08-27-周三_17-09-29
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Python/Python网络编程/Socket编程基础.md
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Python/Python网络编程/Socket编程基础.md
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# 核心概念
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- Socket（套接字）：网络通信的端点，支持不同主机间的进程通信。
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- 协议类型：
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- TCP：
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- UDP：
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- 地址族：...
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# TCP 协议工作流程
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## 服务端
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**实现步骤：**
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1. 创建 Socket 对象：`socket.socket(socket.AF_INET, socket.SOCK_STREAM)`
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2. 绑定地址与端口：`bind(('0.0.0.0', 12345))`（0.0.0.0 表示监听所有 IP）
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3. 监听连接：`listen(5)` （参数为最大等待连接）
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4. 接收连接：`accept()` 返回客户端 Socket 和地址
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5. 数据交换：`send()` 和 `recv()` 方法收发数据
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6. 关闭连接：`close()` 释放资源
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## 客户端
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**实现步骤：**
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1. 创建 Socket 对象：`socket.socket(socket.AF_INET, socket.SOCK_STREAM)`
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2. 连接服务器：`connect(('127.0.0.1', 12345))`
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3. 数据交换：同服务器端 `send()` 和 `recv()`
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## 示例代码
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```python
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# server.py 代码
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import socket
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(("127.0.0.1", 8080))
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server.listen(5)
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conn, client_addr = server.accept()
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print(conn, client_addr, sep="\n")
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from_client_data = conn.recv(1024)
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print(from_client_data.decode("utf-8"))
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conn.send(from_client_data.upper())
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conn.close()
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server.close()
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# client.py 代码
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import socket
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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client.connect(("127.0.0.1", 8080))
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client.send("hello".encode("utf-8"))
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from_server_data = client.recv(1024)
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print(from_server_data)
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client.close()
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```
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# UDP 协议工作流程
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<img src="套接字的工作流程/socket编程2.png" alt="img-socket编程2" style="zoom:80%;" />
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## 服务端
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**实现步骤：**
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1. 创建 Socket 对象：`socket.socket(socket.AF_INET, socket.SOCK_DGRAM)`
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2. 绑定地址与端口：`bind(('0.0.0.0', 12345))`
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3. 数据交换：`sendto()` 和 `recvfrom()` 方法收发数据
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## 客户端
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**实现步骤：**
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1. 创建 Socket 对象：`socket.socket(socket.AF_INET, socket.SOCK_DGRAM)`
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2. 数据交换：同服务器端 `sendto()` 和 `recvfrom()`
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## 示例代码
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```python
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# server.py
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import socket
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server = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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server.bind(("127.0.0.1", 8000))
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from_client_data, addr = server.recvfrom(1024)
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print(from_client_data, addr, sep="\n")
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server.sendto(from_client_data.upper(), addr)
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server.close()
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# client.py
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import socket
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client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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client.sendto("hello".encode("utf-8"), ("127.0.0.1", 8000))
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from_server_data, addr = client.recvfrom(1024)
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print(from_server_data, addr, sep="\n")
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client.close()
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```
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# 相关方法
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服务端套接字函数
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| 函数 | 含义 |
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| :---------- | :-------------------------------------------- |
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| `s.bind()` | 绑定(主机,端口号)到套接字 |
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| `s.listen()` | 开始 TCP 监听 |
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| `s.accept()` | 被动接受 TCP 客户的连接,(阻塞式)等待连接的到来 |
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客户端套接字函数
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| 函数 | 含义 |
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| :-------------- | :------------------------------------------------------- |
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| `s.connect()` | 主动初始化 TCP 服务器连接 |
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| `s.connect_ex()` | `connect()`函数的扩展版本,出错时返回出错码,而不是抛出异常 |
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公共用途的套接字函数
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| 函数 | 含义 |
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| :--------------- | :------------------------------------------------------------ |
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| `s.recv()` | 接收TCP数据 |
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| `s.send()` | 发送TCP数据(send在待发送数据量大于己端缓存区剩余空间时,数据丢失,不会发完) |
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| `s.sendall()` | 发送完整的TCP数据(本质就是循环调用send,sendall在待发送数据量大于己端缓存区剩余空间时,数据不丢失,循环调用send直到发完) |
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| `s.recvfrom()` | 接收UDP数据 |
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| `s.sendto()` | 发送UDP数据 |
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| `s.getpeername()` | 连接到当前套接字的远端的地址 |
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| `s.getsockname()` | 当前套接字的地址 |
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| `s.getsockopt()` | 返回指定套接字的参数 |
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| `s.setsockopt()` | 设置指定套接字的参数 |
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| `s.close()` | 关闭套接字 |
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面向锁的套接字方法
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| 函数 | 含义 |
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| :--------------- | :---------------------------- |
