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Add an LLMNR responder implementation (#2880)
This is a simple implementation of an LLMNR responder for the ESP8266 Arduino package. Only support for advertizing a single hostname is currently implemented. LLMNR is a very similar protocol to MDNS. The primary practical difference is that Windows systems (at least Windows 7 and later; perhaps earlier) support the protocol out-of-the-box, whereas additional software is required to support MDNS. However, Linux support is currently more complex, and MacOS X support appears non-existent.
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‎libraries/ESP8266LLMNR/ESP8266LLMNR.cpp

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/*
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* ESP8266 LLMNR responder
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* Copyright (C) 2017 Stephen Warren <[email protected]>
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*
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* Based on:
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* ESP8266 Multicast DNS (port of CC3000 Multicast DNS library)
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* Version 1.1
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* Copyright (c) 2013 Tony DiCola ([email protected])
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* ESP8266 port (c) 2015 Ivan Grokhotkov ([email protected])
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* MDNS-SD Suport 2015 Hristo Gochkov
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* Extended MDNS-SD support 2016 Lars Englund ([email protected])
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*
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* License (MIT license):
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*
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* Reference:
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* https://tools.ietf.org/html/rfc4795 (LLMNR)
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* https://tools.ietf.org/html/rfc1035 (DNS)
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*/
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#include <debug.h>
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#include <functional>
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#include <ESP8266LLMNR.h>
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#include <WiFiUdp.h>
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extern "C" {
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#include <user_interface.h>
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}
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#include <lwip/udp.h>
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#include <lwip/igmp.h>
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#include <include/UdpContext.h>
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//#define LLMNR_DEBUG
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#define BIT(x) (1 << (x))
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#define FLAGS_QR BIT(15)
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#define FLAGS_OP_SHIFT 11
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#define FLAGS_OP_MASK 0xf
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#define FLAGS_C BIT(10)
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#define FLAGS_TC BIT(9)
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#define FLAGS_T BIT(8)
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#define FLAGS_RCODE_SHIFT 0
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#define FLAGS_RCODE_MASK 0xf
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#define _conn_read16() (((uint16_t)_conn->read() << 8) | _conn->read())
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#define _conn_read8() _conn->read()
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#define _conn_readS(b, l) _conn->read((b), (l));
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static const IPAddress LLMNR_MULTICAST_ADDR(224, 0, 0, 252);
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static const int LLMNR_MULTICAST_TTL = 1;
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static const int LLMNR_PORT = 5355;
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LLMNRResponder::LLMNRResponder() :
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_conn(0) {
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}
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LLMNRResponder::~LLMNRResponder() {
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if (_conn)
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_conn->unref();
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}
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bool LLMNRResponder::begin(const char* hostname) {
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// Max length for a single label in DNS
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if (strlen(hostname) > 63)
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return false;
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_hostname = hostname;
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_hostname.toLowerCase();
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_sta_got_ip_handler = WiFi.onStationModeGotIP([this](const WiFiEventStationModeGotIP& event){
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_restart();
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});
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_sta_disconnected_handler = WiFi.onStationModeDisconnected([this](const WiFiEventStationModeDisconnected& event) {
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_restart();
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});
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return _restart();
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}
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void LLMNRResponder::notify_ap_change() {
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_restart();
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}
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bool LLMNRResponder::_restart() {
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if (_conn) {
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_conn->unref();
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_conn = 0;
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}
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ip_addr_t multicast_addr;
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multicast_addr.addr = (uint32_t)LLMNR_MULTICAST_ADDR;
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if (igmp_joingroup(IP_ADDR_ANY, &multicast_addr) != ERR_OK)
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return false;
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_conn = new UdpContext;
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_conn->ref();
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if (!_conn->listen(*IP_ADDR_ANY, LLMNR_PORT))
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return false;
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_conn->setMulticastTTL(LLMNR_MULTICAST_TTL);
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_conn->onRx(std::bind(&LLMNRResponder::_process_packet, this));
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_conn->connect(multicast_addr, LLMNR_PORT);
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}
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void LLMNRResponder::_process_packet() {
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if (!_conn || !_conn->next())
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return;
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#ifdef LLMNR_DEBUG
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Serial.println("LLMNR: RX'd packet");
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#endif
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uint16_t id = _conn_read16();
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uint16_t flags = _conn_read16();
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uint16_t qdcount = _conn_read16();
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uint16_t ancount = _conn_read16();
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uint16_t nscount = _conn_read16();
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uint16_t arcount = _conn_read16();
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#ifdef LLMNR_DEBUG
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Serial.print("LLMNR: ID=");
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Serial.println(id, HEX);
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Serial.print("LLMNR: FLAGS=");
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Serial.println(flags, HEX);
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Serial.print("LLMNR: QDCOUNT=");
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Serial.println(qdcount);
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Serial.print("LLMNR: ANCOUNT=");
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Serial.println(ancount);
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Serial.print("LLMNR: NSCOUNT=");
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Serial.println(nscount);
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Serial.print("LLMNR: ARCOUNT=");
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Serial.println(arcount);
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#endif
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#define BAD_FLAGS (FLAGS_QR | (FLAGS_OP_MASK << FLAGS_OP_SHIFT) | FLAGS_C)
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if (flags & BAD_FLAGS) {
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#ifdef LLMNR_DEBUG
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Serial.println("Bad flags");
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#endif
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return;
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}
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if (qdcount != 1) {
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#ifdef LLMNR_DEBUG
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Serial.println("QDCOUNT != 1");
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#endif
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return;
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}
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if (ancount || nscount || arcount) {
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#ifdef LLMNR_DEBUG
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Serial.println("AN/NS/AR-COUNT != 0");
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#endif
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return;
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}
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uint8_t namelen = _conn_read8();
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#ifdef LLMNR_DEBUG
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Serial.print("QNAME len ");
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Serial.println(namelen);
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#endif
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if (namelen != _hostname.length()) {
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#ifdef LLMNR_DEBUG
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Serial.println("QNAME len mismatch");
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#endif
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return;
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}
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char qname[64];
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_conn_readS(qname, namelen);
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_conn_read8();
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qname[namelen] = '\0';
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#ifdef LLMNR_DEBUG
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Serial.print("QNAME ");
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Serial.println(qname);
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#endif
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if (strcmp(_hostname.c_str(), qname)) {
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#ifdef LLMNR_DEBUG
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Serial.println("QNAME mismatch");
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#endif
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return;
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}
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uint16_t qtype = _conn_read16();
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uint16_t qclass = _conn_read16();
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#ifdef LLMNR_DEBUG
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Serial.print("QTYPE ");
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Serial.print(qtype);
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Serial.print(" QCLASS ");
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Serial.println(qclass);
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#endif
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bool have_rr =
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(qtype == 1) && /* A */
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(qclass == 1); /* IN */
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_conn->flush();
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#ifdef LLMNR_DEBUG
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Serial.println("Match; responding");
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if (!have_rr)
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Serial.println("(no matching RRs)");
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#endif
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struct ip_info remote_ip_info;
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remote_ip_info.ip.addr = _conn->getRemoteAddress();
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struct ip_info ip_info;
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bool match_ap = false;
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if (wifi_get_opmode() & SOFTAP_MODE) {
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wifi_get_ip_info(SOFTAP_IF, &ip_info);
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if (ip_info.ip.addr && ip_addr_netcmp(&remote_ip_info.ip, &ip_info.ip, &ip_info.netmask))
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match_ap = true;
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}
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if (!match_ap)
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wifi_get_ip_info(STATION_IF, &ip_info);
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uint32_t ip = ip_info.ip.addr;
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// Header
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uint8_t header[] = {
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id >> 8, id & 0xff, // ID
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FLAGS_QR >> 8, 0, // FLAGS
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0, 1, // QDCOUNT
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0, !!have_rr, // ANCOUNT
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0, 0, // NSCOUNT
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0, 0, // ARCOUNT
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};
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_conn->append(reinterpret_cast<const char*>(header), sizeof(header));
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// Question
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_conn->append(reinterpret_cast<const char*>(&namelen), 1);
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_conn->append(qname, namelen);
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uint8_t q[] = {
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0, // Name terminator
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0, 1, // TYPE (A)
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0, 1, // CLASS (IN)
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};
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_conn->append(reinterpret_cast<const char*>(q), sizeof(q));
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// Answer, if we have one
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if (have_rr) {
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_conn->append(reinterpret_cast<const char*>(&namelen), 1);
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_conn->append(qname, namelen);
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uint8_t rr[] = {
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0, // Name terminator
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0, 1, // TYPE (A)
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0, 1, // CLASS (IN)
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0, 0, 0, 30, // TTL (30 seconds)
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0, 4, // RDLENGTH
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ip & 0xff, (ip >> 8) & 0xff, (ip >> 16) & 0xff, (ip >> 24) & 0xff, // RDATA
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};
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_conn->append(reinterpret_cast<const char*>(rr), sizeof(rr));
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}
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_conn->setMulticastInterface(remote_ip_info.ip);
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_conn->send(&remote_ip_info.ip, _conn->getRemotePort());
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}
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#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_LLMNR)
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LLMNRResponder LLMNR;
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#endif

