我正在编写一个点对点消息队列系统,它必须能够在UDP上运行.我可以任意选择一方或另一方作为"服务器",但由于两端都是从另一方发送和接收相同类型的数据,所以它似乎不太正确.
是否可以bind()和connect()两端,以便它们只相互发送/接收？这似乎是一种很好的对称方式.
dat*_*olf 27
UDP是无连接的,因此对于实际进行某种连接的操作系统几乎没有意义.
在BSD套接字中,可以connect在UDP套接字上执行操作,但这基本上只设置了默认目标地址send(而是明确地给出send_to).
在UDP套接字上绑定告诉操作系统实际接受数据包的传入地址(所有到其他地址的数据包都被丢弃),无论套接字的类型如何.
收到后,您必须使用recvfrom来识别数据包来自哪个来源.请注意,如果您需要某种身份验证,那么仅使用所涉及的地址就像没有锁定一样不安全.TCP连接可能被劫持,而裸体UDP确实在其头部编写了IP欺骗.您必须添加某种HMAC
xim*_*ica 23
你好,从遥远的未来,即2018年,到2012年.
事实上,connect()在实践中有一个原因就是UDP套接字背后的原因(虽然理论上没有理由要求你提供POSIX).
普通的UDP套接字对其未来目的地一无所知,因此每次sendmsg()调用时都会执行路由查找.
但是,如果connect()事先使用特定的远程接收器的IP和端口调用,则操作系统内核将能够记下对路由的引用并将其分配给套接字,如果后续sendmsg()调用没有,则发送消息的速度要快得多指定接收器(否则将忽略先前的设置),而是选择默认设置.
看看行1070通过1171:
if (connected)
rt = (struct rtable *)sk_dst_check(sk, 0);
if (!rt) {
[..skip..]
rt = ip_route_output_flow(net, fl4, sk);
[..skip..]
}
在Linux内核4.18之前,此功能主要仅限于IPv4地址系列.但是,自4.18-rc4(以及希望Linux内核版本4.18)以来,它也完全适用于IPv6套接字.
它可能是一个严重的性能优势的来源,但它将在很大程度上取决于您正在使用的操作系统.至少,如果您使用Linux并且不将套接字用于多个远程处理程序,那么您应该尝试一下.
小智 14
这是一个程序,演示了如何将同一UDP套接字上的bind()和connect()分别绑定到一组特定的源端口和目标端口.该程序可以在任何Linux机器上编译,具有以下用途:
usage: ./<program_name> dst-hostname dst-udpport src-udpport
我测试了这个代码打开两个终端.您应该能够向目标节点发送消息并从中接收消息.
在终端1运行
./<program_name> 127.0.0.1 5555 5556
在终端2运行
./<program_name> 127.0.0.1 5556 5555
即使我在一台机器上测试过它,我认为一旦你设置了正确的防火墙设置,它也可以在两台不同的机器上运行
这是流程的描述:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define STDIN 0
int sendall(int s, char *buf, int *len)
{
int total = 0; // how many bytes we've sent
int bytesleft = *len; // how many we have left to send
int n;
while(total < *len) {
n = send(s, buf+total, bytesleft, 0);
fprintf(stdout,"Sendall: %s\n",buf+total);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*len = total; // return number actually sent here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
int main(int argc, char *argv[])
{
int sockfd;
struct addrinfo hints, *dstinfo = NULL, *srcinfo = NULL, *p = NULL;
int rv = -1, ret = -1, len = -1, numbytes = 0;
struct timeval tv;
char buffer[256] = {0};
fd_set readfds;
// don't care about writefds and exceptfds:
// select(STDIN+1, &readfds, NULL, NULL, &tv);
if (argc != 4) {
fprintf(stderr,"usage: %s dst-hostname dst-udpport src-udpport\n");
ret = -1;
goto LBL_RET;
}
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM; //UDP communication
/*For destination address*/
if ((rv = getaddrinfo(argv[1], argv[2], &hints, &dstinfo)) != 0) {
fprintf(stderr, "getaddrinfo for dest address: %s\n", gai_strerror(rv));
ret = 1;
goto LBL_RET;
}
// loop through all the results and make a socket
for(p = dstinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1) {
perror("socket");
continue;
}
/*Taking first entry from getaddrinfo*/
break;
}
/*Failed to get socket to all entries*/
if (p == NULL) {
fprintf(stderr, "%s: Failed to get socket\n");
ret = 2;
goto LBL_RET;
}
/*For source address*/
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM; //UDP communication
hints.ai_flags = AI_PASSIVE; // fill in my IP for me
/*For source address*/
if ((rv = getaddrinfo(NULL, argv[3], &hints, &srcinfo)) != 0) {
fprintf(stderr, "getaddrinfo for src address: %s\n", gai_strerror(rv));
ret = 3;
goto LBL_RET;
}
/*Bind this datagram socket to source address info */
if((rv = bind(sockfd, srcinfo->ai_addr, srcinfo->ai_addrlen)) != 0) {
fprintf(stderr, "bind: %s\n", gai_strerror(rv));
ret = 3;
goto LBL_RET;
}
/*Connect this datagram socket to destination address info */
if((rv= connect(sockfd, p->ai_addr, p->ai_addrlen)) != 0) {
fprintf(stderr, "connect: %s\n", gai_strerror(rv));
ret = 3;
goto LBL_RET;
}
while(1){
FD_ZERO(&readfds);
FD_SET(STDIN, &readfds);
FD_SET(sockfd, &readfds);
/*Select timeout at 10s*/
tv.tv_sec = 10;
tv.tv_usec = 0;
select(sockfd + 1, &readfds, NULL, NULL, &tv);
/*Obey your user, take his inputs*/
if (FD_ISSET(STDIN, &readfds))
{
memset(buffer, 0, sizeof(buffer));
len = 0;
printf("A key was pressed!\n");
if(0 >= (len = read(STDIN, buffer, sizeof(buffer))))
{
perror("read STDIN");
ret = 4;
goto LBL_RET;
}
fprintf(stdout, ">>%s\n", buffer);
/*EOM\n implies user wants to exit*/
if(!strcmp(buffer,"EOM\n")){
printf("Received EOM closing\n");
break;
}
/*Sendall will use send to transfer to bound sockfd*/
if (sendall(sockfd, buffer, &len) == -1) {
perror("sendall");
fprintf(stderr,"%s: We only sent %d bytes because of the error!\n", argv[0], len);
ret = 5;
goto LBL_RET;
}
}
/*We've got something on our socket to read */
if(FD_ISSET(sockfd, &readfds))
{
memset(buffer, 0, sizeof(buffer));
printf("Received something!\n");
/*recv will use receive to connected sockfd */
numbytes = recv(sockfd, buffer, sizeof(buffer), 0);
if(0 == numbytes){
printf("Destination closed\n");
break;
}else if(-1 == numbytes){
/*Could be an ICMP error from remote end*/
perror("recv");
printf("Receive error check your firewall settings\n");
ret = 5;
goto LBL_RET;
}
fprintf(stdout, "<<Number of bytes %d Message: %s\n", numbytes, buffer);
}
/*Heartbeat*/
printf(".\n");
}
ret = 0;
LBL_RET:
if(dstinfo)
freeaddrinfo(dstinfo);
if(srcinfo)
freeaddrinfo(srcinfo);
close(sockfd);
return ret;
}
真的关键是connect():
如果套接字sockfd的类型为SOCK_DGRAM,则addr是默认情况下发送数据报的地址,以及接收数据报的唯一地址.