htmx:redirect:/path and new HtmxDirectView("/path") have different behaviour regarding RedirectAttributes

[wimdeblauwe]

I am writing a blog post on redirect attributes and I was testing this with the new 3.6.0 release. What I have discovered is that there is a difference when using htmx:redirect:/path versus new HtmxDirectView("/path"). The flash attributes are not present after the redirect in the first case, but they do work fine when using new HtmxDirectView("/path").

[wimdeblauwe]

I tried to investigate how to fix it, but I don't quite understand the code at HtmxResponseHandlerMethodArgumentResolver. Should supportsParameter also check for String.class? But what should happen inside resolveArgument when it is a String?

[xhaggi]

There should be, or rather, there is no difference between string-based and view-based redirects. BTW the HtmxResponseHandlerMethodArgumentResolver is not involved in view resolution such as HtmxRedirectView. Instead, this is done by Spring's view resolver implementation, since HtmxRedirectView is a subclass of RedirectView. So we don't do anything special to get it to work. The only difference between the two is that HtmxRedirectView is created by HtmxViewResolver when you use string-based redirection.

To be really sure, I have created two new tests for this in #145.

[xhaggi]

Mhhh you're right @wimdeblauwe. The tests in #145 fail. Didn't check the result before I added my comment 😄 Let me check what's going on here.

[xhaggi]

Bad news. It won't work for string-based redirects because we need to set mavContainer.setRedirectModelScenario(true) on the ModelAndViewContainer, but in this case we do not have access to it, nor we are able to override anything. If a string-based return value is used, Spring's ViewNameMethodReturnValueHandler kicks in before any custom HandlerMethodReturnValueHandler is called, and you cannot change this order or override anything to change it (see RequestMappingHandlerAdapter.java#L770

Of course, this is anything but nice. So what should we do? Point this out in the README or remove support for string-based redirects.

[xhaggi]

Another option would be to change the prefix from htmx:redirect:/path and htmx:location:/path to redirect:htmx:/path, redirect:htmx:location:/path. I have closed #145 in favor of #146, which fixes the problem.

[wimdeblauwe]

Thanks for investigating this. Changing the prefix seems the best option. I tried it in my example with the changes you did in the PR and it works fine. I'll do a 3.6.1 release with the fix.