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From Michael Greco <mike.james.gr...@gmail.com>
Subject Re: Rewriting entire request /body in Servlet Filter not working as expected
Date Mon, 05 Oct 2015 13:37:27 GMT
On Mon, Oct 5, 2015 at 3:30 AM, Mark Thomas <markt@apache.org> wrote:

> On 04/10/2015 19:03, Michael Greco wrote:
> > First time post here.
> >
> > Using :
> > Tomcat 8.0.26
> > JDK1.8.0 update 51
> > Apache MyFaces 2.2.8.
> > Maven build of webapp war file
> > Chrome  45.0.2454.101 m 64 bit
> > Windows 7 64 bit
> >
> > Trying to rewrite the entire request body in a filter using a http
> request
> > wrapper.  Not entirely sure if this is the right approach or even
> possible
> > but researching similar examples it seems this approach should work.
> > Created a simple test case with a one page test app, expecting the
> > index.xhtml page's text value of  "Welcome" to be replaced with the text
> > "NEW TEXT HERE" found in the filter code, but I only get "Welcome" back
> > when the page is rendered in the browser.
> >
> > Below is what I have in the index page, the filter and the web.xml and
> the
> > pom.xml.  The reason I can see is that the getInputStream() or
> getReader()
> > calls are never called by the FacesServlet in the extended
> > HttpServletRequestWrapper.  I did override the getParameter function to
> put
> > some simple debug output in there to ensure the wrapped request was
> > actually used, so I know it's definitely getting into this class but not
> > calling the methods that would return it the new body content.
> >
> > I even tried to re-read the entire request in the getParametersMap() from
> > examples I found on the web, but this didn't seen to do the job either.
> It
> > seems that the request body is somehow cached somewhere / somehow and not
> > changable?
> >
> > Thanks in advance for any insight on this.
>
> First of all welcome files should be exactly that. Files. They should
> not include paths. There is no guarantee that 'faces/index.html' is
> going to work as you think it will and some containers may reject the
> configuration as invalid. That Tomcat lets you get away with this is
> fortunate and - now that I know about it - likely to change in future
> releases.
>
> You seem to be confusing reading the static resource from the file
> system and reading the request body. The request body is the data sent
> by the client with the HTTP request. The static resource (index.xhtml)
> is read from the file system.
>
> I assume that FacesServlet has its own static resource handling and that
> a request for /faces/index.xhtml is expected to return the content
> listed for index.html below.
>
> The FacesServlet will open an input stream but not to the request body.
> It will open one for the static resource on the file system. It will
> then copy those bytes to the response output stream. At no point will it
> attempt to read the request body (unless it is a POST request with
> parameters).
>
> If you want to modify the response body then you need to wrap the
> response and provide Writer and OutputStream implementations that make
> the modifications you require. The simplest way is to buffer the entire
> response body and then edit it but that can get expensive in terms of
> memory. It will be more efficient to use fixed buffer but then more
> complex to ensure your desired edits take place.
>
> Mark
>
> >
> > index page code (index.xhtml) :
> >
> ---------------------------------------------------------------------------------
> > <!DOCTYPE html>
> > <html lang="en"
> >   xmlns="http://www.w3.org/1999/xhtml"
> >   xmlns:jsf="http://xmlns.jcp.org/jsf"
> >   xmlns:h="http://xmlns.jcp.org/jsf/html">
> > <head jsf:id="head">
> > <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
> > <title>Test Webapp</title>
> > </head>
> > <body jsf:id="body">
> >     <div><h1>Welcome</h1></div>
> > </body>
> > </html>
> >
> > Filter code :
> >
> --------------------------------------------------------------------------
> > package com.testwebapp.reqrewrite.filter;
> >
> > import java.io.BufferedReader;
> > import java.io.ByteArrayInputStream;
> > import java.io.IOException;
> > import java.io.InputStreamReader;
> >
> > import javax.servlet.Filter;
> > import javax.servlet.FilterChain;
> > import javax.servlet.FilterConfig;
> > import javax.servlet.ReadListener;
> > import javax.servlet.ServletException;
> > import javax.servlet.ServletInputStream;
> > import javax.servlet.ServletRequest;
> > import javax.servlet.ServletResponse;
> > import javax.servlet.http.HttpServletRequest;
> > import javax.servlet.http.HttpServletRequestWrapper;
> >
> > public class RewriteBodyTestFilter implements Filter {
> >
> > public void init(FilterConfig filterConfig) throws ServletException {
> > return;
> > }
> >
> > public void doFilter(ServletRequest request, ServletResponse response,
> > FilterChain chain)
> > throws IOException, ServletException {
> > String newReqBody = new String("<div><h1>NEW TEXT HERE</h1></div>");
> > HttpServletRequest req = (HttpServletRequest)request;
> > RewriteBodyRequestWrapper rewriteBodyRequestWrapper = new
