Clean up proxy protocol detector service

api/src/main/java/com/viaversion/viaversion/api/Via.java

@@ -25,6 +25,7 @@ package com.viaversion.viaversion.api;
 import com.google.common.base.Preconditions;
 import com.viaversion.viaversion.api.configuration.ViaVersionConfig;
 import com.viaversion.viaversion.api.platform.ViaPlatform;
+import com.viaversion.viaversion.api.platform.ViaServerProxyPlatform;
 
 public final class Via {
     private static ViaManager manager;
@@ -63,6 +64,11 @@ public final class Via {
         return manager().getPlatform();
     }
 
+    public static ViaServerProxyPlatform<?> proxyPlatform() {
+        Preconditions.checkArgument(manager().getPlatform() instanceof ViaServerProxyPlatform, "Platform is not proxying Minecraft servers!");
+        return (ViaServerProxyPlatform<?>) manager().getPlatform();
+    }
+
     /**
      * Register the ViaManager associated with the platform.
      *

api/src/main/java/com/viaversion/viaversion/api/ViaAPI.java

@@ -64,7 +64,7 @@ public interface ViaAPI<T> {
      * @return API version incremented with meaningful API changes
      */
     default int apiVersion() {
-        return 14;
+        return 15;
     }
 
     /**

api/src/main/java/com/viaversion/viaversion/api/platform/ProtocolDetectorService.java

@@ -0,0 +1,65 @@
+/*
+ * This file is part of ViaVersion - https://github.com/ViaVersion/ViaVersion
+ * Copyright (C) 2016-2022 ViaVersion and contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.viaversion.viaversion.api.platform;
+
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+
+public interface ProtocolDetectorService {
+
+    /**
+     * Returns the protocol version of the proxied server, or -1 if unknown.
+     *
+     * @param serverName name of the proxied server
+     * @return protocol version of the proxied server, or -1 if unknown
+     */
+    int serverProtocolVersion(String serverName);
+
+    /**
+     * Probes all registered proxied servers for their protocol version.
+     * This is executed automatically in the interval set in the ViaVersion config.
+     */
+    void probeAllServers();
+
+    /**
+     * Sets the stored protocol version of a proxied server.
+     *
+     * @param serverName      name of the proxied server
+     * @param protocolVersion protocol version of the server
+     */
+    void setProtocolVersion(String serverName, int protocolVersion);
+
+    /**
+     * Uncaches and returns the previously stored protocol version of the proxied server. Returns -1 if none was stored.
+     *
+     * @param serverName name of the proxied server
+     * @return previously stored protocol version of the proxied server, or -1 if none was present
+     */
+    int uncacheProtocolVersion(String serverName);
+
+    /**
+     * Returns an unmodifiable map of detected protocol versions.
+     *
+     * @return unmodifiable map of detected protocol versions
+     */
+    Object2IntMap<String> detectedProtocolVersions();
+}

api/src/main/java/com/viaversion/viaversion/api/platform/ViaServerProxyPlatform.java

@@ -0,0 +1,42 @@
+/*
+ * This file is part of ViaVersion - https://github.com/ViaVersion/ViaVersion
+ * Copyright (C) 2016-2022 ViaVersion and contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.viaversion.viaversion.api.platform;
+
+import com.google.common.annotations.Beta;
+
+/**
+ * Represents a platform that proxies a list of Minecraft servers (Velocity, Bungee).
+ * A platform might not be a proxy platform, even if {@link ViaPlatform#isProxy()} is true.
+ *
+ * @param <T> platform player type
+ */
+@Beta
+public interface ViaServerProxyPlatform<T> extends ViaPlatform<T> {
+
+    /**
+     * Returns a service to get protocol versions for proxied servers.
+     *
+     * @return protocol detector service
+     */
+    ProtocolDetectorService protocolDetectorService();
+}

