Forward MCP client identity in the API User-Agent - #130
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📝 WalkthroughWalkthroughThe server captures MCP client name and version after initialization. User-Agent utilities sanitize and format this identity. Mailtrap clients append the identity to a version-aware base User-Agent and create the default client lazily. ChangesMCP identity forwarding
Estimated code review effort: 3 (Moderate) | ~25 minutes Suggested reviewers: Sequence Diagram(s)sequenceDiagram
participant MCPClient as MCP client
participant MCPServer as src/server.ts
participant APIClients as src/client.ts
participant MailtrapAPI as Mailtrap API
MCPClient->>MCPServer: complete initialization with client name and version
MCPServer->>APIClients: setMcpClientInfo(client metadata)
APIClients->>MailtrapAPI: send request with dynamically built User-Agent
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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Actionable comments posted: 1
🧹 Nitpick comments (1)
src/__tests__/client.test.ts (1)
30-45: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick winAdd coverage for
getDefaultClient/requireClientidentity capture timing.These tests exercise
getSandboxClient, which rebuilds itsMailtrapClienton every call. They do not exercisegetDefaultClient(used byrequireClient), which memoizes its client instance after the first call insrc/client.ts. Add a test that callsgetDefaultClient(or a function that uses it) once beforesetMcpClientInfo, then again after, to confirm intended behavior. This directly documents and would catch the caching risk noted in thesrc/client.tsreview.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@src/__tests__/client.test.ts` around lines 30 - 45, Add coverage in the client identity tests for the memoized getDefaultClient/requireClient path: obtain the default client once before setMcpClientInfo, set the MCP identity, then obtain it again and assert the intended User-Agent behavior. Keep the existing getSandboxClient tests unchanged and use the public helper that exercises getDefaultClient where appropriate.
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Inline comments:
In `@src/client.ts`:
- Around line 6-7: Remove the defaultClient memoization used by getDefaultClient
and construct a fresh MailtrapClient on every call, so later setMcpClientInfo
updates are reflected in the User-Agent. Keep the existing client configuration
and other getters unchanged.
---
Nitpick comments:
In `@src/__tests__/client.test.ts`:
- Around line 30-45: Add coverage in the client identity tests for the memoized
getDefaultClient/requireClient path: obtain the default client once before
setMcpClientInfo, set the MCP identity, then obtain it again and assert the
intended User-Agent behavior. Keep the existing getSandboxClient tests unchanged
and use the public helper that exercises getDefaultClient where appropriate.
🪄 Autofix (Beta)
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
ℹ️ Review info
⚙️ Run configuration
Configuration used: Organization UI
Review profile: CHILL
Plan: Pro Plus
Run ID: a7807afa-4963-4ae8-8bd3-902af63c9454
📒 Files selected for processing (6)
src/__tests__/client.test.tssrc/client.tssrc/config/index.tssrc/server.tssrc/utils/__tests__/userAgent.test.tssrc/utils/userAgent.ts
The MCP server sent a generic User-Agent for every Mailtrap API call, so we could not tell which AI client (Claude Desktop, Cursor, Windsurf, ...) was driving a request. Capture the client name and version reported during the `initialize` handshake and append them to the outgoing API User-Agent, e.g. `mailtrap-mcp/0.6.0 (+https://github.com/mailtrap/mailtrap-mcp) (client: Claude Desktop/1.5.3)`. The identity is read lazily from `server.getClientVersion()` at client construction. That value is populated during the `initialize` request, which always precedes any tool call that builds an API client, so the User-Agent is never stale and no client caches a value captured before the identity was known. The name/version are sanitized before going into the header. The base User-Agent also gains the server version.
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3 participants
What
The MCP server sent a generic User-Agent for every Mailtrap API call, so we couldn't tell which AI client (Claude Desktop, Cursor, Windsurf, Lovable, …) was driving a request. This forwards the client identity so adoption can be measured per client.
How
name+versionfrom theinitializehandshake (server.oninitialized→getClientVersion()).mailtrap-mcp/0.6.0 (+https://github.com/mailtrap/mailtrap-mcp) (client: Claude Desktop/1.5.3).Summary by CodeRabbit
New Features
User-Agent.User-Agentnow includes the server version and repository information.Tests