write the response content into the {@link HttpServletResponse}. If
    * <code>gzipResponse</code> is <code>true</code>, the response content will
    * be gzipped prior to being written into the response.
    *
    * @param servletContext servlet context for this response
    * @param response response instance
    * @param responseContent a string containing the response content
    * @param gzipResponse if <code>true</code> the response content will be gzip
    *          encoded before being written into the response
    * @throws IOException if reading, writing, or closing the response's output
    *           stream fails
    */
   public static void writeResponse(ServletContext servletContext,
       HttpServletResponse response, String responseContent, boolean gzipResponse)
       throws IOException {

     byte[] responseBytes = responseContent.getBytes(CHARSET_UTF8);
     if (gzipResponse) {
       // Compress the reply and adjust headers.
       //
       ByteArrayOutputStream output = null;
       GZIPOutputStream gzipOutputStream = null;
       Throwable caught = null;
       try {
         output = new ByteArrayOutputStream(responseBytes.length);
         gzipOutputStream = new GZIPOutputStream(output);
         gzipOutputStream.write(responseBytes);
         gzipOutputStream.finish();
         gzipOutputStream.flush();
         setGzipEncodingHeader(response);
         responseBytes = output.toByteArray();
       } catch (IOException e) {
         caught = e;
       } finally {
         if (null != gzipOutputStream) {
           gzipOutputStream.close();
         }
         if (null != output) {
           output.close();
         }
       }

       if (caught != null) {
         servletContext.log("Unable to compress response", caught);
         response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
         return;
       }
     }

     // Send the reply.
     //
     response.setContentLength(responseBytes.length);
     response.setContentType(CONTENT_TYPE_APPLICATION_JSON_UTF8);
     response.setStatus(HttpServletResponse.SC_OK);
     response.setHeader(CONTENT_DISPOSITION, ATTACHMENT);
     response.getOutputStream().write(responseBytes);
   }

   /**
    * Called when the servlet itself has a problem, rather than the invoked
    * third-party method. It writes a simple 500 message back to the client.
    *
    * @param servletContext
    * @param response
    * @param failure
    */
   public static void writeResponseForUnexpectedFailure(
       ServletContext servletContext, HttpServletResponse response,
       Throwable failure) {
     servletContext.log("Exception while dispatching incoming RPC call", failure);

     // Send GENERIC_FAILURE_MSG with 500 status.
     //
     try {
       response.setContentType("text/plain");
       response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
       try {
         response.getOutputStream().write(GENERIC_FAILURE_MSG.getBytes("UTF-8"));
       } catch (IllegalStateException e) {
         // Handle the (unexpected) case where getWriter() was previously used
         response.getWriter().write(GENERIC_FAILURE_MSG);
       }
     } catch (IOException ex) {
       servletContext.log(
           "respondWithUnexpectedFailure failed while sending the previous failure to the client",
           ex);
     }
   }

   /**
    * Performs validation of the character encoding, ignoring case.
    *
    * @param request the incoming request
    * @param expectedCharSet the expected charset of the request
    * @throws ServletException if requests encoding is not <code>null</code> and
    *         does not equal, ignoring case, <code>expectedCharSet</code>
    */
   private static void checkCharacterEncodingIgnoreCase(
       HttpServletRequest request, String expectedCharSet)
       throws ServletException {
     boolean encodingOkay = false;
     String characterEncoding = request.getCharacterEncoding();
     if (characterEncoding != null) {
       /*
        * TODO: It would seem that we should be able to use equalsIgnoreCase here
        * instead of indexOf. Need to be sure that servlet engines return a
        * properly parsed character encoding string if we decide to make this
        * change.
        */
       if (characterEncoding.toLowerCase().indexOf(expectedCharSet.toLowerCase())
           != -1) {
         encodingOkay = true;
       }
     }

     if (!encodingOkay) {
       throw new ServletException("Character Encoding is '"
           + (characterEncoding == null ? "(null)" : characterEncoding)
           + "'.  Expected '" + expectedCharSet + "'");
     }
   }

