Directory-ish and file-ish URLs

A quick note on using partial URLs in my hypothetical JSON-based API.

In my sketch of a RESTful API for St Ouses, I used a lot of relative URLs ending with slashes. This is the style preferred when there is a database-driven web server generating the content. When using static files it is more convenient to use URLs ending with something.json

Here is an example of a Cat entity using ‘file-ish’ URLs:

    "href": "doomshadow.json",
    "aloofness": 72,
    "kits": {
        "href": "doomshadow-kits.json"
        "items": [
            {"href": "../kits/boppinjay.json", name": "Boppinjay"},
            {"href": "../kits/quinto.json", name": "Quinto"},
        "more": {
            "href": "doomshadow-kits-page2.json"

If the URL this was retrieved from was file://path/to/cats/doomshadow.json, then the URL of the collection is file://path/to/cats/doomshadow-kits.json. This comes from stripping off everything after the last slash in the original URL and substituting doomshadow-kits.json.

Similarly, the URL of Boppinjay is file://path/to/kits/boppinjay.json: after stripping off doomshadow-kits.json from the collection URL, the .. means we drop cats, and then we add kits/boppinjay.json.

One thing that causes occasional confusion is that the rules for resolving URLs are similar but not identical to those for resolving relative file names. When resolving a URLs, the client does not know whether cats is a file or a directory; creating the absolute URL is entirely a string-manipulation process. This makes it important to not forget to end URLs with a slash if they are intended to be ‘directory-ish’.

One reason for including a self-link in all entities (e.g., the href attribute on the outermost object in the example) is to make resolution of interior URLs less ambiguous. We had trouble with a REST server that had its own ideas about which resources should have slashes at the end of their URLs and as a convenience to sloppy clients would redirect from to if it thought the resource bar was file-ish rather than directory-ish. When interpreting a relative URL baz/quux/ found in the entity it returns, should the client start with the redirected-to URL (resulting in because bar gets stripped)? Or use the URL it originally requested, resulting in ? Including the canonical URL in the entity is intended to insulate us from this confusion.