text: #ifndef FLOW_H
  #define FLOW_H
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #include <stdbool.h>
  #include <stddef.h>
  
  //general error codes that are returned by functions
  #define E_IO -1 //IO error
  #define E_ACCESS_DENIED -2 //access denied
  #define E_BUSY -3 // port is busy
  #define E_INVALID_SETTINGS -4 // some port settings are invalid
  #define E_INTERRUPT -5 // not really an error, function call aborted because port is closed
  #define E_NO_PORT -6 //requested port does not exist
  
  #define PARITY_NONE 0
  #define PARITY_ODD 1
  #define PARITY_EVEN 2
  
  /** Contains internal configuration of an open serial port. */
  struct serial_config;
  
  /**Opens a serial port and allocates memory for storing configuration. Note: if this function fails,
   * any internally allocated resources will be freed.
   * @param port_name name of port
   * @param baud baud rate
   * @param char_size character size of data transmitted through serial device
   * @param two_stop_bits set to use two stop bits instead of one
   * @param parity kind of parity checking to use
   * @param serial pointer to memory that will be allocated with a serial structure
   * @return 0 on success
   * @return E_NO_PORT if the given port does not exist
   * @return E_ACCESS_DENIED if permissions are not sufficient to open port
   * @return E_BUSY if port is already in use
   * @return E_INVALID_SETTINGS if any of the specified settings are invalid
   * @return E_IO on other error */
  int serial_open(
      const char* port_name,
      int baud,
      int char_size,
      bool two_stop_bits,
      int parity,
      struct serial_config** const serial);
  
  /**Closes a previously opened serial port and frees memory containing the configuration. Note: after a call to
   * this function, the 'serial' pointer will become invalid, make sure you only call it once. This function is NOT
   * thread safe, make sure no read or write is in prgress when this function is called (the reason is that per 
   * close manual page, close should not be called on a file descriptor that is in use by another thread). 
   * @param serial pointer to serial configuration that is to be closed (and freed)
   * @return 0 on success
   * @return E_IO on error */
  int serial_close(struct serial_config* const serial);
  
  /**Starts a read from a previously opened serial port. The read is blocking, however it may be
   * interrupted by calling 'serial_cancel_read' on the given serial port.
   * @param serial pointer to serial configuration from which to read
   * @param buffer buffer into which data is read
   * @param size maximum buffer size
   * @return n>0 the number of bytes read into buffer
   * @return E_INTERRUPT if the call to this function was interrupted
   * @return E_IO on IO error */
  int serial_read(struct serial_config* const serial, char* const buffer, size_t size);
  
  /**Cancels a blocked read call. This function is thread safe, i.e. it may be called from a thread even
   * while another thread is blocked in a read call.
   * @param serial_config the serial port to interrupt
   * @return 0 on success
   * @return E_IO on error */
  int serial_cancel_read(struct serial_config* const serial);
  
  /**Writes data to a previously opened serial port. Non bocking.
   * @param serial pointer to serial configuration to which to write
   * @param data data to write
   * @param size number of bytes to write from data
   * @return n>0 the number of bytes written
   * @return E_IO on IO error */
  int serial_write(struct serial_config* const serial, char* const data, size_t size);
  
  /**Sets debugging option. If debugging is enabled, detailed error message are printed from method calls. */
  void serial_debug(bool value);
  
  #ifdef __cplusplus
  }
  #endif
  
  
  #endif /* FLOW_H */
  