1 C/S模型—UDP
UDP处理模型
说明：
由于UDP不需要维护连接，程序逻辑简单了很多，但是UDP协议是不可靠的，实际上有很多保证通讯可靠性的机制需要在应用层实现。
编译运行server，在两个终端里各开一个client与server交互，看看server是否具有并
发服务的能力。用Ctrl+C关闭server，然后再运行server，看此时client还能否和server联
系上。和前面TCP程序的运行结果相比较，体会无连接的含义。
2 案例说明：
Server.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<ctype.h>
#include"wrap.h"
#define MAXLINE 80
#define SERV_PORT 8000
int main(void)
{
struct sockaddr_in servaddr,cliaddr;
socklen_t cliaddr_len;
int sockfd;
char buf[MAXLINE];
char str[INET_ADDRSTRLEN];
int i,n;
sockfd = Socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(SERV_PORT);
Bind(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
printf("Accepting connections...\n");
while(1) {
cliaddr_len = sizeof(cliaddr);
n = recvfrom(sockfd,buf,MAXLINE,0,
(struct sockaddr *)&cliaddr,&cliaddr_len);
if(n == -1)
perr_exit("recvfrom error");
printf("received from %s at PORT %d\n",
inet_ntop(AF_INET,&cliaddr.sin_addr,str,sizeof(str)),
ntohs(cliaddr.sin_port));
for(i = 0;i<n;i++){
buf[i] = toupper(buf[i]);
}
n = sendto(sockfd,buf,n,0,(struct sockaddr *)&cliaddr,sizeof(cliaddr));
if(n== -1)
perr_exit("sendto error");
}
}
Client.c
#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include"wrap.h"
#define MAXLINE 80
#define SERV_PORT 8000
int main(int argc,char *argv[])
{
struct sockaddr_in servaddr;
int sockfd,n;
char buf[MAXLINE];
char str[INET_ADDRSTRLEN];
socklen_t servaddr_len;
sockfd = Socket(AF_INET,SOCK_DGRAM,0);
bzero(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
inet_pton(AF_INET,"127.0.0.1",&servaddr.sin_addr);
servaddr.sin_port = htons(SERV_PORT);
while(fgets(buf,MAXLINE,stdin) != NULL) {
n = sendto(sockfd,buf,strlen(buf),0,(struct sockaddr *)&servaddr,
sizeof(servaddr));
if(n == -1)
perr_exit("sendto error");
n = recvfrom(sockfd,buf,MAXLINE,0,NULL,0);
if(n == -1)
perr_exit("recvfrom error");
Write(STDOUT_FILENO,buf,n);
}
Close(sockfd);
return 0;
}
Wrap.h
#ifndef __WRAP_H_
#define __WRAP_H_
void perr_exit(const char *s);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
void Bind(int fd, const struct sockaddr *sa, socklen_t salen);
void Connect(int fd, const struct sockaddr *sa, socklen_t salen);
void Listen(int fd, int backlog);
int Socket(int family, int type, int protocol);
ssize_t Read(int fd, void *ptr, size_t nbytes);
ssize_t Write(int fd, const void *ptr, size_t nbytes);
void Close(int fd);
ssize_t Readn(int fd, void *vptr, size_t n);
ssize_t Writen(int fd, const void *vptr, size_t n);
static ssize_t my_read(int fd, char *ptr);
ssize_t Readline(int fd, void *vptr, size_t maxlen);
#endif
Wrap.c
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
void perr_exit(const char *s)
{
perror(s);
exit(1);
}
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
{
int n;
again:
if ( (n = accept(fd, sa, salenptr)) < 0) {
if ((errno == ECONNABORTED) || (errno == EINTR))
goto again;
else
perr_exit("accept error");
}
return n;
}
void Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
if (bind(fd, sa, salen) < 0)
perr_exit("bind error");
}
void Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
if (connect(fd, sa, salen) < 0)
perr_exit("connect error");
}
void Listen(int fd, int backlog)
{
if (listen(fd, backlog) < 0)
perr_exit("listen error");
}
int Socket(int family, int type, int protocol)
{
int n;
if ( (n = socket(family, type, protocol)) < 0)
perr_exit("socket error");
return n;
}
ssize_t Read(int fd, void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = read(fd, ptr, nbytes)) == -1) {
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = write(fd, ptr, nbytes)) == -1) {
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
void Close(int fd)
{
if (close(fd) == -1)
perr_exit("close error");
}
ssize_t Readn(int fd, void *vptr, size_t n)
{
size_t nleft;
ssize_t nread;
char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nread = read(fd, ptr, nleft)) < 0) {
if (errno == EINTR)
nread = 0;
else
return -1;
} else if (nread == 0)
break;
nleft -= nread;
ptr += nread;
}
return n - nleft;
}
ssize_t Writen(int fd, const void *vptr, size_t n)
{
size_t nleft;
ssize_t nwritten;
const char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
if (nwritten < 0 && errno == EINTR)
nwritten = 0;
else
return -1;
}
nleft -= nwritten;
ptr += nwritten;
}
return n;
}
static ssize_t my_read(int fd, char *ptr)
{
static int read_cnt;
static char *read_ptr;
static char read_buf[100];
if (read_cnt <= 0) {
again:
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
if (errno == EINTR)
goto again;
return -1;
} else if (read_cnt == 0)
return 0;
read_ptr = read_buf;
}
read_cnt--;
*ptr = *read_ptr++;
return 1;
}
ssize_t Readline(int fd, void *vptr, size_t maxlen)
{
ssize_t n, rc;
char c, *ptr;
ptr = vptr;
for (n = 1; n < maxlen; n++) {
if ( (rc = my_read(fd, &c)) == 1) {
*ptr++ = c;
if (c == '\n')
break;
} else if (rc == 0) {
*ptr = 0;
return n - 1;
} else
return -1;
}
*ptr = 0;
return n;
}
