Add RFC for supporting MCP with Presto

RFC-0022-Model-Context-Protocol.md

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+# **RFC-0022 for Presto**
+
+## Presto Model Context Protocol Support
+
+Proposers
+
+* Reetika Agrawal
+
+## Summary
+
+This proposal introduces support for integrating Model Context Protocol (MCP) with Presto through a separate lightweight process, referred to as the MCP Server.
+The MCP Server acts as a protocol translation layer between AI agents using JSON-RPC and Presto’s existing HTTP-based query protocol.
+
+## Background
+
+Presto exposes a RESTful HTTP API for query submission and result retrieval. Clients submit a query via a POST request and receive a tokenized nextUri chain for incremental result fetching.
+However, AI frameworks like OpenAI MCP operate on a request–response model over JSON-RPC, where clients expect complete results in a single response, not streamed batches.
+Because MCP and Presto differ fundamentally in communication models, a direct integration is impractical. Additionally, direct embedding of MCP into Presto coordinators would disrupt routing and proxy layers that rely on Presto’s native HTTP semantics.
+
+### Goals
+
+- Enable MCP-compatible AI agents (e.g., OpenAI ChatGPT tools) to query Presto seamlessly.
+- Preserve all existing Presto router, proxy, and load-balancing infrastructure without modification.
+- Simplify authentication by reusing existing OAuth/JWT mechanisms.
+- Prevent unbounded queries by applying automatic limits when appropriate.
+
+### Proposed Plan
+
+Introduce a new lightweight service: presto-mcp-server, deployed alongside Presto coordinators and Presto Router.
+
+The MCP server will:
+
+- Expose a JSON-RPC 2.0 HTTP endpoint (`/mcp`, `/v1/mcp`) interface to AI clients.
+- Implement the core MCP primitives:
+  - `tools/list` for tool discovery 
+  - `tools/call` for executing tools
+  - Initially provide a single tool: `query.run`, which executes SQL queries against Presto.
+- Internally communicate with Presto coordinators using standard Presto HTTP APIs.
+- Forward OAuth/JWT Bearer tokens transparently from MCP clients to Presto, ensuring that Presto performs all authentication and authorization checks.
+- Translate between the two protocols, aggregating streaming results into a single response.
+- Remain stateless, delegating all query lifecycle management to Presto.
+
+## Proposed Implementation
+
+#### Core Changes
+
+```json
+JsonRpcServlet  → McpDispatcher → ToolRegistry → QueryRunTool → PrestoQueryClient → Presto Coordinator
+```
+
+1. New Module: `presto-mcp-server`
+
+   - Implements JSON-RPC 2.0 protocol.
+   - Implements core MCP primitive like `tools/list` and `tools/call`
+   - Handles methods like query.run.
+
+2. On `query.run`:
+
+   - Parses SQL input.
+   - Optionally injects a LIMIT clause (if absent) to control data size.
+   - Submits the query to Presto coordinator via /v1/statement.
+   - Polls the returned nextUri until the query completes.
+   - Returns final aggregated results as a single JSON-RPC response.
+
+#### Example Queries
+
+- `tools/list`
+```json
+{
+"jsonrpc": "2.0",
+"id": 1,
+"method": "tools/list",
+"params": {}
+}
+```
+
+- `tools/call → query.run`
+```json
+{
+"jsonrpc": "2.0",
+"id": 2,
+"method": "tools/call",
+"params": {
+  "name": "query.run",
+  "arguments": { "sql": "SELECT 1" }
+  }
+}
+```
+
+### Rationale
+
+  - Introduce a new standalone service (presto-mcp-server) to avoid mixing JSON-RPC with Presto’s stateful HTTP protocol.
+  - Translate MCP tool calls into Presto HTTP queries, using the existing StatementClient to follow nextUri pages and aggregate results into a single MCP response.
+  - Keep the MCP server stateless, with all query lifecycle state remaining on Presto coordinators.
+  - Forward OAuth/JWT Bearer tokens directly from MCP clients to Presto, allowing Presto to perform full authentication and authorization without changes.
+  - Preserve all existing Presto infrastructure (Router, proxies) by keeping MCP outside the coordinator and communicating using standard Presto HTTP APIs.
+
+## Backward Compatibility Considerations
+
+  - MCP server is a new optional component
+  - No impact on existing Presto or Router
+  - All existing Presto deployments remain unchanged
+
+## Test Plan
+
+- **Unit + Integration Tests:**
+Verify ToolRegistry loading, dispatcher routing, SQL execution via QueryRunTool, and JSON-RPC error handling.
+
+- **End-to-End Validation:**
+Deploy MCP server with Router + Coordinator. Confirm Bearer token forwarding works and MCP clients (Gemini, ChatGPT) successfully execute queries.
+
+## Modules involved
+- `presto-mcp` (new module)
+- `presto-client`
+- `airlift` modules
+- `presto-main`
+- `presto-router`
+
+## Final Thoughts
+
+This proposal cleanly bridges Presto with next-generation agent ecosystems (LLMs, AI workflows, model interaction tools). The MCP server architecture respects Presto’s deployment patterns, is backward-compatible, and provides a robust extension point for future interactive functionality such as:
+
+- Schema browsing tools
+- Table metadata tools
+- Query explanation tools
+
+## WIP - Draft PR Changes