Resolve dot segments in linear time when canonicalizing a URL

[koic]

Motivation and Context

Discovery.canonicalize_url resolved dot segments with RFC 3986 Section 5.2.4 applied literally: every . or .. rewrote the remaining input buffer, which copies it each time, so the cost grew with the square of the path's length. The path is the server's to choose, through a Protected Resource Metadata resource or an endpoint URL that reaches the canonicalization: resolving a 2 MB path made of a/../ took over 30 seconds, on every flow that received it.

The segments are now visited once with a stack, which is the same algorithm expressed over segments instead of over the buffer. The output is unchanged, including the RFC's handling of a trailing /. or /.. (the slash stays) and of a relative path (which URI#path never yields), as checked against the previous implementation on 100,000 random paths.

How Has This Been Tested?

New tests in test/mcp/client/oauth/discovery_test.rb canonicalize a URL with 300,000 dot segments within a bound the previous implementation exceeded many times over, and pin the trailing-slash and empty-segment cases.

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed