1.前言
实验基于Linux kernel 3.18.6，实验内容包括：
（1）编写UDP客户端和服务端
（2）将UDP客户端和服务端集成到MenuOS中
（3）UDP发送数据的过程
（4）UDP接收数据的过程
本文中完整源码：https://github.com/dangolqy/udp
实验楼环境：https://www.shiyanlou.com/courses/1198
2.UDP客户端和服务端
参考博客：https://blog.csdn.net/lell3538/article/details/53335472
服务端server.c
1 #include<stdio.h>
2 #include<stdlib.h>
3 #include<unistd.h>
4 #include<errno.h>
5 #include<sys/types.h>
6 #include<sys/socket.h>
7 #include<netinet/in.h>
8 #include<string.h>
9
10 #define MYPORT 5678
11
12
13 #define ERR_EXIT(m) 14 do { 15 perror(m); 16 exit(EXIT_FAILURE); 17 } while (0)
18
19 void echo_ser(int sock)
20 {
21 char recvbuf[1024] = {0};
22 struct sockaddr_in peeraddr;
23 socklen_t peerlen;
24 int n;
25
26 while (1)
27 {
28
29 peerlen = sizeof(peeraddr);
30 memset(recvbuf, 0, sizeof(recvbuf));
31 n = recvfrom(sock, recvbuf, sizeof(recvbuf), 0,
32 (struct sockaddr *)&peeraddr, &peerlen);
33 if (n <= 0)
34 {
35
36 if (errno == EINTR)
37 continue;
38
39 ERR_EXIT("recvfrom error");
40 }
41 else if(n > 0)
42 {
43 printf("接收到的数据：%s\n",recvbuf);
44 sendto(sock, recvbuf, n, 0,
45 (struct sockaddr *)&peeraddr, peerlen);
46 printf("回送的数据：%s\n",recvbuf);
47 }
48 }
49 close(sock);
50 }
51
52 int main(void)
53 {
54 int sock;
55 if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
56 ERR_EXIT("socket error");
57
58 struct sockaddr_in servaddr;
59 memset(&servaddr, 0, sizeof(servaddr));
60 servaddr.sin_family = AF_INET;
61 servaddr.sin_port = htons(MYPORT);
62 servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
63
64 printf("监听%d端口\n",MYPORT);
65 if (bind(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
66 ERR_EXIT("bind error");
67
68 echo_ser(sock);
69
70 return 0;
71 }
客户端代码client.c
1 #include <unistd.h>
2 #include <sys/types.h>
3 #include <sys/socket.h>
4 #include <netinet/in.h>
5 #include <arpa/inet.h>
6 #include <stdlib.h>
7 #include <stdio.h>
8 #include <errno.h>
9 #include <string.h>
10
11 #define MYPORT 5678
12 char* SERVERIP = "127.0.0.1";
13
14 #define ERR_EXIT(m) 15 do 16 { 17 perror(m); 18 exit(EXIT_FAILURE); 19 } while(0)
20
21 void echo_cli(int sock)
22 {
23 struct sockaddr_in servaddr;
24 memset(&servaddr, 0, sizeof(servaddr));
25 servaddr.sin_family = AF_INET;
26 servaddr.sin_port = htons(MYPORT);
27 servaddr.sin_addr.s_addr = inet_addr(SERVERIP);
28
29 int ret;
30 char sendbuf[1024] = {0};
31 char recvbuf[1024] = {0};
32
33 fgets(sendbuf, sizeof(sendbuf), stdin);
34
35 printf("向服务器发送：%s\n",sendbuf);
36 sendto(sock, sendbuf, strlen(sendbuf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));
37
38 ret = recvfrom(sock, recvbuf, sizeof(recvbuf), 0, NULL, NULL);
39 printf("从服务器接收：%s\n",recvbuf);
40
41 close(sock);
42
43
44 }
45
46 int main(void)
47 {
48 int sock;
49 if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
50 ERR_EXIT("socket");
51
52 echo_cli(sock);
53
54 return 0;
55 }
在实验楼环境中的运行结果：
3.将UDP客户端和服务端集成到MenuOS中
仿照老师写好的TCP代码，将上面两个文件中的代码添加进main.c中。
其中，server.c和client.c中的函数部分略作修改写进.h文件中作为要引用的头文件，main函数部分作为新的函数写进main.c中，最后再在main.c的main函数中增加udp菜单选项。具体如下：
server.h
1 #include<stdio.h>
2 #include<stdlib.h>
3 #include<unistd.h>
4 #include<errno.h>
5 #include<sys/types.h>
6 #include<sys/socket.h>
7 #include<netinet/in.h>
8 #include<string.h>
9
10 #define MYPORT 5678
11
12
13 #define ERR_EXIT(m) 14 do { 15 perror(m); 16 exit(EXIT_FAILURE); 17 } while (0)
18
19 void echo_ser(int sock)
20 {
21 char recvbuf[1024] = {0};
22 char reply[1024]={‘h‘,‘i‘};
23 struct sockaddr_in peeraddr;
24 socklen_t peerlen;
25 int n;
26
27 while(1){
28 peerlen = sizeof(peeraddr);
29 memset(recvbuf, 0, sizeof(recvbuf));
