UDP socket partial reading

I have the following problem:
I have to implement a communication with GigE cameras
On the control protocol packet lenghts are under control so i can any time read just as many bytes as needed
On the stream protocol instead evry time i am not sure how many bytes to read cause one packet might be missing and the following packet can be of different length

So the question is:
if a packet arrives of 9000 bytes and i perform a read of 756 bytes di i miss the rest of the packet??
I supposed no but the answre seems yes as i made the following test:

In the control protocol i substitued the following working code

Code:

---

        TimeOut.tv_sec=10;//CABLED
        TimeOut.tv_usec=0;
        if (SocketRead( Camera->CC.Socket, &(CCP_Ack) , sizeof(CCP_Ack), &TimeOut))
        {
                Log(&Lg,PrefixString,"SocketRead() error",0,LOG_ON_ERROR_ALSO);
                sprintf(LogString,"Time out = %d %d ",TimeOut.tv_sec,TimeOut.tv_usec);
                Log(&Lg,PrefixString,LogString,0,LOG_ON_ERROR_ALSO);
                return(1);
        }

---

with the following where the read was split in two

Code:

---

        TimeOut.tv_sec=10;//CABLED
        TimeOut.tv_usec=0;
        if (SocketRead( Camera->CC.Socket, &(CCP_Ack) , sizeof(CCP_Ack)-4, &TimeOut))
        {
                Log(&Lg,PrefixString,"SocketRead() error",0,LOG_ON_ERROR_ALSO);
                sprintf(LogString,"Time out = %d %d ",TimeOut.tv_sec,TimeOut.tv_usec);
                Log(&Lg,PrefixString,LogString,0,LOG_ON_ERROR_ALSO);
                return(1);
        }
        TimeOut.tv_sec=10;//CABLED
        TimeOut.tv_usec=0;
        if (SocketRead( Camera->CC.Socket, &(CCP_Ack.Reserved), 4, &TimeOut))
        {
                Log(&Lg,PrefixString,"SocketRead() error",0,LOG_ON_ERROR_ALSO);
                sprintf(LogString,"Time out = %d %d ",TimeOut.tv_sec,TimeOut.tv_usec);
                Log(&Lg,PrefixString,LogString,0,LOG_ON_ERROR_ALSO);
                return(1);
        }

---

The result was an error!!

here is the code of SocketRead()

Code:

---



int SocketRead ( int sock, unsigned char* iBuffer , unsigned int iToReadByteNumber,          struct timeval * TimeOut)
{
        //to be tested with signaling simulation and partial read (client sends only part of the message or too slowly)
 
        int                ToReadByteNumber;
        int                        ReadByteNumber;
        unsigned char*                Buffer;
       
        fd_set mono_fd_set, read_fd_set;
        int DataReady;
       
        struct timeval  TempTO;
       
        Type_LogString LogString;
       

       

       
    FD_ZERO (&mono_fd_set);
    FD_SET (sock, &mono_fd_set);
 
        ToReadByteNumber = iToReadByteNumber;
        ReadByteNumber = 0;
        Buffer          = iBuffer;
 
        while ( ToReadByteNumber > 0 )
        {
               
        read_fd_set = mono_fd_set;
            TempTO=*TimeOut;
        //to be done upper limit on TimeOut in case of signal
                DataReady=select (FD_SETSIZE, &read_fd_set, NULL, NULL, &TempTO);
        while (DataReady < 0)//Typically 1 sec //only to avoid peer-to-peer deadlock
        {

                              if (errno!=EINTR)
                              {
                                              Log(&Lg,"SocketRead :: ","Read Error",0,LOG_ON_ERROR_ALSO);
                                          return SOCKET_ERROR;
                              }
                        read_fd_set = mono_fd_set;
                            TempTO=*TimeOut;//TempT0;//it is not POSIX compliant to use TempTO cause it is not decremented in all implementations
                        DataReady=select (FD_SETSIZE, &read_fd_set, NULL, NULL, &TempTO);
        } 
       
                //in case of EINTR chars should not be lost before the first read
        if (DataReady)
        {
       
       
                    ReadByteNumber = read( sock , Buffer , ToReadByteNumber );
                    //sprintf(LogString,"ReadByteNumber = %d ",ReadByteNumber);
                    //Log(&Lg,"SocketRead :: ",LogString,0,LOG_ON_ERROR_NO);
                    if        ( ReadByteNumber < 0 )
                              {
                              if        ( errno != EINTR )//also SERVER_NON_CATASTROFIC_ERRNO must cause an error return code here
                                  {
                                      Log(&Lg,"SocketRead :: ","Read Error",0,LOG_ON_ERROR_ALSO);
                                  return SOCKET_ERROR;
                                  }
                              }
                    else if ( ReadByteNumber == 0 )
                              {
                              return SOCKET_CONNECTION_CLOSED;
                              }
                    else
                    {
                            ToReadByteNumber = ToReadByteNumber - ReadByteNumber;
                            Buffer = Buffer + ReadByteNumber;
                    }
           
        }
        else
        {
                Log(&Lg,"SocketRead :: ","TIME OUT",0,LOG_ON_ERROR_ALSO);
                *TimeOut=TempTO;
                      return SOCKET_USER_DEFINED_TIMEOUT;
        }
       
    }
 
        return SOCKET_OK;
 
}

---

same problems holds (+ a thread hanging) if i substitute the previous with this (without select)

Code:

---


int SocketRead ( int sock, unsigned char* iBuffer , unsigned int iToReadByteNumber,          struct timeval * TimeOut)
{
        //to be tested with signaling simulation and partial read (client sends only part of the message or too slowly)
 
        int                ToReadByteNumber;
        int                        ReadByteNumber;
        unsigned char*                Buffer;
       
        fd_set mono_fd_set, read_fd_set;
        int DataReady;
       
        struct timeval  TempTO;
       
        Type_LogString LogString;
       

       
        Log(&Lg,"SocketReadSimple :: ","Read",0,LOG_ON_ERROR_ALSO);

 
        ToReadByteNumber = iToReadByteNumber;
        ReadByteNumber = 0;
        Buffer          = iBuffer;
 
        while ( ToReadByteNumber > 0 )
        {
               

       
       
                    ReadByteNumber = read( sock , Buffer , ToReadByteNumber );
                    //sprintf(LogString,"ReadByteNumber = %d ",ReadByteNumber);
                    //Log(&Lg,"SocketRead :: ",LogString,0,LOG_ON_ERROR_NO);
                    if        ( ReadByteNumber < 0 )
                              {
                              if        ( errno != EINTR )//also SERVER_NON_CATASTROFIC_ERRNO must cause an error return code here
                                  {
                                      Log(&Lg,"SocketRead :: ","Read Error",0,LOG_ON_ERROR_ALSO);
                                  return SOCKET_ERROR;
                                  }
                              }
                    else if ( ReadByteNumber == 0 )
                              {
                              return SOCKET_CONNECTION_CLOSED;
                              }
                    else
                    {
                            ToReadByteNumber = ToReadByteNumber - ReadByteNumber;
                            Buffer = Buffer + ReadByteNumber;
                    }
           
 
       
    }
 
        return SOCKET_OK;
 
}

---

May be the solution is suggested here http://www.opengroup.org/onlinepubs/.../xsh/read.html ?
May be my read is in Message-discard mode ?