SEP-2243: HTTP Header Standardization for Streamable HTTP Transport

Java SDK の streamable HTTP transport client から始め、POST リクエストがどのように構築されるかをたどります。SEP-2243 とここで説明されている request-body フィールドを使ってヘッダー値を決定します。完了条件は、標準を適用するサーバーが受け入れられるよう、該当する POST リクエストが Mcp-Method と Mcp-Name を送信することです。

Description

Per SEP-2243 (HTTP Standard Headers), MCP clients MUST send the following HTTP headers on POST requests:

• Mcp-Method: Set to the JSON-RPC method value from the request body (REQUIRED on every POST)
• Mcp-Name: Set from params.name (for tools/call, prompts/get) or params.uri (for resources/read, resources/subscribe, resources/unsubscribe) when present

Context

The cxxmcp (C++ SDK) conformance testing revealed that the official conformance test suite's reference client (TypeScript SDK) does not send these headers, making the conformance suite self-contradictory. See:

• typescript-sdk#2176 — TypeScript SDK bug report
• conformance#323 — Conformance suite self-contradiction
• typescript-sdk#2178 — Fix PR for TypeScript SDK

Impact

Servers that enforce SEP-2243 (reject missing Mcp-Method with HTTP 400) are incompatible with clients that don't send these headers. This affects cross-SDK interoperability.

Request

Please implement Mcp-Method and Mcp-Name header support per SEP-2243 to ensure cross-SDK compatibility.