WIP: Replacing KDNSSD with mdns.h

KDNSSD only works with Avahi (so, only on Linux) while mdns.h is a
header-only library [1] that implements mdns from scratch and should
work on all platforms.

[1] https://github.com/mjansson/mdns

core/backends/lan/CMakeLists.txt

@@ -12,6 +12,7 @@ if (MDNS_ENABLED)
     set(backends_kdeconnect_SRCS
         ${backends_kdeconnect_SRCS}
         backends/lan/mdnsdiscovery.cpp
+        backends/lan/mdns_wrapper.cpp
     )
 endif()
 

core/backends/lan/mdns_wrapper.cpp

@@ -0,0 +1,796 @@
+/**
+ * SPDX-FileCopyrightText: 2023 Albert Vaca Cintora <albertvaka@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
+#include "mdns_wrapper.h"
+
+#include "core_debug.h"
+
+#include "mdns.h"
+
+#include <errno.h>
+#include <signal.h>
+
+#ifdef _WIN32
+#include <iphlpapi.h>
+#include <winsock2.h>
+#else
+#include <ifaddrs.h>
+#include <net/if.h>
+#include <netdb.h>
+#include <sys/time.h>
+#endif
+
+#include <QNetworkInterface>
+#include <QSocketNotifier>
+
+const char *recordTypeToStr(int rtype)
+{
+    switch (rtype) {
+        case MDNS_RECORDTYPE_PTR: return "PTR";
+        case MDNS_RECORDTYPE_SRV: return "SRV";
+        case MDNS_RECORDTYPE_TXT: return "TXT";
+        case MDNS_RECORDTYPE_A: return "A";
+        case MDNS_RECORDTYPE_AAAA: return "AAAA";
+        case MDNS_RECORDTYPE_ANY: return "ANY";
+        default: return "UNKNOWN";
+    }
+}
+
+const char *entryTypeToStr(int entry)
+{
+    switch (entry) {
+        case MDNS_ENTRYTYPE_QUESTION: return "QUESTION";
+        case MDNS_ENTRYTYPE_ANSWER: return "ANSWER";
+        case MDNS_ENTRYTYPE_AUTHORITY: return "AUTHORITY";
+        case MDNS_ENTRYTYPE_ADDITIONAL: return "ADDITIONAL";
+        default: return "UNKNOWN";
+    }
+}
+
+// Callback that handles responses to a query
+static int query_callback(int sock, const struct sockaddr* from, size_t addrlen, mdns_entry_type_t entry_type,
+               uint16_t query_id, uint16_t record_type, uint16_t rclass, uint32_t ttl, const void* data,
+               size_t size, size_t name_offset, size_t name_length, size_t record_offset,
+               size_t record_length, void* user_data) {
+    Q_UNUSED(sock);
+    Q_UNUSED(addrlen);
+    Q_UNUSED(query_id);
+    Q_UNUSED(entry_type);
+    Q_UNUSED(rclass);
+    Q_UNUSED(ttl);
+    Q_UNUSED(name_offset);
+    Q_UNUSED(name_length);
+
+    //qCDebug(KDECONNECT_CORE) << "Received DNS record of type" << recordTypeToStr(record_type) << "from socket" << sock << "with type" << entryTypeToStr(entry_type);
+
+    MdnsWrapper::MdnsService *discoveredService = (MdnsWrapper::MdnsService *)user_data;
+
+    switch (record_type) {
+    case MDNS_RECORDTYPE_PTR: {
+        mdns_string_pair_t namePos = mdns_get_next_substring(data, size, record_offset);
+        discoveredService->serviceName = QString::fromLatin1((char *)data + namePos.offset, namePos.length);
+        if (discoveredService->address == QHostAddress::Null) {
+            discoveredService->address = QHostAddress(from); // In case we don't receive a A record, use from as address
+        }
+    } break;
+    case MDNS_RECORDTYPE_SRV: {
+        static char auxBuffer[256];
+        mdns_record_srv_t record = mdns_record_parse_srv(data, size, record_offset, record_length, auxBuffer, sizeof(auxBuffer));
+        discoveredService->port = record.port;
+    } break;
+    case MDNS_RECORDTYPE_A: {
+        sockaddr_in addr;
+        mdns_record_parse_a(data, size, record_offset, record_length, &addr);
+        discoveredService->address = QHostAddress(ntohl(addr.sin_addr.s_addr));
+    } break;
+    case MDNS_RECORDTYPE_AAAA:
+        // Ignore IPv6 for now
+        break;
+    case MDNS_RECORDTYPE_TXT: {
+        mdns_record_txt_t records[24];
+        size_t parsed = mdns_record_parse_txt(data, size, record_offset, record_length, records, sizeof(records) / sizeof(mdns_record_txt_t));
+        for (size_t itxt = 0; itxt < parsed; ++itxt) {
+            QString key = QString::fromLatin1(records[itxt].key.str, records[itxt].key.length);
+            QString value = QString::fromLatin1(records[itxt].value.str, records[itxt].value.length);
+            discoveredService->txtRecords[key] = value;
+        }
+    } break;
+    default:
+        // Ignore unknown record types
+        break;
+    }
+
+    return 0;
+}
+
+void MdnsWrapper::startDiscovering(const char *serviceName)
+{
+    int num_sockets = listenForQueryResponses();
+    if (num_sockets <= 0) {
+        qWarning() << "Failed to open any client sockets";
+    } else {
+        sendQuery(serviceName);
+    }
+}
+
+void MdnsWrapper::stopDiscovering()
+{
+    stopListeningForQueryResponses();
+}
+
+void MdnsWrapper::stopListeningForQueryResponses()
+{
+    qCDebug(KDECONNECT_CORE) << "Closing" << responseSocketNotifiers.size() << "sockets";
+    for (QSocketNotifier *socketNotifier : responseSocketNotifiers) {
+        mdns_socket_close(socketNotifier->socket());
+        delete socketNotifier;
+    }
+    responseSocketNotifiers.clear();
+}
+
+int MdnsWrapper::listenForQueryResponses()
+{
+    // Open a socket for each interface
+    QVector<int> sockets;
+    for (const QNetworkInterface &iface : QNetworkInterface::allInterfaces()) {
+        int flags = iface.flags();
+        if (!(flags & QNetworkInterface::IsUp) || !(flags & QNetworkInterface::CanMulticast) || (flags & QNetworkInterface::IsLoopBack)) {
+            continue;
+        }
+        for (const QNetworkAddressEntry &ifaceAddress : iface.addressEntries()) {
+            QHostAddress sourceAddress = ifaceAddress.ip();
+            if (sourceAddress.protocol() == QAbstractSocket::IPv4Protocol && sourceAddress != QHostAddress::LocalHost) {
