如何使用MCP开发一个客户端和服务端
一、MCP和API以及Function Call核心概念对比
特性 | API | Function Call | MCP (Model Context Protocol) | 定位 | 通用应用程序接口 | 大模型原生扩展能力 | 标准化模型-服务交互协议 | 耦合度 | 与具体服务绑定 | 与模型强绑定 (如 GPT-4-turbo) | 与模型解耦,跨平台通用 | 交互模式 | 直接请求-响应 | 模型生成结构化调用建议 | JSON-RPC 2.0 标准化通信 | 典型场景 | 数据集成、微服务通信 | 简单实时操作 (天气/订单查询) | 复杂异步任务 & 跨系统整合 | 二、 MCP 协议
1. 什么是MCP协议
模型上下文协议(Model Context Protocol)是一种专为大语言模型设计的标准化协议,它允许LLM以安全、一致的方式与外部系统交互。MCP协议常被描述为"AI的USB-C接口",提供了一种统一的方式连接LLM与它们可以使用的资源。
MCP协议的核心功能包括:
- • 资源(Resources):类似于GET端点,用于将信息加载到LLM的上下文中
- • 工具(Tools):类似于POST端点,用于执行代码或产生副作用
- • 提示(Prompts):可重用的LLM交互模板
- • 上下文(Context):提供额外的交互功能,如日志记录和进度报告
2. 核心价值
- • 标准化:统一 AI 与外部服务的交互格式,解决工具碎片化问题
- • 解耦设计:模型无需硬编码 API 逻辑,通过声明式函数描述调用服务
- • 异步支持:适用于多步骤工作流(如爬取数据→分析→存储)
3. 工作流程
MCP 大概的工作方式: Claude Desktop、Cursor 这些工具,在内部实现了 MCP Client,然后MCP Client 通过标准的 MCP 协议和 MCP Server 进行交互,由各种三方开发者提供的 MCP Server 负责实现各种和三方资源交互的逻辑,比如访问数据库、浏览器、本地文件,最终再通过 标准的 MCP 协议返回给 MCP Client,最终给用户进行展示。
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L14,7 L9,1 Z"></path></marker></defs><defs><marker orient="auto" markerHeight="40" markerWidth="60" refY="15" refX="15" id="sequencenumber" ><circle r="6" cy="15" cx="15"></circle></marker></defs><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="80" x="214">“查询北京天气”</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="123" x2="351" y1="123" x1="76"></line><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="138" x="356">解析意图,生成MCP调用</text><path marker-end="url(#arrowhead)" stroke="none" stroke-width="2" d="M 356,173 C 416,163 416,203 356,193"></path><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="218" x="591">{ "function": "get_weather", "params": {"city":"北京"} }</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="261" x2="825" y1="261" x1="356"></line><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="276" x="928">调用天气API</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="311" x2="1025" y1="311" x1="830"></line><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="326" x="931">返回原始数据</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="361" x2="833" y1="361" x1="1028"></line><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="376" x="594">{ "temperature": "22°C", "condition": "晴" }</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="411" x2="359" y1="411" x1="828"></line><text dy="1em" alignment-baseline="middle" dominant-baseline="middle" text-anchor="middle" y="426" x="217">“北京今天晴天,气温22°C”</text><line marker-end="url(#arrowhead)" stroke="none" stroke-width="2" y2="469" x2="79" y1="469" x1="354"></line></svg>
复制代码 3. 代码实现mcp客户端和服务端
现在python编写mcp server和mcp client的有两个分别是FastMCP 和MCP,其中MCP是官方的pythonsdk,这两个之间的关系是官方收编了FastMCP的第一个版本的包,但官方集成的是 fastmcp 的 v1.0 版本。然而,jlowin 继续开发 fastmcp,还发布了 v2.0 版本,其中包含代理和客户端采样等新功能。以下的演示以官方版本MCP为例,
安装:uv add "mcp[cli]” 或者pip install "mcp[cli]”
(1) MCP 服务端
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg>from mcp.server.fastmcp import FastMCP
- from mcp.server.fastmcp.prompts import base
- # mcp = FastMCP(name="demo",host="127.0.0.1",port=8256,sse_path="/sse") ### 启动方式为sse时使用
- mcp = FastMCP()
- @mcp.tool()
- def add_2_numbers(a: int, b: int) -> int:
- """两个数字相加"""
- return a + b
- @mcp.resource("config://app")
- def get_config() -> str:
- """Static configuration data"""
- return "App configuration here"
- @mcp.prompt()
- def debug_error(error: str) -> list[base.Message]:
- return [
- base.UserMessage("I'm seeing this error:"),
- base.UserMessage(error),
- base.AssistantMessage("I'll help debug that. What have you tried so far?"),
- @mcp.tool()
- def multiply_2_numbers(a: int, b: int):
- """两个数字相乘"""
- return a * b
- if __name__ == "__main__":