api/src/main/java/com/viaversion/viaversion/api/protocol/Protocol.java

@@ -300,7 +300,7 @@ public interface Protocol<C1 extends ClientboundPacketType, C2 extends Clientbou
      * <p>
      * To be overridden if needed.
      *
-     * @param userConnection The user to initialise
+     * @param connection user to initialise
      */
     default void init(UserConnection connection) {
     }

bungee/src/main/java/com/viaversion/viaversion/BungeePlugin.java

@@ -26,15 +26,15 @@ import com.viaversion.viaversion.api.configuration.ConfigurationProvider;
 import com.viaversion.viaversion.api.data.MappingDataLoader;
 import com.viaversion.viaversion.api.platform.PlatformTask;
 import com.viaversion.viaversion.api.platform.UnsupportedSoftware;
-import com.viaversion.viaversion.api.platform.ViaPlatform;
+import com.viaversion.viaversion.api.platform.ViaServerProxyPlatform;
 import com.viaversion.viaversion.bungee.commands.BungeeCommand;
 import com.viaversion.viaversion.bungee.commands.BungeeCommandHandler;
 import com.viaversion.viaversion.bungee.commands.BungeeCommandSender;
-import com.viaversion.viaversion.bungee.platform.BungeeViaTask;
 import com.viaversion.viaversion.bungee.platform.BungeeViaAPI;
 import com.viaversion.viaversion.bungee.platform.BungeeViaConfig;
 import com.viaversion.viaversion.bungee.platform.BungeeViaInjector;
 import com.viaversion.viaversion.bungee.platform.BungeeViaLoader;
+import com.viaversion.viaversion.bungee.platform.BungeeViaTask;
 import com.viaversion.viaversion.bungee.service.ProtocolDetectorService;
 import com.viaversion.viaversion.dump.PluginInfo;
 import com.viaversion.viaversion.unsupported.UnsupportedServerSoftware;
@@ -52,7 +52,8 @@ import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
-public class BungeePlugin extends Plugin implements ViaPlatform<ProxiedPlayer>, Listener {
+public class BungeePlugin extends Plugin implements ViaServerProxyPlatform<ProxiedPlayer>, Listener {
+    private final ProtocolDetectorService protocolDetectorService = new ProtocolDetectorService();
     private BungeeViaAPI api;
     private BungeeViaConfig config;
 
@@ -200,7 +201,7 @@ public class BungeePlugin extends Plugin implements ViaPlatform<ProxiedPlayer>,
             ));
 
         platformSpecific.add("plugins", GsonUtil.getGson().toJsonTree(plugins));
-        platformSpecific.add("servers", GsonUtil.getGson().toJsonTree(ProtocolDetectorService.getDetectedIds()));
+        platformSpecific.add("servers", GsonUtil.getGson().toJsonTree(protocolDetectorService.detectedProtocolVersions()));
         return platformSpecific;
     }
 
@@ -211,7 +212,7 @@ public class BungeePlugin extends Plugin implements ViaPlatform<ProxiedPlayer>,
 
     @Override
     public Collection<UnsupportedSoftware> getUnsupportedSoftwareClasses() {
-        final Collection<UnsupportedSoftware> list = new ArrayList<>(ViaPlatform.super.getUnsupportedSoftwareClasses());
+        final Collection<UnsupportedSoftware> list = new ArrayList<>(ViaServerProxyPlatform.super.getUnsupportedSoftwareClasses());
         list.add(new UnsupportedServerSoftware.Builder()
                 .name("FlameCord")
                 .addClassName("dev._2lstudios.flamecord.FlameCord")
@@ -224,4 +225,9 @@ public class BungeePlugin extends Plugin implements ViaPlatform<ProxiedPlayer>,
     public boolean hasPlugin(final String name) {
         return getProxy().getPluginManager().getPlugin(name) != null;
     }
+
+    @Override
+    public ProtocolDetectorService protocolDetectorService() {
+        return protocolDetectorService;
+    }
 }

bungee/src/main/java/com/viaversion/viaversion/bungee/commands/subs/ProbeSubCmd.java