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| `s.setblocking()` | 设置套接字的阻塞与非阻塞模式 |
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| `s.settimeout()` | 设置阻塞套接字操作的超时时间 |
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| `s.gettimeout()` | 得到阻塞套接字操作的超时时间 |
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面向文件的套接字的函数
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| 函数 | 含义 |
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| :------------ | :---------------------------- |
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| `s.fileno()` | 套接字的文件描述符 |
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| `s.makefile()` | 创建一个与该套接字相关的文件 |
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# 粘包问题
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## 原因
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**TCP 协议特性**
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- 流式传输：TCP 将数据视为连续字节流，不会自动分割数据包，导致接收端无法区分消息边界
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- 缓冲区机制：发送端和接收端均存在缓冲区，发送端可能将多个小数据包合并发送，接收端可能将多次接收的数据合并处理
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- Nagle算法优化：TCP 为提高传输效率，会合并多个小数据包（例如间隔短且数据量小）后发送
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**代码逻辑缺陷**
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- 连续发送：在未明确分隔消息的情况下连续调用 `send()`，导致数据在缓冲区中合并
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- 接收不完整：接收端 `recv()` 方法未动态调整缓冲区大小，导致部分数据残留
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## 示例代码
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### Demo1
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通过 **连续发送小数据包** 和 **接收缓冲区合并** 的场景模拟粘包现象：
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```python
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# 服务端代码（连续发送两次数据）
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import socket
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(('0.0.0.0', 8888))
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server.listen(5)
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print("服务端已启动，等待客户端连接...")
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conn, addr = server.accept()
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print(f"客户端 {addr} 已连接")
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try:
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# 连续发送两次数据（未处理粘包）
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conn.send(b'Hello') # 第一次发送
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conn.send(b'World') # 第二次发送（可能合并到缓冲区）
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except KeyboardInterrupt:
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print("服务端主动终止")
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finally:
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conn.close()
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server.close()
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# 客户端代码（一次性接收数据）
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import socket
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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client.connect(('127.0.0.1', 8888))
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try:
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# 一次性接收数据（可能合并两次发送的内容）
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data = client.recv(1024)
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print(f"接收到的数据: {data.decode()}") # 预期输出可能是 'HelloWorld'
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except ConnectionResetError:
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print("服务端已关闭连接")
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finally:
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client.close()
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```
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**现象解释**
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1. Nagle 算法：发送端连续调用 `send()` 发送小数据包，可能将两次发送合并为一个包。
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2. 缓冲区机制：接收端 `recv(1024)` 的缓冲区较大，一次性读取了所有待接收数据
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### Demo2
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通过 **大缓冲区发送 + 小缓冲区接收** 的场景模拟接收不完整问题：
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```python
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# 服务端代码（发送 10KB 大数据包）
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import socket
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(('0.0.0.0', 8888))
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server.listen(5)
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print("服务端已启动，等待客户端连接...")
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conn, addr = server.accept()
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try:
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# 发送 10KB 数据（超过常规接收缓冲区）
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big_data = b'A' * 1024 * 10 # 10KB
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conn.sendall(big_data)
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print(f"已发送 {len(big_data)} 字节数据")
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except KeyboardInterrupt:
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print("服务端主动终止")
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finally:
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conn.close()
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server.close()
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# 客户端代码（仅接收 4KB 数据）
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import socket
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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client.connect(('127.0.0.1', 8888))
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try:
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# 设置接收缓冲区为 4KB，且仅接收一次
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partial_data = client.recv(4096) # 只接收一次
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print(f"实际接收长度: {len(partial_data)} 字节") # 输出 4096，残留 6KB 未接收
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except ConnectionResetError:
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print("服务端已关闭连接")
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finally:
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client.close()
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```
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**现象解释**
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1. TCP 流式特性：TCP 将数据视为连续字节流，无边界标识
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2. 缓冲区限制：`recv()` 方法一次性读取的字节数受参数限制，未循环接收导致残留
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## 解决方案
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固定包头法：发送端在数据前附加一个固定长度的包头，标明数据长度，接收端根据包头解析完整数据。
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### struct 模块
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把一个类型，如数字，转成固定长度的 bytes
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**常见用法**
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```python
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import struct
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# 将一个数字转化成等长度的bytes类型。
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ret = struct.pack('i', 18334)
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print(ret, len(ret))
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# 通过unpack反解回来 返回一个元组回来
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ret1 = struct.unpack('i',ret)[0]
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print(ret1)
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```
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### Demo1
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```python
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# 服务端代码（连续发送两次数据）
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import socket
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import struct
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(('0.0.0.0', 8888))
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server.listen(5)
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print("服务端已启动，等待客户端连接...")