- # mcp.run(transport='sse') ## 启动方式为sse
- mcp.run(transport='stdio') ## 启动方式为stdio
复制代码 解释:
- • Tools(工具)是MCP中最常用的功能之一,它允许LLM执行特定的操作或函数。使用@mcp.tool()装饰器可以轻松将Python函数转换为LLM可调用的工具:
- • Resources(资源)用于向LLM提供数据和上下文信息。与工具不同,资源主要用于读取数据而非执行操作
- • Prompts(提示)允许您创建可重用的提示模板,这些模板可以被参数化并用于标准化LLM交互
简单验证服务端功能可以通过mcp dev server.py进入界面检测
(2) MCP 客户端
MCP客户端一般分别按照服务端的stdio和sse分别写了两个,具体融合的最后修改一下即可。
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg>import asyncio
- import json
- import re
- from contextlib import AsyncExitStack
- from typing import Optional
- from lxml import etree
- from mcp import ClientSession, StdioServerParameters, stdio_client
- from mcp.client.sse import sse_client
- from openai import AsyncOpenAI
- class Stdio_MCPClient():
- def __init__(self,api_key, base_url, model):
- self.session: Optional[ClientSession] = None
- self.exit_stack = AsyncExitStack()
- self.client = AsyncOpenAI(api_key=api_key, base_url=base_url)
- self.model = model
- self.message = []
- with open("MCP_Prompt.txt", "r", encoding="utf-8") as f:
- self.system_prompt = f.read()
- async def connect_to_stdio_server(self, mcp_name, command,args,env={}):
- server_params = StdioServerParameters(
- command=command,
- args=args,
- env=env
- )
- stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
- self.stdio,self.write = stdio_transport
- self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
- await self.session.initialize()
- response = await self.session.list_tools()
- tools = response.tools
- print(f"成功链接到{mcp_name}服务,对应的tools:",[tool.name for tool in tools])
- self.available_tools = [{
- "type": "function",
- "function": {
- "name": tool.name,
- "description": tool.description,
- "parameters": tool.inputSchema
- }
- } for tool in response.tools]
- async def process_query(self, query: str, stream: bool = False):
- # self.message.append({"role": "system", "content": self.system_prompt})
- self.message.append({"role": "user", "content": query})
- response = await self.client.chat.completions.create(
- model=self.model,
- messages=self.message,
- tools=self.available_tools
- )
- final_text = []
- assistant_message = response.choices[0].message
- while assistant_message.tool_calls:
- for tool_call in assistant_message.tool_calls:
- tool_name = tool_call.function.name
- tool_args = json.loads(tool_call.function.arguments)
- result = await self.session.call_tool(tool_name, tool_args)
- print(f"calling tools {tool_name},wirh args {tool_args}")
- print("Result:", result.content[0].text)
- self.message.extend([
- {
- "role": "assistant",
- "content": None,
- "tool_calls": [tool_call]
- },
- {
- "role": "tool",
- "content": result.content[0].text,
- "tool_call_id": tool_call.id
- }
- ])
- response = await self.client.chat.completions.create(
- model=self.model,
- messages=self.message,
- tools=self.available_tools,
- max_tokens=8048
- )
- assistant_message = response.choices[0].message
- content = assistant_message.content
- final_text.append(content)
- return "\n".join(final_text)
- async def chat_loop(self,stream_mode=True):
- self.message = []
- while True:
- try:
- query = input("\nQuery: ").strip()
- if query.lower() == 'quit':
- break
- if query.strip() == '':
- continue
- response = await self.process_query(query, stream=stream_mode)
- print("\nAI:", response)
- except Exception as e:
- print(f"\nError: {str(e)}")
- async def cleanup(self):
- await self.exit_stack.aclose()
- async def main():
- with open("config.json", "r") as f:
- config = json.load(f)
- client = Stdio_MCPClient(config["llm"]["api_key"], config["llm"]["base_url"], config["llm"]["model"])
- try:
- env = {}
- await client.connect_to_stdio_server("testserver","python",["server.py",],{})