@@ -21,7 +21,6 @@ import com.viaversion.viaversion.api.Via;
 import com.viaversion.viaversion.api.command.ViaCommandSender;
 import com.viaversion.viaversion.api.command.ViaSubCommand;
 import com.viaversion.viaversion.bungee.platform.BungeeViaConfig;
-import com.viaversion.viaversion.bungee.service.ProtocolDetectorService;
 
 public class ProbeSubCmd extends ViaSubCommand {
     @Override
@@ -38,7 +37,7 @@ public class ProbeSubCmd extends ViaSubCommand {
 
     @Override
     public boolean execute(ViaCommandSender sender, String[] args) {
-        ProtocolDetectorService.getInstance().run();
+        Via.proxyPlatform().protocolDetectorService().probeAllServers();
         sendMessage(sender, "&6Started searching for protocol versions");
         return true;
     }

bungee/src/main/java/com/viaversion/viaversion/bungee/handlers/BungeeServerHandler.java

@@ -29,7 +29,6 @@ import com.viaversion.viaversion.api.protocol.ProtocolPipeline;
 import com.viaversion.viaversion.api.protocol.packet.PacketWrapper;
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion;
 import com.viaversion.viaversion.api.type.Type;
-import com.viaversion.viaversion.bungee.service.ProtocolDetectorService;
 import com.viaversion.viaversion.bungee.storage.BungeeStorage;
 import com.viaversion.viaversion.protocols.protocol1_13to1_12_2.packets.InventoryPackets;
 import com.viaversion.viaversion.protocols.protocol1_9to1_8.ClientboundPackets1_9;
@@ -96,7 +95,7 @@ public class BungeeServerHandler implements Listener {
             user.put(new BungeeStorage(e.getPlayer()));
         }
 
-        int protocolId = ProtocolDetectorService.getProtocolId(e.getTarget().getName());
+        int protocolId = Via.proxyPlatform().protocolDetectorService().serverProtocolVersion(e.getTarget().getName());
         List<ProtocolPathEntry> protocols = Via.getManager().getProtocolManager().getProtocolPath(user.getProtocolInfo().getProtocolVersion(), protocolId);
 
         // Check if ViaVersion can support that version
@@ -164,7 +163,7 @@ public class BungeeServerHandler implements Listener {
 
                     storage.setCurrentServer(serverName);
 
-                    int protocolId = ProtocolDetectorService.getProtocolId(serverName);
+                    int protocolId = Via.proxyPlatform().protocolDetectorService().serverProtocolVersion(serverName);
 
                     if (protocolId <= ProtocolVersion.v1_8.getVersion()) { // 1.8 doesn't have BossBar packet
                         if (storage.getBossbar() != null) {

bungee/src/main/java/com/viaversion/viaversion/bungee/platform/BungeeViaAPI.java

@@ -18,6 +18,7 @@
 package com.viaversion.viaversion.bungee.platform;
 
 import com.viaversion.viaversion.ViaAPIBase;
+import com.viaversion.viaversion.api.Via;
 import com.viaversion.viaversion.bungee.service.ProtocolDetectorService;
 import io.netty.buffer.ByteBuf;
 import net.md_5.bungee.api.config.ServerInfo;
@@ -41,6 +42,6 @@ public class BungeeViaAPI extends ViaAPIBase<ProxiedPlayer> {
      * @param serverInfo The serverinfo to probe
      */
     public void probeServer(ServerInfo serverInfo) {
-        ProtocolDetectorService.probeServer(serverInfo);
+        ((ProtocolDetectorService) Via.proxyPlatform().protocolDetectorService()).probeServer(serverInfo);
     }
 }

bungee/src/main/java/com/viaversion/viaversion/bungee/platform/BungeeViaLoader.java

