Question

我编写了一个基本的客户端服务器代码来了解TCP状态。客户代码：

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main(){
int clientSocket;
char buffer[1024];
struct sockaddr_in serverAddr;
socklen_t addr_size;

/*---- Create the socket. The three arguments are: ----*/
/* 1) Internet domain 2) Stream socket 3) Default protocol (TCP in this case) */
clientSocket = socket(PF_INET, SOCK_STREAM, 0);

/*---- Configure settings of the server address struct ----*/
/* Address family = Internet */
serverAddr.sin_family = AF_INET;
/* Set port number, using htons function to use proper byte order */
serverAddr.sin_port = htons(7891);
/* Set IP address to localhost */
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
/* Set all bits of the padding field to 0 */
memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);  

/*---- Connect the socket to the server using the address struct ----*/
addr_size = sizeof serverAddr;
connect(clientSocket, (struct sockaddr *) &serverAddr, addr_size);

/*---- Read the message from the server into the buffer ----*/
recv(clientSocket, buffer, 1024, 0);

/*---- Print the received message ----*/
printf("Data received: %s",buffer);   

return 0;
}

服务器代码：

/****************** SERVER CODE ****************/

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main(){
int welcomeSocket, newSocket;
char buffer[1024];
struct sockaddr_in serverAddr;
struct sockaddr_storage serverStorage;
socklen_t addr_size;
welcomeSocket = socket(PF_INET, SOCK_STREAM, 0);
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(7891);
serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
memset(serverAddr.sin_zero, '\0', sizeof serverAddr.sin_zero);  

bind(welcomeSocket, (struct sockaddr *) &serverAddr, sizeof(serverAddr));

if(listen(welcomeSocket,5)==0)
printf("Listening\n");
else
  printf("Error\n");

addr_size = sizeof serverStorage;
newSocket = accept(welcomeSocket, (struct sockaddr *) &serverStorage, &addr_size);

strcpy(buffer,"Hello World\n");
send(newSocket,buffer,13,0);

return 0;
}

我正在运行命令netstat -an | grep 7891，因此在不同的时间点，我将获得状态ESTABLISHED，LISTENING，FINWAIT2，CLOSE_WAIT和TIME_WAIT。如何获取SYN_RECV，SYN_SENT，FINWAIT1，CLOSING和LAST ACK等其他状态。

我尝试了各种netstat选项和ss选项，但没有白费。

Answer 1

您没有看到SYN_RECV，SYN_SENT等，因为这些阶段太短。例如，在服务器端的成功accept()之后，您已经获得了ESTABLISHED，所有先前的状态将由TCP堆栈快速执行。所以，你只是在观察tcp连接的长状态。

您可以通过模拟SYN-flood来实现SYN_ *状态：在服务器端使用listen(...,1)的backlog参数并在return 0之前休眠。并尝试启动几个单独的客户端。结果你会得到：ETSABLISHED中的1和SYN_ *中的几个。

关于完成状态。您应该拨打shutdown()和close()并在它们之间设置睡眠状态。我建议您使用fork()进行子进程并使用同步原语来理解TCP状态

某些TCP状态未显示在终端中

1 个答案: