Update metaschema URI format in input_schema.rb #132
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Fixes modelcontextprotocol#131. Tested on Windows and Linux. Added a "file://" prefix to prevent the JSON library from not identifying the URI correctly.
atesgoral
reviewed
Sep 13, 2025
lib/mcp/tool/input_schema.rb
Outdated
| @@ -50,7 +50,7 @@ def validate_schema! | |||
| accept_uri: false, | |||
| accept_file: ->(path) { path.to_s.start_with?(Gem.loaded_specs["json-schema"].full_gem_path) }, | |||
| ) | |||
| metaschema = JSON::Validator.validator_for_name("draft4").metaschema | |||
| metaschema = "file://#{JSON::Validator.validator_for_name("draft4").metaschema}" | |||
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Using string interpolation with "file://#{…}" works most of the time, but it’s a bit fragile. A safer, cross-platform approach is to let Ruby build the file: URI:
path = Pathname.new(JSON::Validator.validator_for_name("draft4").metaschema)
uri = URI::File.build(host: "", path: path.expand_path.cleanpath.to_s.tr("\\", "/"))
metaschema = uri.to_sTwo reasons this is safer:
- Windows compatibility:
Pathname#to_sreturns backslashes on Windows (C:\…).URI::File.buildexpects forward slashes, so.tr("\\", "/")ensures we get a standards-compliantfile:///C:/…form. - Path normalization:
expand_path.cleanpathremoves./..components and guarantees an absolute path.
The gem’s own metaschema files don’t contain spaces or special characters, so escaping isn’t critical here, but this makes the URI building step robust and RFC-compliant.
5 tasks
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It would be helpful to add source code comments explaining what kind of issues on Windows environments the added logic is intended to address. It would also be preferable to add regression tests to |
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Added a "file://" prefix to prevent the JSON library from not identifying the URI correctly.
Motivation and Context
Fixes #131. The lib wasn't working for STDIO servers on any Windows environment i tested.
How Has This Been Tested?
Tested on Windows and Linux.
(The issue was occuring only on Windows, but i wanted to see if it would break Linux and it didn't.
Breaking Changes
Not expected.
Types of changes
Checklist
Additional context