@@ -30,7 +30,6 @@ import com.viaversion.viaversion.bungee.providers.BungeeEntityIdProvider;
 import com.viaversion.viaversion.bungee.providers.BungeeMainHandProvider;
 import com.viaversion.viaversion.bungee.providers.BungeeMovementTransmitter;
 import com.viaversion.viaversion.bungee.providers.BungeeVersionProvider;
-import com.viaversion.viaversion.bungee.service.ProtocolDetectorService;
 import com.viaversion.viaversion.protocols.protocol1_9to1_8.providers.BossBarProvider;
 import com.viaversion.viaversion.protocols.protocol1_9to1_8.providers.EntityIdProvider;
 import com.viaversion.viaversion.protocols.protocol1_9to1_8.providers.MainHandProvider;
@@ -44,10 +43,9 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 public class BungeeViaLoader implements ViaPlatformLoader {
-    private final BungeePlugin plugin;
-
     private final Set<Listener> listeners = new HashSet<>();
     private final Set<ScheduledTask> tasks = new HashSet<>();
+    private final BungeePlugin plugin;
 
     public BungeeViaLoader(BungeePlugin plugin) {
         this.plugin = plugin;
@@ -82,7 +80,7 @@ public class BungeeViaLoader implements ViaPlatformLoader {
         if (plugin.getConf().getBungeePingInterval() > 0) {
             tasks.add(plugin.getProxy().getScheduler().schedule(
                     plugin,
-                    new ProtocolDetectorService(plugin),
+                    () -> Via.proxyPlatform().protocolDetectorService().probeAllServers(),
                     0, plugin.getConf().getBungeePingInterval(),
                     TimeUnit.SECONDS
             ));

bungee/src/main/java/com/viaversion/viaversion/bungee/service/ProtocolDetectorService.java

@@ -17,93 +17,77 @@
  */
 package com.viaversion.viaversion.bungee.service;
 
-import com.viaversion.viaversion.BungeePlugin;
 import com.viaversion.viaversion.api.Via;
 import com.viaversion.viaversion.bungee.platform.BungeeViaConfig;
 import com.viaversion.viaversion.bungee.providers.BungeeVersionProvider;
-import net.md_5.bungee.api.Callback;
-import net.md_5.bungee.api.ServerPing;
+import com.viaversion.viaversion.platform.AbstractProtocolDetectorService;
+import net.md_5.bungee.api.ProxyServer;
 import net.md_5.bungee.api.config.ServerInfo;
 
-import java.util.HashMap;
+import java.util.Collection;
+import java.util.HashSet;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.Set;
 
-public class ProtocolDetectorService implements Runnable {
-    private static final Map<String, Integer> detectedProtocolIds = new ConcurrentHashMap<>();
-    private static ProtocolDetectorService instance;
-    private final BungeePlugin plugin;
+public final class ProtocolDetectorService extends AbstractProtocolDetectorService {
 