30 n = recvfrom(sock, recvbuf, sizeof(recvbuf), 0,
31 (struct sockaddr *)&peeraddr, &peerlen);
32
33 if(n > 0)
34 {
35 printf("server receive:%s\n",recvbuf);
36 sendto(sock, reply, strlen(reply), 0,
37 (struct sockaddr *)&peeraddr, peerlen);
38 printf("server reply:%s\n",reply);
39 }
40 else
41 break;
42 }
43
44 close(sock);
45 }
client.h
1 #include <unistd.h>
2 #include <sys/types.h>
3 #include <sys/socket.h>
4 #include <netinet/in.h>
5 #include <arpa/inet.h>
6 #include <stdlib.h>
7 #include <stdio.h>
8 #include <errno.h>
9 #include <string.h>
10
11 #define MYPORT 5678
12 char* SERVERIP = "127.0.0.1";
13
14
15 void echo_cli(int sock)
16 {
17 struct sockaddr_in servaddr;
18 memset(&servaddr, 0, sizeof(servaddr));
19 servaddr.sin_family = AF_INET;
20 servaddr.sin_port = htons(MYPORT);
21 servaddr.sin_addr.s_addr = inet_addr(SERVERIP);
22
23 int ret;
24 char sendbuf[1024] = {‘h‘,‘e‘,‘l‘,‘l‘,‘o‘};
25 char recvbuf[1024] = {0};
26
27 printf("client send to server:%s\n",sendbuf);
28 sendto(sock, sendbuf, strlen(sendbuf), 0, (struct sockaddr *)&servaddr, sizeof(servaddr));
29
30 ret = recvfrom(sock, recvbuf, sizeof(recvbuf), 0, NULL, NULL);
31 printf("client receive from server:%s\n",recvbuf);
32
33 close(sock);
34
35 }
main.c（部分）
1 #include "server.h"
2 #include "client.h"
3
4 int UdpReplyhi()
5 {
6 int sock;
7 if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
8 ERR_EXIT("socket error");
9
10 struct sockaddr_in servaddr;
11 memset(&servaddr, 0, sizeof(servaddr));
12 servaddr.sin_family = AF_INET;
13 servaddr.sin_port = htons(MYPORT);
14 servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
15
16 printf("server listen to port:%d\n",MYPORT);
17 if (bind(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
18 ERR_EXIT("bind error");
19
20 echo_ser(sock);
21
22 return 0;
23 }
24
25 int StartUdpReplyHi(int argc, char *argv[])
26 {
27 int pid;
28 /* fork another process */
29 pid = fork();
30 if (pid < 0)
31 {
32 /* error occurred */
33 fprintf(stderr, "Fork Failed!");
34 exit(-1);
35 }
36 else if (pid == 0)
37 {
38 /* child process */
39 UdpReplyhi();
40 printf("Reply hi UDP Service Started!\n");
41 }
42 else
43 {
44 /* parent process */
45 printf("Please input hello...\n");
46 }
47 }
48
49 int UdpHello(int argc, char *argv[])
50 {
51 int sock;
52 if ((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
53 ERR_EXIT("socket");
54
55 echo_cli(sock);
56
57 return 0;
58 }
1 MenuConfig("udpreplyhi", "Reply hi UDP Service", StartUdpReplyHi);
2 MenuConfig("udphello", "Hello UDP Client", UdpHello);
在实验楼中的运行结果：
4.UDP发送数据的过程
参考博客：https://blog.csdn.net/u010246947/article/details/18253345
http://blog.chinaunix.net/uid-14528823-id-4468600.html
UDP报文发送的内核主要调用流程如下图：
在udp_sendmsg处设置断点，查看函数调用栈：
查看inet_sendmsg函数的代码（http://codelab.shiyanlou.com/source/xref/linux-3.18.6/net/ipv4/af_inet.c#721），在红色框标注出来的地方，调用对应传输层协议的sendmsg方法，在这里就是udp_sendmsg。
单步执行至ip_make_skb，查看该函数的源码，它调用了__ip_make_skb（http://codelab.shiyanlou.com/source/xref/linux-3.18.6/net/ipv4/ip_output.c#1320）。
在这个函数中，主要进行从缓冲队列中拿出数据送至skb中，添加IP协议头等操作。
1342 while ((tmp_skb = __skb_dequeue(queue)) != NULL) {
1343 __skb_pull(tmp_skb, skb_network_header_len(skb));
1344 *tail_skb = tmp_skb;
1345 tail_skb = &(tmp_skb->next);
1346 skb->len += tmp_skb->len;
1347 skb->data_len += tmp_skb->len;
1348 skb->truesize += tmp_skb->truesize;
1349 tmp_skb->destructor = NULL;
1350 tmp_skb->sk = NULL;
1351 }
1353 /* Unless user demanded real pmtu discovery (IP_PMTUDISC_DO), we allow
1354 * to fragment the frame generated here. No matter, what transforms
1355 * how transforms change size of the packet, it will come out.
