File content as of revision 0:5d9cf80e1669:

// mbed packet watcher by musashinodenpa
//

#include "mbed.h"
#include "HTTPClient.h"

void analyse(char *buf, int size);
int search(char* hay, int size, char* needle);
unsigned long getTime();
void alert ();
void printtime();

DigitalOut led_link(LED1);
DigitalOut led_detect(LED2);
DigitalOut led_3(LED3);
DigitalOut led_4(LED4);
DigitalOut led_red(p20);

PwmOut motor(p21);

Serial usb(USBTX, USBRX);
Serial com(p13, p14); // for printer

int count = 0;
#define LIMIT 5

int main() {
    Ethernet ether;
    char buffer[0x600];
    int size = 0;

    usb.baud(38400);
    com.baud(9600);
    com.format(8, Serial::Odd, 2); // stopbit=2, parity=odd
    led_red = 1;

    set_time(getTime());
    printtime();
    com.printf(" initialized.\n");

    while (1) {
        if ((size = ether.receive()) != 0) {
            led_link = 0;
            ether.read(buffer, size);
            analyse(buffer, size);
        }
        led_link = ether.link();
        if (count == LIMIT) {
            alert();
            count++; // keep counting
        }
    }
}

void analyse(char *buf, int size) {
    if (size < 42) return; // too small packet
    if (buf[23] != 0x06) return; // not TCP/IP
    if ((buf[36]*256 + buf[37]) != 80) return; // not http port

    int r = search(buf, size, "Host:"); // retrieving host name
    if (r > 0) {
        char hostname[32] = "";
        strncpy(hostname, &buf[r+1], strcspn(&buf[r+1], "\r\n"));

        if (NULL != strstr(hostname, "komachi.yomiuri.co.jp")) {
            //usb.printf("%s ", hostname);

            r = search(buf, r, "GET");
            if (r > 0) {
                char uri[256] = "";
                strncpy(uri, &buf[r+1], strcspn(&buf[r+1], "\r\n"));

                if (NULL != strstr(uri, ".htm")) {
                    led_detect = 1;
                    printtime();
                    com.printf(" %d/%d\n", ++count, LIMIT);
                    //com.printf("%s\n", uri);
                }
            }
        }
    }
}

int search(char* hay, int size, char* needle) {
    int i = 0, pos = 0;
    int len = strlen(needle);

    for (i = 0; i < size; i++) {
        if (hay[i] == needle[pos]) {
            if (++pos > len-1) return(i+1);
        } else {
            pos = 0;
        }
    }
    return(-1);
}

unsigned long getTime() {
    char t[64];
    char r[] = "1234567890.123";

    HTTPClient http;
    http.get("http://ntp-a1.nict.go.jp/cgi-bin/jst", t);

    strncpy(r, strpbrk(t,"12"), sizeof(r)-1); // hacking
    return(atol(r) + 3600 * 9); // UCT to JST ;-)
}

void printtime() {
    time_t t = time(NULL);
    char buf[32];
    strftime(buf, 32, "%Y/%m/%d %H:%M:%S", localtime(&t));
    com.printf("%s", buf);
}

void alert () {
    motor = 0.1f; // drive slow
    wait_ms(3000);
    motor = 0;
}