-    public ProtocolDetectorService(BungeePlugin plugin) {
-        this.plugin = plugin;
-        instance = this;
-    }
-
-    public static Integer getProtocolId(String serverName) {
-        // Step 1. Check Config
-        Map<String, Integer> servers = ((BungeeViaConfig) Via.getConfig()).getBungeeServerProtocols();
-        Integer protocol = servers.get(serverName);
-        if (protocol != null) {
-            return protocol;
-        }
-        // Step 2. Check Detected
-        Integer detectedProtocol = detectedProtocolIds.get(serverName);
-        if (detectedProtocol != null) {
-            return detectedProtocol;
-        }
-        // Step 3. Use Default
-        Integer defaultProtocol = servers.get("default");
-        if (defaultProtocol != null) {
-            return defaultProtocol;
-        }
-        // Step 4: Use bungee lowest supported... *cries*
-        return BungeeVersionProvider.getLowestSupportedVersion();
-    }
-
-    @Override
-    public void run() {
-        for (final Map.Entry<String, ServerInfo> lists : plugin.getProxy().getServers().entrySet()) {
-            probeServer(lists.getValue());
-        }
-    }
-
-    public static void probeServer(final ServerInfo serverInfo) {
-        final String key = serverInfo.getName();
-        serverInfo.ping(new Callback<ServerPing>() {
-            @Override
-            public void done(ServerPing serverPing, Throwable throwable) {
-                if (throwable == null && serverPing != null && serverPing.getVersion() != null) {
+    public void probeServer(final ServerInfo serverInfo) {
+        final String serverName = serverInfo.getName();
+        serverInfo.ping((serverPing, throwable) -> {
             // Ensure protocol is positive, some services will return -1
-                    if (serverPing.getVersion().getProtocol() > 0) {
-                        detectedProtocolIds.put(key, serverPing.getVersion().getProtocol());
+            if (throwable != null || serverPing == null || serverPing.getVersion() == null || serverPing.getVersion().getProtocol() <= 0) {
+                return;
+            }
+
+            final int oldProtocolVersion = serverProtocolVersion(serverName);
+            if (oldProtocolVersion == serverPing.getVersion().getProtocol()) {
+                // Same value as previously
+                return;
+            }
+
+            setProtocolVersion(serverName, serverPing.getVersion().getProtocol());
+
             if (((BungeeViaConfig) Via.getConfig()).isBungeePingSave()) {
-                            Map<String, Integer> servers = ((BungeeViaConfig) Via.getConfig()).getBungeeServerProtocols();
-                            Integer protocol = servers.get(key);
+                final Map<String, Integer> servers = ((BungeeViaConfig) Via.getConfig()).getBungeeServerProtocols();
+                final Integer protocol = servers.get(serverName);
                 if (protocol != null && protocol == serverPing.getVersion().getProtocol()) {
                     return;
                 }
+
                 // Ensure we're the only ones writing to the config
                 synchronized (Via.getPlatform().getConfigurationProvider()) {
-                                servers.put(key, serverPing.getVersion().getProtocol());
+                    servers.put(serverName, serverPing.getVersion().getProtocol());
                 }
-                            // Save
                 Via.getPlatform().getConfigurationProvider().saveConfig();
             }
-                    }
-                }
-            }
         });
     }
 
-    public static Map<String, Integer> getDetectedIds() {
-        return new HashMap<>(detectedProtocolIds);
+    @Override
+    public void probeAllServers() {
+        final Collection<ServerInfo> servers = ProxyServer.getInstance().getServers().values();
+        final Set<String> serverNames = new HashSet<>(servers.size());
+        for (final ServerInfo serverInfo : servers) {
+            probeServer(serverInfo);
+            serverNames.add(serverInfo.getName());
         }
 
-    public static ProtocolDetectorService getInstance() {
-        return instance;
+        // Remove servers that aren't registered anymore
+        lock.writeLock().lock();
+        try {
+            detectedProtocolIds.keySet().retainAll(serverNames);
+        } finally {
+            lock.writeLock().unlock();
+        }
     }
 
-    public BungeePlugin getPlugin() {
-        return plugin;
+    @Override
+    protected Map<String, Integer> configuredServers() {
+        return ((BungeeViaConfig) Via.getConfig()).getBungeeServerProtocols();
+    }
+
+    @Override
+    protected int lowestSupportedProtocolVersion() {
+        return BungeeVersionProvider.getLowestSupportedVersion();
     }
 }

common/src/main/java/com/viaversion/viaversion/ViaManagerImpl.java

@@ -157,7 +157,7 @@ public class ViaManagerImpl implements ViaManager {
         loader.load();
         // Common tasks
         mappingLoadingTask = Via.getPlatform().runRepeatingSync(() -> {
-            if (protocolManager.checkForMappingCompletion()) {
+            if (protocolManager.checkForMappingCompletion() && mappingLoadingTask != null) {
                 mappingLoadingTask.cancel();
                 mappingLoadingTask = null;
             }

common/src/main/java/com/viaversion/viaversion/platform/AbstractProtocolDetectorService.java