1356 */
1357 skb->ignore_df = ip_sk_ignore_df(sk);
1358
1359 /* DF bit is set when we want to see DF on outgoing frames.
1360 * If ignore_df is set too, we still allow to fragment this frame
1361 * locally. */
1362 if (inet->pmtudisc == IP_PMTUDISC_DO ||
1363 inet->pmtudisc == IP_PMTUDISC_PROBE ||
1364 (skb->len <= dst_mtu(&rt->dst) &&
1365 ip_dont_fragment(sk, &rt->dst)))
1366 df = htons(IP_DF);
1367
1368 if (cork->flags & IPCORK_OPT)
1369 opt = cork->opt;
1370
1371 if (cork->ttl != 0)
1372 ttl = cork->ttl;
1373 else if (rt->rt_type == RTN_MULTICAST)
1374 ttl = inet->mc_ttl;
1375 else
1376 ttl = ip_select_ttl(inet, &rt->dst);
1377
1378 iph = ip_hdr(skb);
1379 iph->version = 4;
1380 iph->ihl = 5;
1381 iph->tos = (cork->tos != -1) ? cork->tos : inet->tos;
1382 iph->frag_off = df;
1383 iph->ttl = ttl;
1384 iph->protocol = sk->sk_protocol;
1385 ip_copy_addrs(iph, fl4);
1386 ip_select_ident(skb, sk);
1387
1388 if (opt) {
1389 iph->ihl += opt->optlen>>2;
1390 ip_options_build(skb, opt, cork->addr, rt, 0);
1391 }
1392
1393 skb->priority = (cork->tos != -1) ? cork->priority: sk->sk_priority;
1394 skb->mark = sk->sk_mark;
1395 /*
1396 * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
1397 * on dst refcount
1398 */
1399 cork->dst = NULL;
1400 skb_dst_set(skb, &rt->dst);
1401
1402 if (iph->protocol == IPPROTO_ICMP)
1403 icmp_out_count(net, ((struct icmphdr *)
1404 skb_transport_header(skb))->type);
1405
1406 ip_cork_release(cork);
继续单步执行到udp_send_skb函数（http://codelab.shiyanlou.com/source/xref/linux-3.18.6/net/ipv4/udp.c#783）。
该函数中为数据包添加了udp报头，包括计算校验和等内容。
794 /*
795 * Create a UDP header
796 */
797 uh = udp_hdr(skb);
798 uh->source = inet->inet_sport;
799 uh->dest = fl4->fl4_dport;
800 uh->len = htons(len);
801 uh->check = 0;
802
803 if (is_udplite) /* UDP-Lite */
804 csum = udplite_csum(skb);
805
806 else if (sk->sk_no_check_tx) { /* UDP csum disabled */
807
808 skb->ip_summed = CHECKSUM_NONE;
809 goto send;
810
811 } else if (skb->ip_summed == CHECKSUM_PARTIAL) { /* UDP hardware csum */
812
813 udp4_hwcsum(skb, fl4->saddr, fl4->daddr);
814 goto send;
815
816 } else
817 csum = udp_csum(skb);
818
819 /* add protocol-dependent pseudo-header */
820 uh->check = csum_tcpudp_magic(fl4->saddr, fl4->daddr, len,
821 sk->sk_protocol, csum);
822 if (uh->check == 0)
823 uh->check = CSUM_MANGLED_0;
继续单步执行，到这里udp数据包已经准备好，即将交给IP层进行发送。传输层的数据发送相关流程到此结束。
5.UDP接收数据的过程
UDP数据包的接收分为两部分：
（1）网络层将数据包递交给UDP，UDP接收数据包并对其进行校验，校验成功后放入接收队列中等待用户进程的读取；
（2）用户进程使用系统调用来读取已经在接收队列中的数据。
下面分两步来介绍：
5.1 从IP层接收数据包
这部分函数的调用过程如下图：
在udp_rcv处设置断点，首先调用__udp4_lib_rcv函数（http://codelab.shiyanlou.com/source/xref/linux-3.18.6/net/ipv4/udp.c#1730）。
该函数中验证数据包是否完整，
原文地址：https://www.cnblogs.com/dangolqy/p/10152971.html
时间： 2024-11-05 19:39:58