[whatwg/url] Skipping an item while iterating is undefined (Issue #768)

The [URL Standard](https://github.com/whatwg/url/blob/ae3c28b84e3e7122c2807401c26b8a63cb2ab445/url.bs#L398-L436), when parsing percent-encoded bytes while percent-decoding, makes use of an undefined byte sequence method "skip" on L430. It seems to get a variable number of items from an iterator and immediately dispose of them, like in the following Python code:

```py
def skip(iterator: iterator, n: int):
    for i in range(n):
        next(iterator)
```

It would seem that the byte sequence `input` holds a reference to the iterator instance, as implied by the language `Skip the next two bytes in <var>input</var>.`

As the creation of an iterator is currently implicit in the Infra Standard, I believe explicitly defining a generic iterator data structure, implementing the "skip" method for it, and changing all "iterate" and "for each" definitions to use iterators would be the best course of action. If this were to go through, the URL Standard would then have to wait for https://github.com/whatwg/infra/issues/571 to be resolved.

An initial concern with the approach described above is the edge case of handling a skip on an empty iterator: would we throw an exception or have skipping be a no-op?

On the other hand, this one step in the URL Standard is the only place where this method is used; if "skip" were to be left undefined, it would then be on the URL Standard to revise the percent-encoding algorithm.

Copy of https://github.com/whatwg/infra/issues/572

-- 
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/url/issues/768
You are receiving this because you are subscribed to this thread.

Message ID: <whatwg/url/issues/768@github.com>