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conn, addr = server.accept()
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print(f"客户端 {addr} 已连接")
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try:
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data = b'Hello'
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header = struct.pack("!I", len(data))
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conn.send(header + data) # 第一次发送
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data = b'World'
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header = struct.pack("!I", len(data))
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conn.send(header + data) # 第二次发送
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except KeyboardInterrupt:
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print("服务端主动终止")
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finally:
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conn.close()
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server.close()
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# 客户端代码
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import socket
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import struct
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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client.connect(('127.0.0.1', 8888))
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try:
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# 接收固定长度包头
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header = client.recv(4)
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data_size = struct.unpack("!I", header)[0]
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received_data = client.recv(data_size)
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print(f"实际接收长度: {len(received_data)} 字节")
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print(received_data)
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except ConnectionResetError:
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print("服务端已关闭连接")
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finally:
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client.close()
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```
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### Demo2
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```python
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# 服务端代码（发送 10KB 大数据包）
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import socket
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import struct
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(('0.0.0.0', 8888))
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server.listen(5)
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print("服务端已启动，等待客户端连接...")
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conn, addr = server.accept()
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try:
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# 发送 10KB 数据
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big_data = b'A' * 1024 * 10 # 10KB
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# 发送固定长度包头
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header = struct.pack("!I", len(big_data))
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conn.sendall(header + big_data)
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print(f"已发送 {len(big_data)} 字节数据")
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except KeyboardInterrupt:
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print("服务端主动终止")
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finally:
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conn.close()
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server.close()
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# 客户端代码
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import socket
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import struct
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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client.connect(('127.0.0.1', 8888))
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try:
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# 接收固定长度包头
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header = client.recv(4)
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data_size = struct.unpack("!I", header)[0]
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# 接收完整数据
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received_data = b""
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while len(received_data) < data_size:
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remaining = data_size - len(received_data)
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chunk = client.recv(min(remaining, 1024))
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if not chunk:
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break
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received_data += chunk
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print(f"实际接收长度: {len(received_data)} 字节")
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except ConnectionResetError:
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print("服务端已关闭连接")
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finally:
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client.close()
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```
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# 实践案例
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## 循环通信
|
||||
|
||||
服务端和客户端之间可以循环进行通信。
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||||
|
||||
```python
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||||
# server.py
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import socket
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||||
import struct
|
||||
|
||||
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.bind(("127.0.0.1", 8080))
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server.listen(5)
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print("服务端已启动，等待连接...")
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conn = None
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||||
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||||
try:
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while True:
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||||
conn, client_addr = server.accept()
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||||
print(f"客户端 {client_addr} 已连接")
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||||
while True:
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header = conn.recv(4)
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data_size = struct.unpack("!I", header)[0]
|
||||
received_data = b""
|
||||
while len(received_data) < data_size:
|
||||
remaining = data_size - len(received_data)
|
||||
chunk = conn.recv(min(remaining, 1024))
|
||||
if not chunk:
|
||||
break
|
||||
received_data += chunk
|
||||
if (
|
||||
not received_data
|
||||
or received_data.decode("utf-8").strip().upper() == "EXIT"
|
||||
):
|
||||
break
|
||||
print(f"收到消息: {received_data.decode('utf-8')}")
|
||||
|
||||
response = received_data.decode("utf-8").upper()
|
||||
header = struct.pack("!I", len(received_data))
|
||||
conn.send(header + response.encode("utf-8"))
|
||||
except ConnectionResetError:
|
||||
print("客户端异常断开")
|
||||
except KeyboardInterrupt:
|
||||
print("服务端主动终止")
|
||||
except Exception as e:
|
||||
print(f"未知异常: {e}")
|
||||
finally:
|
||||
if conn:
|
||||
conn.close()
|
||||
server.close()
|
||||
|
||||
|
||||
# client.py
|
||||
import socket
|
||||
import struct
|
||||
|
||||
client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
|
||||
client.connect(("127.0.0.1", 8080))
|
||||
|
||||
try:
|
||||
while True:
|
||||
msg = input("请输入消息 (输入 EXIT 退出): ")
|
||||
if not msg.strip():
|
||||
print("消息不能为空，请重新输入")
|
||||
continue
|
||||
if msg.strip().upper() == "EXIT":
|
||||
break
|
||||
header = struct.pack("!I", len(msg.encode("utf-8")))
|
||||
client.send(header + msg.encode("utf-8"))
|
||||
|
||||
header = client.recv(4)
|
||||
data_size = struct.unpack("!I", header)[0]
|
||||
received_data = b""
|
||||
while len(received_data) < data_size:
|
||||
remaining = data_size - len(received_data)
|
||||
chunk = client.recv(min(remaining, 1024))
|
||||
if not chunk: break
|
||||
received_data += chunk
|
||||
print(f"服务端返回: {received_data.decode('utf-8')}")
|
||||
except KeyboardInterrupt:
|
||||
print("客户端主动终止")
|
||||
except BrokenPipeError:
|
||||
print("服务端已关闭连接，终止发送")
|
||||
except Exception as e:
|
||||
print(f"异常 {e}")
|
||||
finally:
|
||||
client.close()
|
||||
|
||||
```
|
||||
|
||||
## 远程命令执行
|
||||
|
||||
客户端发送执行指令给服务端，服务端接收到指令并执行后将结果返回给客户端。
|
||||
|
||||
```python
|
||||
import socket
|
||||
import subprocess
|
||||
|
||||
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
|
||||
server.bind(("127.0.0.1", 8080))
|
||||
server.listen(5)
|
||||
print("服务端已启动，等待连接...")
