Problem with GWT behind a reverse proxy - either nginx or apache

Question

I'm having this problem with GWT when it's behind a reverse proxy. The backend app is deployed within a context - let's call it /context.

The GWT app works fine when I hit it directly:

http://host:8080/context/

I can configure a reverse proxy in front it it. Here's my nginx example:

upstream backend {
    server 127.0.0.1:8080;
}

...

location / {
   proxy_pass        http://backend/context/;
}

But, when I run through the reverse proxy, GWT gets confused, saying:

2009-10-04 14:05:41.140:/:WARN:  Login: ERROR: The serialization policy file '/C7F5ECA5E3C10B453290DE47D3BE0F0E.gwt.rpc' was not found; did you forget to include it in this deployment?
2009-10-04 14:05:41.140:/:WARN:  Login: WARNING: Failed to get the SerializationPolicy 'C7F5ECA5E3C10B453290DE47D3BE0F0E' for module 'https://hostname:444/'; a legacy, 1.3.3 compatible, serialization policy will be used.  You may experience SerializationExceptions as a result.
2009-10-04 14:05:41.292:/:WARN:  StoryService: ERROR: The serialization policy file '/0445C2D48AEF2FB8CB70C4D4A7849D88.gwt.rpc' was not found; did you forget to include it in this deployment?
2009-10-04 14:05:41.292:/:WARN:  StoryService: WARNING: Failed to get the SerializationPolicy '0445C2D48AEF2FB8CB70C4D4A7849D88' for module 'https://hostname:444/'; a legacy, 1.3.3 compatible, serialization policy will be used.  You may experience SerializationExceptions as a result.

In other words, GWT isn't getting the word that it needs to prepend /context/ hen look for C7F5ECA5E3C10B453290DE47D3BE0F0E.gwt.rpc, but only when the request comes throught proxy. A workaround is to add the context to the url for the web site:

location /context/ {
    proxy_pass        http://backend/context/;
}

but that means the context is now part of the url that the user sees, and that's ugly.

Anybody know how to make GWT happy in this case?

Software versions:
GWT - 1.7.0 (same problem with 1.7.1)
Jetty - 6.1.21 (but the same problem existed under tomcat)
nginx - 0.7.62 (same problem under apache 2.x)

I've looked at the traffic between the proxy and the backend using DonsProxy, but there's nothing noteworthy there.

Answer 1

I have the same problem, and I opened a bug report:

http://code.google.com/p/google-web-toolkit/issues/detail?id=4817

The problem is that it was marked "As Design", so I don't think it will be fixed.

I found this solution for me. I extended the class RemoteServiceServlet and I forced GWT to load serialization policy file starting from ContextName instead of URL. Then I extended my service my class instead of RemoteServiceServlet class. In this way the application will be unlinked from the url from where it will be called.

Here there is my custom class:

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.text.ParseException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;

import com.google.gwt.user.server.rpc.RemoteServiceServlet;
import com.google.gwt.user.server.rpc.SerializationPolicy;
import com.google.gwt.user.server.rpc.SerializationPolicyLoader;

public class MyRemoteServiceServlet extends RemoteServiceServlet
{
    @Override
    protected SerializationPolicy doGetSerializationPolicy(HttpServletRequest request, String moduleBaseURL, String strongName)
    {
        return MyRemoteServiceServlet.loadSerializationPolicy(this, request, moduleBaseURL, strongName);
    }


    /**
      * Used by HybridServiceServlet.
      */
      static SerializationPolicy loadSerializationPolicy(HttpServlet servlet,
      HttpServletRequest request, String moduleBaseURL, String strongName) {
    // The serialization policy path depends only by contraxt path
    String contextPath = request.getContextPath();

    SerializationPolicy serializationPolicy = null;


    String contextRelativePath = contextPath + "/";



      String serializationPolicyFilePath = SerializationPolicyLoader.getSerializationPolicyFileName(contextRelativePath
          + strongName);

      // Open the RPC resource file and read its contents.
      InputStream is = servlet.getServletContext().getResourceAsStream(
          serializationPolicyFilePath);
      try {
        if (is != null) {
          try {
        serializationPolicy = SerializationPolicyLoader.loadFromStream(is,
            null);
          } catch (ParseException e) {
        servlet.log("ERROR: Failed to parse the policy file '"
            + serializationPolicyFilePath + "'", e);
          } catch (IOException e) {
        servlet.log("ERROR: Could not read the policy file '"
            + serializationPolicyFilePath + "'", e);
          }
        } else {
          String message = "ERROR: The serialization policy file '"
          + serializationPolicyFilePath
          + "' was not found; did you forget to include it in this deployment?";
          servlet.log(message);
        }
      } finally {
        if (is != null) {
          try {
        is.close();
          } catch (IOException e) {
        // Ignore this error
          }
        }
      }

    return serializationPolicy;
      }
}