- await client.chat_loop()
- except Exception as e:
- print(e)
- finally:
- await client.cleanup()
- if __name__ == '__main__':
- asyncio.run(main())
复制代码- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg>import asyncio
- import json
- import re
- from contextlib import AsyncExitStack
- from typing import Optional
- from lxml import etree
- from mcp import ClientSession, StdioServerParameters, stdio_client
- from mcp.client.sse import sse_client
- from openai import AsyncOpenAI
- class SSE_MCPClient():
- def __init__(self,api_key, base_url, model):
- self.session: Optional[ClientSession] = None
- self.exit_stack = AsyncExitStack()
- self.client = AsyncOpenAI(api_key=api_key, base_url=base_url)
- self.model = model
- self.message = []
- with open("MCP_Prompt.txt", "r", encoding="utf-8") as f:
- self.system_prompt = f.read()
- async def connect_to_sse_server(self, mcp_name, server_url,headers=None):
- self.service = [{
- "name": mcp_name,
- "url": server_url,
- "headers": headers
- }]
- sse_transport = await self.exit_stack.enter_async_context(sse_client(server_url, headers,timeout=30,sse_read_timeout=30))
- self.sse,self.write = sse_transport
- self.session = await self.exit_stack.enter_async_context(ClientSession(self.sse, self.write))
- await self.session.initialize()
- response = await self.session.list_tools()
- tools = response.tools
- print(f"成功链接到{mcp_name}服务,对应的tools:",[tool.name for tool in tools])
- self.available_tools = [{
- "type": "function",
- "function": {
- "name": tool.name,
- "description": tool.description,
- "parameters": tool.inputSchema
- }
- } for tool in response.tools]
- async def reconnect_sse_server(self):
- for service in self.service:
- mcp_name = service["name"]
- server_url = service["url"]
- headers = service.get("headers", None)
- sse_transport = await self.exit_stack.enter_async_context(sse_client(server_url, headers))
- self.sse, self.write = sse_transport
- self.session = await self.exit_stack.enter_async_context(ClientSession(self.sse, self.write))
- await self.session.initialize()
- print(f"重新成功链接到 {mcp_name} 服务")
-
- async def process_query(self, query: str, stream: bool = False):
- # self.message.append({"role": "system", "content": self.system_prompt})
- self.message.append({"role": "user", "content": query})
- response = await self.client.chat.completions.create(
- model=self.model,
- messages=self.message,
- tools=self.available_tools
- )
- final_text = []
- assistant_message = response.choices[0].message
- while assistant_message.tool_calls:
- for tool_call in assistant_message.tool_calls:
- tool_name = tool_call.function.name
- tool_args = json.loads(tool_call.function.arguments)
- await self.reconnect_sse_server()
- result = await self.session.call_tool(tool_name, tool_args)
- print(f"calling tools {tool_name},wirh args {tool_args}")
- print("Result:", result.content[0].text)
- self.message.extend([
- {
- "role": "assistant",
- "content": None,
- "tool_calls": [tool_call]
- },
- {
- "role": "tool",
- "content": result.content[0].text,
- "tool_call_id": tool_call.id
- }
- ])
- response = await self.client.chat.completions.create(
- model=self.model,
- messages=self.message,
- tools=self.available_tools,
- max_tokens=8048
- )
- assistant_message = response.choices[0].message
- content = assistant_message.content
- final_text.append(content)
- return "\n".join(final_text)
- async def chat_loop(self,stream_mode=True):
- self.message = []
- while True:
- try:
- query = input("\nQuery: ").strip()
- if query.lower() == 'quit':
- break
- if query.strip() == '':
- continue
- response = await self.process_query(query, stream=stream_mode)
