tabby/src/printer.c

#include <errno.h>

#include <tabby/link.h>
#include <tabby/printer.h>

#define PACKET_RECV_ERROR_THRESHOLD 30

static uint16_t checksum(tabby_printer_packet_header *header, void *body) {
    uint16_t checksum = header->data[2]
                      + header->data[3]
                      + header->data[4]
                      + header->data[5];

    size_t i;

    for (i=0; i<header->size; i++) {
        checksum += ((uint8_t *)body)[i];
    }

    return checksum;
}

int tabby_printer_packet_recv(int fd, tabby_printer_packet_header *header,
                                      void *body,
                                      tabby_printer_packet_footer *footer) {
    ssize_t len;

    size_t i = 0,
           b = 0,
           f = 0;

    uint8_t value,
            last;

    int started = 0;

    memset(header, '\0', sizeof(*header));
    memset(footer, '\0', sizeof(*footer));

    while ((len = tabby_link_recv(fd, &value, 1)) >= 0) {
        if (started) {
            if (i == 2) {
                header->type = value;
            } else if (i == 3) {
                header->compression = value;
            } else if (i == 4 || i == 5) {
                header->size <<= 8;
                header->size  |= value;
            } else if (i > 5 && b < header->size) {
                ((uint8_t *)body)[b++] = value;
            } else if (b >= header->size && f < 2) {
                footer->checksum <<= 8;
                footer->checksum  |= value;

                f++;
            } else if (f >= 2) {
                footer->data[f++] = value;

                if (f == sizeof(*footer)) {
                    if (checksum(header, body) != footer->checksum) {
                        errno = EIO;

                        goto error_io;
                    }

                    return 0;
                }
            }
        } else {
            if (last == 0x88 && value == 0x33) {
                started = 1;
                      i = 2;
                      b = 0;
                      f = 0;
            } else if (i == PACKET_RECV_ERROR_THRESHOLD) {
                errno = EIO;

                goto error_io;
            }
        }

        last = value;

        i++;
    }

    return errno = 0;

error_io:
    return -errno;
}

int tabby_printer_response_send(int fd, uint8_t device, uint8_t status) {
    uint8_t response[2] = {
        device, status
    };

    return tabby_link_send(fd, &response, sizeof(response));
}