@@ -0,0 +1,94 @@
+/*
+ * This file is part of ViaVersion - https://github.com/ViaVersion/ViaVersion
+ * Copyright (C) 2016-2022 ViaVersion and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package com.viaversion.viaversion.platform;
+
+import com.viaversion.viaversion.api.platform.ProtocolDetectorService;
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
+
+import java.util.Map;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+public abstract class AbstractProtocolDetectorService implements ProtocolDetectorService {
+    protected final Object2IntMap<String> detectedProtocolIds = new Object2IntOpenHashMap<>();
+    protected final ReadWriteLock lock = new ReentrantReadWriteLock();
+
+    @Override
+    public int serverProtocolVersion(final String serverName) {
+        // Step 1. Check detected
+        lock.readLock().lock();
+        try {
+            final int detectedProtocol = detectedProtocolIds.getInt(serverName);
+            if (detectedProtocol != -1) {
+                return detectedProtocol;
+            }
+        } finally {
+            lock.readLock().unlock();
+        }
+
+        // Step 2. Check config (CME moment?)
+        final Map<String, Integer> servers = configuredServers();
+        final Integer protocol = servers.get(serverName);
+        if (protocol != null) {
+            return protocol;
+        }
+
+        // Step 3. Use Default (CME moment intensifies?)
+        final Integer defaultProtocol = servers.get("default");
+        if (defaultProtocol != null) {
+            return defaultProtocol;
+        }
+
+        // Step 4: Use the proxy's lowest supported... *cries*
+        return lowestSupportedProtocolVersion();
+    }
+
+    @Override
+    public void setProtocolVersion(final String serverName, final int protocolVersion) {
+        lock.writeLock().lock();
+        try {
+            detectedProtocolIds.put(serverName, protocolVersion);
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
+    @Override
+    public int uncacheProtocolVersion(final String serverName) {
+        lock.writeLock().lock();
+        try {
+            return detectedProtocolIds.removeInt(serverName);
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
+    @Override
+    public Object2IntMap<String> detectedProtocolVersions() {
+        try {
+            return new Object2IntOpenHashMap<>(detectedProtocolIds);
+        } finally {
+            lock.readLock().unlock();
+        }
+    }
+
+    protected abstract Map<String, Integer> configuredServers();
+
+    protected abstract int lowestSupportedProtocolVersion();
+}

velocity/src/main/java/com/viaversion/viaversion/VelocityPlugin.java

@@ -32,7 +32,7 @@ import com.viaversion.viaversion.api.command.ViaCommandSender;
 import com.viaversion.viaversion.api.configuration.ConfigurationProvider;
 import com.viaversion.viaversion.api.data.MappingDataLoader;
 import com.viaversion.viaversion.api.platform.PlatformTask;
-import com.viaversion.viaversion.api.platform.ViaPlatform;
+import com.viaversion.viaversion.api.platform.ViaServerProxyPlatform;
 import com.viaversion.viaversion.dump.PluginInfo;
 import com.viaversion.viaversion.util.ChatColorUtil;
 import com.viaversion.viaversion.util.GsonUtil;
@@ -64,7 +64,7 @@ import java.util.concurrent.TimeUnit;
         description = "Allow newer Minecraft versions to connect to an older server version.",
         url = "https://viaversion.com"
 )
-public class VelocityPlugin implements ViaPlatform<Player> {
+public class VelocityPlugin implements ViaServerProxyPlatform<Player> {
     public static final LegacyComponentSerializer COMPONENT_SERIALIZER = LegacyComponentSerializer.builder().character(ChatColorUtil.COLOR_CHAR).extractUrls().build();
     public static ProxyServer PROXY;
 
@@ -76,6 +76,7 @@ public class VelocityPlugin implements ViaPlatform<Player> {
     @DataDirectory
     private Path configDir;
 