   /**
    * Performs Content-Type validation of the incoming request, ignoring case
    * and any <code>charset</code> parameter.
    *
    * @see   #checkCharacterEncodingIgnoreCase(HttpServletRequest, String)
    * @param request the incoming request
    * @param expectedContentType the expected Content-Type for the incoming
    *        request
    * @throws ServletException if the request's content type is not
    *         <code>null</code> and does not, ignoring case, equal
    *         <code>expectedContentType</code>,
    */
   private static void checkContentTypeIgnoreCase(
       HttpServletRequest request, String expectedContentType)
       throws ServletException {
     String contentType = request.getContentType();
     boolean contentTypeIsOkay = false;

     if (contentType != null) {
       contentType = contentType.toLowerCase();
       /*
        * NOTE:We use startsWith because some servlet engines, i.e. Tomcat, do
        * not remove the charset component but others do.
        */
       if (contentType.startsWith(expectedContentType.toLowerCase())) {
         contentTypeIsOkay = true;
       }
     }

     if (!contentTypeIsOkay) {
       throw new ServletException("Content-Type was '"
           + (contentType == null ? "(null)" : contentType) + "'. Expected '"
           + expectedContentType + "'.");
     }
   }

   private RPCServletUtils() {
     // Not instantiable
   }
 }
	/*
	* Copyright 2008 Google Inc.
	*
	* 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 com.google.gwt.user.server.rpc;

	import java.io.ByteArrayOutputStream;
	import java.io.IOException;
	import java.io.InputStream;
	import java.lang.reflect.Method;
	import java.util.zip.GZIPOutputStream;

	import javax.servlet.ServletContext;
	import javax.servlet.ServletException;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletResponse;

	/**
	* Utility class containing helper methods used by servlets that integrate with
	* the RPC system.
	*/
	public class RPCServletUtils {
	/**
	* Package protected for use in tests.
	*/
	static final int BUFFER_SIZE = 4096;

	private static final String ACCEPT_ENCODING = "Accept-Encoding";

	private static final String ATTACHMENT = "attachment";

	/**
	* Used both as expected request charset and encoded response charset.
	*/
	private static final String CHARSET_UTF8 = "UTF-8";

	private static final String CONTENT_DISPOSITION = "Content-Disposition";

	private static final String CONTENT_ENCODING = "Content-Encoding";

	private static final String CONTENT_ENCODING_GZIP = "gzip";

	private static final String CONTENT_TYPE_APPLICATION_JSON_UTF8 = "application/json; charset=utf-8";

	private static final String GENERIC_FAILURE_MSG = "The call failed on the server; see server log for details";

	private static final String GWT_RPC_CONTENT_TYPE = "text/x-gwt-rpc";

	/**
	* Controls the compression threshold at and below which no compression will
	* take place.
	*/
	private static final int UNCOMPRESSED_BYTE_SIZE_LIMIT = 256;

	/**
	* Returns <code>true</code> if the {@link HttpServletRequest} accepts Gzip
	* encoding. This is done by checking that the accept-encoding header
	* specifies gzip as a supported encoding.
	*
	* @param request the request instance to test for gzip encoding acceptance
	* @return <code>true</code> if the {@link HttpServletRequest} accepts Gzip
	* encoding
	*/
	public static boolean acceptsGzipEncoding(HttpServletRequest request) {
	assert (request != null);

	String acceptEncoding = request.getHeader(ACCEPT_ENCODING);
	if (null == acceptEncoding) {
	return false;
	}

	return (acceptEncoding.indexOf(CONTENT_ENCODING_GZIP) != -1);
	}

	/**
	* Returns <code>true</code> if the response content's estimated UTF-8 byte
	* length exceeds 256 bytes.
	*
	* @param content the contents of the response
	* @return <code>true</code> if the response content's estimated UTF-8 byte
	* length exceeds 256 bytes
	*/
	public static boolean exceedsUncompressedContentLengthLimit(String content) {
	return (content.length() * 2) > UNCOMPRESSED_BYTE_SIZE_LIMIT;
	}

