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User should set RootsListChanged capability #871

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User should set RootsListChanged capability #871

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lorenzocesconetto
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SDK user will set whether it supports RootsListChanged.
To fall into the safe side, the capability defaults to False.

Motivation and Context

I was thinking of a more robust solution for this, but since it's the user providing the callback, I don't think there's much we can do here.

How Has This Been Tested?

Locally.

Breaking Changes

No. I added a new arg, but it's in the end of the args list and has a default value.

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

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@lorenzocesconetto
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@ihrpr this is a follow up from #802

@lorenzocesconetto lorenzocesconetto changed the title Pass responsibility to user User should set RootsListChanged capability Jun 3, 2025
hesreallyhim
hesreallyhim reviewed Jun 3, 2025
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@hesreallyhim hesreallyhim left a comment •
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yup lgtm 👍

this could be a separate PR, but it might be nice to support "good" default callbacks as well, like if most users want to respond to "roots/list" with a paginated result of roots in some default way, we might consider providing such a facility. Same with roots/listChanged - if I want to support "listChanged" but am happy with some default response, why make each user write their own callback?

EDIT: Irrelevant edit removed.

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lorenzocesconetto commented Jun 3, 2025 •
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@hesreallyhim yeah, agreed... I was thinking about implementing something nicer than this simple PR.

A suggestion could be:

  • The session takes an optional list of roots as an argument.
  • SDK implements a simple default callback that returns the list of roots upon request (user doesn't need to write his own callback).
  • Session implements an add_root method that automatically sends a RootsListChanged notification to the connected MCP server (this would be super nice, users would get RootsListChanged support for free).

I can implement this if @ihrpr or @Kludex are on-board (will wait for their blessing, I don't want to waste time implementing it if the core maintainers don't agree).

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@lorenzocesconetto @hesreallyhim