Agent-Native/runtime/mcp/fakeserver.go

package mcp

// 本文件是跨测试二进制复用的最小 MCP fake server（stdio JSON-RPC）。
// 测试以「自身可执行文件 + AGENT_NATIVE_TEST_MCP_STDIO=1」re-exec 方式拉起，
// 供真实传输链路测试使用；非测试代码不得调用。

import (
	"bufio"
	"encoding/json"
	"os"
	"time"
)

// RunFakeServer 在 stdin/stdout 上运行最小 MCP server（echo / boom / 未知方法），
// 直到 stdin 关闭。测试二进制在 TestMain 的 re-exec 分支调用。
func RunFakeServer() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Buffer(make([]byte, 1<<20), 1<<20)
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()
	for scanner.Scan() {
		var req rpcRequest
		if err := json.Unmarshal(scanner.Bytes(), &req); err != nil {
			continue
		}
		if req.ID == 0 {
			continue // 通知帧
		}
		resp := fakeServerHandle(req)
		body, _ := json.Marshal(resp)
		w.Write(body)
		w.WriteByte('\n')
		w.Flush()
	}
}

func fakeServerHandle(req rpcRequest) rpcResponse {
	respond := func(result any) rpcResponse {
		raw, _ := json.Marshal(result)
		return rpcResponse{JSONRPC: "2.0", ID: &req.ID, Result: raw}
	}
	fail := func(code int, msg string) rpcResponse {
		return rpcResponse{JSONRPC: "2.0", ID: &req.ID, Error: &rpcError{Code: code, Message: msg}}
	}
	switch req.Method {
	case "initialize":
		// 协商：取(客户端请求, 自身上限)的较小者（ISO 日期字典序可比）；
		// AGENT_NATIVE_TEST_MCP_VERSION 可压低上限以测回落路径。
		own := ProtocolVersion
		if v := os.Getenv("AGENT_NATIVE_TEST_MCP_VERSION"); v != "" {
			own = v
		}
		negotiated := own
		var p initializeParams
		if req.Params != nil {
			raw, _ := json.Marshal(req.Params)
			_ = json.Unmarshal(raw, &p)
			if p.ProtocolVersion != "" && p.ProtocolVersion < negotiated {
				negotiated = p.ProtocolVersion
			}
		}
		return respond(initializeResult{
			ProtocolVersion: negotiated,
			ServerInfo:      clientInfo{Name: "fake-mcp", Version: "0"},
		})
	case "tools/list":
		return respond(toolsListResult{Tools: fakeServerTools()})
	case "tools/call":
		var p callToolParams
		if req.Params != nil {
			raw, _ := json.Marshal(req.Params)
			_ = json.Unmarshal(raw, &p)
		}
		switch p.Name {
		case "echo":
			var args struct {
				Text string `json:"text"`
			}
			_ = json.Unmarshal(p.Arguments, &args)
			return respond(callToolResult{Content: []contentBlock{{Type: "text", Text: "echo: " + args.Text}}})
		case "boom":
			return respond(callToolResult{
				Content: []contentBlock{{Type: "text", Text: "boom failed"}},
				IsError: true,
			})
		case "slow":
			time.Sleep(2 * time.Second)
			return respond(callToolResult{Content: []contentBlock{{Type: "text", Text: "slow done"}}})
		case "need_input":
			// 2026-07-28 协议级 input_required：tasks/update 投递后重试得终结果。
			if input, ok := fakeTaskInputs()["task-1"]; ok {
				fakeTaskInputs()["task-1"] = ""
				return respond(callToolResult{Content: []contentBlock{{Type: "text", Text: "答案已收到: " + input}}})
			}
			return respond(callToolResult{
				Content:    []contentBlock{{Type: "text", Text: "要答案"}},
				ResultType: "input_required",
				TaskID:     "task-1",
			})
		case "legacy_ask":
			return respond(callToolResult{Content: []contentBlock{{Type: "input_required", Text: "选一个颜色"}}})
		default:
			return fail(-32602, "unknown tool "+p.Name)
		}
	case "tasks/update":
		var p struct {
			TaskID string `json:"taskId"`
			Input  string `json:"input"`
		}
		if req.Params != nil {
			raw, _ := json.Marshal(req.Params)
			_ = json.Unmarshal(raw, &p)
		}
		fakeTaskInputs()[p.TaskID] = p.Input
		return respond(map[string]any{"ok": true})
	case "tasks/get":
		var p struct {
			TaskID string `json:"taskId"`
		}
		if req.Params != nil {
			raw, _ := json.Marshal(req.Params)
			_ = json.Unmarshal(raw, &p)
		}
		return respond(taskResult{TaskID: p.TaskID, Status: "running"})
	case "tasks/cancel":
		var p struct {
			TaskID string `json:"taskId"`
		}
		if req.Params != nil {
			raw, _ := json.Marshal(req.Params)
			_ = json.Unmarshal(raw, &p)
		}
		delete(fakeTaskInputs(), p.TaskID)
		return respond(map[string]any{"ok": true})
	default:
		return fail(-32601, "method not found: "+req.Method)
	}
}

// fakeTaskInputs 是 need_input 工具的任务输入存储（进程内）。
func fakeTaskInputs() map[string]string {
	return taskInputStore
}

var taskInputStore = map[string]string{}

func fakeServerTools() []toolInfo {
	return []toolInfo{
		{
			Name:        "echo",
			Description: "Echo the text back",
			InputSchema: json.RawMessage(`{"type":"object","required":["text"],"properties":{"text":{"type":"string"}}}`),
		},
		{
			Name:        "boom",
			Description: "Always fails",
			InputSchema: json.RawMessage(`{"type":"object","properties":{}}`),
		},
		{
			Name:        "slow",
			Description: "Responds after a delay",
			InputSchema: json.RawMessage(`{"type":"object","properties":{}}`),
		},
		{
			Name:        "need_input",
			Description: "Requires user input (2026-07-28 resultType)",
			InputSchema: json.RawMessage(`{"type":"object","properties":{}}`),
		},
		{
			Name:        "legacy_ask",
			Description: "Requires user input (legacy content block)",
			// 故意无 InputSchema：触发 manager 的合成默认 schema 路径。
		},
	}
}

// FakeServerEnv 是拉起 fake server 的环境变量名。
const FakeServerEnv = "AGENT_NATIVE_TEST_MCP_STDIO"