Add support for _meta attributes in resource contents #1638
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This change enables MCP servers to include metadata in resource content using the _meta field, which is part of the MCP specification. This allows servers to provide additional context about resources, such as domain information or other custom metadata. Changes: - Added meta field to ReadResourceContents helper class - Added _meta field to Resource base class with proper alias - Updated lowlevel server handler to pass through _meta when creating TextResourceContents and BlobResourceContents - Updated FastMCP server to pass resource._meta to ReadResourceContents - Added comprehensive tests for _meta support in both lowlevel and FastMCP resources The implementation maintains backward compatibility - resources without _meta continue to work as before with meta=None.
Adds tests to verify that _meta attributes are correctly serialized with the underscore prefix in JSON output, not as "meta". This ensures the implementation conforms to the MCP specification where metadata fields use the _meta key. Tests verify: - Resource serialization includes "_meta" key in JSON - Response content serialization includes "_meta" key - JSON strings contain the literal "_meta" key - No "meta" key appears in serialized output
…ontents
Use the field name 'meta' instead of the alias '_meta' when constructing
Pydantic model instances. The alias is only used for JSON serialization.
This fixes a bug where passing **{'_meta': meta} would cause Pydantic
validation errors since '_meta' is an alias, not a field name.
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related: #1476 |
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This change enables MCP servers to include metadata in resource content using the _meta field, which is part of the MCP specification. This allows servers to provide additional context about resources, such as domain information or other custom metadata.
Changes:
The implementation maintains backward compatibility - resources without _meta continue to work as before with meta=None.
Motivation and Context
How Has This Been Tested?
Breaking Changes
Types of changes
Checklist
Additional context