[Bugfix] Allow single-label hostnames in URL validation

[osaimi]

Fix validate_url to accept URLs with single-label hosts like http://oss-20b:8000, which are common in Docker and internal networking setups.

[gemini-code-assist]

Summary of Changes

Hello @osaimi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a crucial bugfix to the URL validation mechanism, allowing it to properly handle URLs containing single-label hostnames. This enhancement is vital for environments such as Docker and internal networks, where such hostnames are prevalent, ensuring that valid internal addresses are no longer erroneously rejected by the system.

Highlights

• Bugfix: Resolved an issue in the validate_url function that previously rejected URLs with single-label hostnames.
• URL Validation: The URL validation regex has been updated to correctly recognize and accept single-label hostnames (e.g., http://myhost:8000).
• Compatibility: This change improves compatibility with common internal networking setups and containerized environments like Docker, where single-label hostnames are frequently used.

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[gemini-code-assist]

Code Review

This pull request updates the URL validation regex to allow single-label hostnames, which is useful for internal networking environments. The implementation adds a new alternative to the regex. However, the new pattern is too permissive and allows invalid hostnames (e.g., starting/ending with a hyphen), which poses a security risk. I've provided a suggestion to tighten the regex. I also noted a minor issue with pattern ordering that makes the localhost check redundant.

[gemini-code-assist]

This regex for single-label hostnames is too permissive. It allows hostnames that start or end with a hyphen (e.g., -host or host-), which is invalid according to RFCs 952 and 1123. This could potentially lead to security vulnerabilities like Server-Side Request Forgery (SSRF).

Additionally, this general pattern makes the localhost alternative on the next line redundant. It's better to have specific patterns like localhost come before more general ones.

For security and correctness, please use a stricter pattern. Note that the multi-label domain regex on line 159 has a similar vulnerability and should also be considered for an update.

Suggested change

	r"[a-zA-Z0-9_-]+|" # single-label
	r"(?!-)[a-zA-Z0-9_-]+(?<!-)|" # single-label