Spec conformance: meta support and spec updates by aharvard · Pull Request #415 · modelcontextprotocol/rust-sdk

aharvard · 2025-09-03T12:38:59Z

This PR updates the Rust SDK to align more closely with the 2025-06-18 Model Context Protocol specification and adds first-class support for meta.

Summary

Protocol/version: set LATEST to 2025-06-18
meta support: added to text and image content, and embedded resources
Annotated model: rename timestamp -> last_modified (schema lastModified)
Prompt helpers: added function to create text messages with meta
Tests: kept existing Rust tests passing locally; Python-dependent tests are skipped due to local env

Key changes

crates/rmcp/src/model.rs
- Update LATEST constant to 2025-06-18
crates/rmcp/src/model/content.rs
- Add optional meta to RawTextContent and RawImageContent
- Comments clarifying meta intent and examples
crates/rmcp/src/model/prompt.rs
- new_text_with_meta helper for convenience
- Test updates to include meta in RawImageContent case
crates/rmcp/src/model/annotated.rs
- Rename timestamp to last_modified and update accessors
crates/rmcp/tests/test_message_schema.rs
- Reviewed; remains compatible

Notes

Local environment lacks Python, so Python-dependent tests were not executed; Rust tests pass.
Happy to extend meta to any additional surfaced interfaces if maintainers prefer a broader/narrower interpretation of where meta is allowed in the June 18, 2025 spec.

Follow-ups (open to maintainer guidance)

Confirm the precise set of interfaces that should expose meta in the SDK surface area
Add helpers for setting params._meta on requests (if desired)
Tighten schema/tests once final interpretation is agreed

Thanks!

…rces; update schemas

crates/rmcp/src/model.rs

aharvard · 2025-09-03T13:05:18Z

crates/rmcp/src/model/annotated.rs

-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub timestamp: Option<DateTime<Utc>>,
+    #[serde(skip_serializing_if = "Option::is_none", rename = "lastModified")]
+    pub last_modified: Option<DateTime<Utc>>,


I was curious about this, I asked Goose, why did we change the timestamp to last_modified?

Short answer: to match the spec and be precise.

Details:

Spec alignment: The current MCP spec uses lastModified (camelCase on the wire) to mean “when this content/resource was last updated.” Our previous timestamp field was an SDK-ism and didn’t match the spec name.

Clearer semantics: timestamp was ambiguous (creation time? event time?); lastModified explicitly conveys modification time, which also aligns with common HTTP/metadata semantics.

Cross‑SDK consistency: Other SDKs and examples use lastModified, so this keeps the Rust SDK consistent.

Rust naming: In Rust we expose last_modified and serialize as lastModified to conform to the JSON field name.

aharvard · 2025-09-03T13:06:37Z

@alexhancock, this PR addresses your comment #386 (review)

alexhancock · 2025-09-03T14:11:48Z

crates/rmcp/src/model/prompt.rs

    }
+
+    /// Create a new text message with meta
+    pub fn new_text_with_meta<S: Into<String>>(


Seems like we should have ways to create each kind of prompt message with meta optionally supplied vs just this one type that has new_text and new_text_with_meta

ok, I think I've addressed this. LMK if me and Goose got it wrong, thanks!

…-06-18 compliance

- Keep text helper; meta is currently ignored for text until schema supports it.

…uplicate non-meta variants

alexhancock · 2025-09-04T17:31:22Z

crates/rmcp/src/model/prompt.rs

-        mime_type: String,
+        mime_type: Option<String>,
        text: Option<String>,
+        top_meta: Option<crate::model::Meta>,


resource_meta and resource_content_meta perhaps better naming here

@alexhancock, can you check if I executed as you expected? thanks!

… clarity

…#415) * feat: add _meta to content blocks and embedded resources; update schemas * feat: set default protocol version; add _meta to content blocks/resources; update schemas * chore: format content.rs via rustfmt * chore(protocol): keep LATEST at 2025-03-26 per review until full 2025-06-18 compliance * feat(prompt): add constructors with optional meta for image and resource - Keep text helper; meta is currently ignored for text until schema supports it. * refactor(prompt): simplify constructors so meta is optional; remove duplicate non-meta variants * fix: modify code comment about version * refactor(prompt): rename meta parameters in new_resource function for clarity

github-actions bot added T-test Testing related changes T-config Configuration file changes T-core Core library changes T-model Model/data structure changes labels Sep 3, 2025

aharvard force-pushed the feat/spec-conformance-meta-support branch from b52133d to e6902c6 Compare September 3, 2025 12:39

aharvard added 2 commits September 3, 2025 08:43

feat: add _meta to content blocks and embedded resources; update schemas

2a7e60d

feat: set default protocol version; add _meta to content blocks/resou…

3180808

…rces; update schemas

aharvard force-pushed the feat/spec-conformance-meta-support branch from e6902c6 to 3180808 Compare September 3, 2025 12:45

chore: format content.rs via rustfmt

76d5533

aharvard commented Sep 3, 2025

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crates/rmcp/src/model.rs Outdated Show resolved Hide resolved

aharvard commented Sep 3, 2025

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aharvard marked this pull request as ready for review September 3, 2025 13:06

alexhancock reviewed Sep 3, 2025

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aharvard added 4 commits September 3, 2025 11:26

chore(protocol): keep LATEST at 2025-03-26 per review until full 2025…

f021b00

…-06-18 compliance

feat(prompt): add constructors with optional meta for image and resource

e9c8069

- Keep text helper; meta is currently ignored for text until schema supports it.

refactor(prompt): simplify constructors so meta is optional; remove d…

1af6906

…uplicate non-meta variants

fix: modify code comment about version

c8ff500

aharvard force-pushed the feat/spec-conformance-meta-support branch from 4f95e7f to c8ff500 Compare September 3, 2025 15:53

aharvard requested a review from alexhancock September 3, 2025 16:08

alexhancock previously approved these changes Sep 4, 2025

View reviewed changes

refactor(prompt): rename meta parameters in new_resource function for…

6ef61bb

… clarity

aharvard dismissed alexhancock’s stale review via 6ef61bb September 4, 2025 18:05

aharvard requested a review from alexhancock September 4, 2025 18:12

alexhancock approved these changes Sep 4, 2025

View reviewed changes

alexhancock merged commit 4eb413b into modelcontextprotocol:main Sep 4, 2025
11 checks passed

github-actions bot mentioned this pull request Sep 4, 2025

chore: release v0.6.2 #407

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Spec conformance: meta support and spec updates#415

Spec conformance: meta support and spec updates#415
alexhancock merged 8 commits intomodelcontextprotocol:mainfrom
aharvard:feat/spec-conformance-meta-support

aharvard commented Sep 3, 2025

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