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fix: improve misleading warning for progress callback exceptions #775

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fix: improve misleading warning for progress callback exceptions #775

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lorenzocesconetto
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Currently if the progress notification callback throws an exception we get a misleading warning message.
This PR aims to fix it.

Motivation and Context

How Has This Been Tested?

Ran a few tests locally.

Breaking Changes

No breaking changes.

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

Additional context

@lorenzocesconetto lorenzocesconetto mentioned this pull request May 21, 2025
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ihrpr
ihrpr requested changes May 23, 2025
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@ihrpr ihrpr left a comment

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Thank you so much for working on this!

There are some suggestion would be good to address before merging:

  • please can you add tests
  • replace use of try-except-else to make it consistent in the project

@lorenzocesconetto
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lorenzocesconetto commented May 23, 2025 •
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Hi @ihrpr thank you for the review. I'll add the tests.

@lorenzocesconetto
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Hi @ihrpr, ready for another pass!
I've added the unit test and removed the try-except-else as you've requested.

@Kludex
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Kludex commented May 26, 2025

Why is it misleading? Do you have a MRE that I can check this locally?

Also, if this makes sense, we should except on ValidationError, not on Exception.

ihrpr
ihrpr requested changes May 27, 2025
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Thank you for adding tests! Few things to address - please see comments in PR

  1. As Kludex pointed out, the PR catches Exception which is too broad.
  2. The warning could include more context about which progress token/request triggered the exception.

@lorenzocesconetto
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Thank you for your reviews and comments @Kludex and @ihrpr!
Totally agree with you guys and changed to ValidationError in the try-except.
I only kept the generic Exception around the callback execution since we don't know what kind of exception might be raised in there.

@Kludex the "misleading" part is that it prints Failed to validate notification... when the user's callback raises an exception. When I saw that for the first time I thought the server notification message was not following the protocol's standard (or the client validation was broken). That message is very misleading. The root cause was a bad implementation of the callback.

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@ihrpr ihrpr ihrpr requested changes

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3 participants
@lorenzocesconetto @Kludex @ihrpr