Bad File Descriptor with Linux Socket write() Bad File Descriptor C

c linux sockets tcp file-descriptor

135,698

Solution 1

In general, when "Bad File Descriptor" is encountered, it means that the socket file descriptor you passed into the API is not valid, which has multiple possible reasons:

The fd is already closed somewhere.
The fd has a wrong value, which is inconsistent with the value obtained from socket() api

Solution 2

The value you have passed as the file descriptor is not valid. It is either negative or does not represent a currently open file or socket.

So you have either closed the socket before calling write() or you have corrupted the value of 'sockfd' somewhere in your code.

It would be useful to trace all calls to close(), and the value of 'sockfd' prior to the write() calls.

Your technique of only printing error messages in debug mode seems to me complete madness, and in any case calling another function between a system call and perror() is invalid, as it may disturb the value of errno. Indeed it may have done so in this case, and the real underlying error may be different.

Solution 3

I had this error too, my problem was in some part of code I didn't close file descriptor and in other part, I tried to open that file!! use close(fd) system call after you finished working on a file.

135,698

Author by

user1336117

Updated on July 28, 2022

Comments

user1336117 almost 2 years

I have an interesting problem with write(2) function. PrepareResponseForSetCoordinates function causes bad file descriptor error on write.

Here is the line of error: perror("ERROR writing to socket"); total output: ERROR writing to socket: Bad file descriptor

I am sure that I have established the connection because PrepareResponseForConnectionTest works like a charm.

Can you have any idea about the reason of the error?

When I use gcc as compiler there was no problem. After that because of using multiple new cpp sources I am using g++ as compiler and I have this error.

Regards

Here below my code:

#define MAX_PMS_MESSAGE_LEN (4096)
unsigned char baCommBuffer[MAX_PMS_MESSAGE_LEN];
unsigned char PrepareResponseForSetCoordinates(void)
{
    unsigned char baTempBuff[255]={0};
    unsigned short bCnt=0,i=0,bCsum=0,bCnt2=0;
time_t lEpochTime;
time_t lSessionTime;

memset(baTempBuff,0,sizeof(baTempBuff));
memset(baCommBuffer,0,sizeof(baCommBuffer));
bzero(baCommBuffer,MAX_PMS_MESSAGE_LEN);
bzero(baTempBuff,sizeof(baTempBuff));


lEpochTime = time(NULL);
baCommBuffer[bCnt++]    =   START_CHAR;
baCommBuffer[bCnt++]    =   START_CHAR;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
sprintf((char*)baTempBuff,"%ld",(unsigned long)lEpochTime);
memcpy(baCommBuffer+bCnt,baTempBuff,10);

bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=10;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
//  lSessionTime = time(NULL);
if(SPMSMessage.lSessionID)
lSessionTime = SPMSMessage.lSessionID; 
else
lSessionTime=lEpochTime;
sprintf((char*)baTempBuff,"%ld",(unsigned long)lSessionTime);
memcpy(baCommBuffer+bCnt,baTempBuff,10);
bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=10;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   PMC_ID;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   PMS_ID;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'R';
baCommBuffer[bCnt++]    =   'E';
baCommBuffer[bCnt++]    =   'P';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'O';
baCommBuffer[bCnt++]    =   'O';
baCommBuffer[bCnt++]    =   'S';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
if(SPMSMessage.bParam== SET_COOR_CAM1_PARAM)
{
baCommBuffer[bCnt++]    =   '2';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'O';
baCommBuffer[bCnt++]    =   'N';
baCommBuffer[bCnt++]    =   'E';
baCommBuffer[bCnt++]    =   PARAMETER_SEPERATOR;
baCommBuffer[bCnt++]    =   'A';
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'K';
}
else if(SPMSMessage.bParam== SET_COOR_CAM2_PARAM)
{
baCommBuffer[bCnt++]    =   '2';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'T';
baCommBuffer[bCnt++]    =   'W';
baCommBuffer[bCnt++]    =   'O';
baCommBuffer[bCnt++]    =   PARAMETER_SEPERATOR;
baCommBuffer[bCnt++]    =   'A';
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'K';    
}
else
{
baCommBuffer[bCnt++]    =   '1';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'N';
baCommBuffer[bCnt++]    =   'A';
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'K';        
}
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   '*';
memset(baTempBuff,0,sizeof(baTempBuff));
bCsum = CalculateCheckSum(baCommBuffer);
sprintf((char*)baTempBuff,"%.2X",bCsum);
memcpy(baCommBuffer+bCnt,baTempBuff,2);
bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=2;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   END_CHAR;
baCommBuffer[bCnt++]    =   END_CHAR;

