[TYPO3-50-general] How can I manipulate Arguments before they are passed to an actionMethod

[Christoph Blömer]

Hi all,
maybe someone can help me out with this.

I have a URL /webdav/folder1/subfolder2/
Routing defines: /webdav/{path}
My argument path would then be: folder1/folder2/

Some revisions ago I could register a newArgument in the 
initializeArguments() metod.
And read the value with $this->arguments['path']->getValue() in the 
initializeAction() method.
Als also tried to register it in the initializeAction but the value is 
empty.

This does not work anymore.

I figured out that I get the path in an actionMethod. For example: 
getAction($path)
Sometimes my $path is send UTF-8 and urlencoded so I need to decode the 
value. And I would like to do this before it is passed to the ActionMethod.

How and where can I do this?

Furthermore, where can I register additionalArguments which should be 
passed to an actionMethod().
For example a header value like "Destination: /myurl/"

Thanks
Christoph