feat: 实现MCP工具调用链路(streamable_http) - chat中MCP作为function calling真实调用tools/call

backend/python/app/mcp_client.py

@@ -0,0 +1,187 @@
+"""
+MCP (Model Context Protocol) 客户端 —— 异步实现 streamable_http 传输。
+
+支持：
+- initialize / notifications/initialized / tools/list / tools/call 标准流程
+- streamable_http：POST JSON-RPC，响应可能是 SSE（event: message / data: {...}）或纯 JSON
+- SSE 解析兼容
+- 直连外部端点（trust_env=False，不绕容器代理）
+
+供 chat.py 在 AI 对话中把 MCP 工具暴露为 function calling，并代理执行 tools/call。
+"""
+
+import json
+import logging
+import asyncio
+from typing import Optional
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+MCP_PROTOCOL_VERSION = "2024-11-05"
+
+# 工具列表缓存（url -> (timestamp, tools)），避免同一请求内 / 短时间重复握手
+_TOOLS_CACHE: dict = {}
+_TOOLS_CACHE_TTL = 120  # 秒
+
+
+def _parse_sse(text: str):
+    """从响应文本解析 JSON-RPC 结果。兼容 SSE（data: 行）与纯 JSON。"""
+    if not text:
+        return None
+    text = text.strip()
+    # SSE 格式：多行 "event: message" / "data: {...}"
+    data_lines = []
+    for line in text.splitlines():
+        ls = line.strip()
+        if ls.startswith("data:"):
+            data_lines.append(ls[5:].strip())
+    if data_lines:
+        last = data_lines[-1]
+        try:
+            return json.loads(last)
+        except Exception:
+            pass
+    # 纯 JSON
+    try:
+        return json.loads(text)
+    except Exception:
+        return None
+
+
+async def _handshake_and_request(
+    url: str,
+    headers: dict,
+    method: str,
+    params: dict,
+    timeout: float = 30.0,
+):
+    """
+    完成一次完整 MCP 会话（initialize -> initialized -> 目标请求）。
+    返回解析后的 JSON-RPC 响应 dict，或 None。
+    """
+    base_headers = {
+        "Content-Type": "application/json",
+        "Accept": "application/json, text/event-stream",
+    }
+    base_headers.update(headers or {})
+
+    async with httpx.AsyncClient(timeout=timeout, trust_env=False) as client:
+        # 1) initialize
+        r = await client.post(
+            url,
+            headers=base_headers,
+            json={
+                "jsonrpc": "2.0",
+                "id": 1,
+                "method": "initialize",
+                "params": {
+                    "protocolVersion": MCP_PROTOCOL_VERSION,
+                    "capabilities": {},
+                    "clientInfo": {"name": "aiflow", "version": "1.0"},
+                },
+            },
+        )
+        if r.status_code >= 400:
+            logger.warning(f"[MCP] initialize 失败 {url} -> HTTP {r.status_code}")
+            return None
+        sid = r.headers.get("mcp-session-id") or r.headers.get("Mcp-Session-Id")
+        req_headers = dict(base_headers)
+        if sid:
+            req_headers["Mcp-Session-Id"] = sid
+
+        # 2) initialized 通知（不需要响应）
+        try:
+            await client.post(
+                url,
+                headers=req_headers,
+                json={"jsonrpc": "2.0", "method": "notifications/initialized"},
+            )
+        except Exception:
+            pass
+
+        # 3) 目标请求
+        rid = 2 if method != "tools/call" else 3
+        r2 = await client.post(
+            url,
+            headers=req_headers,
+            json={
+                "jsonrpc": "2.0",
+                "id": rid,
+                "method": method,
+                "params": params,
+            },
+        )
+        if r2.status_code >= 400:
+            logger.warning(f"[MCP] {method} 失败 {url} -> HTTP {r2.status_code}")
+            return None
+        return _parse_sse(r2.text)
+
+
+async def list_mcp_tools(server: dict, timeout: float = 30.0) -> list:
+    """
+    拉取 MCP 服务器的工具列表。
+    server: {url, transport_type, headers}
+    返回 MCP tools 数组（每个含 name/description/inputSchema）。
+    """
+    url = (server.get("url") or "").strip()
+    if not url:
+        return []
+    # 缓存
+    now = asyncio.get_event_loop().time()
+    cached = _TOOLS_CACHE.get(url)
+    if cached and (now - cached[0]) < _TOOLS_CACHE_TTL:
+        return cached[1]
+    try:
+        data = await _handshake_and_request(
+            url, server.get("headers") or {}, "tools/list", {}, timeout
+        )
+        tools = []
+        if data and "result" in data:
+            tools = data["result"].get("tools", []) or []
+        _TOOLS_CACHE[url] = (now, tools)
+        return tools
+    except Exception as e:
+        logger.warning(f"[MCP] 拉取工具失败 {url}: {e}")
+        return []
+
+
+async def call_mcp_tool(
+    server: dict, tool_name: str, arguments: dict, timeout: float = 60.0
+) -> str:
+    """
+    在 MCP 服务器上执行一个工具，返回可供 LLM 消费的文本结果。
+    """
+    url = (server.get("url") or "").strip()
+    if not url:
+        return f"[MCP 工具 {tool_name} 执行失败：服务端地址为空]"
+    logger.info(f"[MCP] 执行工具调用 tool={tool_name} server={server.get('name')} url={url}")
+    try:
+        data = await _handshake_and_request(
+            url,
+            server.get("headers") or {},
+            "tools/call",
+            {"name": tool_name, "arguments": arguments or {}},
+            timeout,
+        )
+        if not data:
+            return f"[MCP 工具 {tool_name} 调用失败：无响应]"
+        if "error" in data:
+            err = data["error"]
+            return f"[MCP 工具 {tool_name} 返回错误] {json.dumps(err, ensure_ascii=False)}"
+        result = data.get("result", {})
+        content = result.get("content", []) or []
+        parts = []
+        for item in content:
+            if isinstance(item, dict) and item.get("type") == "text":
+                parts.append(item.get("text", ""))
+            else:
+                parts.append(json.dumps(item, ensure_ascii=False))
+        text = "\n".join(parts).strip()
+        if result.get("isError"):
+            return f"[MCP 工具 {tool_name} 执行报错]\n{text}"
+        return text or f"[MCP 工具 {tool_name} 返回空结果]"
+    except Exception as e:
+        logger.warning(f"[MCP] 工具执行异常 {tool_name} @ {url}: {e}")
+        return f"[MCP 工具 {tool_name} 执行异常：{e}]"