AwsProxyServletContext Does Not Support Servlet Filter Registration

[blakeney]

Hello,

I am trying to use this library along with Spring Boot to create a REST application that uses javax.servlet.Filter implementations to transform responses. I see that all of the filter-related methods in AwsProxyServletContext are overridden to simply return null or to do nothing (source). This would seem to indicate that Filters are not supported with this container. Is that correct?

I have attempted several methods of registering Filters, which work properly with my local tests, but do not seem to have any effect when running in a live Lambda.

If I cannot use Filter, I will try to use Spring's HandlerInterceptor mechanism instead.

[blakeney]

I did some more investigation and determined with more certainty that indeed, the current implementation does not support Filter registration (or Servlet registration, for that matter). I also determined that HandlerInterceptors will not serve my particular need, so I am just going to work around this in the handleRequest method of my own project for the time being, essentially bypassing Spring for part of my code.

I probably will not have time to patch this library to add Filter support myself any time soon, so unfortunately I can't offer a Pull Request at the moment. I'll leave the ticket open for now in case anyone else is interested in this as a feature, but I'm also okay with it if this is a "Won't Fix." Thanks!

[sapessi]

Correct, at the moment it does not. I'd be interested to take a look at your filter code and see if/how we can add support for it. Anything you can share on GitHub or here?

[AlainJanssens]

Is this also the reason why '@Valid' isn't working?

[sapessi]

I'm no spring expert but doing some research I can see that the @Valid annotation does run as a filter. We are currently designing filters support based on this issue and we'll have something in a branch over the next few weeks.

[AlainJanssens]

Thanks for the answer @sapessi ..

I created a separated issue for this...

[sapessi]

I'll keep that issue open until I can confirm for certain that this is the cause of the issue. If it is, then I'll close the separate issue and group everything in here. Otherwise we'll address it there.

[sapessi]

Hey @blakeney, could you share some sample code on how you initialize (and add) filters in your spring application?

[sapessi]

I've pushed a first version of the filter support to the servlet-improvements branch. This is the commit d7bec0a. You can register filters with the setStartupHandler lambda:

try {
    handler = SpringLambdaContainerHandler.getAwsProxyHandler(EchoSpringAppConfig.class);
    handler.setStartupHandler(c -> {
        FilterRegistration.Dynamic registration = c.addFilter("CustomHeaderFilter", CustomHeaderFilter.class);
        // update the registration to map to a path
        registration.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), true, "/*");
        // servlet name mappings are disabled and will throw an exception
    });
} catch (ContainerInitializationException e) {
    e.printStackTrace();
}

Next I will work on supporting the filter annotations.

[sapessi]

Version 0.4 is out and adds support for servlet filter:

handler.setStartupHandler(c -> {
    FilterRegistration.Dynamic registration = c.addFilter("CustomHeaderFilter", CustomHeaderFilter.class);
    // update the registration to map to a path
    registration.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), true, "/*");
    // servlet name mappings are disabled and will throw an exception
});

Closing this issue.