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用Go语言重写Linux系统命令 – nc简化版

1. 引言

netcat，简称 nc，被誉为网络工具中的“瑞士军刀”，是网络调试与分析的利器。它的功能十分强大，然而平时我们经常使用的就是他的连通性测试功能，但是nc是被设计用来测试TCP和UDP的，对于HTTP支持不是太好，于是，我决定用 Go 语言重新实现一个简化版的 nc，专注于联通性测试功能，并扩展支持测试HTTP和Ping的连通性测试。通过这个项目，你不仅能深入学习网络编程，还能体验用 Go 语言开发系统工具的乐趣！

小目标：让我们的工具小而美，轻松搞定网络连通性调试！

2. 需求分析

在开始编写代码之前，我们需要明确工具的功能和设计目标：

• 核心功能：

  1. TCP 测试：检查指定 IP 和端口是否可建立连接，支持数据发送与接收。
  2. UDP 测试：发送 UDP 数据包并接收响应。
  3. HTTP 测试：测试指定 URL 是否可访问，支持自定义请求方法（如 GET/POST）。
  4. Ping 测试：检查目标 IP 是否可达，并测量响应时间。

• 用户体验设计：

  • 使用命令行参数指定测试类型和选项（如目标 IP、端口、超时）。
  • 错误提示清晰直观，方便排查问题。

• 性能目标：快速响应，保持简洁。

3. 项目初始化

3.1 安装开发环境

确保已安装 Go 编译器（推荐版本 ≥ 1.20）。执行以下命令检查 Go 是否可用：

go version

3.2 初始化项目

创建项目目录并初始化 Go 模块：

mkdir gonc
cd gonc
go mod init gonc

项目结构：

gonc/
├── main.go        # 入口文件
├── tcp.go         # TCP 测试模块
├── udp.go         # UDP 测试模块
├── http.go        # HTTP 测试模块
├── ping.go        # Ping 测试模块
└── go.mod         # 依赖管理文件

4. 模块实现

4.1 实现 TCP 测试功能

在 tcp.go 中编写代码，建立 TCP 连接，发送和接收数据：

package myncimport ("fmt""log""net""time"
)// TestTCP 测试TCP端口是否连通，并支持发送和接收数据
func FireTCP(ip string, port, timeout int, data string) error {address := fmt.Sprintf("%s:%d", ip, port)// 设置连接超时时间conn, err := net.DialTimeout("tcp", address, time.Duration(timeout)*time.Second)if err != nil {log.Printf("Failed to connect to %s: %v\n", address, err)return err}defer conn.Close()fmt.Printf("Successfully connected to %s\n", address)// 发送数据if data != "" {fmt.Printf("Sending data: %s\n", data)_, err = conn.Write([]byte(data))if err != nil {log.Printf("Failed to send data: %v\n", err)} else {fmt.Println("Data sent successfully")}}// 接收响应数据buffer := make([]byte, 1024)conn.SetReadDeadline(time.Now().Add(time.Duration(timeout) * time.Second))// 读取响应数据// 如果超时则提示用户, 服务器没有发送数据n, err := conn.Read(buffer)if err != nil {if netErr, ok := err.(net.Error); ok && netErr.Timeout() {fmt.Println("No response from server")} else {log.Printf("Failed to read response: %v\n", err)}} else {fmt.Printf("Received: %s\n", string(buffer[:n]))}return err
}

4.2 实现 UDP 测试功能

在 udp.go 中实现 UDP 数据包的发送与接收：

package myncimport ("fmt""log""net""time"
)// TestUDP 测试UDP端口是否连通，并支持发送和接收数据
func FireUDP(ip string, port, timeout int, data string) error {address := fmt.Sprintf("%s:%d", ip, port)conn, err := net.Dial("udp", address)if err != nil {log.Printf("Failed to connect to %s: %v\n", address, err)return err}defer conn.Close()fmt.Printf("Successfully connected to %s\n", address)// 设置写超时conn.SetWriteDeadline(time.Now().Add(time.Duration(timeout) * time.Second))_, err = conn.Write([]byte(data))if err != nil {log.Printf("Failed to send data: %v\n", err)return err}fmt.Println("Data sent successfully")// 设置读超时conn.SetReadDeadline(time.Now().Add(time.Duration(timeout) * time.Second))buffer := make([]byte, 1024)n, err := conn.Read(buffer)if err != nil {log.Printf("No response received: %v\n", err)} else {fmt.Printf("Received: %s\n", string(buffer[:n]))}return err
}

