Using PThread in Serial Programming in Windows - c

Question

I am a noob in serial programming and I am trying to build a com port sniffer to sniff bytes between two ports by using pthreads. I am using com0com emulator for the com ports. The emulator creates COM ports in connected pairs. At first, I wanted to sniff using this scenario:
Application1<--->COM3<--->Sniffer<--->COM4<--->Application2
However, I am unable to read what goes on between the two ports even when I set the ports in the code to non-exclusive mode before the running the application, also, the applications are unable to access the ports (error is "Access Denied").
I tried to this scenario:
Application1<--->COM3<--->COM4<--->Sniffer<--->COM5<--->COM4<--->Application2
With this, code is able to read COM4 and COM5 while the applications take COM3 and COM4. In this scenario, I am able to see the bytes and write in one direction with one thread. But when I try to use two threads to ensure bi-directional communication, it fails at the first read.
Code for the second scenario:
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <pthread.h>
void setupPort(HANDLE * handle, char * portName);
void * readFromPort(void * handles);
void writeToPort(HANDLE * handle, char data[]);
typedef struct
{
HANDLE from;
HANDLE to;
} bi_ports;
int main()
{
HANDLE first_port, second_port;
char * first_port_name = "COM4";
char * second_port_name = "COM5";
bi_ports *ports_first, *ports_second;
pthread_t firstToSecondThread, secondToFirstThread;
setupPort(&first_port, first_port_name);
setupPort(&second_port, second_port_name);
ports_first = (bi_ports *) malloc(sizeof(bi_ports));
ports_second = (bi_ports *) malloc(sizeof(bi_ports));
ports_first->from = first_port;
ports_first->to = second_port;
ports_second->from = second_port;
ports_second->to = first_port;
pthread_create(&firstToSecondThread, NULL, readFromPort, (void *) ports_first);
pthread_create(&secondToFirstThread, NULL, readFromPort, (void *) ports_second);
pthread_join(firstToSecondThread, NULL);
pthread_join(secondToFirstThread,NULL);
return 0;
}
void setupPort(HANDLE * handle, char * portName)
{
BOOL status;
*handle = CreateFile(portName, //port name
GENERIC_READ | GENERIC_WRITE, //Read/Write
0, // No Sharing
NULL, // No Security
OPEN_EXISTING,// Open existing port only
0, // Non Overlapped I/O
NULL); // Null for Comm Devices
if (handle == INVALID_HANDLE_VALUE)
{
printf("\n%s could not be opened\n", portName);
}
else
{
printf("\n%s successfully opened.\n", portName);
}
DCB dcbSerialParams = { 0 }; // Initializing DCB structure
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
status = GetCommState(*handle, &dcbSerialParams); //retreives the current settings
if (status == FALSE)
printf("\n Error! in GetCommState()");
dcbSerialParams.BaudRate = CBR_9600; // Setting BaudRate = 9600
dcbSerialParams.ByteSize = 8; // Setting ByteSize = 8
dcbSerialParams.StopBits = ONESTOPBIT; // Setting StopBits = 1
dcbSerialParams.Parity = NOPARITY; // Setting Parity = None
status = SetCommState(*handle, &dcbSerialParams); //Configuring the port according to settings in DCB
if (status == FALSE)
{
printf("\n Error! in Setting DCB Structure");
}
else //If Successful display the contents of the DCB Structure
{
printf("\n\n Setting DCB Structure Successful\n");
printf("\n Baudrate = %d", dcbSerialParams.BaudRate);
printf("\n ByteSize = %d", dcbSerialParams.ByteSize);
printf("\n StopBits = %d", dcbSerialParams.StopBits);
printf("\n Parity = %d", dcbSerialParams.Parity);
}
/*------------------------------------ Setting Timeouts --------------------------------------------------*/
COMMTIMEOUTS timeouts = { 0 };
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if (SetCommTimeouts(*handle, &timeouts) == FALSE)
printf("\n\n Error! in Setting Time Outs");
else
printf("\n\n Setting Serial Port Timeouts Successful");
/*------------------------------------ Setting Receive Mask ----------------------------------------------*/
status = SetCommMask(*handle, EV_RXCHAR); //Configure Windows to Monitor the serial device for Character Reception
if (status == FALSE)
printf("\n\n Error! in Setting CommMask");
else
printf("\n\n Setting CommMask successful");
}
void * readFromPort(void * handles)
{
bi_ports* ports;
ports = (bi_ports*) handles;
HANDLE handleFrom;
HANDLE handleTo;
handleFrom = ports->from;
handleTo = ports->to;
BOOL status;
DWORD dwEventMask; // Event mask to trigger
char TempChar; // Temporary Character
char SerialBuffer[256]; // Buffer Containing Rxed Data
DWORD NoBytesRead; // Bytes read by ReadFile()
int i = 0;
DWORD dNoOFBytestoWrite;
DWORD dNoOfBytesWritten = 0; // No of bytes written to the port
/*------------------------------------ Setting WaitComm() Event ----------------------------------------*/
while(TRUE)
{
printf("\n\n Waiting for Data Reception");
status = TRUE;//WaitCommEvent(handleFrom, &dwEventMask, NULL); //Wait for the character to be received
/*-------------------------- Program will Wait here till a Character is received ------------------------*/
if (status == FALSE)
{
printf("\n Error! in Setting WaitCommEvent()");
}
else //If WaitCommEvent()==True Read the RXed data using ReadFile();
{
printf("\n\n Characters Received\n");
do
{
status = ReadFile(handleFrom, &TempChar, sizeof(TempChar), &NoBytesRead, NULL);
SerialBuffer[i] = TempChar;
i++;
}
while (NoBytesRead > 0);
/*------------Printing the RXed String to Console----------------------*/
if(NoBytesRead > 0){
printf("\n\n ");
int j =0;
for (j = 0; j < i-1; j++) // j < i-1 to remove the dupliated last character
{
printf("%02X", (unsigned int)(unsigned char)SerialBuffer[j]);
}
dNoOFBytestoWrite = sizeof(SerialBuffer);
status = WriteFile(handleTo, // Handle to the Serialport
SerialBuffer, // Data to be written to the port
dNoOFBytestoWrite, // No of bytes to write into the port
&dNoOfBytesWritten, // No of bytes written to the port
NULL);
if (status == TRUE)
{
printf("\n\n %X - Written to port", (unsigned int)(unsigned char)SerialBuffer);
}
else
{
printf("\n\n Error %d in Writing to Serial Port",GetLastError());
}
//CloseHandle(handleTo);
i=0;
}
}
//CloseHandle(handleFrom);//Closing the Serial Port
printf("\n +==========================================+\n");
}
}