Arduino and ENC28J60 Ethernet module

// EtherShield webserver that control an LED. 
/*
Sample code originally created by nuelectronics.com, but this has been modified by denhart.dk 
to take advatage of the new EtherShield Library from https://github.com/thiseldo/EtherShield\
*/
#include "EtherShield.h"
 
// please modify the following two lines. mac and ip have to be unique
// in your local area network. You can not have the same numbers in
// two devices:
static uint8_t mymac[6] = {
  0x54,0x55,0x58,0x10,0x00,0x25}; 
 
static uint8_t myip[4] = {
  192,168,1,25};
static char baseurl[]="http://192.168.1.25/";
#define MYWWWPORT 80
#define BUFFER_SIZE 550
#define LED_PIN 4
static uint8_t buf[BUFFER_SIZE+1];
uint16_t print_webpage(uint8_t *buf, byte on_off);
// The ethernet shield
EtherShield es=EtherShield();
 
uint16_t http200ok(void)
{
  return(es.ES_fill_tcp_data_p(buf,0,PSTR("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\nPragma: no-cache\r\n\r\n")));
}
 
 
// prepare the webpage by writing the data to the tcp send buffer
uint16_t print_webpage(uint8_t *buf, byte on_off)
{
  uint16_t plen;
  plen=http200ok();
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<center><h1>Welcome to Arduino ENC28J60 Ethernet Shield V1.1</h1>"));
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<hr><br><form METHOD=get action=\""));
  plen=es.ES_fill_tcp_data(buf,plen,baseurl);
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("\">"));
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<br> Control digital outputs"));
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<h1><font color=\"#00FF00\"> "));
 
        if(on_off)
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("ON"));
        else 
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("OFF"));
 
        plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("  </font></h1><br> ") );
 
        if(on_off){
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<input type=hidden name=cmd value=2>"));
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<input type=submit value=\"Switch off\"></form>")); 
        }
        else {
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<input type=hidden name=cmd value=1>"));
        	plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("<input type=submit value=\"Switch on\"></form>"));
        }
 
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("</center><hr>"));;  
  plen=es.ES_fill_tcp_data_p(buf,plen,PSTR("</body></html>"));
 
  return(plen);
}
 
 
void setup(){
  pinMode(LED_PIN, OUTPUT);
  // Initialise SPI interface
  es.ES_enc28j60SpiInit();
 
  // initialize enc28j60
  es.ES_enc28j60Init(mymac);
 
  // init the ethernet/ip layer:
  es.ES_init_ip_arp_udp_tcp(mymac,myip, MYWWWPORT);
}
 
void loop(){
  byte on_off=0;
  int8_t cmd;
  uint16_t plen, dat_p;
 
  while(1) {
    // read packet, handle ping and wait for a tcp packet:
    dat_p=es.ES_packetloop_icmp_tcp(buf,es.ES_enc28j60PacketReceive(BUFFER_SIZE, buf));
 
    /* dat_p will be unequal to zero if there is a valid 
     * http get */
    if(dat_p==0){
      // no http request
      continue;
    }
    // tcp port 80 begin
    if (strncmp("GET ",(char *)&(buf[dat_p]),4)!=0){
      // head, post and other methods:
      dat_p=http200ok();
      dat_p=es.ES_fill_tcp_data_p(buf,dat_p,PSTR("<h1>200 OK</h1>"));
      goto SENDTCP;
    }
    // just one web page in the "root directory" of the web server
    if (strncmp("/ ",(char *)&(buf[dat_p+4]),2)==0){
      dat_p=print_webpage(buf, on_off);
      goto SENDTCP;
    }
  //This will be our switches, which control the LED   
    cmd=analyse_cmd((char *)&(buf[dat_p+5]));
 switch (cmd) {
    case 1:
      //do something when var equals 1
      digitalWrite(LED_PIN, HIGH);
      on_off=1;
      dat_p=print_webpage(buf, on_off);
      break;
    case 2:
      //do something when var equals 2
      digitalWrite(LED_PIN, LOW);
      on_off=0;
      dat_p=print_webpage(buf, on_off);
      break;
  }
 
 
SENDTCP:
    es.ES_www_server_reply(buf,dat_p); // send web page data
    // tcp port 80 end
 
  }
 
}
//Taken from the orginal sample code provided by http://nuelectronics.com/
uint8_t find_key_val(char *str,char *key)
{
        uint8_t found=0;
        uint8_t i=0;
        char *kp;
        kp=key;
        while(*str &&  *str!=' ' && found==0){
                if (*str == *kp){
                        kp++;
                        if (*kp == '\0'){
                                str++;
                                kp=key;
                                if (*str == '='){
                                        found=1;
                                }
                        }
                }else{
                        kp=key;
                }
                str++;
        }
        if (found==1){
                // copy the value to a buffer and terminate it with '\0'
                while(*str &&  *str!=' ' && *str!='&' && i<BUFFER_SIZE){
                        buf[i]=*str;
                        i++;
                        str++;
                }
                buf[i]='\0';
        }
        return(found);
}
 
//Taken from the orginal sample code provided by http://nuelectronics.com/
int8_t analyse_cmd(char *str)
{
        int8_t r=-1;
 
        if (find_key_val(str,"cmd")){
                if (*buf < 0x3a && *buf > 0x2f){
                        // is a ASCII number, return it
                        r=(*buf-0x30);
                }
        }
        return r;
}