N2KConnection.c

/*
 *  Copyright (C) 2023 Swansea University
 *
 *  This file is part of the SELKIELogger suite of tools.
 *
 *  SELKIELogger is free software: you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the Free
 *  Software Foundation, either version 3 of the License, or (at your option)
 *  any later version.
 *
 *  SELKIELogger is distributed in the hope that it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 *  more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this SELKIELogger product.
 *  If not, see <http://www.gnu.org/licenses/>.
*/
 
#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
 
#include "N2KConnection.h"
 
#include "SELKIELoggerBase.h"
 
int n2k_openConnection(const char *device, const int baud) {
    if (device == NULL) { return -1; }
    return openSerialConnection(device, baud);
}
 
void n2k_closeConnection(int handle) {
    errno = 0;
    close(handle);
}
 
bool n2k_act_readMessage(int handle, n2k_act_message *out) {
    static uint8_t buf[N2K_BUFF];
    static size_t index = 0; // Current read position
    static size_t hw = 0;    // Current array end
    return n2k_act_readMessage_buf(handle, out, buf, &index, &hw);
}
 
bool n2k_act_readMessage_buf(int handle, n2k_act_message *out, uint8_t buf[N2K_BUFF], size_t *index, size_t *hw) {
    int ti = 0;
    if ((*hw) < N2K_BUFF - 1) {
        errno = 0;
        ti = read(handle, &(buf[(*hw)]), N2K_BUFF - (*hw));
        if (ti >= 0) {
            (*hw) += ti;
        } else {
            if (errno != EAGAIN) {
                fprintf(stderr, "Unexpected error while reading from serial port (handle ID: 0x%02x)\n",
                        handle);
                fprintf(stderr, "read returned \"%s\" in readMessage\n", strerror(errno));
                out->priority = 0xAA;
                return false;
            }
        }
    }
    if (((*hw) == N2K_BUFF) && (*index) > 0 && (*index) > ((*hw) - 25)) {
        // Full buffer, very close to the fill limit
        // Assume we're full of garbage before index
        memmove(buf, &(buf[(*index)]), N2K_BUFF - (*index));
        (*hw) -= (*index);
        (*index) = 0;
        out->priority = 0xFF;
        if (ti == 0) { out->priority = 0xFD; }
        return false;
    }
 
    n2k_act_message *t = NULL;
    bool r = n2k_act_from_bytes(buf, *hw, &t, index, false);
    if (t) {
        (*out) = (*t);
        free(t); // Shallow copied into out, so don't free ->data
        t = NULL;
    } else {
        out->priority = 0xEE;
    }
 
    if (!r) { out->priority = 0xEE; }
 
    if ((*hw) > 0 && ((*hw) >= (*index))) {
        // Move data from index back to zero position
        memmove(buf, &(buf[(*index)]), N2K_BUFF - (*index));
        (*hw) -= (*index);
        (*index) = 0;
    }
    return r;
}