feat: support context decorator in MCP controllers by akitaSummer · Pull Request #458 · eggjs/tegg

akitaSummer · 2026-06-17T08:14:30Z

Checklist

npm test passes
tests and/or benchmarks are included
documentation is changed or added
commit message follows commit guidelines

Affected core subsystem(s)

Description of change

Summary by CodeRabbit

Release Notes

New Features
- Added context parameter support for MCP tools, resources, and prompts—handlers can now inject and access request context via the @Context() decorator.
Tests
- Updated MCP tests to validate context parameter injection and retrieval in handler operations.

gemini-code-assist

Code Review

This pull request introduces context parameter injection support for MCP (Model Context Protocol) prompts, tools, and resources. It updates metadata builders, metadata models, and the MCPServerHelper to resolve and inject the context parameter index. Additionally, it integrates AsyncLocalStorage in the service worker register to store and retrieve the fetch context. The feedback recommends adding error handling to the unawaited transport.handleRequest call to prevent unhandled promise rejections, and using optional chaining when validating the ctx object in test fixtures to avoid potential runtime TypeErrors.

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coderabbitai · 2026-06-17T11:03:21Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c0b57f01-d35f-464b-86fa-a2219bd76289

📥 Commits

Reviewing files that changed from the base of the PR and between bf89468 and a3088a8.

📒 Files selected for processing (16)

core/controller-decorator/src/impl/mcp/MCPControllerPromptMetaBuilder.ts
core/controller-decorator/src/impl/mcp/MCPControllerResourceMetaBuilder.ts
core/controller-decorator/src/impl/mcp/MCPControllerToolMetaBuilder.ts
core/controller-decorator/src/model/MCPPromptMeta.ts
core/controller-decorator/src/model/MCPResourceMeta.ts
core/controller-decorator/src/model/MCPToolMeta.ts
core/controller-decorator/test/MCPMeta.test.ts
core/controller-decorator/test/fixtures/MCPController.ts
plugin/controller/lib/impl/mcp/MCPControllerRegister.ts
plugin/controller/lib/impl/mcp/MCPServerHelper.ts
plugin/controller/test/fixtures/apps/mcp-app/app/controller/McpController.ts
plugin/controller/test/fixtures/apps/mcp-app/app/controller/TestController.ts
plugin/controller/test/mcp/helper.test.ts
standalone/service-worker/src/mcp/MCPControllerRegister.ts
standalone/service-worker/src/mcp/MCPServerHelper.ts
standalone/service-worker/test/fixtures/mcp/MCPTestController.ts

📝 Walkthrough

Walkthrough

This PR adds @Context() parameter injection support to MCP (tool, prompt, resource) handlers. MCPToolMeta, MCPPromptMeta, and MCPResourceMeta now implement MethodMeta and carry a contextParamIndex field populated by the meta builders. Both the plugin and service-worker MCPServerHelper classes gain centralized build*Args helpers that insert the request context at the declared index, wired via a getContext callback.

Changes

MCP Context Parameter Injection

Layer / File(s)	Summary
MCP meta models: `contextParamIndex` and `MethodMeta` `core/controller-decorator/src/model/MCPToolMeta.ts`, `core/controller-decorator/src/model/MCPPromptMeta.ts`, `core/controller-decorator/src/model/MCPResourceMeta.ts`	`MCPToolMeta`, `MCPPromptMeta`, and `MCPResourceMeta` each implement `MethodMeta` and gain an optional `contextParamIndex: number \| undefined` property and constructor option.
Meta builders: read `contextParamIndex` `core/controller-decorator/src/impl/mcp/MCPControllerToolMetaBuilder.ts`, `.../MCPControllerPromptMetaBuilder.ts`, `.../MCPControllerResourceMetaBuilder.ts`	All three builder `build()` methods now call `MethodInfoUtil.getMethodContextIndex(...)` and pass the result into the meta constructor.
Plugin `MCPServerHelper`: `getContext` and centralized arg builders `plugin/controller/lib/impl/mcp/MCPServerHelper.ts`, `plugin/controller/lib/impl/mcp/MCPControllerRegister.ts`	`MCPServerHelperOptions` gains optional `getContext`; three private `build*Args` helpers centralize argument cloning and context injection at `contextParamIndex`. Registration handlers delegate to these builders. `MCPControllerRegister` wires `getContext` to `app.currentContext`.
Service-worker `MCPServerHelper` and `MCPControllerRegister`: context via `AsyncLocalStorage` `standalone/service-worker/src/mcp/MCPServerHelper.ts`, `standalone/service-worker/src/mcp/MCPControllerRegister.ts`	Mirrors the plugin helper changes; `MCPControllerRegister` creates an `AsyncLocalStorage<ServiceWorkerFetchContext>`, wraps stream request handling in `contextStorage.run(ctx, ...)`, and passes `getContext` returning the stored context.
Tests and fixtures: `@Context()` usage and assertions `core/controller-decorator/test/fixtures/MCPController.ts`, `core/controller-decorator/test/MCPMeta.test.ts`, `plugin/controller/test/mcp/helper.test.ts`, `plugin/controller/test/fixtures/apps/mcp-app/app/controller/McpController.ts`, `plugin/controller/test/fixtures/apps/mcp-app/app/controller/TestController.ts`, `standalone/service-worker/test/fixtures/mcp/MCPTestController.ts`	Fixture controllers inject `@Context()` into MCP handlers; tests assert `contextParamIndex` values on metadata and verify handlers receive the correct context object.

