udp与tcp数据模式区别-用代码解释

所有接触过网络编程的，都会被告之：udp传输的是数据报，tcp传输的是流。但是数据报和流到底有什么不同，怎么测试他们的不同呢？今天的这个小程序能很好的解释这个问题。

udp server

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
struct sockaddr_in s_addr;
struct sockaddr_in c_addr;
int sock;
socklen_t addr_len;
int len;
char buff[128];

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket");
exit(errno);
}

memset(&s_addr, 0, sizeof(struct sockaddr_in));
s_addr.sin_family = AF_INET;

if (argv[2])
s_addr.sin_port = htons(atoi(argv[2]));
else
s_addr.sin_port = htons(7838);
if (argv[1])
s_addr.sin_addr.s_addr = inet_addr(argv[1]);
else
s_addr.sin_addr.s_addr = INADDR_ANY;

if ((bind(sock, (struct sockaddr *) &s_addr, sizeof(s_addr))) == -1) {
perror("bind");
exit(errno);
}

addr_len = sizeof(c_addr);
while (1) {//接收client发送的数据并打印到屏幕
len = recvfrom(sock, buff, sizeof(buff) - 1, 0,
(struct sockaddr *) &c_addr, &addr_len);
if (len < 0) {
perror("recvfrom");
exit(errno);
}

buff[len] = '\0';

printf("recv from: %s:%d message: %s\n", inet_ntoa(c_addr.sin_addr), ntohs(c_addr.sin_port), buff);
}
return 0;
}

udp client

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
struct sockaddr_in d_addr;
int sock;
int addr_len;
int len, i;
char buff[3] = {'a', 'b', 'c'};//要发送的字符

if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket");
exit(errno);
}

d_addr.sin_family = AF_INET;

if (argv[2])
d_addr.sin_port = htons(atoi(argv[2]));
else
d_addr.sin_port = htons(7838);

if (argv[1])
d_addr.sin_addr.s_addr = inet_addr(argv[1]);
else {
printf("reciver's ip must be set\n");
exit(0);
}

addr_len = sizeof(d_addr);

for (i = 0; i < sizeof(buff); i++)//分3次，每次发送一个字符
{
len = sendto(sock, &buff[i], 1, 0,
(struct sockaddr *) &d_addr, addr_len);
if (len < 0) {
printf("send error.\n");
return -1;
}
}

printf("complete.\n");
return 0;
}

tcp server

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
struct sockaddr_in s_addr;
struct sockaddr_in c_addr;
int sock, new_sock;
socklen_t addr_len;
int len;
char buff[128];

if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(errno);
}

memset(&s_addr, 0, sizeof(struct sockaddr_in));
s_addr.sin_family = AF_INET;

if (argv[2])
s_addr.sin_port = htons(atoi(argv[2]));
else
s_addr.sin_port = htons(7838);
if (argv[1])
s_addr.sin_addr.s_addr = inet_addr(argv[1]);
else
s_addr.sin_addr.s_addr = INADDR_ANY;

if ((bind(sock, (struct sockaddr *) &s_addr, sizeof(s_addr))) == -1) {
perror("bind");
exit(errno);
}

if (listen(sock, 3) < 0)
{
perror("listen");
exit(errno);
}

addr_len = sizeof(c_addr);
while (1) {//接收client端发送过来的数据，并打印到终端
new_sock = accept(sock, (struct sockaddr *)&c_addr, &addr_len);
if (new_sock == -1)
{
perror("accept");
exit(errno);
}

memset(buff, 0, sizeof(buff));

len = recv(new_sock, buff, sizeof(buff) - 1, 0);
if (len < 0) {
perror("recv");
exit(errno);
}

buff[len] = '\0';

printf("recv from: %s:%d message: %s\n", inet_ntoa(c_addr.sin_addr), ntohs(c_addr.sin_port), buff);
}
return 0;
}

tcp client

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
struct sockaddr_in d_addr;
int sock;
int addr_len;
int len, i;
char buff[3] = {'a', 'b', 'c'};

if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(errno);
}

d_addr.sin_family = AF_INET;
if (argv[2])
d_addr.sin_port = htons(atoi(argv[2]));
else
d_addr.sin_port = htons(7838);
if (argv[1])
d_addr.sin_addr.s_addr = inet_addr(argv[1]);
else {
printf("reciver's ip must be set\n");
exit(0);
}

addr_len = sizeof(d_addr);

if (connect(sock, (struct sockaddr *) &d_addr, addr_len) != 0) {
perror("Connect ");
exit(errno);
}

for (i = 0; i < sizeof(buff); i++)//分3次发送，每次发送一个字符
{
len = send(sock, &buff[i], 1, 0);
if (len < 0) {
printf("send error.\n");
return -1;
}
}

printf("complete.\n");
return 0;
}

执行结果：

udp:

$ ./udp_server 192.168.7.130 5678

recv from: 192.168.7.145:37102 message: a

recv from: 192.168.7.145:37102 message: b

recv from: 192.168.7.145:37102 message: c

tcp:

$ ./tcp_server 192.168.7.130 5678

recv from: 192.168.7.145:43973 message: abc

从上面的执行结果可以看到，udp每次接收到的是一个字符，而tcp则是组成了一个字符串，提供出来。这就所谓的udp数据报，和tcp流的区别。形成这样的原因是，在kernel中，udp数据有结束标志，可以知道这个数据包有多少数据，但是tcp则没有，所以调用recv获取的时候，就会将kernel接收到的数据全部copy过来。