From bbfbd53123ca765d343374a8ed4a95c574e94f9b Mon Sep 17 00:00:00 2001
From: Albert Vaca Cintora <albertvaka@gmail.com>
Date: Mon, 31 Jul 2023 11:04:16 +0200
Subject: [PATCH] Implement IP match function

---
 core/backends/lan/mdns_wrapper.cpp | 55 +++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/core/backends/lan/mdns_wrapper.cpp b/core/backends/lan/mdns_wrapper.cpp
index ac41722d0..c4104f4af 100644
--- a/core/backends/lan/mdns_wrapper.cpp
+++ b/core/backends/lan/mdns_wrapper.cpp
@@ -243,13 +243,60 @@ static mdns_string_t createMdnsString(const QByteArray &str)
     return mdns_string_t{str.constData(), (size_t)str.length()};
 }
 
-static QHostAddress findBestAddressMatch(QVector<QHostAddress> hostAddresses, const struct sockaddr *fromAddress)
+int countCommonLeadingBits(quint32 int1, quint32 int2) {
+    int count = 0;
+    while (int1 != 0 && int2 != 0) {
+        if ((int1 & 0x80000000) == (int2 & 0x80000000)) {
+            count++;
+            int1 <<= 1;
+            int2 <<= 1;
+        } else {
+            break;
+        }
+    }
+    return count;
+}
+
+static QHostAddress findBestAddressMatchV4(QVector<QHostAddress> hostAddresses, const struct sockaddr *fromAddress)
 {
+    Q_ASSERT(!hostAddresses.empty());
     if (hostAddresses.size() == 1 || fromAddress == nullptr) {
         return hostAddresses[0];
     }
-    // FIXME
+
+    QHostAddress otherIp = QHostAddress(fromAddress);
+
+    if (otherIp.protocol() != QAbstractSocket::IPv4Protocol) {
+        return hostAddresses[0];
+    }
+
+    // qDebug() << "I have more than one IP address:" << hostAddresses << "- Finding best match for source IP:" << otherIp;
+
+    QHostAddress matchingIp = hostAddresses[0];
+    int matchingBits = -1;
+    quint32 rawOtherIp = otherIp.toIPv4Address();
+    for (const QHostAddress& ip : hostAddresses) {
+        Q_ASSERT(ip.protocol() == QAbstractSocket::IPv4Protocol);
+        quint32 rawMyIp = ip.toIPv4Address();
+        // Since we don't have the network mask, we just compare the prefixes of the IPs to find the longest match
+        int matchingBitsCount = countCommonLeadingBits(rawMyIp, rawOtherIp);
+        if (matchingBitsCount > matchingBits) {
+            matchingIp = ip;
+            matchingBits = matchingBitsCount;
+        }
+    }
+
+    // qDebug() << "Found match:" << matchingIp;
+
+    return matchingIp;
+}
+
+static QHostAddress findBestAddressMatchV6(QVector<QHostAddress> hostAddresses, const struct sockaddr *fromAddress)
+{
+    Q_ASSERT(!hostAddresses.empty());
+    // We could do the same logic for v6 that we do for V4, but we don't care that much about IPv6
     return hostAddresses[0];
+    Q_UNUSED(fromAddress);
 }
 
 static mdns_record_t createMdnsRecord(const Announcer::AnnouncedInfo &self,
@@ -275,11 +322,11 @@ static mdns_record_t createMdnsRecord(const Announcer::AnnouncedInfo &self,
         break;
     case MDNS_RECORDTYPE_A: // maps "<hostname>.local." to IPv4
         answer.name = createMdnsString(self.hostname);
-        answer.data.a.addr = qHostAddresstoSockaddr(findBestAddressMatch(self.addressesV4, fromAddress));
+        answer.data.a.addr = qHostAddressToSockaddr(findBestAddressMatchV4(self.addressesV4, fromAddress));
         break;
     case MDNS_RECORDTYPE_AAAA: // maps "<hostname>.local." to IPv6
         answer.name = createMdnsString(self.hostname);
-        answer.data.aaaa.addr = qHostAddresstoSockaddr6(findBestAddressMatch(self.addressesV6, fromAddress));
+        answer.data.aaaa.addr = qHostAddressToSockaddr6(findBestAddressMatchV6(self.addressesV6, fromAddress));
         break;
     case MDNS_RECORDTYPE_TXT:
         answer.name = createMdnsString(self.serviceInstance);