nm.c

#include "nm.h"
#include "arg.h"
#include <stdio.h>

#define TO_KBITS(b) ((float) (b) / 125)

static unsigned long long int netReCache = 0;
static unsigned long long int netSeCache = 0;

void
nm(Args *arg, char *buff, int bufflen)
{
        (void) arg;
        unsigned long long int bytes_re, bytes_se;
        char *fmt = "⬆ %.2fKi ⬇ %.2fKi";

        FILE *fr = fopen("/sys/class/net/eth0/statistics/rx_bytes", "r");
        if (!fr) return;

        fscanf(fr, "%llu", &bytes_re);
        fclose(fr);

        FILE *fs = fopen("/sys/class/net/eth0/statistics/tx_bytes", "r");
        if (!fs) return;

        fscanf(fs, "%llu", &bytes_se);
        fclose(fs);

        unsigned long long int reDiff = bytes_re - netReCache;
        unsigned long long int seDiff = bytes_se - netSeCache;

        snprintf(buff, bufflen, fmt, TO_KBITS(seDiff), TO_KBITS(reDiff));

        netReCache = bytes_re;
        netSeCache = bytes_se;
}