KISS.c

#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include "KISS.h"
#include "Serial.h"

int frame_len;
bool IN_FRAME;
bool ESCAPE;

uint8_t kiss_command = CMD_UNKNOWN;
uint8_t frame_buffer[MAX_PAYLOAD];
uint8_t write_buffer[MAX_PAYLOAD*2+3];

extern bool verbose;
extern bool daemonize;
extern int attached_if;
extern int device_type;
extern void cleanup(void);

void kiss_frame_received(int frame_len) {
    if ( (device_type == IF_TUN && frame_len >= TUN_MIN_FRAME_SIZE) || (device_type == IF_TAP && frame_len >= ETHERNET_MIN_FRAME_SIZE) )  {
        int written = write(attached_if, frame_buffer, frame_len);
        if (written == -1) {
            if (verbose && !daemonize) printf("Could not write received KISS frame (%d bytes) to network interface, is the interface up?\r\n", frame_len);
        } else if (written != frame_len) {
            if (!daemonize) printf("Error: Could only write %d of %d bytes to interface", written, frame_len);
            cleanup();
            exit(1);
        }
        if (verbose && !daemonize) printf("Got %d bytes from TNC, wrote %d bytes to interface\r\n", frame_len, written);
    }
}

void kiss_serial_read(uint8_t sbyte) {
    if (IN_FRAME && sbyte == FEND && kiss_command == CMD_DATA) {
        IN_FRAME = false;
        kiss_frame_received(frame_len);
    } else if (sbyte == FEND) {
        IN_FRAME = true;
        kiss_command = CMD_UNKNOWN;
        frame_len = 0;
    } else if (IN_FRAME && frame_len < MAX_PAYLOAD) {
        // Have a look at the command byte first
        if (frame_len == 0 && kiss_command == CMD_UNKNOWN) {
            // Strip of port nibble
            kiss_command = sbyte & 0x0F;
        } else if (kiss_command == CMD_DATA) {
            if (sbyte == FESC) {
                ESCAPE = true;
            } else {
                if (ESCAPE) {
                    if (sbyte == TFEND) sbyte = FEND;
                    if (sbyte == TFESC) sbyte = FESC;
                    ESCAPE = false;
                }

                if (frame_len < MAX_PAYLOAD) {
                    frame_buffer[frame_len++] = sbyte;
                }
            }
        }
    }
}

int kiss_write_frame(int serial_port, uint8_t* buffer, int frame_len) {
    int write_len = 0;
    write_buffer[write_len++] = FEND;
    write_buffer[write_len++] = CMD_DATA;
    for (int i = 0; i < frame_len; i++) {
        uint8_t byte = buffer[i];
        if (byte == FEND) {
            write_buffer[write_len++] = FESC;
            write_buffer[write_len++] = TFEND;
        } else if (byte == FESC) {
            write_buffer[write_len++] = FESC;
            write_buffer[write_len++] = TFESC;
        } else {
            write_buffer[write_len++] = byte;
        }
    }
    write_buffer[write_len++] = FEND;

    return write(serial_port, write_buffer, write_len);
}