> > RewriteBodyRequestWrapper(req, newReqBody);
> > chain.doFilter(rewriteBodyRequestWrapper, response);
> > }
> >
> > public void destroy() {
> > return;
> > }
> > class RewriteBodyRequestWrapper extends HttpServletRequestWrapper {
> >
> > private byte[] buffer;
> >
> > public RewriteBodyRequestWrapper(HttpServletRequest req, String reqBody)
> > throws IOException {
> > super(req);
> > System.out.println("entering RewriteBodyRequestWrapper() constructor");
> > this.buffer = reqBody.getBytes();
> > }
> >
> > @Override
> > public ServletInputStream getInputStream() {
> > System.out.println("entering
> RewriteBodyRequestWrapper().getInputStream()");
> > try {
> > ByteArrayInputStream bais = new ByteArrayInputStream(buffer);
> > BufferedServletInputStream bsis = new BufferedServletInputStream(bais);
> > return bsis;
> > } catch (Exception ex) {
> > ex.printStackTrace();
> > throw new RuntimeException(ex);
> > }
> > }
> >
> > @Override
> > public BufferedReader getReader() {
> > System.out.println("entering RewriteBodyRequestWrapper().getReader()");
> > InputStreamReader isr = new InputStreamReader(getInputStream());
> > return new BufferedReader(isr);
> > }
> >
> > }
> > class BufferedServletInputStream extends ServletInputStream  {
> >
> > ByteArrayInputStream bais;
> >
> > public BufferedServletInputStream(ByteArrayInputStream bais) {
> > this.bais = bais;
> > }
> >
> > @Override
> > public int available() {
> > return bais.available();
> > }
> >
> > @Override
> > public boolean isFinished() {
> > return bais.available() == 0;
> > }
> >
> > @Override
> > public boolean isReady() {
> > return true;
> > }
> >
> > @Override
> > public void setReadListener(ReadListener readListener) {
> > return;
> > }
> >
> > @Override
> > public int read() {
> > return bais.read();
> > }
> >
> > @Override
> > public int read(byte[] buf) {
> > return this.read(buf, 0, buf.length);
> > }
> >
> > @Override
> > public int read(byte[] buf, int off, int len) {
> > return bais.read(buf, off, len);
> > }
> >
> > }
> > }
> >
> > web.xml code:
> >
> --------------------------------------------------------------------------------------------------
> > <?xml version="1.0" encoding="ISO-8859-1"?>
> > <web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="
> > http://www.w3.org/2001/XMLSchema-instance"
> > xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
> > http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
> > metadata-complete="true" version="3.0">
> >
> > <display-name>Test Webapp Req Rewrite</display-name>
> >
> > <!-- Change to "Production" when you are ready to deploy -->
> > <context-param>
> > <param-name>javax.faces.PROJECT_STAGE</param-name>
> > <param-value>Development</param-value>
> > </context-param>
> >
> > <!-- JSF mapping -->
> > <servlet>
> > <servlet-name>FacesServlet</servlet-name>
> > <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
> > <load-on-startup>1</load-on-startup>
> > </servlet>
> >
> > <!-- Map these files with JSF -->
> > <servlet-mapping>
> > <servlet-name>FacesServlet</servlet-name>
> > <url-pattern>/faces/*</url-pattern>
> > </servlet-mapping>
> >
> > <!-- Session timeout -->
> > <session-config>
> > <session-timeout>30</session-timeout>
> > </session-config>
> >
> > <!-- Welcome page -->
> > <welcome-file-list>
> > <welcome-file>faces/index.xhtml</welcome-file>
> > </welcome-file-list>
> >
> > <!-- Filters -->
> > <filter>
> > <filter-name>RewriteBodyTestFilter</filter-name>
> > <filter-class>com.testwebapp.reqrewrite.filter.RewriteBodyTestFilter
> > </filter-class>
> > </filter>
> >
> > <!-- Filter mappings / chain ordering -->
> > <filter-mapping>
> > <filter-name>RewriteBodyTestFilter</filter-name>
> > <servlet-name>FacesServlet</servlet-name>
> > <dispatcher>REQUEST</dispatcher>
> > <dispatcher>FORWARD</dispatcher>
> > </filter-mapping>
> >
> > </web-app>
> >
> > pom.xml :
> >
> -------------------------------------------------------------------------------------
> > <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="
> > http://www.w3.org/2001/XMLSchema-instance"
> >   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
> > http://maven.apache.org/maven-v4_0_0.xsd">
> >   <modelVersion>4.0.0</modelVersion>
> >   <groupId>com.testwebapp.reqrewrite</groupId>
> >   <artifactId>reqrewrite</artifactId>
> >   <packaging>war</packaging>
> >   <version>1.0-SNAPSHOT</version>
> >   <name>reqrewrite Maven Webapp</name>
> >   <url>http://maven.apache.org</url>
> > <dependencies>
> > <dependency>
> > <groupId>javax.servlet</groupId>
> > <artifactId>javax.servlet-api</artifactId>
> > <version>3.1.0</version>
> > <scope>provided</scope>
> > </dependency>
> > <dependency>
> > <groupId>org.apache.myfaces.core</groupId>
> > <artifactId>myfaces-api</artifactId>
> > <version>2.2.8</version>
> > </dependency>
> > <dependency>
> > <groupId>org.apache.myfaces.core</groupId>
> > <artifactId>myfaces-impl</artifactId>
> > <version>2.2.8</version>
> > </dependency>
> > </dependencies>
> >   <build>
> >     <finalName>reqrewrite</finalName>
> >   </build>
> > </project>
> >
>
>
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>
Chris, Mark,

