Encoded forward slashes in URL cause wrong links

For example when calling this URL: http://localhost:8080/things/%2Fsome%2Fthing, then this is produced in the controller method:

@RequestMapping(value = "/{id}", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public ResponseEntity<ThingResource> get(@PathVariable("id") String id) {
    Link link = linkTo(ThingController.class).slash(id).withSelfRel();
    System.out.println(link.getHref());
    //...
}

It prints http://localhost:8080/things/some/thing/things/some/thing where it should produce http://localhost:8080/things/%2Fsome%2Fthing.

There are two problems:

1. It takes the decoded path-variable as the base-path of the request mapping. This only happens when there is a leading %2F. If the leading character is another one the mapping works
2. It appends the id unencoded where it should be encoded (I guess)

I'm well aware that slashes in path variables are problematic, but they do work in Spring MVC now, see https://jira.spring.io/browse/SPR-7919 & https://jira.spring.io/browse/SPR-11101

The problem could be in ServletUriComponentsBuilder.fromServletMapping(HttpServletRequest) where a UrlPathHelper is instantiated which defaults to urlDecode = true. The fix for having encoded slashes in Spring MVC is to set urlDecode = false, I guess that's related. Maybe that could be made configurable?

Start with ServletUriComponentsBuilder.fromServletMapping(HttpServletRequest) and the UrlPathHelper configuration mentioned in the report. Reproduce the encoded-slash request and trace how the decoded path variable becomes the mapping base and how the id is appended. Done means linkTo(...).slash(id) preserves the leading %2F and produces the expected URL without duplicated path segments.