McpClientSession/McpServerSession: pending response entries leak when a request times out or is cancelled

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难度
3/5
预计耗时
1-2 天
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
java
领域
api, backend, testing

调研方向

先从 McpClientSession.sendRequest 和 McpServerSession.sendRequest 开始，然后与 McpStreamableServerSession.McpStreamableServerSessionStream.sendRequest 进行比较。运行指定的 McpClientSessionTests 回归测试，并为超时和取消路径添加等效覆盖；任一条件发生后 pendingResponses 为空即表示完成。

由索引模型根据 Issue 内容生成。

描述

area/client area/server area/transport bug P2

Bug description

McpClientSession.sendRequest and McpServerSession.sendRequest put an entry into pendingResponses when a request is sent, but only remove it when a response arrives or the send itself fails. If the downstream .timeout(...) fires — or the caller cancels the Mono — no cleanup hook runs, so the entry stays in pendingResponses forever (request IDs are unique per request, so it is never overwritten).

The streamable variant already cleans up after its timeout (McpStreamableServerSession.McpStreamableServerSessionStream.sendRequest calls this.pendingResponses.remove(requestId) in a doOnError after .timeout(requestTimeout)), which suggests the legacy paths missing this is an oversight.

Amplifier

KeepAliveScheduler pings every session periodically via sendRequest(PING, ...). A dead or hung session therefore accumulates one leaked entry per ping interval on both the client and the server side; long-lived sessions grow unboundedly until close().

Suggested fix

Mirror the streamable pattern in both sendRequest methods:

.timeout(this.requestTimeout)
.doOnError(e -> this.pendingResponses.remove(requestId))
.doOnCancel(() -> this.pendingResponses.remove(requestId))
.handle(...)

Removal is idempotent, and the late-response path already tolerates a missing key.

I have the fix plus a regression test (testRequestTimeoutRemovesPendingResponse in McpClientSessionTests, asserting the map is empty after a timeout) ready and will open a PR referencing this issue.

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