network: fix room socket races and share the room network check

bsd:s, bsd:u and bsd:a share one file descriptor table, but each
service bound its own proxy packet callback, so every room packet was
queued three times on each socket. Bind the callback once.

The room thread walked the descriptor table without a lock while bsd
created and closed sockets, so it could reach a destroyed or not yet
created socket. Guard the table with a mutex, and publish a socket only
after it is created and initialized. Check airplane mode before an fd
is taken, so a refused socket no longer leaks its slot.

ProxySocket now initializes protocol, decompresses packets outside the
packet lock without copying the compressed data first, and keeps a read
offset for partial TCP reads instead of erasing from the front.

Add Network::GetRoomIPv4Address(), set only in the Joined and Moderator
states. NIFM uses it for network availability and for every reported
address, including EnumerateNetworkInterfaces and GetCurrentIpAddress,
so no call reports the room address while another rejects the network.

Assisted-by: Claude Opus 5.5 (investigation and implementation)

4 files changed, 39 insertions, 8 deletions

diff --git a/src/core/internal_network/network.cpp b/src/core/internal_network/network.cpp
index 01d37fb35b..d1c436aa08 100644
--- a/src/core/internal_network/network.cpp
+++ b/src/core/internal_network/network.cpp
@@ -722,6 +722,17 @@ std::optional<IPv4Address> GetHostIPv4Address() {
     return TranslateIPv4(network_interface->ip_address);
 }
 
+std::optional<IPv4Address> GetRoomIPv4Address() {
+    if (const auto room_member = GetRoomMember().lock()) {
+        // The room host and moderators are in the Moderator state instead of Joined
+        const auto state = room_member->GetState();
+        if (state == RoomMember::State::Joined || state == RoomMember::State::Moderator) {
+            return room_member->GetFakeIpAddress();
+        }
+    }
+    return std::nullopt;
+}
+
 std::string IPv4AddressToString(IPv4Address ip_addr) {
     std::array<char, INET_ADDRSTRLEN> buf = {};
     ASSERT(inet_ntop(AF_INET, &ip_addr, buf.data(), sizeof(buf)) == buf.data());
diff --git a/src/core/internal_network/network.h b/src/core/internal_network/network.h
index 2c9ae523c5..a598f75348 100644
--- a/src/core/internal_network/network.h
+++ b/src/core/internal_network/network.h
@@ -121,6 +121,10 @@ constexpr IPv4Address TranslateIPv4(in_addr addr) {
 /// @return human ordered IPv4 address (e.g. 192.168.0.1) as an array
 std::optional<IPv4Address> GetHostIPv4Address();
 
+/// @brief Returns the fake IPv4 address of the joined room, the emulated network while in a room
+/// @return nullopt outside a room and while still joining it
+std::optional<IPv4Address> GetRoomIPv4Address();
+
 std::string IPv4AddressToString(IPv4Address ip_addr);
 u32 IPv4AddressToInteger(IPv4Address ip_addr);
 
diff --git a/src/core/internal_network/socket_proxy.cpp b/src/core/internal_network/socket_proxy.cpp
index 83eb2ce9d0..6c2f79da6e 100644
--- a/src/core/internal_network/socket_proxy.cpp
+++ b/src/core/internal_network/socket_proxy.cpp
@@ -43,9 +43,21 @@ void ProxySocket::HandleProxyPacket(const ProxyPacket& packet) {
             LOG_INFO(Network, "Received broadcast packet, but not configured for broadcast mode");
             return;
         }
+    }
 
-        auto decompressed = packet;
-        decompressed.data = Common::Compression::DecompressDataZSTD(packet.data);
+    // Decompress without the lock, so the game thread does not wait for it
+    ProxyPacket decompressed{
+        .local_endpoint = packet.local_endpoint,
+        .remote_endpoint = packet.remote_endpoint,
+        .protocol = packet.protocol,
+        .broadcast = packet.broadcast,
+        .data = Common::Compression::DecompressDataZSTD(packet.data),
+    };
+    {
+        std::lock_guard guard(packets_mutex);
+        if (closed) {
+            return;
+        }
         received_packets.push(std::move(decompressed));
     }
     packets_cv.notify_one();
@@ -152,26 +164,28 @@ std::pair<s32, Errno> ProxySocket::RecvFrom(int flags, std::span<u8> message, So
 
 std::pair<s32, Errno> ProxySocket::ReceivePacket(int flags, std::span<u8> message, SockAddrIn* addr,
                                                  std::size_t max_length) {
-    ProxyPacket& packet = received_packets.front();
+    const ProxyPacket& packet = received_packets.front();
     if (addr) {
         addr->family = Domain::INET;
         addr->ip = packet.local_endpoint.ip;         // The senders ip address
         addr->portno = packet.local_endpoint.portno; // The senders port number
     }
 
-    const std::size_t read_bytes = (std::min)(packet.data.size(), max_length);
-    std::memcpy(message.data(), packet.data.data(), read_bytes);
+    const std::span<const u8> unread = std::span{packet.data}.subspan(front_read_offset);
+    const std::size_t read_bytes = (std::min)(unread.size(), max_length);
+    std::memcpy(message.data(), unread.data(), read_bytes);
 
     if ((flags & FLAG_MSG_PEEK) != 0) {
         return {static_cast<s32>(read_bytes), Errno::SUCCESS};
     }
 
-    if (protocol == Protocol::TCP && read_bytes < packet.data.size()) {
+    if (protocol == Protocol::TCP && read_bytes < unread.size()) {
         // Keep the unread part of the stream for the next call
-        packet.data.erase(packet.data.begin(), packet.data.begin() + read_bytes);
+        front_read_offset += read_bytes;
     } else {
         // Like BSD recv(), the rest of a datagram that does not fit is discarded
         received_packets.pop();
+        front_read_offset = 0;
     }
 
     return {static_cast<s32>(read_bytes), Errno::SUCCESS};
@@ -240,6 +254,7 @@ Errno ProxySocket::Close() {
         fd = INVALID_SOCKET;
         closed = true;
         received_packets = {};
+        front_read_offset = 0;
     }
     packets_cv.notify_all();
 
diff --git a/src/core/internal_network/socket_proxy.h b/src/core/internal_network/socket_proxy.h
index 8343fcbae1..d2bd7aae77 100644
--- a/src/core/internal_network/socket_proxy.h
+++ b/src/core/internal_network/socket_proxy.h
@@ -90,7 +90,8 @@ private:
     SockAddrIn local_endpoint{};
     bool blocking = true;
     std::queue<ProxyPacket> received_packets;
-    Protocol protocol;
+    std::size_t front_read_offset = 0; ///< Bytes of the front TCP packet that were already read
+    Protocol protocol{};
 
     std::mutex packets_mutex;
     std::condition_variable packets_cv;