#ifndef SERIALSOURCE_H#define SERIALSOURCE_Htypedef struct serial_source *serial_source;typedef enum {  msg_unknown_packet_type,	/* packet of unknown type received */  msg_ack_timeout, 		/* ack not received within timeout */  msg_sync,			/* sync achieved */  msg_too_long,			/* greater than MTU (256 bytes) */  msg_too_short,		/* less than 4 bytes */  msg_bad_sync,			/* unexpected sync byte received */  msg_bad_crc,			/* received packet has bad crc */  msg_closed,			/* serial port closed itself */  msg_no_memory,		/* malloc failed */  msg_unix_error		/* check errno for details */} serial_source_msg;serial_source open_serial_source(const char *device, int baud_rate,				 int non_blocking,				 void (*message)(serial_source_msg problem));/* Effects: opens serial port device at specified baud_rate. If non_blocking     is true, read_serial_packet calls will be non-blocking (writes are     always blocking, for now at least)     If non-null, message will be called to signal various problems during     execution.   Returns: descriptor for serial forwarder at host:port, or     NULL for failure */int serial_source_fd(serial_source src);/* Returns: the file descriptor used by serial source src (useful when     non-blocking reads were requested)*/int serial_source_empty(serial_source src);/* Returns: true if serial source does not contain any pending data, i.e.,     if the result is true and there is no data available on the source's     file descriptor, then read_serial_packet will:       - return NULL if the source is non-blocking       - block if it is blocking    (Note: the presence of this calls allows the serial_source to do some    internal buffering)*/int close_serial_source(serial_source src);/* Effects: closes serial source src   Returns: 0 if successful, -1 if some problem occured (but source is     considered closed anyway) */void *read_serial_packet(serial_source src, int *len);/* Effects: Read the serial source src. If a packet is available, return it.     If in blocking mode and no packet is available, wait for one.   Returns: the packet read (in newly allocated memory), with *len is     set to the packet length, or NULL if no packet is yet available and     the serial source is in non-blocking mode*/int write_serial_packet(serial_source src, const void *packet, int len);/* Effects: writes len byte packet to serial source src   Returns: 0 if packet successfully written, 1 if successfully written     but not acknowledged, -1 otherwise*/#endif