|
||||
conn = None
|
||||
|
||||
try:
|
||||
while True:
|
||||
conn, client_addr = server.accept()
|
||||
print(f"客户端 {client_addr} 已连接")
|
||||
while True:
|
||||
cmd = conn.recv(1024)
|
||||
if not cmd or cmd.decode('utf-8').strip().upper() == 'EXIT':
|
||||
break
|
||||
print(f"收到的命令: {cmd.decode('utf-8')}")
|
||||
ret = subprocess.Popen(cmd.decode('utf-8'), shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
|
||||
correct_msg = ret.stdout.read()
|
||||
error_msg = ret.stderr.read()
|
||||
conn.send(correct_msg + error_msg)
|
||||
|
||||
except ConnectionResetError:
|
||||
print("客户端异常断开")
|
||||
except KeyboardInterrupt:
|
||||
print("服务端主动终止")
|
||||
except Exception as e:
|
||||
print(f"未知异常: {e}")
|
||||
finally:
|
||||
if conn:
|
||||
conn.close()
|
||||
server.close()
|
||||
```
|
||||
|
||||
## 时间服务端
|
||||
|
||||
```python
|
||||
# server.py
|
||||
import socket
|
||||
import time
|
||||
import struct
|
||||
|
||||
# 创建UDP套接字，设置端口复用
|
||||
server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
|
||||
server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) # 避免端口占用
|
||||
server_socket.bind(('', 8090))
|
||||
|
||||
print("时间服务器已启动，等待客户端请求...")
|
||||
|
||||
try:
|
||||
while True:
|
||||
# 接收客户端请求（空消息即可触发）
|
||||
data, client_addr = server_socket.recvfrom(1024)
|
||||
print(f"收到来自 {client_addr} 的请求")
|
||||
|
||||
# 获取当前时间并封装为二进制数据
|
||||
current_time = int(time.time()) # 获取时间戳（秒级）
|
||||
packed_time = struct.pack("!I", current_time) # 转为网络字节序的4字节数据，提升传输效率
|
||||
|
||||
# 发送时间数据
|
||||
server_socket.sendto(packed_time, client_addr)
|
||||
except KeyboardInterrupt:
|
||||
print("\n服务端主动终止")
|
||||
finally:
|
||||
server_socket.close()
|
||||
|
||||
|
||||
# client.py
|
||||
import socket
|
||||
import struct
|
||||
import time
|
||||
|
||||
# 创建UDP套接字
|
||||
client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
|
||||
server_address = ('127.0.0.1', 8090)
|
||||
|
||||
try:
|
||||
# 发送空消息触发时间请求
|
||||
client_socket.sendto(b'', server_address)
|
||||
print("已发送时间请求，等待响应...")
|
||||
|
||||
# 接收时间数据（最多等待2秒）
|
||||
client_socket.settimeout(2)
|
||||
data, _ = client_socket.recvfrom(1024)
|
||||
|
||||
# 解析时间数据
|
||||
if len(data) == 4:
|
||||
timestamp = struct.unpack("!I", data)[0] # 解析网络字节序数据
|
||||
print(f"服务器时间: {time.ctime(timestamp)}")
|
||||
else:
|
||||
print("错误：收到无效时间数据")
|
||||
except socket.timeout:
|
||||
print("请求超时，服务端未响应")
|
||||
except ConnectionRefusedError:
|
||||
print("连接被拒绝，请检查服务端是否运行")
|
||||
except KeyboardInterrupt:
|
||||
print("\n客户端主动终止")
|
||||
finally:
|
||||
client_socket.close()
|
||||
|
||||
```
|
||||
Reference in New Issue
Block a user