+    private final ProtocolDetectorService protocolDetectorService = new ProtocolDetectorService();
     private VelocityViaAPI api;
     private java.util.logging.Logger logger;
     private VelocityViaConfig conf;
@@ -230,7 +231,7 @@ public class VelocityPlugin implements ViaPlatform<Player> {
             ));
         }
         extra.add("plugins", GsonUtil.getGson().toJsonTree(plugins));
-        extra.add("servers", GsonUtil.getGson().toJsonTree(ProtocolDetectorService.getDetectedIds()));
+        extra.add("servers", GsonUtil.getGson().toJsonTree(protocolDetectorService.detectedProtocolVersions()));
         return extra;
     }
 
@@ -249,6 +250,11 @@ public class VelocityPlugin implements ViaPlatform<Player> {
         return logger;
     }
 
+    @Override
+    public ProtocolDetectorService protocolDetectorService() {
+        return protocolDetectorService;
+    }
+
     private boolean hasConnectionEvent() {
         try {
             Class.forName("com.velocitypowered.proxy.protocol.VelocityConnectionEvent");

velocity/src/main/java/com/viaversion/viaversion/velocity/command/subs/ProbeSubCmd.java

@@ -21,7 +21,6 @@ import com.viaversion.viaversion.api.Via;
 import com.viaversion.viaversion.api.command.ViaCommandSender;
 import com.viaversion.viaversion.api.command.ViaSubCommand;
 import com.viaversion.viaversion.velocity.platform.VelocityViaConfig;
-import com.viaversion.viaversion.velocity.service.ProtocolDetectorService;
 
 public class ProbeSubCmd extends ViaSubCommand {
     @Override
@@ -38,7 +37,7 @@ public class ProbeSubCmd extends ViaSubCommand {
 
     @Override
     public boolean execute(ViaCommandSender sender, String[] args) {
-        ProtocolDetectorService.getInstance().run();
+        Via.proxyPlatform().protocolDetectorService().probeAllServers();
         sendMessage(sender, "&6Started searching for protocol versions");
         return true;
     }

velocity/src/main/java/com/viaversion/viaversion/velocity/platform/VelocityViaLoader.java

@@ -29,9 +29,9 @@ import com.viaversion.viaversion.velocity.listeners.UpdateListener;
 import com.viaversion.viaversion.velocity.providers.VelocityBossBarProvider;
 import com.viaversion.viaversion.velocity.providers.VelocityMovementTransmitter;
 import com.viaversion.viaversion.velocity.providers.VelocityVersionProvider;
-import com.viaversion.viaversion.velocity.service.ProtocolDetectorService;
 
 public class VelocityViaLoader implements ViaPlatformLoader {
+
     @Override
     public void load() {
         Object plugin = VelocityPlugin.PROXY.getPluginManager()
@@ -51,7 +51,7 @@ public class VelocityViaLoader implements ViaPlatformLoader {
         int pingInterval = ((VelocityViaConfig) Via.getPlatform().getConf()).getVelocityPingInterval();
         if (pingInterval > 0) {
             Via.getPlatform().runRepeatingSync(
-                    new ProtocolDetectorService(),
+                    () -> Via.proxyPlatform().protocolDetectorService().probeAllServers(),
                     pingInterval * 20L);
         }
     }

velocity/src/main/java/com/viaversion/viaversion/velocity/providers/VelocityVersionProvider.java

@@ -24,7 +24,6 @@ import com.viaversion.viaversion.api.connection.UserConnection;
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion;
 import com.viaversion.viaversion.protocols.base.BaseVersionProvider;
 import com.viaversion.viaversion.velocity.platform.VelocityViaInjector;
-import com.viaversion.viaversion.velocity.service.ProtocolDetectorService;
 import io.netty.channel.ChannelHandler;
 
 import java.lang.reflect.Method;
@@ -50,7 +49,7 @@ public class VelocityVersionProvider extends BaseVersionProvider {
     private int getBackProtocol(UserConnection user) throws Exception {
         //TODO use newly added Velocity netty event
         ChannelHandler mcHandler = user.getChannel().pipeline().get("handler");
-        return ProtocolDetectorService.getProtocolId(
+        return Via.proxyPlatform().protocolDetectorService().serverProtocolVersion(
                 ((ServerConnection) getAssociation.invoke(mcHandler)).getServerInfo().getName());
     }
 

velocity/src/main/java/com/viaversion/viaversion/velocity/service/ProtocolDetectorService.java