	/**
	* Returns true if the {@link java.lang.reflect.Method Method} definition on
	* the service is specified to throw the exception contained in the
	* InvocationTargetException or false otherwise. NOTE we do not check that the
	* type is serializable here. We assume that it must be otherwise the
	* application would never have been allowed to run.
	*
	* @param serviceIntfMethod the method from the RPC request
	* @param cause the exception that the method threw
	* @return true if the exception's type is in the method's signature
	*/
	public static boolean isExpectedException(Method serviceIntfMethod,
	Throwable cause) {
	assert (serviceIntfMethod != null);
	assert (cause != null);

	Class<?>[] exceptionsThrown = serviceIntfMethod.getExceptionTypes();
	if (exceptionsThrown.length <= 0) {
	// The method is not specified to throw any exceptions
	//
	return false;
	}

	Class<? extends Throwable> causeType = cause.getClass();

	for (Class<?> exceptionThrown : exceptionsThrown) {
	assert (exceptionThrown != null);

	if (exceptionThrown.isAssignableFrom(causeType)) {
	return true;
	}
	}

	return false;
	}

	/**
	* Returns the content of an {@link HttpServletRequest} by decoding it using
	* <code>expectedCharSet</code>, or <code>UTF-8</code> if
	* <code>expectedCharSet</code> is <code>null</null>.
	*
	* @param request the servlet request whose content we want to read
	* @param expectedContentType the expected content (i.e. 'type/subtype' only)
	* in the Content-Type request header, or <code>null</code> if no
	* validation is to be performed, and you are willing to allow for
	* some types of cross type security attacks
	* @param expectedCharSet the expected request charset, or <code>null</code>
	* if no charset validation is to be performed and <code>UTF-8</code>
	* should be assumed
	* @return the content of an {@link HttpServletRequest} by decoding it using
	* <code>expectedCharSet</code>, or <code>UTF-8</code> if
	* <code>expectedCharSet</code> is <code>null</null>
	* @throws IOException if the request's input stream cannot be accessed, read
	* from or closed
	* @throws ServletException if the request's content type does not
	* equal the supplied <code>expectedContentType</code> or
	* <code>expectedCharSet</code>
	*/
	public static String readContent(HttpServletRequest request,
	String expectedContentType, String expectedCharSet)
	throws IOException, ServletException {
	if (expectedContentType != null) {
	checkContentTypeIgnoreCase(request, expectedContentType);
	}
	if (expectedCharSet != null) {
	checkCharacterEncodingIgnoreCase(request, expectedCharSet);
	}

	/*
	* Need to support 'Transfer-Encoding: chunked', so do not rely on
	* presence of a 'Content-Length' request header.
	*/
	InputStream in = request.getInputStream();
	byte[] buffer = new byte[BUFFER_SIZE];
	ByteArrayOutputStream out = new ByteArrayOutputStream(BUFFER_SIZE);
	try {
	while (true) {
	int byteCount = in.read(buffer);
	if (byteCount == -1) {
	break;
	}
	out.write(buffer, 0, byteCount);
	}
	String contentCharSet = expectedCharSet != null
	? expectedCharSet : CHARSET_UTF8;
	return out.toString(contentCharSet);
	} finally {
	if (in != null) {
	in.close();
	}
	}
	}

	/**
	* Returns the content of an {@link HttpServletRequest}, after verifying a
	* <code>gwt/x-gwt-rpc; charset=utf-8</code> content type.
	*
	* @param request the servlet request whose content we want to read
	* @return the content of an {@link HttpServletRequest} by decoding it using
	* <code>UTF-8</code>
	* @throws IOException if the request's input stream cannot be accessed, read
	* from or closed
	* @throws ServletException if the request's content type is not
	* <code>gwt/x-gwt-rpc; charset=utf-8</code>, ignoring case
	*/
	public static String readContentAsGwtRpc(HttpServletRequest request)
	throws IOException, ServletException {
	return readContent(request, GWT_RPC_CONTENT_TYPE, CHARSET_UTF8);
	}

