6.2 UDP的传输特性 P112

ch06/README.md

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+## 第 6 章 基于 UDP 的服务端/客户端
+
+本章代码，在[TCP-IP-NetworkNote](https://github.com/riba2534/TCP-IP-NetworkNote)中可以找到。
+
+TCP 是内容较多的一个协议，而本章中的 UDP 内容较少，但是也很重要。
+
+### 6.1 理解 UDP
+

ch06/bound_host1.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define BUF_SIZE 30
+void error_handling(char *message);
+
+int main(int argc, char *argv[])
+{
+    int sock;
+    char message[BUF_SIZE];
+    struct sockaddr_in my_adr, your_adr;
+    socklen_t adr_sz;
+    int str_len, i;
+    if (argc != 2)
+    {
+        printf("Usage : %s <port>\n", argv[0]);
+        exit(1);
+    }
+    sock = socket(PF_INET, SOCK_DGRAM, 0);
+    if (sock == -1)
+        error_handling("socket() error");
+
+    memset(&my_adr, 0, sizeof(my_adr));
+    my_adr.sin_family = AF_INET;
+    my_adr.sin_addr.s_addr = htonl(INADDR_ANY);
+    my_adr.sin_port = htons(atoi(argv[1]));
+
+    if (bind(sock, (struct sockaddr *)&my_adr, sizeof(my_adr)) == -1)
+        error_handling("bind() error");
+
+    for (i = 0; i < 3; i++)
+    {
+        sleep(5);
+        adr_sz = sizeof(your_adr);
+        str_len = recvfrom(sock, message, BUF_SIZE, 0,
+                           (struct sockaddr *)&your_adr, &adr_sz);
+        printf("Message %d: %s \n", i + 1, message);
+    }
+    close(sock);
+    return 0;
+}
+
+void error_handling(char *message)
+{
+    fputs(message, stderr);
+    fputc('\n', stderr);
+    exit(1);
+}

ch06/bound_host2.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define BUF_SIZE 30
+void error_handling(char *message);
+
+int main(int argc, char *argv[])
+{
+    int sock;
+    char msg1[] = "Hi!";
+    char msg2[] = "I'm another UDP host!";
+    char msg3[] = "Nice to meet you";
+
+    struct sockaddr_in your_adr;
+    socklen_t your_adr_sz;
+    if (argc != 3)
+    {
+        printf("Usage : %s <IP> <port>\n", argv[0]);
+        exit(1);
+    }
+    sock = socket(PF_INET, SOCK_DGRAM, 0);
+    if (sock == -1)
+        error_handling("socket() error");
+    memset(&your_adr, 0, sizeof(your_adr));
+    your_adr.sin_family = AF_INET;
+    your_adr.sin_addr.s_addr = inet_addr(argv[1]);
+    your_adr.sin_port = htons(atoi(argv[2]));
+
+    sendto(sock, msg1, sizeof(msg1), 0,
+           (struct sockaddr *)&your_adr, sizeof(your_adr));
+    sendto(sock, msg2, sizeof(msg2), 0,
+           (struct sockaddr *)&your_adr, sizeof(your_adr));
+    sendto(sock, msg3, sizeof(msg3), 0,
+           (struct sockaddr *)&your_adr, sizeof(your_adr));
+    close(sock);
+    return 0;
+}
+
+void error_handling(char *message)
+{
+    fputs(message, stderr);
+    fputc('\n', stderr);
+    exit(1);
+}

ch06/uecho_client.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define BUF_SIZE 30
+void error_handling(char *message);
+
+int main(int argc, char *argv[])
+{
+    int sock;
+    char message[BUF_SIZE];
+    int str_len;
+    socklen_t adr_sz;
+
+    struct sockaddr_in serv_adr, from_adr;
+    if (argc != 3)
+    {
+        printf("Usage : %s <IP> <port>\n", argv[0]);
+        exit(1);
+    }
+    //创建 UDP 套接字
+    sock = socket(PF_INET, SOCK_DGRAM, 0);
+    if (sock == -1)
+        error_handling("socket() error");
+
+    memset(&serv_adr, 0, sizeof(serv_adr));
+    serv_adr.sin_family = AF_INET;
+    serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
+    serv_adr.sin_port = htons(atoi(argv[2]));
+
+    while (1)
+    {
+        fputs("Insert message(q to quit): ", stdout);
+        fgets(message, sizeof(message), stdin);
+        if (!strcmp(message, "q\n") || !strcmp(message, "Q\n"))
+            break;
+        //向服务器传输数据,会自动给自己分配IP地址和端口号
+        sendto(sock, message, strlen(message), 0,
+               (struct sockaddr *)&serv_adr, sizeof(serv_adr));
+        adr_sz = sizeof(from_adr);
+        str_len = recvfrom(sock, message, BUF_SIZE, 0,
+                           (struct sockaddr *)&from_adr, &adr_sz);
+        message[str_len] = 0;
+        printf("Message from server: %s", message);
+    }
+    close(sock);
+    return 0;
+}
+
+void error_handling(char *message)
+{
+    fputs(message, stderr);
+    fputc('\n', stderr);
+    exit(1);
+}

ch06/uecho_server.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define BUF_SIZE 30
+void error_handling(char *message);
+
+int main(int argc, char *argv[])
+{
+    int serv_sock;
+    char message[BUF_SIZE];
+    int str_len;
+    socklen_t clnt_adr_sz;
+
+    struct sockaddr_in serv_adr, clnt_adr;
+    if (argc != 2)
+    {
+        printf("Usage : %s <port>\n", argv[0]);
+        exit(1);
+    }
+    //创建 UDP 套接字后，向 socket 的第二个参数传递 SOCK_DGRAM
+    serv_sock = socket(PF_INET, SOCK_DGRAM, 0);
+    if (serv_sock == -1)
+        error_handling("UDP socket creation eerror");
+
+    memset(&serv_adr, 0, sizeof(serv_adr));
+    serv_adr.sin_family = AF_INET;
+    serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
+    serv_adr.sin_port = htons(atoi(argv[1]));
+    //分配地址接受数据，不限制数据传输对象
+    if (bind(serv_sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1)
+        error_handling("bind() error");
+
+    while (1)
+    {
+        clnt_adr_sz = sizeof(clnt_adr);
+        str_len = recvfrom(serv_sock, message, BUF_SIZE, 0,
+                           (struct sockaddr *)&clnt_adr, &clnt_adr_sz);
+        //通过上面的函数调用同时获取数据传输端的地址。正是利用该地址进行逆向重传
+        sendto(serv_sock, message, str_len, 0,
+               (struct sockaddr *)&clnt_adr, clnt_adr_sz);
+    }
+    close(serv_sock);
+    return 0;
+}
+
+void error_handling(char *message)
+{
+    fputs(message, stderr);
+    fputc('\n', stderr);
+    exit(1);
+}