4.3 实现 HTTP 测试功能

在 http.go 中构建 HTTP 请求：

package myncimport ("fmt""io""log""net/http""time"
)// TestHTTP 测试HTTP/HTTPS连接
func FireHTTP(url, method string, headers map[string]string, timeout int) error {client := &http.Client{Timeout: time.Duration(timeout) * time.Second,}// 创建HTTP请求req, err := http.NewRequest(method, url, nil)if err != nil {log.Printf("Failed to create HTTP request: %v\n", err)return err}// 设置请求头for key, value := range headers {req.Header.Set(key, value)}// 发送HTTP请求resp, err := client.Do(req)if err != nil {log.Printf("HTTP request failed: %v\n", err)return err}defer resp.Body.Close()// 读取响应内容body, err := io.ReadAll(resp.Body)if err != nil {log.Printf("Failed to read response body: %v\n", err)return err}fmt.Printf("HTTP Status: %s\n", resp.Status)fmt.Printf("Response Body:\n%s\n", string(body))return err
}

4.4 实现 Ping 测试功能

在 ping.go 中：

import ("fmt""log""net""os""time"
)const icmpEchoRequest = 8// Ping 测试目标IP是否可达
func Ping(ip string, timeout int) error {conn, err := net.Dial("ip4:icmp", ip)if err != nil {log.Printf("Failed to connect to %s: %v\n", ip, err)return err}defer conn.Close()// 构造ICMP请求包id := os.Getpid() & 0xffffseq := 1msg := []byte{icmpEchoRequest, 0, 0, 0, // ICMP Type, Code, and Checksum placeholderbyte(id >> 8), byte(id & 0xff), // Identifierbyte(seq >> 8), byte(seq & 0xff), // Sequence number}checksum := calculateChecksum(msg)msg[2] = byte(checksum >> 8)msg[3] = byte(checksum & 0xff)// 设置写超时conn.SetDeadline(time.Now().Add(time.Duration(timeout) * time.Second))start := time.Now()_, err = conn.Write(msg)if err != nil {log.Printf("Failed to send ICMP request: %v\n", err)return err}// 接收ICMP响应buffer := make([]byte, 1024)_, err = conn.Read(buffer)if err != nil {log.Printf("Failed to receive ICMP response: %v\n", err)return err}elapsed := time.Since(start)fmt.Printf("Ping %s successful! Time=%v\n", ip, elapsed)return err
}// calculateChecksum 计算ICMP校验和
func calculateChecksum(data []byte) uint16 {var sum intfor i := 0; i < len(data)-1; i += 2 {sum += int(data[i])<<8 | int(data[i+1])}if len(data)%2 == 1 {sum += int(data[len(data)-1]) << 8}for (sum >> 16) > 0 {sum = (sum >> 16) + (sum & 0xffff)}return uint16(^sum)
}