+                qCDebug(KDECONNECT_CORE) << "Opening socket for address" << sourceAddress;
+                struct sockaddr_in saddr;
+                memset(&saddr, 0, sizeof(saddr));
+                saddr.sin_family = AF_INET;
+                saddr.sin_port = 0;
+                saddr.sin_addr.s_addr = htonl(sourceAddress.toIPv4Address());
+                int socket = mdns_socket_open_ipv4(&saddr);
+                sockets.append(socket);
+            }
+            // Ignore IPv6 interfaces for now
+        }
+    }
+
+    // Start listening on all sockets
+    for (int socket : sockets) {
+        QSocketNotifier *socketNotifier = new QSocketNotifier(socket, QSocketNotifier::Read);
+        QObject::connect(socketNotifier, &QSocketNotifier::activated, [this](QSocketDescriptor socket) {
+            MdnsService discoveredService;
+
+            size_t capacity = 2048;
+            void *buffer = malloc(capacity);
+            size_t num_records = mdns_query_recv(socket, buffer, capacity, query_callback, (void *)&discoveredService, 0);
+            free(buffer);
+
+            // qCDebug(KDECONNECT_CORE) << "Discovered service" << discoveredService.serviceName << "at" << discoveredService.address << "in" <<  num_records <<
+            // "records via socket" << socket;
+
+            Q_EMIT serviceFound(discoveredService);
+        });
+        responseSocketNotifiers.append(socketNotifier);
+    }
+
+    qCDebug(KDECONNECT_CORE) << "Opened" << sockets.size() << "sockets to listen for MDNS query responses";
+
+    return sockets.size();
+}
+
+void MdnsWrapper::sendQuery(const char *serviceName)
+{
+    qCDebug(KDECONNECT_CORE) << "Sending MDNS query for service" << serviceName;
+
+    mdns_query_t query;
+    query.name = serviceName;
+    query.length = strlen(serviceName);
+    query.type = MDNS_RECORDTYPE_PTR;
+
+    size_t capacity = 2048;
+    void *buffer = malloc(capacity);
+    for (QSocketNotifier *socketNotifier : responseSocketNotifiers) {
+        int socket = socketNotifier->socket();
+        qCDebug(KDECONNECT_CORE) << "Sending mDNS query via socket" << socket;
+        int ret = mdns_multiquery_send(socket, &query, 1, buffer, capacity, 0);
+        if (ret < 0) {
+            qWarning() << "Failed to send mDNS query:" << strerror(errno);
+        }
+    }
+    free(buffer);
+}
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+// Those are the IPs we will announce. They are the first IP we find. Maybe we should announce all our IPs instead?
+struct sockaddr_in service_address_ipv4;
+struct sockaddr_in6 service_address_ipv6;
+
+
+static mdns_string_t ipv4_address_to_string(char* buffer, size_t capacity, const struct sockaddr_in* addr,
+                       size_t addrlen) {
+    char host[NI_MAXHOST] = {0};
+    char service[NI_MAXSERV] = {0};
+    int ret = getnameinfo((const struct sockaddr*)addr, (socklen_t)addrlen, host, NI_MAXHOST,
+                          service, NI_MAXSERV, NI_NUMERICSERV | NI_NUMERICHOST);
+    int len = 0;
+    if (ret == 0) {
+        if (addr->sin_port != 0)
+            len = snprintf(buffer, capacity, "%s:%s", host, service);
+        else
+            len = snprintf(buffer, capacity, "%s", host);
+    }
+    if (len >= (int)capacity)
+        len = (int)capacity - 1;
+    mdns_string_t str;
+    str.str = buffer;
+    str.length = len;
+    return str;
+}
+
+static mdns_string_t ipv6_address_to_string(char* buffer, size_t capacity, const struct sockaddr_in6* addr,
+                       size_t addrlen) {
+    char host[NI_MAXHOST] = {0};
+    char service[NI_MAXSERV] = {0};
+    int ret = getnameinfo((const struct sockaddr*)addr, (socklen_t)addrlen, host, NI_MAXHOST,
+                          service, NI_MAXSERV, NI_NUMERICSERV | NI_NUMERICHOST);
+    int len = 0;
+    if (ret == 0) {
+        if (addr->sin6_port != 0)
+            len = snprintf(buffer, capacity, "[%s]:%s", host, service);
+        else
+            len = snprintf(buffer, capacity, "%s", host);
+    }
+    if (len >= (int)capacity)
+        len = (int)capacity - 1;
+    mdns_string_t str;
+    str.str = buffer;
+    str.length = len;
+    return str;
+}
+
+static mdns_string_t ip_address_to_string(char* buffer, size_t capacity, const struct sockaddr* addr, size_t addrlen) {
+    if (addr->sa_family == AF_INET6)
+        return ipv6_address_to_string(buffer, capacity, (const struct sockaddr_in6*)addr, addrlen);
+    return ipv4_address_to_string(buffer, capacity, (const struct sockaddr_in*)addr, addrlen);
+}
+
+
+
+char service_instance_buffer[256] = {0};
+char qualified_hostname_buffer[256] = {0};
+
+// Data for our service including the mDNS records
+typedef struct {
+    mdns_string_t service;
+    mdns_string_t hostname;
+    mdns_string_t service_instance;
+    mdns_string_t hostname_qualified;
+    struct sockaddr_in address_ipv4;
+    struct sockaddr_in6 address_ipv6;
+    int port;
+    mdns_record_t record_ptr;
+    mdns_record_t record_srv;
+    mdns_record_t record_a;
+    mdns_record_t record_aaaa;
+    mdns_record_t txt_record[2];
+} service_t;
+service_t service = {};
+
+// Open sockets to listen to incoming mDNS queries on port 5353
+static int open_service_sockets(int* sockets)
+{
+    // When recieving, each socket can recieve data from all network interfaces
+    // Thus we only need to open one socket for each address family
+    int num_sockets = 0;
+
+    {
+        struct sockaddr_in sock_addr;
+        memset(&sock_addr, 0, sizeof(struct sockaddr_in));
+        sock_addr.sin_family = AF_INET;
+    #ifdef _WIN32
+        sock_addr.sin_addr = in4addr_any;
