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3socket编程：UDP编程

發布時間：2024/9/27 编程问答 19 豆豆

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1 C/S模型—UDP

UDP處理模型

說明：

由于UDP不需要維護連接，程序邏輯簡單了很多，但是UDP協議是不可靠的，實際上有很多保證通訊可靠性的機制需要在應用層實現。

編譯運行server，在兩個終端里各開一個client與server交互，看看server是否具有并

發服務的能力。用Ctrl+C關閉server，然后再運行server，看此時client還能否和server聯

系上。和前面TCP程序的運行結果相比較，體會無連接的含義。

2 案例說明：

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;

}

總結

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