4.5 命令行解析与功能整合

在 main.go 中，将上述模块整合，并解析命令行参数：

package mainimport ("flag""fmt""net/url""os""strconv""strings""mync"
)func main() {// 定义命令行参数var method, data stringvar httpHeaders httpHeaderMapvar timeout intflag.StringVar(&method, "method", "GET", "HTTP method to use (default: GET)")flag.StringVar(&data, "data", "", "Data to send (for TCP or UDP)")flag.Var(&httpHeaders, "header", "Custom HTTP header (key=value pairs, can use multiple times)")flag.IntVar(&timeout, "timeout", 5, "Timeout in seconds (default: 5)")// 自定义 Usageflag.Usage = func() {fmt.Fprintf(os.Stderr, "Usage: %s <protocol>://<target> [options]\n\n", os.Args[0])fmt.Fprintf(os.Stderr, "options:\n")fmt.Fprintf(os.Stderr, "  -method <method>     HTTP method to use (default: GET)\n")fmt.Fprintf(os.Stderr, "  -data <data>         Data to send (for TCP or UDP)\n")fmt.Fprintf(os.Stderr, "  -header <header>   Custom HTTP header (key=value pairs, can use multiple times)\n")fmt.Fprintf(os.Stderr, "  -timeout <seconds>   Timeout in seconds (default: 5)\n")fmt.Fprintf(os.Stderr, "Examples:\n")fmt.Fprintf(os.Stderr, "  Test TCP connection:\n")fmt.Fprintf(os.Stderr, "    %s tcp://192.168.1.1:80 -data \"Hello, TCP!\" -timeout 10\n", os.Args[0])fmt.Fprintf(os.Stderr, "  Test UDP connection:\n")fmt.Fprintf(os.Stderr, "    %s udp://192.168.1.1:53 -data \"Hello, UDP!\" -timeout 5\n", os.Args[0])fmt.Fprintf(os.Stderr, "  Test HTTP connection:\n")fmt.Fprintf(os.Stderr, "    %s http://example.com -method GET -timeout 5\n", os.Args[0])fmt.Fprintf(os.Stderr, "  Ping a target:\n")fmt.Fprintf(os.Stderr, "    %s ping://192.168.1.1 -timeout 3\n", os.Args[0])}// 解析 flag 参数flag.Parse()// 必须至少有一个非 flag 参数args := flag.Args()if len(args) < 1 {fmt.Println("Error: Missing protocol and target. Example usage: tcp://192.168.1.1:80")flag.Usage()os.Exit(1)}// 解析第一个参数为协议和目标targetURL := args[0]parsedURL, err := url.Parse(targetURL)if err != nil || parsedURL.Scheme == "" || parsedURL.Host == "" {fmt.Printf("Error: Invalid protocol or target format: %s\n", targetURL)flag.Usage()os.Exit(1)}protocol := parsedURL.Schemetarget := parsedURL.Host// 根据协议执行对应的功能switch protocol {case "tcp":ip, port, err := parseTarget(target)if err != nil {fmt.Println("Error:", err)os.Exit(1)}if err := mync.FireTCP(ip, port, timeout, data); err != nil {fmt.Println("TCP Test Error:", err)}case "udp":ip, port, err := parseTarget(target)if err != nil {fmt.Println("Error:", err)os.Exit(1)}if err := mync.FireUDP(ip, port, timeout, data); err != nil {fmt.Println("UDP Test Error:", err)}case "http", "https":headerMap := httpHeaders.ToMap()if err := mync.FireHTTP(targetURL, method, headerMap, timeout); err != nil {fmt.Println("HTTP Test Error:", err)}case "ping":if err := mync.Ping(target, timeout); err != nil {fmt.Println("Ping Test Error:", err)}default:fmt.Printf("Error: Unsupported protocol: %s\n", protocol)flag.Usage()os.Exit(1)}
}// parseTarget 解析 <ip>:<port> 格式
func parseTarget(target string) (string, int, error) {parts := strings.Split(target, ":")if len(parts) != 2 {return "", 0, fmt.Errorf("invalid target format: %s, expected format <ip>:<port>", target)}ip := parts[0]port, err := strconv.Atoi(parts[1])if err != nil {return "", 0, fmt.Errorf("invalid port number: %s", parts[1])}return ip, port, nil
}// httpHeaderMap 用于保存用户指定的多个 -header 参数
type httpHeaderMap []stringfunc (h *httpHeaderMap) String() string {return strings.Join(*h, ", ")
}func (h *httpHeaderMap) Set(value string) error {*h = append(*h, value)return nil
}// ToMap 将 httpHeaderMap 转换为 map
func (h *httpHeaderMap) ToMap() map[string]string {headerMap := make(map[string]string)for _, header := range *h {parts := strings.SplitN(header, "=", 2)if len(parts) == 2 {headerMap[parts[0]] = parts[1]}}return headerMap
}

5 测试

#!/bin/bashset -eip=192.168.100.10
port=3333timeout=2# 测试tcp端口
echo ">>> Testing tcp port $port..."
./gonc tcp://$ip:$port -data "Hello" -timeout $timeout# 测试udp端口
echo ">>> Testing udp port $port..."
./gonc udp://$ip:$port -data "Hello" -timeout $timeout# 测试http服务
echo ">>> Testing http service..."
./gonc http://example.com -method GET -timeout $timeout# 测试ping
echo ">>> Testing ping..."
sudo ./gonc ping://$ip -timeout $timeout

由于测试ping时使用了原始套接字,所以需要root权限