Elicitation results are not checked against `requested_schema`, but the docs say they match it

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@atesgoral 已經在處理了。

開始於 2026年11月6日。

  • #669 來自 @atesgoral —— 未關閉

評估

難度
3/5
預估耗時
1-2 天
新手友好度
35/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
停滯
技術堆疊
ruby
領域
backend-api-design, security

研究方向

Start with lib/mcp/server_session.rb at create_form_elicitation, create_url_elicitation, and fulfill_input_request, then read docs/_server/elicitation.md for the documented contract. Check how the SDK represents validation errors and test these methods with the supplied invalid action and schema values. Done means invalid actions and invalid accepted content are rejected, with tests covering the stated cases.

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描述

bug

docs/_server/elicitation.md says: "Per the MCP specification, the client validates the user's input against this schema before returning it, so the content of an accept response matches the requested shape." The server does not check this.

ServerSession#create_form_elicitation (server_session.rb:209-224), #create_url_elicitation (:231-246) and #fulfill_input_request (:253-255, used by the legacy input_required shim) return the client's result as received. action is not limited to accept, decline and cancel, and content is not checked against requested_schema (types, required, enum). A buggy or non-compliant client can return wrong types or values outside an enum, and handlers that follow the docs use them as-is.

Repro

Run from the repository root with bundle exec ruby -I lib repro.rb. The stub transport plays the client's reply.

require "mcp"

class ClientReply
  def initialize(reply)
    @reply = reply
  end

  def send_request(_method, _params = nil, **)
    @reply
  end

  def send_notification(*, **)
    true
  end
end

reply = { action: "accept", content: { replicas: "lots", environment: "unlisted" } }
server = MCP::Server.new(name: "example")
session = MCP::ServerSession.new(server: server, transport: ClientReply.new(reply), session_id: "A")
session.store_client_info(client: { name: "client", version: "1" }, capabilities: { elicitation: {} })

result = session.create_form_elicitation(
  message: "Deploy settings",
  requested_schema: {
    type: "object",
    properties: {
      replicas: { type: "integer" },
      environment: { type: "string", enum: ["staging", "production"] },
    },
    required: ["replicas", "environment"],
  },
  related_request_id: 1,
)

p result

Expected: an error (or at least not an accept result), because replicas is not an integer and environment is not in the enum.

Actual: {action: "accept", content: {replicas: "lots", environment: "unlisted"}}

The same happens with an unknown action such as {action: "approve-everything"}.

Suggested fix

Check action and, for accept, check content against the flat requested_schema before returning it from these methods, and raise a validation error on a mismatch. The elicitation schema subset is small (flat object, primitive types, enum, required). If validation is out of scope, change the docs to say that handlers must validate content themselves.

主要語言
Ruby
星號
940
分支
143
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1 天 3 小時
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