+    #else
+        sock_addr.sin_addr.s_addr = INADDR_ANY;
+    #endif
+        sock_addr.sin_port = htons(MDNS_PORT);
+    #ifdef __APPLE__
+        sock_addr.sin_len = sizeof(struct sockaddr_in);
+    #endif
+        int sock = mdns_socket_open_ipv4(&sock_addr);
+        if (sock >= 0)
+            sockets[num_sockets++] = sock;
+    }
+
+    {
+        struct sockaddr_in6 sock_addr;
+        memset(&sock_addr, 0, sizeof(struct sockaddr_in6));
+        sock_addr.sin6_family = AF_INET6;
+        sock_addr.sin6_addr = in6addr_any;
+        sock_addr.sin6_port = htons(MDNS_PORT);
+    #ifdef __APPLE__
+        sock_addr.sin6_len = sizeof(struct sockaddr_in6);
+    #endif
+        int sock = mdns_socket_open_ipv6(&sock_addr);
+        if (sock >= 0)
+            sockets[num_sockets++] = sock;
+    }
+
+    return num_sockets;
+}
+
+static char sendbuffer[1024];
+
+// Callback handling questions incoming on service sockets
+static int service_callback(int sock, const struct sockaddr* from, size_t addrlen, mdns_entry_type_t entry,
+                 uint16_t query_id, uint16_t rtype_int, uint16_t rclass, uint32_t ttl, const void* data,
+                 size_t size, size_t name_offset, size_t name_length, size_t record_offset,
+                 size_t record_length, void* user_data) {
+
+    static mdns_record_txt_t txtbuffer[128];
+    static char addrbuffer[64];
+    static char entrybuffer[256];
+    static char namebuffer[256];
+
+    mdns_record_type_t rtype = (mdns_record_type_t)rtype_int;
+
+    (void)sizeof(ttl);
+    if (entry != MDNS_ENTRYTYPE_QUESTION)
+        return 0;
+
+    const char dns_sd[] = "_services._dns-sd._udp.local.";
+
+    mdns_string_t fromaddrstr = ip_address_to_string(addrbuffer, sizeof(addrbuffer), from, addrlen);
+
+    size_t offset = name_offset;
+    mdns_string_t name = mdns_string_extract(data, size, &offset, namebuffer, sizeof(namebuffer));
+
+    const char* record_name = 0;
+    if (rtype == MDNS_RECORDTYPE_PTR)
+        record_name = "PTR";
+    else if (rtype == MDNS_RECORDTYPE_SRV)
+        record_name = "SRV";
+    else if (rtype == MDNS_RECORDTYPE_A)
+        record_name = "A";
+    else if (rtype == MDNS_RECORDTYPE_AAAA)
+        record_name = "AAAA";
+    else if (rtype == MDNS_RECORDTYPE_TXT)
+        record_name = "TXT";
+    else if (rtype == MDNS_RECORDTYPE_ANY)
+        record_name = "ANY";
+    else
+        return 0;
+    printf("Query %s %.*s\n", record_name, MDNS_STRING_FORMAT(name));
+
+    if ((name.length == (sizeof(dns_sd) - 1)) &&
+        (strncmp(name.str, dns_sd, sizeof(dns_sd) - 1) == 0)) {
+        if ((rtype == MDNS_RECORDTYPE_PTR) || (rtype == MDNS_RECORDTYPE_ANY)) {
+            // The PTR query was for the DNS-SD domain, send answer with a PTR record for the
+            // service name we advertise, typically on the "<_service-name>._tcp.local." format
+
+            // Answer PTR record reverse mapping "<_service-name>._tcp.local." to
+            // "<hostname>.<_service-name>._tcp.local."
+            mdns_record_t answer = {
+                .name = name, .type = MDNS_RECORDTYPE_PTR, .data.ptr.name = service.service};
+
+            // Send the answer, unicast or multicast depending on flag in query
+            uint16_t unicast = (rclass & MDNS_UNICAST_RESPONSE);
+            printf("  --> answer %.*s (%s)\n", MDNS_STRING_FORMAT(answer.data.ptr.name),
+                   (unicast ? "unicast" : "multicast"));
+
+            if (unicast) {
+                mdns_query_answer_unicast(sock, (void*)from, addrlen, (void*)sendbuffer, sizeof(sendbuffer),
+                                          query_id, rtype, name.str, name.length, answer, NULL, 0, NULL, 0);
+            } else {
+                mdns_query_answer_multicast(sock, sendbuffer, sizeof(sendbuffer), answer, 0, 0, 0,
+                                            0);
+            }
+        }
+    } else if ((name.length == service.service.length) &&
+               (strncmp(name.str, service.service.str, name.length) == 0)) {
+        if ((rtype == MDNS_RECORDTYPE_PTR) || (rtype == MDNS_RECORDTYPE_ANY)) {
+            // The PTR query was for our service (usually "<_service-name._tcp.local"), answer a PTR
+            // record reverse mapping the queried service name to our service instance name
+            // (typically on the "<hostname>.<_service-name>._tcp.local." format), and add
+            // additional records containing the SRV record mapping the service instance name to our
+            // qualified hostname (typically "<hostname>.local.") and port, as well as any IPv4/IPv6
+            // address for the hostname as A/AAAA records, and two test TXT records
+
+            // Answer PTR record reverse mapping "<_service-name>._tcp.local." to
+            // "<hostname>.<_service-name>._tcp.local."
+            mdns_record_t answer = service.record_ptr;
+
+            mdns_record_t additional[5] = {0};
+            size_t additional_count = 0;
+
+            // SRV record mapping "<hostname>.<_service-name>._tcp.local." to
+            // "<hostname>.local." with port. Set weight & priority to 0.
+            additional[additional_count++] = service.record_srv;
+
+            // A/AAAA records mapping "<hostname>.local." to IPv4/IPv6 addresses
+            if (service.address_ipv4.sin_family == AF_INET)
+                additional[additional_count++] = service.record_a;
+            if (service.address_ipv6.sin6_family == AF_INET6)
+                additional[additional_count++] = service.record_aaaa;
+
+            // Add two test TXT records for our service instance name, will be coalesced into
