用於Linux的套接字程序中的recvfrom api

Question

int acceptSocket;
char buf[100];
long sentbytes;
socklen_t len;
int port = 18227;

int CreateSocket()
{
    long rc;
    struct sockaddr_in addr, client;

       // Socket creation for UDP
       acceptSocket=socket(AF_INET,SOCK_DGRAM,0);

       if(acceptSocket==-1)
       {
         printf("Failure: socket creation is failed, failure code\n");
         return 1;
       }
       else
       {
         printf("Socket started!\n");
       }

     memset(&addr, 0, sizeof(struct sockaddr_in));
     addr.sin_family=AF_INET;
     addr.sin_port=htons(port);
     addr.sin_addr.s_addr=htonl(INADDR_ANY);
     rc=bind(acceptSocket,(struct sockaddr*)&addr,sizeof(addr));

     if(rc== -1)
     {
       printf("Failure: listen, failure code:\n");
       return 1;
     }
     else
     {
       printf("Socket an port %d \n",port);
     }

     while(rc!=-1)
         {
         len =sizeof(client);
         rc=recvfrom(acceptSocket,buf, sizeof(buf), 0, (struct sockaddr*) &client, &len);
         if(rc==0)
         {
           printf("Server has no connection..\n");
           break;
         }
         if(rc==-1)
         {
             printf("something went wrong with data %s", strerror(errno));
           break;
         }

         XcpIp_RxCallback( (uint16) rc, (uint8*) buf, (uint16) port );

            makeTimer("First Timer", &firstTimerID, 2, 2);   //2ms
                makeTimer("Second Timer", &secondTimerID, 10, 10);    //10ms
                makeTimer("Third Timer", &thirdTimerID, 100, 100);  //100ms
          }

       close(acceptSocket);
       return 0;
     }

int main()
{
     Xcp_Initialize();
     CreateSocket();
     return 0;
}

//API for sending the data to the client.
void XcpApp_IpTransmit( uint16 XcpPort,  Xcp_StatePtr8 pBytes, uint16 numBytes )
{
    struct sockaddr_in client;

        if ((long)XcpPort==port){
                sentbytes = sendto(acceptSocket,(char*)pBytes,(long)numBytes,0, (struct sockaddr*)&client, sizeof(client));
        }
        XcpIp_TxCallback(port,(uint16)sentbytes);
}

我創建了一個服務器端程序，用於從客戶端接收數據並將響應發送回客戶端。 我不知道上面程序中的錯誤在哪里，我能夠從客戶端接收數據，在這種情況下rc值為zer0。 然后，我正在檢查rc的值，它從程序中出來。 以后沒有任何響應返回給客戶端。 客戶端是用於將數據發送到指定端口和IP地址的工具。

可能是什么問題，為什么在recvfrom api之后rc值為零？ 注意：客戶端將繼續發送數據。 有人可以幫我嗎？

Answer 1

根據recvfrom手冊頁

成功完成后，recvfrom（）將以字節為單位返回消息的長度。 如果沒有消息可供接收並且對等方已執行有序的關閉，則recvfrom（）將返回0。否則，該函數將返回-1並設置errno以指示錯誤。

因此，我認為在您的情況下，當連接被另一台主機關閉時， recvfrom()的返回值為0（此斷開是否正常還是無關緊要）

我也更新了您的代碼，請嘗試一下

#define BUFLEN 100  //Max length of buffer
#define PORT 18227   //The port on which to listen for incoming data

void die(char *s)
{
    perror(s);
exit(1);
}

int acceptSocket;
char buf[BUFLEN];
long sentbytes;

int CreateSocket()
{
    struct sockaddr_in si_me, si_other, si_other2;

    int s, i, slen = sizeof(si_other) , recv_len;

    //create a UDP socket
    if ((acceptSocket=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
    {
        die("socket");
    }

    // zero out the structure
    memset((char *) &si_me, 0, sizeof(si_me));

    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(PORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);

    //bind socket to port
    if( bind(acceptSocket , (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)
    {
        die("bind");
    }

    //keep listening for data
    while(1)
    {
        printf("Waiting for data...");
        fflush(stdout);

        //try to receive some data, this is a blocking call
        if ((recv_len = recvfrom(acceptSocket, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen)) == -1)   // read datagram from server socket
        {
            die("recvfrom()");
        }

        //print details of the client/peer and the data received
        printf("Received packet from %s:%d\n", inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));         printf("Data: %s\n" , buf);

        XcpIp_RxCallback( (uint16) rc, (uint8*) buf, (uint16) port );

        makeTimer("First Timer", &firstTimerID, 2, 2);   //2ms
        makeTimer("Second Timer", &secondTimerID, 10, 10);    //10ms
        makeTimer("Third Timer", &thirdTimerID, 100, 100);  //100ms
    }

    close(s);
 }