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,
                                      uint16_t *sum) {
    ssize_t len;

    size_t i = 0,
           b = 0;

    uint8_t value;

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

    *sum = 0;

    while ((len = read(fd, &value, 1)) >= 0) {
        if (i == 0) {
            if (value == 0x88) {
                header->preamble[0] = value;
                i++;
            } else {
                continue;
            }
        } else if (i == 1) {
            if (value == 0x33) {
                header->preamble[1] = value;
                i++;
            } else {
                i = 0;
                continue;
            }
        } else if (i == 2) {
            header->type = value;
            i++;
        } else if (i == 3) {
            header->compression = value;
            i++;
        } else if (i == 4) {
            header->size = value;
            i++;
        } else if (i == 5) {
            header->size |= value << 8;
            i++;

            b = 0;
        } else if (b < header->size) {
            ((uint8_t *)body)[b++] = value;
        } else if (b == header->size) {
            *sum = value;
            b++;
        } else if (b == header->size + 1) {
            *sum |= value << 8;

            if (checksum(header, body) != *sum) {
                errno = EIO;

                goto error_io;
            }

            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 write(fd, &response, sizeof(response));
}