"Let pointer be a pointer to first code point in..."

[mfalken]

https://url.spec.whatwg.org/commit-snapshots/5fc4c4c17f3077beda5e3647df73f4b1b0ba7084/#url-parsing

Let pointer be a pointer to first code point in input.

What happens if input is the empty string? See some confusion in whatwg/fetch#669

[TimothyGu]

See https://url.spec.whatwg.org/commit-snapshots/5fc4c4c17f3077beda5e3647df73f4b1b0ba7084/#eof-code-point, and also #308.

[mfalken]

Thanks but I'm still not sure what the spec is saying. Let's run the basic URL parser where input="" and base="https://www.example.com". Here's my reading:

After step 1, url is a new URL.

After step 10. "Let pointer be a pointer to first code point in input.", pointer points to EOF.

In step 11. we enter the state machine at "scheme start state". c is undefined, so we set state to "no scheme state" and decrease pointer by one. Now the state machine step is over, so increase pointer by one and continue. pointer is again pointing to EOF, so the state machine is done. So we return url, which is a new URL.

Is that correct as-written, and as-intended?

[annevk]

No, that seems like a bug. 😟

This should basically return the base URL except for the fragment.

[GPHemsley]

I was never satisfied with the resolution to #343, as I didn't think it implemented what I wrote in #308, which is what I used in my Perl implementation.

I haven't taken the time to confirm whether this issue revolves around those differences, but I figured I'd bring it up again for the sake of discussion.

[rmisev]

Step 11 in specification:

11. Keep running the following state machine by switching on state. (1) If after a run pointer points to the EOF code point, go to the next step. (2) Otherwise, increase pointer by one and continue with the state machine.

From @mattto's #373 (comment):

... Now the state machine step is over, (2) so increase pointer by one and continue. (1) pointer is again pointing to EOF, so the state machine is done.

The order of (1) and (2) operations here is different than in the spec, so result is incorrect.

If follow specification, then after (2) operation we enter the "no scheme state":

... set state to relative state and decrease pointer by one.

Then we enter the "relative state", and c is EOF:

Set url’s scheme to base’s scheme, and then, switching on c:

• The EOF code point
  Set url’s username to base’s username, url’s password to base’s password, url’s host to base’s host, url’s port to base’s port, url’s path to a copy of base’s path, and url’s query to base’s query.

Now the pointer isn't decreased, so it points to EOF and the state machine is done after (1) operation. The result is as specified in @annevk's #373 (comment).

[annevk]

Aah right. That always annoyed me about how this state machine is written. If we can rewrite it somehow to be more basic that'd be good.

[stephanebastian]

Step 11 in specification:

1. Keep running the following state machine by switching on state. (1) If after a run pointer points to the EOF code point, go to the next step. (2) Otherwise, increase pointer by one and continue with the state machine.

From @mattto's #373 (comment):

... Now the state machine step is over, (2) so increase pointer by one and continue. (1) pointer is again pointing to EOF, so the state machine is done.

The order of (1) and (2) operations here is different than in the spec, so result is incorrect.

If follow specification, then after (2) operation we enter the "no scheme state":

... set state to relative state and decrease pointer by one.

Then we enter the "relative state", and c is EOF:

Hi all,
Let me give my 2 cents ;)
Based on the current wording of the spec, I don't think that we ever get into the 'relative state', thus I would expect to return a new URL (as initially reported by @mattto )
If we've got an empty input then the state machine runs 'scheme start state'
After that run, and according to the spec, we simply go to step 12

If after a run pointer points to the EOF code point, go to the next step (-> step 12 return url)

To me we are at EOF after the 1st run since there is no stream per say as there is no content. Quick info from the spec

The EOF code point is a conceptual code point that signifies the end of a string or code point stream

So I am puzzled as to how it is possible to enter the "relative state" ?
Could you please shed some light ?
Thanks in advance

[annevk]

I think it is indeed somewhat broken, but if we assume that we start out by pointer pointing at EOF (it's the empty string after all), it is then decreased by 1. Unclear what it now points at, but let's say not EOF so we continue and increase it by 1, at which point it again points to EOF but we're doing another run at least.

But we should rewrite this in terms of Infra, possibly using https://infra.spec.whatwg.org/#collect-a-sequence-of-code-points.