如何确保服务器区分从同一台计算机上的两个不同 shell 运行的两个不同 TCP 客户端？

Question

如果我从两个不同的 shell 运行客户端程序，服务器应该如何确定他当前正在与谁交谈？

平台：Linux、GCC

客户端代码：此客户端将主机名作为参数。

#define SERVERPORT 3490
#define MAXDATASIZE 1000 

int main (int argc, char *argv[])
{
    int             clientSocketFD;
    int                 numOfBytesReceived;
    char                    receivedData[MAXDATASIZE];
    struct hostent                  *objHostent;
    struct sockaddr_in              serverAddress;

    if (argc != 2) 
    {
        fprintf (stderr,"usage: key in client hostname.\n");
        exit (1);
    }

    if ((objHostent = gethostbyname (argv[1])) == NULL)
    {
        herror ("error: incorrect host name specified.");
        exit (1);
    }

    if ((clientSocketFD = socket (PF_INET, SOCK_STREAM, 0)) == -1) 
    {
        perror ("error: socket system call failed.");
        exit (1);
    }

    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port    = htons (SERVERPORT);
    serverAddress.sin_addr   = *((struct in_addr *)objHostent->h_addr);
    memset (serverAddress.sin_zero, '\0', sizeof serverAddress.sin_zero);

    if (connect (clientSocketFD, (struct sockaddr *)&serverAddress, sizeof serverAddress) == -1)
    {
        perror ("connect() error");
        exit (1);
    }

    while (1)
    {
        if ((numOfBytesReceived = recv (clientSocketFD, receivedData, MAXDATASIZE-1, 0)) == -1)
        {
            perror ("\nrecv() error");
        }

        receivedData [numOfBytesReceived] = '\0';

        if (send (clientSocketFD, "Get Lost", 15, 0) == -1)
        {
            perror ("send() error");
        }
    }
    close (clientSocketFD);
    return 0;
}

服务器代码：

#define SERVERPORT 3490
#define BACKLOG 10

struct threadArguments
{
    int    threadId;
    int    listeningSocketDescriptor;
    char *message;
};

struct threadArguments threadDataArray [5];

void* genericThreadFunction (void* threadData)
{
    struct threadArguments *temp;
    temp         = (struct threadArguments *) threadData;

    printf ("Hello World! It's me, thread #%ld!\n", (long) temp->threadId);

    while (1)
    {
        if (send (temp->listeningSocketDescriptor, temp->message, 14, 0) == -1)
            perror ("\nsend() error\n");

        char receivedData [14];
        int    numOfBytesReceived;
        if ((numOfBytesReceived = recv (temp->listeningSocketDescriptor, receivedData, 14-1, 0)) == -1)
        {
            perror ("\nrecv() error\n");
        }
        else
        {
            receivedData [numOfBytesReceived] = '\0';
            printf ("\nReceived: %s\n", receivedData);
        }
    }
}

int main (void)
{
    int                 serverSocketFD;
    int                 newServersocketFD;
    struct sockaddr_in          serverAddress;

    struct sockaddr_in          clientAddress;
    socklen_t           sin_size;

    if ((serverSocketFD = socket (AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror ("socket");
        exit (1);
    }
    int yes=1;
    if (setsockopt (serverSocketFD, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
    {
        perror ("setsockopt");
        exit (1);
    }

    serverAddress.sin_family     = AF_INET;                 // host byte order
    serverAddress.sin_port       = htons (SERVERPORT);      // short, network byte order
    serverAddress.sin_addr.s_addr = INADDR_ANY;             // automatically fill with my IP
    memset (serverAddress.sin_zero, '\0', sizeof serverAddress.sin_zero);

    if (bind (serverSocketFD, (struct sockaddr *)&serverAddress, sizeof serverAddress) == -1)
    {
        perror ("bind");
        exit (1);
    }

    if (listen (serverSocketFD, BACKLOG) == -1)
    {
        perror ("listen"); 
        exit (1);
    }

    pthread_t threads [5];
    int     returnValueOfPthreadCreate;
    long    threadId = -1;

    while (1) 
    {
        sin_size = sizeof clientAddress;
        if ((newServersocketFD = accept (serverSocketFD, (struct sockaddr *)&clientAddress, &sin_size)) == -1) 
        {
                perror ("accept");
                continue;
        }
        printf ("accept(): got connection from %s\n", inet_ntoa (clientAddress.sin_addr));

        threadId++;

        threadDataArray [threadId].threadId                  = threadId;
        threadDataArray [threadId].listeningSocketDescriptor = newServersocketFD;
        threadDataArray [threadId].message                   = "Excuse Me, please!";

        returnValueOfPthreadCreate = pthread_create (&threads [threadId], NULL, genericThreadFunction, (void*) &threadDataArray[threadId]);

        if (returnValueOfPthreadCreate)
        {
            printf ("ERROR; return code from pthread_create() is %d\n", returnValueOfPthreadCreate);
        }
    }

    pthread_exit (NULL);
    return 0;
}

编辑 1.

Peername 返回 0：

if ((newServersocketFD                                                 = accept (serverSocketFD, (struct sockaddr *)&clientAddress, &sin_size)) == -1) 
        {
                perror ("accept");
                continue;
        }
        printf ("accept(): got connection from %s\n", inet_ntoa (clientAddress.sin_addr));
        printf ("\npeername: %d", getpeername (newServersocketFD, (struct sockaddr *)&clientAddress, &sin_size));

Answer 1

客户端的 IP 地址和（源-）端口（如下所述获取）唯一标识客户端（-连接）。

如果您使用地址族IF_INET 创建listen()ing 套接字，您可以从struct sockaddr_in 类型的变量中提取客户端的IP 地址和（客户端的特定连接）（源-）端口，这是参考通过使用它的成员sin_addr 和sin_port 传递给accept()，每次accept() 成功返回。

根据您所在的平台，您需要更改此类成员的字节顺序（有关如何执行此操作，请参阅ntoh() 的手册页）。要直接将成员 sin_addr 转换为字符数组，您已经在使用一种处理字节顺序的方法 (inet_ntoa())。

在成功的accept() 返回的文件描述符上使用getpeername()（并且，在服务器进程的上下文中，也是唯一标识客户端的连接）应返回相同与accept() 的调用一样，对等方的 IP 地址和端口的值。

Answer 2

每个客户端都有一个单独的接受套接字（代码中的newServersocketFD）。
如果你在每一个上使用getpeername()，你会发现它们使用不同的源端口。