Thanks for your time and responses.  I'll try to respond to both of your
comments with this single bottom post.

I created this one page webapp to simply test the ability to modify the
request object's content.  In this example I only have one page and wanted
it to go through the FacesServlet therefore "faking" its url pattern in the
web.xml's welcome file element triggers the FacesServlet execution path and
therefore my filter as well.  Maybe I should have created a more "static"
index.html page and then placed a meta refresh tag in the page to redirect
to a separate faces/index.xhtml page instead but this is just an experiment
with trying to modify or change with the request content.

One of the use cases described in the Java EE 6 documentation is to do just
that (modify the request data), so I was hoping I could but it doesn't seem
to be possible in this particular chain setup.  (See
http://docs.oracle.com/javaee/6/tutorial/doc/bnagb.html in case I'm
confused).  I think this referenced tutorial translates to modifying just
the request headers, attributes and parameters only if you don't have
control over what the Servlet is going to do with the inputStream after
your filter(s) executes.  So in this simplified test webapp the request
inputStream definitely contains the index.xhtml content when i'm in my
filter, a simple request wrapper to buffer and display it shows this (I
tried that already), so there's no doubt in my mind it's coming in and
available to at least read in the filter via the stream.  I could probably
just as well have used my own Servlet in this example (I can try this and
post it) but if I'm in complete control at the Servlet level I could just
pull in the content there and rewrite the response as Mark mentioned.
Unfortunately beyond this simple test case I would be using JSF so I wanted
to be sure I can change the content in components I can control (the
filter, not the Servlet).

Outside this test case, the "real" use case/experiment was where I was
trying to weave together several technologies (without using Spring) in
this order via the web.xml filter chain:

URLRewriteFilter (http://tuckey.org/urlrewrite/) ==> Custom Thymeleaf
Filter (http://www.thymeleaf.org/) ==> JSF Servlet (MyFaces or any other
implementation, didn't matter).

So the URLRewriteFilter would forward a page request outside the WEB-INF
folder inward to a page within WEB-INF.  Then the Thymeleaf Filter would
read the request inputStream through it's templating engine and produce the
appropriate HTML5 page without the Thymeleaf tags (at this point the bigger
test case was working) and then finally the FacesServlet would process the
remaining jsf: tags before returning the response (failed here too, the
response was basically the original request input).  So unfortunately I ran
into this same issue, where the FacesServlet does take in my wrapped
request object but since the request inputStream is either not executed by
the FacesServlet logic and it simply goes the filesystem to get the input
stream as Mark mentioned... or... there is an "indirect" call to the
wrapper superclass' getInputStream or getReader through for example
getParameterMap() on the superclass in which case my custom wrapper
subclass overrides to getInputStream() or getReader() never have a chance
to execute.

Thanks for the "input stream" everyone, but it appears this test case is a
fail for me.  But I did learn a lot so definitely not all bad.  Again,
thanks for your time and I hope to try to post more stuff here.  Great
resources!

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