‎libraries/ESP8266LLMNR/ESP8266LLMNR.h

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/*
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* ESP8266 LLMNR responder
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* Copyright (C) 2017 Stephen Warren <[email protected]>
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*
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* Based on:
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* ESP8266 Multicast DNS (port of CC3000 Multicast DNS library)
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* Version 1.1
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* Copyright (c) 2013 Tony DiCola ([email protected])
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* ESP8266 port (c) 2015 Ivan Grokhotkov ([email protected])
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* MDNS-SD Suport 2015 Hristo Gochkov
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* Extended MDNS-SD support 2016 Lars Englund ([email protected])
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*
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* License (MIT license):
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
17+
* in the Software without restriction, including without limitation the rights
18+
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
19+
* copies of the Software, and to permit persons to whom the Software is
20+
* furnished to do so, subject to the following conditions:
21+
*
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* The above copyright notice and this permission notice shall be included in
23+
* all copies or substantial portions of the Software.
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*
25+
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
26+
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
27+
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
28+
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
29+
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifndef ESP8266LLMNR_H
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#define ESP8266LLMNR_H
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#include <ESP8266WiFi.h>
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class UdpContext;
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class LLMNRResponder {
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public:
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LLMNRResponder();
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~LLMNRResponder();
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/* Initialize and start responding to LLMNR requests on all interfaces */
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bool begin(const char* hostname);
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/* Application should call this whenever AP is configured/disabled */
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void notify_ap_change();
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private:
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String _hostname;
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UdpContext *_conn;
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WiFiEventHandler _sta_got_ip_handler;
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WiFiEventHandler _sta_disconnected_handler;
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bool _restart();
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void _process_packet();
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};
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#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_LLMNR)
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extern LLMNRResponder LLMNR;
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#endif
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#endif

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