3socket编程：UDP编程

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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;

}

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