- print("\nAI:", response)
- except Exception as e:
- print(f"\nError: {str(e)}")
- async def cleanup(self):
- await self.exit_stack.aclose()
- async def main():
- with open("config.json", "r") as f:
- config = json.load(f)
- client = Stdio_MCPClient(config["llm"]["api_key"], config["llm"]["base_url"], config["llm"]["model"])
- try:
- await client.connect_to_sse_server(mcp_name="test", server_url="https://127.0.0.1:7860/sse")
- await client.chat_loop()
- except Exception as e:
- print(e)
- finally:
- await client.cleanup()
- if __name__ == '__main__':
- asyncio.run(main())
复制代码 注意: sse链接,我增加了一个reconnect_sse_server 函数,主要原因是sse链接过程中过2分钟会自然断开,不论什么办法都无法处理,因此增加这样一个操作。
(3)版本的自然更新
有了上面两种客户端的连接方法,自然而然结合两个就可以做到同时结合sse和stdio的方法只需要增加一个分别调用的方法即可,后续代码微微改动便可使用。
当然官方的MCP也是在不段更新的,看了官方有发布Streamable HTTP Transport ,这种方式在取代sse,以及通过with来启动执行服务的更新等等,一些简单的更新参考下面,更多更新可以前往github上看- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg>from mcp.server.fastmcp import FastMCP
- # Stateful server (maintains session state)
- mcp = FastMCP("StatefulServer")
- # Stateless server (no session persistence)
- mcp = FastMCP("StatelessServer", stateless_http=True)
- # Stateless server (no session persistence, no sse stream with supported client)
- mcp = FastMCP("StatelessServer", stateless_http=True, json_response=True)
- # Run server with streamable_http transport
- mcp.run(transport="streamable-http")
复制代码 其余高级用法可参考页面:https://github.com/modelcontextprotocol/python-sdk#advanced-usage
三、典型应用场景
1. MCP 适用场景
- • 企业系统整合 将 CRM/ERP 封装为 MCP 服务,供多个 Agent 安全调用
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg># MCP 连接数据库示例
- @app.post("/mcp")
- def query_database(request: dict):
- if request["function"] == "get_user_orders":
- user_id = request["parameters"]["user_id"]
- # 执行SQL查询 (伪代码)
- return {"orders": db.query(f"SELECT * FROM orders WHERE user_id={user_id}")}
复制代码 - • 跨平台自动化 组合 GitHub + Slack 的 MCP 服务实现 CI/CD 流程:
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg># 自动化工作流:提交代码→构建→通知
- def ci_cd_pipeline():
- call_mcp("github", {"action": "pull_code", "repo": "my-app"})
- build_result = call_mcp("jenkins", {"job": "build"})
- call_mcp("slack", {"channel": "dev-team", "message": f"构建结果:{build_result}"})
复制代码 2. Function Call 适用场景
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg># 简单实时查询(无需MCP)
- def get_stock_price(symbol: str):
- return yahoo_finance_api(symbol)
- # 注册函数到模型
- functions = [{
- "name": "get_stock_price",
- "parameters": {"symbol": {"type": "string"}}
- }]
- # 模型直接调用
- response = model.generate("AAPL当前股价?", functions=functions)
- if response.function_call:
- print(get_stock_price(response.function_call.arguments["symbol"]))
复制代码 3. 传统 API 调用
- <svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" width="45px" height="13px" viewBox="0 0 450 130">
- <ellipse cx="50" cy="65" rx="50" ry="52" stroke="rgb(220,60,54)" stroke-width="2" fill="rgb(237,108,96)"></ellipse>
- <ellipse cx="225" cy="65" rx="50" ry="52" stroke="rgb(218,151,33)" stroke-width="2" fill="rgb(247,193,81)"></ellipse>
- <ellipse cx="400" cy="65" rx="50" ry="52" stroke="rgb(27,161,37)" stroke-width="2" fill="rgb(100,200,86)"></ellipse>
- </svg># 直接调用 REST API(无AI参与)
- import requests
- def fetch_weather(city: str):
- response = requests.get(f"https://api.weather.com/v1/{city}")
- return response.json()["temperature"]
复制代码 四、技术选型建议
场景 | 推荐方案 | 原因 | 简单同步任务(天气/股价查询) | Function Call | 低延迟,与模型紧密集成 | 跨系统异步任务(数据分析流水线) | MCP | 标准化协议支持复杂工作流 | 企业内部系统暴露服务 | MCP | 统一认证 + 访问控制 | 第三方公共服务调用 | API + Function Call | 无需额外协议层 | 关键结论:MCP 的核心价值在于建立企业级 AI 基础设施。当系统需要连接多个异构数据源、要求严格的协议标准化或涉及长周期任务时,MCP 是优于 Function Call 的选择。
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