连接一个没有监听的端口结果会怎样

一句话总结：消息可达的情况下服务端直接抛个RST过来

服务端：

#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

using namespace std;
int main()
{
struct sockaddr_in serAddr;
int listenSock, cnntSock;
listenSock = socket(AF_INET, SOCK_STREAM, 0);
serAddr.sin_family = AF_INET;
serAddr.sin_addr.s_addr = INADDR_ANY;
serAddr.sin_port = htons(1248);

bind(listenSock, (const struct sockaddr *)&serAddr, sizeof(sockaddr_in));
listen(listenSock, 10);

struct sockaddr_in cliAddr;
socklen_t len = sizeof(sockaddr_in);
cnntSock = accept(listenSock, (struct sockaddr*)&cliAddr, &len);
cout<< "IP:" <<inet_ntoa(cliAddr.sin_addr) <<", port:"<<cliAddr.sin_port<<endl;
unsigned int total = 0;
while(1)
{
getchar();
cout <<"read msg..."<<endl;
char buf[6000] = {0};
int ret = recv(cnntSock, buf, sizeof(buf), 0);
total += ret;
cout << "msg:" <<endl;
cout << buf;
cout << "recv msg size:" << ret << "total size:" << total <<endl;
break;
}
close(cnntSock);
close(listenSock);
return 0;
}

看结果，客户端发送syn给服务端，服务端直接回了个RST。