fix(services/vercel-blob): send the pagination cursor so listing terminates

[PDGGK]

Which issue does this PR close?

None — found while reading the service.

Rationale for this change

VercelBlobLister::next_page stores the cursor the server returns:

ctx.done = !resp.has_more;

if let Some(cursor) = resp.cursor {
    ctx.token = cursor;
}

and nothing ever reads it back — that assignment is the only mention of ctx.token in the crate. VercelBlobCore::list took only a prefix and a limit:

let mut url = format!(
    "https://blob.vercel-storage.com?prefix={}",
    percent_encode_path(prefix)
);

if let Some(limit) = limit {
    url.push_str(&format!("&limit={limit}"))
}

so page two is byte-identical to page one. PageLister::next loops while ctx.done is false:

loop {
    if let Some(entry) = self.ctx.entries.pop_front() { return Ok(Some(entry)); }
    if self.ctx.done { return Ok(None); }
    self.inner.next_page(&mut self.ctx).await?;
}

A truncated listing therefore never advances: the same page is fetched and pushed again for as long as has_more stays true. Operator::list collects into a Vec and grows without bound; lister() streams the same entries forever.

Vercel documents cursor alongside prefix and limit — "A string obtained from a previous list response to be used for reading the next page of results" — and notes the default limit is 1000, so any prefix holding more than that reaches this with the caller setting no options at all.

What changes are included in this PR?

list now takes the cursor and appends it when non-empty, and the URL construction moves into build_list_url so it can be asserted directly. The four internal lookups pass "" — each asks for Some(1) to resolve a single blob's URL and never paginates.

One extra guard in the lister: has_more true with no cursor now ends the listing rather than leaving ctx.done false. That truncates, but the only other option is re-requesting the same page indefinitely. Happy to drop it if you would rather not carry the branch.

Tests

Four unit tests. Removing the cursor from the URL again fails exactly the two that involve one:

	the_first_page_carries_no_cursor	a_later_page_resumes_from_the_cursor	the_cursor_is_percent_encoded	the_root_prefix_is_sent_empty
cursor not sent (current main)	ok	FAILED	FAILED	ok
this PR	ok	ok	ok	ok

The cursor is percent-encoded because it is an opaque server token: an unescaped & or = would silently graft extra parameters onto the query, the same reason prefix is encoded one line above.

cargo test -p opendal-service-vercel-blob --lib → 6 passed. cargo fmt --all -- --check and cargo clippy -p opendal-service-vercel-blob --all-targets both clean.

Are there any user-facing changes?

Yes — a vercel-blob listing that the server truncates now advances through its pages and terminates, instead of re-emitting the first page indefinitely. VercelBlobCore::list gains a cursor parameter, but mod core is private and the crate re-exports only VercelBlobBuilder and VercelBlobConfig, so nothing outside the crate can name it.

[erickguan]

Use Option<&str>

[erickguan]

Inline function.

[erickguan]

Remove tests

[PDGGK]

All three applied in 7f1812c.

Option<&str> is the better shape — an empty string standing in for "no cursor" was encoding absence in the value. The four single-blob lookups pass None, and the lister turns an empty ctx.token into None:

let cursor = if ctx.token.is_empty() {
    None
} else {
    Some(ctx.token.as_str())
};

build_list_url is gone and the format! is back inline, with the cursor appended when present:

if let Some(cursor) = cursor {
    url.push_str(&format!("&cursor={}", percent_encode_path(cursor)));
}

Flagging one thing that goes with the tests, not to argue for keeping them: one of the four asserted that the cursor is percent-encoded. A Vercel cursor is an opaque server token, so an unescaped & or = in it would graft extra parameters onto the query — the same failure mode as the marker parameter in #8073. The percent_encode_path call itself stays; it is just no longer pinned by anything. Your call entirely.

cargo fmt --all -- --check and cargo clippy -p opendal-service-vercel-blob --all-targets are clean.