	/**
	* Returns the content of an {@link HttpServletRequest} by decoding it using
	* the UTF-8 charset.
	*
	* @param request the servlet request whose content we want to read
	* @return the content of an {@link HttpServletRequest} by decoding it using
	* the UTF-8 charset
	* @throws IOException if the requests input stream cannot be accessed, read
	* from or closed
	* @throws ServletException if the content length of the request is not
	* specified of if the request's content type is not
	* 'text/x-gwt-rpc' and 'charset=utf-8'
	* @deprecated Use {@link readContent} instead.
	*/
	@Deprecated
	public static String readContentAsUtf8(HttpServletRequest request)
	throws IOException, ServletException {
	return readContent(request, null, null);
	}

	/**
	* Returns the content of an {@link HttpServletRequest} by decoding it using
	* the UTF-8 charset.
	*
	* @param request the servlet request whose content we want to read
	* @param checkHeaders Specify 'true' to check the Content-Type header to see
	* that it matches the expected value 'text/x-gwt-rpc' and the
	* content encoding is UTF-8. Disabling this check may allow some
	* types of cross type security attacks.
	* @return the content of an {@link HttpServletRequest} by decoding it using
	* the UTF-8 charset
	* @throws IOException if the requests input stream cannot be accessed, read
	* from or closed
	* @throws ServletException if the content length of the request is not
	* specified of if the request's content type is not
	* 'text/x-gwt-rpc' and 'charset=utf-8'
	* @deprecated Use {@link readContent} instead.
	*/
	@Deprecated
	public static String readContentAsUtf8(HttpServletRequest request,
	boolean checkHeaders) throws IOException, ServletException {
	return readContent(request, GWT_RPC_CONTENT_TYPE, CHARSET_UTF8);
	}

	/**
	* Sets the correct header to indicate that a response is gzipped.
	*/
	public static void setGzipEncodingHeader(HttpServletResponse response) {
	response.setHeader(CONTENT_ENCODING, CONTENT_ENCODING_GZIP);
	}

	/**
	* Returns <code>true</code> if the request accepts gzip encoding and the the
	* response content's estimated UTF-8 byte length exceeds 256 bytes.
	*
	* @param request the request associated with the response content
	* @param responseContent a string that will be
	* @return <code>true</code> if the request accepts gzip encoding and the the
	* response content's estimated UTF-8 byte length exceeds 256 bytes
	*/
	public static boolean shouldGzipResponseContent(HttpServletRequest request,
	String responseContent) {
	return acceptsGzipEncoding(request)
	&& exceedsUncompressedContentLengthLimit(responseContent);
	}

	/**
	* Write the response content into the {@link HttpServletResponse}. If
	* <code>gzipResponse</code> is <code>true</code>, the response content will
	* be gzipped prior to being written into the response.
	*
	* @param servletContext servlet context for this response
	* @param response response instance
	* @param responseContent a string containing the response content
	* @param gzipResponse if <code>true</code> the response content will be gzip
	* encoded before being written into the response
	* @throws IOException if reading, writing, or closing the response's output
	* stream fails
	*/
	public static void writeResponse(ServletContext servletContext,
	HttpServletResponse response, String responseContent, boolean gzipResponse)
	throws IOException {

	byte[] responseBytes = responseContent.getBytes(CHARSET_UTF8);
	if (gzipResponse) {
	// Compress the reply and adjust headers.
	//
	ByteArrayOutputStream output = null;
	GZIPOutputStream gzipOutputStream = null;
	Throwable caught = null;
	try {
	output = new ByteArrayOutputStream(responseBytes.length);
	gzipOutputStream = new GZIPOutputStream(output);
	gzipOutputStream.write(responseBytes);
	gzipOutputStream.finish();
	gzipOutputStream.flush();
	setGzipEncodingHeader(response);
	responseBytes = output.toByteArray();
	} catch (IOException e) {
	caught = e;
	} finally {
	if (null != gzipOutputStream) {
	gzipOutputStream.close();
	}
	if (null != output) {
	output.close();
	}
	}

	if (caught != null) {
	servletContext.log("Unable to compress response", caught);
	response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
	return;
	}
	}