+            // one record with both key-value pair strings by the library
+            additional[additional_count++] = service.txt_record[0];
+            additional[additional_count++] = service.txt_record[1];
+
+            // Send the answer, unicast or multicast depending on flag in query
+            uint16_t unicast = (rclass & MDNS_UNICAST_RESPONSE);
+            printf("  --> answer %.*s (%s)\n",
+                   MDNS_STRING_FORMAT(service.record_ptr.data.ptr.name),
+                   (unicast ? "unicast" : "multicast"));
+
+            if (unicast) {
+                mdns_query_answer_unicast(sock, from, addrlen, sendbuffer, sizeof(sendbuffer),
+                                          query_id, rtype, name.str, name.length, answer, 0, 0,
+                                          additional, additional_count);
+            } else {
+                mdns_query_answer_multicast(sock, sendbuffer, sizeof(sendbuffer), answer, 0, 0,
+                                            additional, additional_count);
+            }
+        }
+    } else if ((name.length == service.service_instance.length) &&
+               (strncmp(name.str, service.service_instance.str, name.length) == 0)) {
+        if ((rtype == MDNS_RECORDTYPE_SRV) || (rtype == MDNS_RECORDTYPE_ANY)) {
+            // The SRV query was for our service instance (usually
+            // "<hostname>.<_service-name._tcp.local"), answer a SRV record mapping the service
+            // instance name to our qualified hostname (typically "<hostname>.local.") and port, as
+            // well as any IPv4/IPv6 address for the hostname as A/AAAA records, and two test TXT
+            // records
+
+            // Answer PTR record reverse mapping "<_service-name>._tcp.local." to
+            // "<hostname>.<_service-name>._tcp.local."
+            mdns_record_t answer = service.record_srv;
+
+            mdns_record_t additional[5] = {0};
+            size_t additional_count = 0;
+
+            // A/AAAA records mapping "<hostname>.local." to IPv4/IPv6 addresses
+            if (service.address_ipv4.sin_family == AF_INET)
+                additional[additional_count++] = service.record_a;
+            if (service.address_ipv6.sin6_family == AF_INET6)
+                additional[additional_count++] = service.record_aaaa;
+
+            // Add two test TXT records for our service instance name, will be coalesced into
+            // one record with both key-value pair strings by the library
+            additional[additional_count++] = service.txt_record[0];
+            additional[additional_count++] = service.txt_record[1];
+
+            // Send the answer, unicast or multicast depending on flag in query
+            uint16_t unicast = (rclass & MDNS_UNICAST_RESPONSE);
+            printf("  --> answer %.*s port %d (%s)\n",
+                   MDNS_STRING_FORMAT(service.record_srv.data.srv.name), service.port,
+                   (unicast ? "unicast" : "multicast"));
+
+            if (unicast) {
+                mdns_query_answer_unicast(sock, from, addrlen, sendbuffer, sizeof(sendbuffer),
+                                          query_id, rtype, name.str, name.length, answer, 0, 0,
+                                          additional, additional_count);
+            } else {
+                mdns_query_answer_multicast(sock, sendbuffer, sizeof(sendbuffer), answer, 0, 0,
+                                            additional, additional_count);
+            }
+        }
+    } else  {
+
+            qWarning() << "Is this for me?" << name.str << "VS" << service.hostname_qualified.str << "i" << service.address_ipv4.sin_family;
+
+            if ((name.length == service.hostname_qualified.length) &&
+                (strncmp(name.str, service.hostname_qualified.str, name.length) == 0)) {
+            if (((rtype == MDNS_RECORDTYPE_A) || (rtype == MDNS_RECORDTYPE_ANY)) &&
+                (service.address_ipv4.sin_family == AF_INET)) {
+                // The A query was for our qualified hostname (typically "<hostname>.local.") and we
+                // have an IPv4 address, answer with an A record mappiing the hostname to an IPv4
+                // address, as well as any IPv6 address for the hostname, and two test TXT records
+
+                // Answer A records mapping "<hostname>.local." to IPv4 address
+                mdns_record_t answer = service.record_a;
+
+                mdns_record_t additional[5] = {0};
+                size_t additional_count = 0;
+
+                // AAAA record mapping "<hostname>.local." to IPv6 addresses
+                if (service.address_ipv6.sin6_family == AF_INET6)
+                    additional[additional_count++] = service.record_aaaa;
+
+                // Add two test TXT records for our service instance name, will be coalesced into
+                // one record with both key-value pair strings by the library
+                additional[additional_count++] = service.txt_record[0];
+                additional[additional_count++] = service.txt_record[1];
+
+                // Send the answer, unicast or multicast depending on flag in query
+                uint16_t unicast = (rclass & MDNS_UNICAST_RESPONSE);
+                mdns_string_t addrstr = ip_address_to_string(
+                    addrbuffer, sizeof(addrbuffer), (struct sockaddr*)&service.record_a.data.a.addr,
+                    sizeof(service.record_a.data.a.addr));
+                printf("  --> answer %.*s IPv4 %.*s (%s)\n", MDNS_STRING_FORMAT(service.record_a.name),
+                    MDNS_STRING_FORMAT(addrstr), (unicast ? "unicast" : "multicast"));
+
+                if (unicast) {
