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feat!: add MRTR model types (SEP-2322) - #915
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| /// Result type discriminator. Always serialized; older peers ignore it. | ||
| #[serde(default)] | ||
| pub result_type: ResultType, |
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I found this to be not actually happening with all peers. Notably, the MCP inspector explicitly rejected
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I think it might have only been on the EmptyResult type though so perhaps here specifically is ok. This PR doesn't actually change EmptyResult to have ResultType.
In my work on this I ended up using Option<ResultType> to make it so we could avoid serializing this for older peers
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Good point, @howardjohn. I removed the wording that implied all older peers tolerate the extra field. This PR is focused on model changes, so I'll tackle your concern in a follow-up PR.
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Motivation and Context
SEP-2322 introduces a stateless pattern where a server responds to
tools/call,prompts/get, orresources/readwith anInputRequiredResult(carryinginputRequestsand/orrequestState), and the client retries withinputResponses. This replaces the previousURLElicitationRequiredError(-32042) approach. Relates to #871.The draft spec also adds a
resultTypediscriminator to the baseResulttype (requiredin the JSON schema). This PR addsresult_type: ResultTypeto all server result types that require it per the schema:CallToolResult,GetPromptResult,ReadResourceResult,CompleteResult, and the four paginated results (ListToolsResult,ListPromptsResult,ListResourcesResult,ListResourceTemplatesResult).resultTypeis always serialized (matching the Python SDK's approach per the spec's MUST). Types that don't haveresultTypein the schema (InitializeResult, task results, client results) are unchanged.This PR adds only the model/serde layer. Behavior wiring (server emit, client retry, version gating) is planned for a follow-up.
How Has This Been Tested?
13 unit tests in
model/mrtr.rscovering serde round-trips against spec example JSON, rejection of missing/wrongresultType, unknown extension value preservation, and constructor behavior. Full suite passes with 0 failures.Breaking Changes
All server result types gain a
result_type: ResultTypefield. The field defaults to"complete"and is always serialized, so responses now include"resultType": "complete". Struct literals that construct result types directly (not through constructors or..Default::default()) will need the new field added. The#[tool_handler]and#[prompt_handler]proc macros have been updated. AddingInputRequiredResultto the exhaustiveServerResultunion is an API-breaking change.Types of changes
Checklist