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158 support resource links #244

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@dstibbe dstibbe commented Sep 4, 2025 •
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Support resource links in tool result content #158

  • Refactored PromptMessageContent to ContentBlock
  • Added the ResourceLink as a ContentBlock type

Motivation and Context

The new spec introduced a new ContentBlock type: ResourceLink. This type however hasn't been implemented yet.
Noticed that there was actually no ContentBlock type at all in the core as the latest schema reference specified. Instead there is a PromptMessageContent.

How Has This Been Tested?

Added unit tests. Ran all tests.
Also used the build in a standalone project:

  • calling a tool returning a ResourceLink via de client directly
  • called a tool using Jetbrains Koog framework

Breaking Changes

Added the following:

  • ContentBlock
  • CreateMessageResultContent, and
  • SamplingMessageContent

However, I kept the two intrefaces PromptMessageContent and PromptMessageContentMultimodal purely for backwards compatibility. They are deprecated however.

Types of changes

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

Checklist

  • [ x ] I have read the MCP Documentation
  • [ x ] My code follows the repository's style guidelines
  • [ x ] New and existing tests pass locally
  • [ x ] I have added appropriate error handling - none needed
  • [ x ] I have added or updated documentation as needed

Additional context

@Copilot Copilot AI review requested due to automatic review settings September 12, 2025 09:59
@devcrocod devcrocod force-pushed the 158-support-resource-links branch from 23d2726 to c3746a4 Compare September 12, 2025 09:59
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Copilot AI reviewed Sep 12, 2025
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Pull Request Overview

This PR adds support for ResourceLink ContentBlock type to align with the MCP specification, refactoring the existing PromptMessageContent type hierarchy to use the more structured ContentBlock interface.

  • Introduces ResourceLink as a new ContentBlock type for linking to external resources
  • Refactors type hierarchy from PromptMessageContent to ContentBlock with specialized content types
  • Maintains backwards compatibility by deprecating old interfaces while keeping them functional

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file
File Description
kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt Adds ResourceLink class and ContentBlock interface hierarchy
kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.util.kt Updates polymorphic serializers for new ContentBlock types
kotlin-sdk-core/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/TypesTest.kt Adds tests for ResourceLink and updates existing tests
kotlin-sdk-core/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/TypesUtilTest.kt Updates serialization tests for ContentBlock types
kotlin-sdk-core/api/kotlin-sdk-core.api API documentation for new types and interfaces
CONTRIBUTING.md Minor update to build instructions

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@kpavlov kpavlov force-pushed the 158-support-resource-links branch from 6589ccf to 5136548 Compare September 16, 2025 17:18
@kpavlov kpavlov added the enhancement New feature or request label Sep 16, 2025
kpavlov
kpavlov reviewed Sep 29, 2025
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#294 introduces model generation from MCP json schema. It should solve the issue of models are out of sync with the schema.

I would push #294 forward and then migrate to generated models, so this PR would not be necessary.

devcrocod
devcrocod requested changes Oct 22, 2025
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I have a few questions regarding this PR.
Could you please take a moment to answer them?

@dstibbe
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dstibbe commented Oct 23, 2025

I have a few questions regarding this PR. Could you please take a moment to answer them?

So, to be clear, the approach I took was to add the content definitions of the 'new' (2025-06-18) schema while not immediately breaking it for anyone upgrading. Such that I could get the resourcelink in the tool call result as quick as possible and get some work done with it. While the SDK project could then softly phase out the deprecated classes.

Alas, #294 is the way of the future, which means I will probably will have to wait a while till an official release with resourcelink will be available...
I will be using a custom build till then I guess.

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@devcrocod devcrocod devcrocod requested changes

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@dstibbe @kpavlov @devcrocod