	// Send the reply.
	//
	response.setContentLength(responseBytes.length);
	response.setContentType(CONTENT_TYPE_APPLICATION_JSON_UTF8);
	response.setStatus(HttpServletResponse.SC_OK);
	response.setHeader(CONTENT_DISPOSITION, ATTACHMENT);
	response.getOutputStream().write(responseBytes);
	}

	/**
	* Called when the servlet itself has a problem, rather than the invoked
	* third-party method. It writes a simple 500 message back to the client.
	*
	* @param servletContext
	* @param response
	* @param failure
	*/
	public static void writeResponseForUnexpectedFailure(
	ServletContext servletContext, HttpServletResponse response,
	Throwable failure) {
	servletContext.log("Exception while dispatching incoming RPC call", failure);

	// Send GENERIC_FAILURE_MSG with 500 status.
	//
	try {
	response.setContentType("text/plain");
	response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
	try {
	response.getOutputStream().write(GENERIC_FAILURE_MSG.getBytes("UTF-8"));
	} catch (IllegalStateException e) {
	// Handle the (unexpected) case where getWriter() was previously used
	response.getWriter().write(GENERIC_FAILURE_MSG);
	}
	} catch (IOException ex) {
	servletContext.log(
	"respondWithUnexpectedFailure failed while sending the previous failure to the client",
	ex);
	}
	}

	/**
	* Performs validation of the character encoding, ignoring case.
	*
	* @param request the incoming request
	* @param expectedCharSet the expected charset of the request
	* @throws ServletException if requests encoding is not <code>null</code> and
	* does not equal, ignoring case, <code>expectedCharSet</code>
	*/
	private static void checkCharacterEncodingIgnoreCase(
	HttpServletRequest request, String expectedCharSet)
	throws ServletException {
	boolean encodingOkay = false;
	String characterEncoding = request.getCharacterEncoding();
	if (characterEncoding != null) {
	/*
	* TODO: It would seem that we should be able to use equalsIgnoreCase here
	* instead of indexOf. Need to be sure that servlet engines return a
	* properly parsed character encoding string if we decide to make this
	* change.
	*/
	if (characterEncoding.toLowerCase().indexOf(expectedCharSet.toLowerCase())
	!= -1) {
	encodingOkay = true;
	}
	}

	if (!encodingOkay) {
	throw new ServletException("Character Encoding is '"
	+ (characterEncoding == null ? "(null)" : characterEncoding)
	+ "'. Expected '" + expectedCharSet + "'");
	}
	}

	/**
	* Performs Content-Type validation of the incoming request, ignoring case
	* and any <code>charset</code> parameter.
	*
	* @see #checkCharacterEncodingIgnoreCase(HttpServletRequest, String)
	* @param request the incoming request
	* @param expectedContentType the expected Content-Type for the incoming
	* request
	* @throws ServletException if the request's content type is not
	* <code>null</code> and does not, ignoring case, equal
	* <code>expectedContentType</code>,
	*/
	private static void checkContentTypeIgnoreCase(
	HttpServletRequest request, String expectedContentType)
	throws ServletException {
	String contentType = request.getContentType();
	boolean contentTypeIsOkay = false;

	if (contentType != null) {
	contentType = contentType.toLowerCase();
	/*
	* NOTE:We use startsWith because some servlet engines, i.e. Tomcat, do
	* not remove the charset component but others do.
	*/
	if (contentType.startsWith(expectedContentType.toLowerCase())) {
	contentTypeIsOkay = true;
	}
	}

	if (!contentTypeIsOkay) {
	throw new ServletException("Content-Type was '"
	+ (contentType == null ? "(null)" : contentType) + "'. Expected '"
	+ expectedContentType + "'.");
	}
	}

	private RPCServletUtils() {
	// Not instantiable
	}
	}