+                    mdns_query_answer_unicast(sock, from, addrlen, sendbuffer, sizeof(sendbuffer),
+                                            query_id, rtype, name.str, name.length, answer, 0, 0,
+                                            additional, additional_count);
+                } else {
+                    mdns_query_answer_multicast(sock, sendbuffer, sizeof(sendbuffer), answer, 0, 0,
+                                                additional, additional_count);
+                }
+            } else if (((rtype == MDNS_RECORDTYPE_AAAA) || (rtype == MDNS_RECORDTYPE_ANY)) &&
+                    (service.address_ipv6.sin6_family == AF_INET6)) {
+                // The AAAA query was for our qualified hostname (typically "<hostname>.local.") and we
+                // have an IPv6 address, answer with an AAAA record mappiing the hostname to an IPv6
+                // address, as well as any IPv4 address for the hostname, and two test TXT records
+
+                // Answer AAAA records mapping "<hostname>.local." to IPv6 address
+                mdns_record_t answer = service.record_aaaa;
+
+                mdns_record_t additional[5] = {0};
+                size_t additional_count = 0;
+
+                // A record mapping "<hostname>.local." to IPv4 addresses
+                if (service.address_ipv4.sin_family == AF_INET)
+                    additional[additional_count++] = service.record_a;
+
+                // Add two test TXT records for our service instance name, will be coalesced into
+                // one record with both key-value pair strings by the library
+                additional[additional_count++] = service.txt_record[0];
+                additional[additional_count++] = service.txt_record[1];
+
+                // Send the answer, unicast or multicast depending on flag in query
+                uint16_t unicast = (rclass & MDNS_UNICAST_RESPONSE);
+                mdns_string_t addrstr =
+                    ip_address_to_string(addrbuffer, sizeof(addrbuffer),
+                                        (struct sockaddr*)&service.record_aaaa.data.aaaa.addr,
+                                        sizeof(service.record_aaaa.data.aaaa.addr));
+                printf("  --> answer %.*s IPv6 %.*s (%s)\n",
+                    MDNS_STRING_FORMAT(service.record_aaaa.name), MDNS_STRING_FORMAT(addrstr),
+                    (unicast ? "unicast" : "multicast"));
+
+                if (unicast) {
+                    mdns_query_answer_unicast(sock, from, addrlen, sendbuffer, sizeof(sendbuffer),
+                                            query_id, rtype, name.str, name.length, answer, 0, 0,
+                                            additional, additional_count);
+                } else {
+                    mdns_query_answer_multicast(sock, sendbuffer, sizeof(sendbuffer), answer, 0, 0,
+                                                additional, additional_count);
+                }
+            }
+        }
+    }
+    return 0;
+}
+
+
+int sockets[32];
+
+int MdnsWrapper::startAnnouncing(const char* hostname, const char* service_name, int service_port)
+{
+    int num_sockets = open_service_sockets(sockets);
+    if (num_sockets <= 0) {
+        printf("Failed to open any client sockets\n");
+        return -1;
+    }
+    printf("Opened %d socket%s for mDNS service\n", num_sockets, num_sockets ? "s" : "");
+
+    size_t service_name_length = strlen(service_name);
+    if (!service_name_length) {
+        printf("Invalid service name\n");
+        return -1;
+    }
+
+    char* service_name_buffer = (char*)malloc(service_name_length + 2);
+    memcpy(service_name_buffer, service_name, service_name_length);
+    if (service_name_buffer[service_name_length - 1] != '.')
+        service_name_buffer[service_name_length++] = '.';
+    service_name_buffer[service_name_length] = 0;
+    service_name = service_name_buffer;
+
+    printf("Service mDNS: %s:%d\n", service_name, service_port);
+    printf("Hostname: %s\n", hostname);
+
+    size_t capacity = 2048;
+    void* buffer = malloc(capacity);
+
+    mdns_string_t service_string = (mdns_string_t){service_name, strlen(service_name)};
+    mdns_string_t hostname_string = (mdns_string_t){hostname, strlen(hostname)};
+
+    // Build the service instance "<hostname>.<_service-name>._tcp.local." string
+    snprintf(service_instance_buffer, sizeof(service_instance_buffer) - 1, "%.*s.%.*s",
+             MDNS_STRING_FORMAT(hostname_string), MDNS_STRING_FORMAT(service_string));
+
+    qWarning() << service_instance_buffer;
+    // Build the "<hostname>.local." string
+
+    snprintf(qualified_hostname_buffer, sizeof(qualified_hostname_buffer) - 1, "%.*s.local.",
+             MDNS_STRING_FORMAT(hostname_string));
+
+    memset(&service, 0, sizeof(service));
+    service.service.str = service_name;
+    service.service.length =  strlen(service_name);
+    service.hostname.str = hostname;
+    service.hostname.length =  strlen(hostname);
+    service.service_instance.str = service_instance_buffer;
+    service.service_instance.length = strlen(service_instance_buffer);
+    service.hostname_qualified.str = qualified_hostname_buffer;
+    service.hostname_qualified.length = strlen(qualified_hostname_buffer);
+    service.address_ipv4 = service_address_ipv4;
+    service.address_ipv6 = service_address_ipv6;
+    service.port = service_port;
+
+    // Setup our mDNS records
+
+    // PTR record reverse mapping "<_service-name>._tcp.local." to
+    // "<hostname>.<_service-name>._tcp.local."
+    service.record_ptr = (mdns_record_t){.name = service.service,
