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
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#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
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#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
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#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
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#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; } |