examples: clean up crawler link parsing resources

[minnnjuuu]

What is the purpose of the change?

follow_links() owns the libxml document returned by htmlReadMemory() and each xmlChar URL returned by xmlNodeListGetString() or xmlBuildURI(). The document was not released on several returns or after a successful scan, and short links and the link-limit exit could leave the current URL allocated.

The existing post-increment limit check also admitted one more HTTP(S) link than max_link_per_page. With the default limit of 5, the function could add 6 handles.

What does this change do?

• Handle a failed XPath-context allocation.
• Release the parsed document on all paths after a successful parse.
• Release the current URL before short-link continue and limit break paths.
• Check the link cap before adding a handle and increment the count once per accepted HTTP(S) link.

Testing

• perl scripts/checksrc.pl docs/examples/crawler.c
• Built crawler.c with GCC using -Wall -Wextra -Werror
• Verified the link cap and cleanup paths with a focused ASan/UBSan harness

AI-assisted discovery disclosure

This issue was initially identified with AI-assisted tooling. The patch was then manually reviewed and validated with the tests described above.

[Copilot]

Copilot review overview

🟢 Approval recommended

The cleanup paths and link-counting logic are complete and consistent with libxml ownership requirements.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes resource leaks and enforces the crawler’s per-page link limit correctly.

Changes:

• Frees libxml documents and URL allocations on all exit paths.
• Handles XPath context allocation failure.
• Prevents exceeding max_link_per_page.

File	Description
docs/​examples/​crawler.c	Corrects link parsing cleanup and limit enforcement.

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[bagder]

Thanks!