Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
branch: master
118 lines (104 sloc) 3.629 kb
// DNS look-up functions based on the udp client
// Author: Guido Socher
// Copyright: GPL V2
//
// 2010-05-20 <jc@wippler.nl>
#include "EtherCard.h"
#include "net.h"
#define gPB ether.buffer
static byte dnstid_l; // a counter for transaction ID
#define DNSCLIENT_SRC_PORT_H 0xE0
static void dnsRequest (const char *hostname, bool fromRam) {
++dnstid_l; // increment for next request, finally wrap
if (ether.dnsip[0] == 0)
memset(ether.dnsip, 8, 4); // use 8.8.8.8 Google DNS as default
ether.udpPrepare((DNSCLIENT_SRC_PORT_H << 8) | dnstid_l, ether.dnsip, 53);
memset(gPB + UDP_DATA_P, 0, 12);
byte *p = gPB + UDP_DATA_P + 12;
char c;
do {
byte n = 0;
for(;;) {
c = fromRam ? *hostname : pgm_read_byte(hostname);
++hostname;
if (c == '.' || c == 0)
break;
p[++n] = c;
}
*p++ = n;
p += n;
} while (c != 0);
*p++ = 0; // terminate with zero, means root domain.
*p++ = 0;
*p++ = 1; // type A
*p++ = 0;
*p++ = 1; // class IN
byte i = p - gPB - UDP_DATA_P;
gPB[UDP_DATA_P] = i;
gPB[UDP_DATA_P+1] = dnstid_l;
gPB[UDP_DATA_P+2] = 1; // flags, standard recursive query
gPB[UDP_DATA_P+5] = 1; // 1 question
ether.udpTransmit(i);
}
/** @brief Check if packet is DNS response.
@param plen Size of packet
@return <i>bool</i> True if DNS response has error. False if not DNS response or DNS response OK.
@note hisip contains IP address of requested host or 0.0.0.0 on failure
*/
static bool checkForDnsAnswer (uint16_t plen) {
byte *p = gPB + UDP_DATA_P; //start of UDP payload
if (plen < 70 || gPB[UDP_SRC_PORT_L_P] != 53 || //from DNS source port
gPB[UDP_DST_PORT_H_P] != DNSCLIENT_SRC_PORT_H || //response to same port as we sent from (MSB)
gPB[UDP_DST_PORT_L_P] != dnstid_l || //response to same port as we sent from (LSB)
p[1] != dnstid_l) //message id same as we sent
return false; //not our DNS response
if((p[3] & 0x0F) != 0)
return true; //DNS response recieved with error
p += *p; // we encoded the query len into tid
for (;;) {
if (*p & 0xC0)
p += 2;
else
while (++p < gPB + plen) {
if (*p == 0) {
++p;
break;
}
}
if (p + 14 > gPB + plen)
break;
if (p[1] == 1 && p[9] == 4) { // type "A" and IPv4
ether.copyIp(ether.hisip, p + 10);
break;
}
p += p[9] + 10;
}
return false; //No error
}
// use during setup, as this discards all incoming requests until it returns
bool EtherCard::dnsLookup (const char* name, bool fromRam) {
word start = millis();
while(!isLinkUp())
{
if ((word) (millis() - start) >= 30000)
return false; //timeout waiting for link
}
while(clientWaitingDns())
{
packetLoop(packetReceive());
if ((word) (millis() - start) >= 30000)
return false; //timeout waiting for gateway ARP
}
memset(hisip, 0, 4);
dnsRequest(name, fromRam);
start = millis();
while (hisip[0] == 0) {
if ((word) (millis() - start) >= 30000)
return false; //timout waiting for dns response
word len = packetReceive();
if (len > 0 && packetLoop(len) == 0) //packet not handled by tcp/ip packet loop
if(checkForDnsAnswer(len))
return false; //DNS response recieved with error
}
return true;
}
Jump to Line
Something went wrong with that request. Please try again.