Python aiohttp 全面指南：异步HTTP客户端/服务器框架

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什么是 aiohttp？

aiohttp 是一个基于 Python asyncio 的异步 HTTP 客户端/服务器框架，专为高性能网络编程设计。它提供了：

1. 异步 HTTP 客户端（类似异步版 requests）
2. 异步 HTTP 服务器（类似异步版 Flask/Django）
3. 完整的 WebSocket 支持
4. 高效的连接池管理

核心优势

基础用法 - HTTP客户端

安装

pip install aiohttp

基本GET请求

import aiohttp
import asyncio

async def main():
    async with aiohttp.ClientSession() as session:
        async with session.get('https://api.example.com/data') as response:
            print("状态码:", response.status)
            print("响应内容:", await response.text())

asyncio.run(main())

POST请求示例

async def post_example():
    async with aiohttp.ClientSession() as session:
        # 表单数据
        async with session.post(
            'https://httpbin.org/post', 
            data={'key': 'value'}
        ) as response:
            print(await response.json())
        
        # JSON数据
        async with session.post(
            'https://api.example.com/users',
            json={'name': 'Alice', 'age': 30}
        ) as response:
            print(await response.json())

高级用法

并发请求

async def fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.text()

async def concurrent_requests():
    urls = [
        'https://api.example.com/item/1',
        'https://api.example.com/item/2',
        'https://api.example.com/item/3'
    ]
    
    tasks = [fetch(url) for url in urls]
    results = await asyncio.gather(*tasks)
    
    for url, content in zip(urls, results):
        print(f"{url}: {content[:50]}...")

asyncio.run(concurrent_requests())

超时控制

async def timeout_example():
    timeout = aiohttp.ClientTimeout(total=5)  # 5秒总超时
    
    async with aiohttp.ClientSession(timeout=timeout) as session:
        try:
            async with session.get('https://slow-api.example.com') as response:
                return await response.text()
        except asyncio.TimeoutError:
            print("请求超时!")

流式处理大响应

async def stream_response():
    async with aiohttp.ClientSession() as session:
        async with session.get('https://large-file.example.com') as response:
            with open('large_file.txt', 'wb') as f:
                async for chunk in response.content.iter_chunked(1024):
                    f.write(chunk)
                    print(f"已接收 {len(chunk)} 字节")

服务器端开发

基本HTTP服务器

from aiohttp import web

async def handle(request):
    name = request.match_info.get('name', "World")
    return web.Response(text=f"Hello, {name}!")

app = web.Application()
app.add_routes([
    web.get('/', handle),
    web.get('/{name}', handle)
])

if __name__ == '__main__':
    web.run_app(app, port=8080)

REST API示例

async def get_users(request):
    users = [{'id': 1, 'name': 'Alice'}, {'id': 2, 'name': 'Bob'}]
    return web.json_response(users)

async def create_user(request):
    data = await request.json()
    # 实际应用中这里会保存到数据库
    return web.json_response({'id': 3, **data}, status=201)

app = web.Application()
app.add_routes([
    web.get('/api/users', get_users),
    web.post('/api/users', create_user)
])

WebSocket服务器

async def websocket_handler(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)
    
    async for msg in ws:
        if msg.type == aiohttp.WSMsgType.TEXT:
            if msg.data == 'close':
                await ws.close()
            else:
                await ws.send_str(f"ECHO: {msg.data}")
        elif msg.type == aiohttp.WSMsgType.ERROR:
            print('WebSocket连接异常关闭')
    
    return ws

app.add_routes([web.get('/ws', websocket_handler)])

进阶扩展

中间件示例

async def auth_middleware(app, handler):
    async def middleware(request):
        # 验证API密钥
        if request.headers.get('X-API-Key') != 'SECRET_KEY':
            return web.json_response({'error': 'Unauthorized'}, status=401)
        return await handler(request)
    return middleware

app = web.Application(middlewares=[auth_middleware])

HTTP/2客户端支持

async def http2_request():
    conn = aiohttp.TCPConnector(force_close=True, enable_cleanup_closed=True)
    async with aiohttp.ClientSession(connector=conn) as session:
        async with session.get(
            'https://http2.akamai.com/',
            headers={'accept': 'text/html'}
        ) as response:
            print("HTTP版本:", response.version)
            print("内容:", await response.text()[:200])

性能优化配置

# 自定义连接器配置
connector = aiohttp.TCPConnector(
    limit=100,  # 最大并发连接数
    limit_per_host=20,  # 单主机最大连接数
    ssl=False,  # 禁用SSL验证（仅用于测试）
    force_close=True  # 避免连接延迟关闭
)

# 自定义会话配置
session = aiohttp.ClientSession(
    connector=connector,
    timeout=aiohttp.ClientTimeout(total=30),
    headers={'User-Agent': 'MyApp/1.0'},
    cookie_jar=aiohttp.CookieJar(unsafe=True)
)

最佳实践

1. 重用ClientSession：避免为每个请求创建新会话
2. 使用连接池：合理配置TCPConnector参数
3. 超时设置：总是配置合理的超时时间
4. 资源清理：使用async with确保资源释放
5. 错误处理：捕获并处理常见网络异常

   try:
       async with session.get(url) as response:
           response.raise_for_status()
           return await response.json()
   except aiohttp.ClientError as e:
       print(f"请求错误: {e}")
   

完整示例

import aiohttp
import asyncio
from aiohttp import web

# 客户端示例
async def fetch_data():
    async with aiohttp.ClientSession() as session:
        # 并发请求多个API
        urls = [
            'https://jsonplaceholder.typicode.com/posts/1',
            'https://jsonplaceholder.typicode.com/comments/1',
            'https://jsonplaceholder.typicode.com/albums/1'
        ]
        
        tasks = []
        for url in urls:
            tasks.append(session.get(url))
        
        responses = await asyncio.gather(*tasks)
        
        results = []
        for response in responses:
            results.append(await response.json())
        
        return results

# 服务器示例
async def handle_index(request):
    return web.Response(text="Welcome to aiohttp server!")

async def handle_api(request):
    data = await fetch_data()
    return web.json_response(data)

# 创建应用
app = web.Application()
app.add_routes([
    web.get('/', handle_index),
    web.get('/api', handle_api)
])

# 启动服务器
async def start_server():
    runner = web.AppRunner(app)
    await runner.setup()
    site = web.TCPSite(runner, 'localhost', 8080)
    await site.start()
    print("Server running at http://localhost:8080")
    
    # 保持运行
    while True:
        await asyncio.sleep(3600)  # 每小时唤醒一次

if __name__ == '__main__':
    asyncio.run(start_server())

总结

aiohttp 是 Python 异步生态中处理 HTTP 通信的首选工具，它提供了：

1. 高效客户端：用于高性能爬虫、API调用
2. 轻量级服务器：构建高性能Web服务和API
3. WebSocket支持：实现实时双向通信
4. 连接池管理：优化资源利用率

通过合理利用 aiohttp 的异步特性，开发者可以轻松构建出能够处理数万并发连接的高性能网络应用，同时保持代码的简洁性和可维护性。