给UDP增加可靠性

最新推荐文章于 2023-09-06 00:37:41 发布

littlehedgehog

最新推荐文章于 2023-09-06 00:37:41 发布

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分类专栏： Unix/Linux Programming 文章标签： struct null socket signal 算法 fp

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本文介绍了一个基于UDP协议的可靠数据传输实现案例。通过对计算往返时间（RTT）算法的改进及采用pselect与signal的方式，提高了UDP数据传输的稳定性和效率。

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给UDP增加可靠性

刺猬@http://blog.youkuaiyun.com/littlehedgehog

UNP里面的例子程序，把计算rtt的算法改了下，参考的TCP/IP详解里面介绍的一个稍微简单的算法，另外，不喜欢setjmp这种编程模式，感觉程序代码可读性较差，最后还是改成使用pselect＋signal，这样代码会清晰些。

下面是主函数

#include "./unix.h" #include "./rtt.h" static int rttinit; static struct r_info rtt; static struct udphdr { unsigned seq; /* sequence */ unsigned ts; /* timestamp/ms */ }hdr_send, hdr_recv; static void alarm_handler(int signo) { return; } ssize_t send_recv(int sockfd, void *sendbuff, size_t sendbytes, void *recvbuff, size_t recvbytes, const struct sockaddr *praddr, socklen_t len) { ssize_t ret; int maxfd; struct timeval tv; fd_set rset; struct sigaction sa; sigset_t sigset_alarm, sigset_empty; struct msghdr msg_send, msg_recv; struct iovec iov_send[2], iov_recv[2]; if (!rttinit) { rttinit = 1; rtt_init(&rtt); } memset(&msg_send, 0x00, sizeof(struct msghdr)); memset(&msg_recv, 0x00, sizeof(struct msghdr)); iov_send[0].iov_base = &hdr_send; iov_send[0].iov_len = sizeof(struct udphdr); iov_send[1].iov_base = sendbuff; iov_send[1].iov_len = sendbytes; iov_recv[0].iov_base = &hdr_recv; iov_recv[0].iov_len = sizeof(struct udphdr); iov_recv[1].iov_base = recvbuff; iov_recv[1].iov_len = recvbytes; msg_send.msg_name = praddr; msg_send.msg_namelen = len; msg_send.msg_iov = iov_send; msg_send.msg_iovlen = 2; msg_recv.msg_name = praddr; msg_recv.msg_namelen = len; msg_recv.msg_iov = iov_recv; msg_recv.msg_iovlen = 2; hdr_send.seq++; /* 该次数据包发送序列号 */ sigemptyset(&sigset_alarm); sigemptyset(&sigset_empty); sigaddset(&sigset_alarm, SIGALRM); sa.sa_handler = alarm_handler; sa.sa_flags = 0; sigemptyset(&sa.sa_mask); if (sigaction(SIGALRM, &sa, NULL) < 0) { perror("sigaction"); return; } rtt_newpack(&rtt); FD_ZERO(&rset); for ( ; ; ) { hdr_send.ts = rtt_timestamp(&rtt); if ((ret = sendmsg(sockfd, &msg_send, 0)) < 0) { perror("sendmsg"); return; } alarm(rtt_start(&rtt)); loop: FD_SET(sockfd, &rset); sigprocmask(SIG_BLOCK, &sigset_alarm, NULL); if ((ret = pselect(sockfd+1, &rset, NULL, NULL, NULL, &sigset_empty)) < 0) { if (errno == EINTR) { if (rtt_timeout(&rtt) < 0) /* limit */ { rttinit = 0; errno = ETIMEDOUT; return (-1); } /* send again */ continue; } } if (FD_ISSET(sockfd, &rset)) { if ((ret = recvmsg(sockfd, &msg_recv, 0)) < 0) { perror("recvmsg"); goto loop; } if (ret < sizeof(struct udphdr) || hdr_recv.seq != hdr_send.seq) { goto loop; } rtt_stop(&rtt, hdr_send.ts); return ret-sizeof(struct udphdr); } } } void echo(int sockfd, struct sockaddr *praddr, socklen_t len, struct FILE *fp) { int ret; char sendline[MAXLINE], recvline[MAXLINE]; memset(sendline, 0x00, MAXLINE); memset(recvline, 0x00, MAXLINE); while (fgets(sendline, MAXLINE, fp) != NULL) { if ((ret = send_recv(sockfd, sendline, strlen(sendline), recvline, MAXLINE, praddr, len)) < 0) { return; } recvline[ret] = 0; fputs(recvline, stdout); } } int main(int argc, char *argv[]) { int connfd; struct sockaddr_in servaddr; if ((connfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) { perror("socket"); exit(-1); } memset(&servaddr, 0x00, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(1988); servaddr.sin_addr.s_addr = inet_addr("210.32.34.137"); echo(connfd, (struct sockaddr *)&servaddr, sizeof(struct sockaddr_in), stdin); close(connfd); return 0; }

rtt.c

#include "./unix.h" #include "./rtt.h" #define MAXXMT 4 void rtt_init(struct r_info *rtt) { struct timeval tv; gettimeofday(&tv, NULL); rtt->r_tbase = tv; rtt->r_rtt = 0; rtt->r_rto = 3; } void rtt_newpack(struct r_info *rtt) { rtt->r_rexmt = 0; } int rtt_start(struct r_info *rtt) { return (int)rtt->r_rto; } unsigned rtt_timestamp(struct r_info *rtt) { struct timeval tv; gettimeofday(&tv, NULL); return (tv.tv_sec-rtt->r_tbase.tv_sec)*1000+(tv.tv_usec-rtt->r_tbase.tv_usec)/1000; } void rtt_time(struct r_info *rtt, struct timeval *tv) { tv->tv_sec = rtt->r_rto; tv->tv_usec = 0; return; } int rtt_timeout(struct r_info *rtt) { rtt->r_rto *= 2; if (++rtt->r_rexmt > MAXXMT) return (-1); return 0; } void rtt_stop(struct r_info *rtt, unsigned sendts) { float temp = (rtt_timestamp(rtt)-sendts)/1000; rtt->r_rtt = rtt->r_rtt*0.9 + temp*0.1; rtt->r_rto = rtt->r_rtt*2; }