+                                         .type = MDNS_RECORDTYPE_PTR,
+                                         .data.ptr.name = service.service_instance,
+                                         .rclass = 0,
+                                         .ttl = 0};
+
+    // SRV record mapping "<hostname>.<_service-name>._tcp.local." to
+    // "<hostname>.local." with port. Set weight & priority to 0.
+    service.record_srv = (mdns_record_t){.name = service.service_instance,
+                                         .type = MDNS_RECORDTYPE_SRV,
+                                         .data.srv.name = service.hostname_qualified,
+                                         .data.srv.port = (uint16_t)service.port,
+                                         .data.srv.priority = 0,
+                                         .data.srv.weight = 0,
+                                         .rclass = 0,
+                                         .ttl = 0};
+
+    // A/AAAA records mapping "<hostname>.local." to IPv4/IPv6 addresses
+    service.record_a = (mdns_record_t){.name = service.hostname_qualified,
+                                       .type = MDNS_RECORDTYPE_A,
+                                       .data.a.addr = service.address_ipv4,
+                                       .rclass = 0,
+                                       .ttl = 0};
+
+    service.record_aaaa = (mdns_record_t){.name = service.hostname_qualified,
+                                          .type = MDNS_RECORDTYPE_AAAA,
+                                          .data.aaaa.addr = service.address_ipv6,
+                                          .rclass = 0,
+                                          .ttl = 0};
+
+    // Add two test TXT records for our service instance name, will be coalesced into
+    // one record with both key-value pair strings by the library
+    service.txt_record[0] = (mdns_record_t){.name = service.service_instance,
+                                            .type = MDNS_RECORDTYPE_TXT,
+                                            .data.txt.key = {MDNS_STRING_CONST("test")},
+                                            .data.txt.value = {MDNS_STRING_CONST("1")},
+                                            .rclass = 0,
+                                            .ttl = 0};
+    service.txt_record[1] = (mdns_record_t){.name = service.service_instance,
+                                            .type = MDNS_RECORDTYPE_TXT,
+                                            .data.txt.key = {MDNS_STRING_CONST("other")},
+                                            .data.txt.value = {MDNS_STRING_CONST("value")},
+                                            .rclass = 0,
+                                            .ttl = 0};
+
+    // Send an announcement on startup of service
+    {
+        printf("Sending announce\n");
+        mdns_record_t additional[5] = {0};
+        size_t additional_count = 0;
+        additional[additional_count++] = service.record_srv;
+        if (service.address_ipv4.sin_family == AF_INET)
+            additional[additional_count++] = service.record_a;
+        if (service.address_ipv6.sin6_family == AF_INET6)
+            additional[additional_count++] = service.record_aaaa;
+        additional[additional_count++] = service.txt_record[0];
+        additional[additional_count++] = service.txt_record[1];
+
+        for (int isock = 0; isock < num_sockets; ++isock)
+            mdns_announce_multicast(sockets[isock], buffer, capacity, service.record_ptr, 0, 0,
+                                    additional, additional_count);
+    }
+
+    // This is a crude implementation that checks for incoming queries
+    while (true) {
+        int nfds = 0;
+        fd_set readfs;
+        FD_ZERO(&readfs);
+        for (int isock = 0; isock < num_sockets; ++isock) {
+            if (sockets[isock] >= nfds)
+                nfds = sockets[isock] + 1;
+            FD_SET(sockets[isock], &readfs);
+        }
+
+        struct timeval timeout;
+        timeout.tv_sec = 0;
+        timeout.tv_usec = 100000;
+
+        if (select(nfds, &readfs, 0, 0, &timeout) >= 0) {
+            for (int isock = 0; isock < num_sockets; ++isock) {
+                if (FD_ISSET(sockets[isock], &readfs)) {
+                    mdns_socket_listen(sockets[isock], buffer, capacity, service_callback,
+                                       &service);
+                }
+                FD_SET(sockets[isock], &readfs);
+            }
+        } else {
+            break;
+        }
+    }
+
+    free(buffer);
+    free(service_name_buffer);
+
+    return 0;
+}
+
+
+
+
+void MdnsWrapper::stopAnnouncing()
+{
+    printf("Sending goodbye\n");
+    mdns_record_t additional[5] = {};
+    size_t additional_count = 0;
+    additional[additional_count++] = service.record_srv;
+    if (service.address_ipv4.sin_family == AF_INET)
+        additional[additional_count++] = service.record_a;
+    if (service.address_ipv6.sin6_family == AF_INET6)
+        additional[additional_count++] = service.record_aaaa;
+    additional[additional_count++] = service.txt_record[0];
+    additional[additional_count++] = service.txt_record[1];
+
+    size_t capacity = 2048;
+    void *buffer = malloc(capacity);
+
+    int num_sockets = 2; // FIXME
+    for (int isock = 0; isock < num_sockets; ++isock) {
+        mdns_goodbye_multicast(sockets[isock], buffer, capacity, service.record_ptr, 0, 0, additional, additional_count);
+    }
+
+    for (int isock = 0; isock < num_sockets; ++isock) {
+        mdns_socket_close(sockets[isock]);
+    }
+
+    free(buffer);
+    printf("Closed socket%s\n", num_sockets ? "s" : "");
+}