Sequence Diagram(s)

sequenceDiagram
  rect rgba(173, 216, 230, 0.5)
    Note over MCPControllerRegister,MethodInfoUtil: Metadata build time
    MCPControllerRegister->>MCPControllerToolMetaBuilder: build(clazz, method)
    MCPControllerToolMetaBuilder->>MethodInfoUtil: getMethodContextIndex(clazz, method)
    MethodInfoUtil-->>MCPControllerToolMetaBuilder: contextParamIndex
    MCPControllerToolMetaBuilder-->>MCPControllerRegister: MCPToolMeta { contextParamIndex }
  end
  rect rgba(144, 238, 144, 0.5)
    Note over MCPControllerRegister,ControllerMethod: Request invocation time
    MCPControllerRegister->>MCPServerHelper: new MCPServerHelper({ getContext: () => currentContext })
    MCPServerHelper->>MCPServerHelper: buildToolArgs(args, toolMeta, hasSchema)
    MCPServerHelper->>MCPServerHelper: getContext?.() → ctx
    MCPServerHelper->>MCPServerHelper: newArgs[contextParamIndex] = ctx
    MCPServerHelper->>ControllerMethod: Reflect.apply(method, target, newArgs)
  end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

eggjs/tegg#307: Introduced the MCP controller metadata and server registration plumbing that this PR extends with contextParamIndex.
eggjs/tegg#321: Refactored MCPServerHelper and MCPControllerRegister in the plugin, directly in the same files this PR modifies.
eggjs/tegg#436: Introduced the standalone service-worker MCP stack (MCPServerHelper, MCPControllerRegister) that this PR extends with getContext/AsyncLocalStorage support.

Suggested labels

enhancement

Suggested reviewers

killagu

🐇 Hops through context with glee,
@Context() injected, plain to see!
contextParamIndex marks the spot,
AsyncLocalStorage ties the knot.
Now MCP handlers know who's there —
A rabbit's gift, passed with care! 🎉

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: support context decorator in MCP controllers' directly aligns with the main changes, which add contextParamIndex support and `@Context`() decorator functionality across all MCP controller metadata builders and handlers.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Commit on current branch

🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch feat/mcp-context-decorator

Warning

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🔧 ESLint

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core/controller-decorator/src/impl/mcp/MCPControllerPromptMetaBuilder.ts

ESLint skipped: missing config or dependency (missing-dependency). The ESLint configuration references a package that is not available in the sandbox.

core/controller-decorator/src/impl/mcp/MCPControllerResourceMetaBuilder.ts

ESLint skipped: the ESLint configuration for this file references a package that is not available in the sandbox.

core/controller-decorator/src/impl/mcp/MCPControllerToolMetaBuilder.ts

ESLint skipped: the ESLint configuration for this file references a package that is not available in the sandbox.

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gxkl

LGTM

feat: support context decorator in MCP controllers

478edc2

gemini-code-assist Bot reviewed Jun 17, 2026

View reviewed changes

Comment thread standalone/service-worker/src/mcp/MCPControllerRegister.ts

Comment thread standalone/service-worker/test/fixtures/mcp/MCPTestController.ts Outdated

fix: address MCP context review comments

a3088a8

gxkl approved these changes Jun 17, 2026

View reviewed changes

akitaSummer merged commit 283a331 into master Jun 17, 2026
12 checks passed

akitaSummer deleted the feat/mcp-context-decorator branch June 17, 2026 11:32

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feat: support context decorator in MCP controllers#458

feat: support context decorator in MCP controllers#458
akitaSummer merged 2 commits into
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feat/mcp-context-decorator

akitaSummer commented Jun 17, 2026 •

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akitaSummer commented Jun 17, 2026 •

edited by coderabbitai Bot

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