#ifdef _DEBUG_DEEP_DETAILED
            if(EDebugDeepDetail<GetDebugLevelOfPMC())
            {
                    printf("WILL BE sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    sprintf(caLogStr,"WILL BE sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    PrintToLogFile(caLogStr);
                    memset(caLogStr,0,MAX_LOG_STRLEN);
                }
#endif

        if((ETcpConnectionState== ETcpStateConnected) || (ETcpConnectionState== ETcpStateConnectedAndWaitingToWrite) )
        {

            if (write(sockfd,baCommBuffer,bCnt) < 0)
            {
                #ifdef _DEBUG_DETAILED
                if(EDebugDetail<GetDebugLevelOfPMC())
                {
                     perror("ERROR writing to socket"); 
                     PrintToLogFile("ERROR writing to socket");

                 }
                 #endif
             return 0;
            }
                #ifdef _DEBUG_DEEP_DETAILED
                if(EDebugDeepDetail<GetDebugLevelOfPMC())
                {
                    printf("sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    sprintf(caLogStr,"sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    PrintToLogFile(caLogStr);
                    memset(caLogStr,0,MAX_LOG_STRLEN);
                }
                #endif
        }
        else
        {
                #ifdef _DEBUG_DETAILED
                    if(EDebugDetail<GetDebugLevelOfPMC())
                    {
                    PrintToLogFile("Henüz Bağlantı Yok\n");
                    }
                #endif
                return 0;
        }


return (bCnt);

}

Here below you can see the code which run without error:

unsigned char PrepareResponseForConnectionTest(void)
{

unsigned char baTempBuff[20]={0};
unsigned char bCnt=0,i=0,bCsum=0;
time_t lEpochTime;
time_t lSessionTime;

memset(baTempBuff,0,sizeof(baTempBuff));
memset(baCommBuffer,0,sizeof(baCommBuffer));
bzero(baCommBuffer,MAX_PMS_MESSAGE_LEN);
bzero(baTempBuff,sizeof(baTempBuff));


lEpochTime = time(NULL);
baCommBuffer[bCnt++]    =   START_CHAR;
baCommBuffer[bCnt++]    =   START_CHAR;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
sprintf((char*)baTempBuff,"%ld",(unsigned long)lEpochTime);
memcpy(baCommBuffer+bCnt,baTempBuff,10);

bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=10;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;

lSessionTime = SPMSMessage.lSessionID; 
sprintf((char*)baTempBuff,"%ld",(unsigned long)lSessionTime);
memcpy(baCommBuffer+bCnt,baTempBuff,10);
bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=10;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   PMC_ID;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   PMS_ID;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'R';
baCommBuffer[bCnt++]    =   'E';
baCommBuffer[bCnt++]    =   'P';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'O';
baCommBuffer[bCnt++]    =   'N';
baCommBuffer[bCnt++]    =   'T';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   '1';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   'A';
baCommBuffer[bCnt++]    =   'C';
baCommBuffer[bCnt++]    =   'K';
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   '*';
memset(baTempBuff,0,sizeof(baTempBuff));
bCsum = CalculateCheckSum(baCommBuffer);
sprintf((char*)baTempBuff,"%.2X",bCsum);
memcpy(baCommBuffer+bCnt,baTempBuff,2);
bzero(baTempBuff,sizeof(baTempBuff));
bCnt+=2;
baCommBuffer[bCnt++]    =   PACKET_SEPERATOR;
baCommBuffer[bCnt++]    =   END_CHAR;
baCommBuffer[bCnt++]    =   END_CHAR;



        if((ETcpConnectionState== ETcpStateConnected) || (ETcpConnectionState== ETcpStateConnectedAndWaitingToWrite) )
        {

            if (write(sockfd,baCommBuffer,bCnt) < 0)
            {
             perror("ERROR writing to socket\n");
             PrintToLogFile("ERROR writing to socket\n");
            }
                #ifdef _DEBUG_DEEP_DETAILED
                if(EDebugDeepDetail<GetDebugLevelOfPMC())
                {
                    printf("sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    sprintf(caLogStr,"sent: %s uzunluk:%d\n", baCommBuffer,bCnt);
                    PrintToLogFile(caLogStr);
                    memset(caLogStr,0,MAX_LOG_STRLEN);
                }
                #endif
                return 0;
        }
        else
        {
                #ifdef _DEBUG_DETAILED
                    if(EDebugDetail<GetDebugLevelOfPMC())
                    {
                    PrintToLogFile("There is no connection yet\n");
                    }
                #endif
                //return 0;
        }

