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