core/backends/lan/mdns_wrapper.h

@@ -0,0 +1,50 @@
+/**
+ * SPDX-FileCopyrightText: 2023 Albert Vaca Cintora <albertvaka@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+ */
+
+#ifndef KDECONNECT_MDNS_WRAPPER_H
+#define KDECONNECT_MDNS_WRAPPER_H
+
+#include <QHostAddress>
+#include <QMap>
+#include <QSocketNotifier>
+#include <QString>
+#include <QVector>
+
+/*
+ * A Qt wrapper for the mdns.h header-only library
+ * from https://github.com/mjansson/mdns
+ */
+class MdnsWrapper : public QObject
+{
+    Q_OBJECT
+
+public:
+    struct MdnsService {
+        QString serviceName;
+        int port;
+        QHostAddress address;
+        QMap<QString, QString> txtRecords;
+    };
+
+    int startAnnouncing(const char *hostname, const char *service_name, int service_port);
+    void stopAnnouncing();
+
+    void startDiscovering(const char *serviceName);
+    void stopDiscovering();
+
+    void sendQuery(const char *serviceName);
+
+Q_SIGNALS:
+    void serviceFound(const MdnsService &service);
+
+private:
+    int listenForQueryResponses();
+    void stopListeningForQueryResponses();
+
+    QVector<QSocketNotifier *> responseSocketNotifiers;
+};
+
+#endif

core/backends/lan/mdnsdiscovery.cpp

@@ -10,26 +10,22 @@
 #include "kdeconnectconfig.h"
 #include "lanlinkprovider.h"
 
-#include <KDNSSD/DNSSD/PublicService>
-#include <KDNSSD/DNSSD/RemoteService>
-#include <KDNSSD/DNSSD/ServiceBrowser>
+#include "mdns_wrapper.h"
 
-const QString kServiceName = QStringLiteral("_kdeconnect._udp");
+#include <QHostInfo>
+const char *kServiceName = "_kdeconnect._udp.local";
 