        //printf("\n\n");
return (bCnt);
}

Here is my InitializeConnection function and ConnectToServer function:

void InitializeTcpConnection(int argc, char *argv[])
{
   int optval;
   socklen_t optlen = sizeof(optval);
ETcpConnectionState = ETcpStateNotConnected;
    if (argc < 3) 
    {
       fprintf(stderr,"usage: %s hostname_or_ip port\n", argv[0]);
       #ifdef _DEBUG_PROCESS
       if(EDebugProcess<GetDebugLevelOfPMC())
       {
        sprintf(caLogStr,"usage: %s hostname_or_ip port\n", argv[0]);
        PrintToLogFile(caLogStr);
        memset(caLogStr,0,MAX_LOG_STRLEN);
        }
       #endif
       exit(0);
    }
    portno = atoi(argv[2]);
    /* int socket(domain,type,protocol)
     * socket creates an endpoint for communication and returns a descriptor
     * AF_INET: ARPA Internet protocols
     * SOCK_STREAM: sequenced, two way connection based byte streams
     * 
     * return: Socket returns a non-negative descriptor on success.
     * On failure it returns -1 and sets errno to indicate the error
     * */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        #ifdef _DEBUG_PROCESS
        if(EDebugProcess<GetDebugLevelOfPMC())
        {
        perror("ERROR creating socket");
        PrintToLogFile("ERROR creating socket\n");

        }
        #endif
        exit(1);
    }

    /**/


   /* Set the option active */
   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) 
   {
      #ifdef _DEBUG_PROCESS
      if(EDebugProcess<GetDebugLevelOfPMC())
        {
          perror("setsockopt()");
          PrintToLogFile("ERROR creating socket\n");
        }
      #endif
      close(sockfd);
      exit(EXIT_FAILURE);
   }
   #ifdef _DEBUG_PROCESS
   if(EDebugProcess<GetDebugLevelOfPMC())
   {
    printf("SO_KEEPALIVE set on socket\n");
    PrintToLogFile("SO_KEEPALIVE set on socket\n");
    }
      #endif
   /* Check the status again */
   if(getsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
       #ifdef _DEBUG_PROCESS
       if(EDebugProcess<GetDebugLevelOfPMC())
       {
          perror("getsockopt()");
          PrintToLogFile("getsockopt()");
      }
      #endif
      close(sockfd);
      exit(EXIT_FAILURE);
   }
   #ifdef _DEBUG_PROCESS
   if(EDebugProcess<GetDebugLevelOfPMC())
   {
   printf("SO_KEEPALIVE is %s\n", (optval ? "ON" : "OFF"));
   }
   #endif

   #ifdef _DEBUG_PROCESS

    if(EDebugProcess<GetDebugLevelOfPMC())
    {
    PrintToLogFile("Setting socket for reusability\n");
    }
   #endif

   if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(int)) == -1) 
   {
       #ifdef _DEBUG_PROCESS
       if(EDebugProcess<GetDebugLevelOfPMC())
       {
                perror("setsockopt");
                PrintToLogFile("Setting socket option error\n");
       }
       #endif
                exit(1);
   }

   /*********/

    //get the address info by either host name or IP address
    SetTcpServerIpAddress(argv[1]);
    server = gethostbyname(argv[1]);
    if (server == NULL) 
    {
        #ifdef _DEBUG_PROCESS
        if(EDebugProcess<GetDebugLevelOfPMC())
        {
        PrintToLogFile("ERROR, no such host\n");
        }
        #endif
        exit(1);
    }

    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length);
    //serv_addr.sin_port: unsigned short 
    //htons converts the unsigned short hostshort from host byte order to network byte order
    serv_addr.sin_port = htons(portno);


    ETcpConnectionState = ETcpStateWaitingForConnection;

}

int ConnectToServer(void)
{
                    if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)  
                    {
                        #ifdef _DEBUG_DETAILED
                        if(EDebugDetail<GetDebugLevelOfPMC())
                        {
                        PrintToLogFile("ERROR connecting");
                        }
                        #endif
                        return 1; // connection error
                        //exit(1);
                    }
                    else
                    {
                        #ifdef _DEBUG_DETAILED
                        if(EDebugDetail<GetDebugLevelOfPMC())
                        {
                        PrintToLogFile("connection established\n");
                        }
                        #endif
                    #ifndef PMS_COMM_POLL_MODE
                        #ifdef _DEBUG_DETAILED
                        if(EDebugDetail<GetDebugLevelOfPMC())
                        {
                        PrintToLogFile("State is non poll mode\n");
                        }
                        #endif
                    ETcpConnectionState = ETcpStateConnected;
                    #endif
                    #ifdef PMS_COMM_POLL_MODE
                        #ifdef _DEBUG_DETAILED
                        if(EDebugDetail<GetDebugLevelOfPMC())
                        {
                        PrintToLogFile("State is poll mode\n"); 
                        }
                        #endif
                    ETcpConnectionState = ETcpStateConnectedAndWaitingToRead;
                    #endif

                    SendRequestToGetImageUploadInfo();
                    }
return 0;   
}

user207421 about 4 years

This problem is caused by prematurely closing it, not by not closing it.
Steven almost 3 years

Thanks for your analyze about possible reasons, those are helpful to find out where cause the bug.