Fix buffer overflow

[ybastide]

Fix buffer overflow in MaybeEscapePattern (%[a-f] at pattern's end). Also replace new byte[] with ArrayPool<byte>.

[Copilot]

Pull request overview

This PR addresses a buffer overflow vulnerability in the MaybeEscapePattern method and improves memory management by replacing heap allocations with ArrayPool<byte>.

Key Changes:

• Fixed buffer overflow caused by incorrect index manipulation in the percent-encoding capitalization logic
• Replaced new byte[] allocations with ArrayPool<byte>.Shared.Rent() for better memory efficiency
• Updated method signature to return the rented array via an out parameter for proper cleanup

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
RobotsTxt/RobotsTxtParser.cs	Fixed buffer overflow in percent-encoding logic and replaced direct byte array allocation with ArrayPool
TestRobotsTxt/TestRobotsTxtParser.cs	Updated test to handle new ArrayPool-based method signature and added cleanup logic
TestRobotsTxt/GoogleTests.cs	Updated test to handle new ArrayPool-based method signature, added cleanup logic, and added test case for the buffer overflow scenario

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

Returning a span over a rented array that will be returned to the pool creates a potential use-after-free scenario. The caller receives a span pointing to memory that may be reused once ArrayPool<byte>.Shared.Return(dst) is called. Consider either returning the array itself with the length, or copying the data to a new array before returning.

Suggested change

	return dst.AsSpan(0, j);
	var result = new byte[j];
	System.Array.Copy(dst, 0, result, 0, j);
	return result.AsSpan();

[Copilot]

Calling .ToArray() on the span creates a copy before the rented buffer is returned to the pool, but this pattern is fragile. If the .ToArray() call were removed or reordered, it would read from freed memory. Consider restructuring to make the dependency on copying before return more explicit.