 MdnsDiscovery::MdnsDiscovery(LanLinkProvider *lanLinkProvider)
     : lanLinkProvider(lanLinkProvider)
 {
-    switch (KDNSSD::ServiceBrowser::isAvailable()) {
-    case KDNSSD::ServiceBrowser::Stopped:
-        qCWarning(KDECONNECT_CORE) << "mDNS or Avahi daemons are not running, mDNS discovery not available";
-        break;
-    case KDNSSD::ServiceBrowser::Working:
-        qCDebug(KDECONNECT_CORE) << "mDNS discovery is available";
-        break;
-    case KDNSSD::ServiceBrowser::Unsupported:
-        qCWarning(KDECONNECT_CORE) << "mDNS discovery not available (library built without DNS-SD support)";
-        break;
-    }
+    connect(&mdnsWrapper, &MdnsWrapper::serviceFound, [lanLinkProvider](const MdnsWrapper::MdnsService &service) {
+        if (KdeConnectConfig::instance().deviceId() == service.serviceName) {
+            qCDebug(KDECONNECT_CORE) << "Discovered myself, ignoring";
+            return;
+        }
+        qCDebug(KDECONNECT_CORE) << "Discovered" << service.serviceName << "at" << service.address;
+        lanLinkProvider->sendUdpIdentityPacket(QList<QHostAddress>{service.address});
+    });
 }
 
 MdnsDiscovery::~MdnsDiscovery()
@@ -38,8 +34,13 @@ MdnsDiscovery::~MdnsDiscovery()
     stopDiscovering();
 }
 
+QString hostName = QHostInfo::localHostName();
+
 void MdnsDiscovery::startAnnouncing()
 {
+    // mdnsWrapper.startAnnouncing(hostName.toLatin1().data(), kServiceName, LanLinkProvider::UDP_PORT);
+
+    /*
     if (m_publisher != nullptr) {
         qCDebug(KDECONNECT_CORE) << "MDNS already announcing";
         return;
@@ -68,53 +69,26 @@ void MdnsDiscovery::startAnnouncing()
     });
 
     m_publisher->publishAsync();
+    */
 }
 
 void MdnsDiscovery::stopAnnouncing()
 {
-    if (m_publisher != nullptr) {
-        qCDebug(KDECONNECT_CORE) << "MDNS stop announcing";
-        delete m_publisher;
-        m_publisher = nullptr;
-    }
+    // mdnsWrapper.stopAnnouncing();
+
+    // if (m_publisher != nullptr) {
+    //     qCDebug(KDECONNECT_CORE) << "MDNS stop announcing";
+    //     delete m_publisher;
+    //     m_publisher = nullptr;
+    // }
 }
 
 void MdnsDiscovery::startDiscovering()
 {
-    if (m_serviceBrowser != nullptr) {
-        qCDebug(KDECONNECT_CORE) << "MDNS already discovering";
-        return;
-    }
-    qCDebug(KDECONNECT_CORE) << "MDNS start discovering";
-
-    m_serviceBrowser = new KDNSSD::ServiceBrowser(kServiceName, true);
-
-    connect(m_serviceBrowser, &KDNSSD::ServiceBrowser::serviceAdded, [this](KDNSSD::RemoteService::Ptr service) {
-        if (KdeConnectConfig::instance().deviceId() == service->serviceName()) {
-            qCDebug(KDECONNECT_CORE) << "Discovered myself, ignoring";
-            return;
-        }
-        qCDebug(KDECONNECT_CORE) << "Discovered " << service->serviceName() << " at " << service->hostName();
-        QHostAddress address(service->hostName());
-        lanLinkProvider->sendUdpIdentityPacket(QList<QHostAddress>{address});
-    });
-
-    connect(m_serviceBrowser, &KDNSSD::ServiceBrowser::serviceRemoved, [](KDNSSD::RemoteService::Ptr service) {
-        qCDebug(KDECONNECT_CORE) << "Lost " << service->serviceName();
-    });
-
-    connect(m_serviceBrowser, &KDNSSD::ServiceBrowser::finished, []() {
-        qCDebug(KDECONNECT_CORE) << "Finished discovery";
-    });
-
-    m_serviceBrowser->startBrowse();
+    mdnsWrapper.startDiscovering(kServiceName);
 }
 
 void MdnsDiscovery::stopDiscovering()
 {
-    if (m_serviceBrowser != nullptr) {
-        qCDebug(KDECONNECT_CORE) << "MDNS stop discovering";
-        delete m_serviceBrowser;
-        m_serviceBrowser = nullptr;
-    }
+    mdnsWrapper.stopDiscovering();
 }

core/backends/lan/mdnsdiscovery.h

@@ -11,12 +11,9 @@
 
 #include "kdeconnectcore_export.h"
 
+#include "mdns_wrapper.h"
+
 class LanLinkProvider;
-namespace KDNSSD
-{
-class PublicService;
-class ServiceBrowser;
-};
 
 class KDECONNECTCORE_EXPORT MdnsDiscovery : public QObject
 {
@@ -34,8 +31,7 @@ public:
 
 private:
     LanLinkProvider *lanLinkProvider = nullptr;
-    KDNSSD::PublicService *m_publisher = nullptr;
-    KDNSSD::ServiceBrowser *m_serviceBrowser = nullptr;
+    MdnsWrapper mdnsWrapper;
 };
 
 #endif // KDECONNECT_SERVER_H