@@ -21,80 +21,77 @@ import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.viaversion.viaversion.VelocityPlugin;
 import com.viaversion.viaversion.api.Via;
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion;
+import com.viaversion.viaversion.platform.AbstractProtocolDetectorService;
 import com.viaversion.viaversion.velocity.platform.VelocityViaConfig;
 
-import java.util.HashMap;
+import java.util.Collection;
+import java.util.HashSet;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.Set;
 
-public class ProtocolDetectorService implements Runnable {
-    private static final Map<String, Integer> detectedProtocolIds = new ConcurrentHashMap<>();
-    private static ProtocolDetectorService instance;
-
-    public ProtocolDetectorService() {
-        instance = this;
-    }
-
-    public static Integer getProtocolId(String serverName) {
-        // Step 1. Check Config
-        Map<String, Integer> servers = ((VelocityViaConfig) Via.getConfig()).getVelocityServerProtocols();
-        Integer protocol = servers.get(serverName);
-        if (protocol != null) {
-            return protocol;
-        }
-        // Step 2. Check Detected
-        Integer detectedProtocol = detectedProtocolIds.get(serverName);
-        if (detectedProtocol != null) {
-            return detectedProtocol;
-        }
-        // Step 3. Use Default
-        Integer defaultProtocol = servers.get("default");
-        if (defaultProtocol != null) {
-            return defaultProtocol;
-        }
-        // Step 4: Use bungee lowest supported... *cries*
-        try {
-            return ProtocolVersion.getProtocol(Via.getManager().getInjector().getServerProtocolVersion()).getVersion();
-        } catch (Exception e) {
-            e.printStackTrace();
-            return ProtocolVersion.v1_8.getVersion();
-        }
-    }
+public final class ProtocolDetectorService extends AbstractProtocolDetectorService {
 
     @Override
-    public void run() {
-        for (final RegisteredServer serv : VelocityPlugin.PROXY.getAllServers()) {
-            probeServer(serv);
+    public void probeAllServers() {
+        final Collection<RegisteredServer> servers = VelocityPlugin.PROXY.getAllServers();
+        final Set<String> serverNames = new HashSet<>(servers.size());
+        for (final RegisteredServer server : servers) {
+            probeServer(server);
+            serverNames.add(server.getServerInfo().getName());
+        }
+
+        // Remove servers that aren't registered anymore
+        lock.writeLock().lock();
+        try {
+            detectedProtocolIds.keySet().retainAll(serverNames);
+        } finally {
+            lock.writeLock().unlock();
         }
     }
 
-    public static void probeServer(final RegisteredServer serverInfo) {
-        final String key = serverInfo.getServerInfo().getName();
-        serverInfo.ping().thenAccept((serverPing) -> {
-            if (serverPing != null && serverPing.getVersion() != null) {
-                detectedProtocolIds.put(key, serverPing.getVersion().getProtocol());
+    public void probeServer(final RegisteredServer server) {
+        final String serverName = server.getServerInfo().getName();
+        server.ping().thenAccept(serverPing -> {
+            if (serverPing == null || serverPing.getVersion() == null) {
+                return;
+            }
+
+            final int oldProtocolVersion = serverProtocolVersion(serverName);
+            if (oldProtocolVersion != -1 && oldProtocolVersion == serverPing.getVersion().getProtocol()) {
+                // Same value as previously
+                return;
+            }
+
+            setProtocolVersion(serverName, serverPing.getVersion().getProtocol());
+
             if (((VelocityViaConfig) Via.getConfig()).isVelocityPingSave()) {
-                    Map<String, Integer> servers = ((VelocityViaConfig) Via.getConfig()).getVelocityServerProtocols();
-                    Integer protocol = servers.get(key);
+                final Map<String, Integer> servers = configuredServers();
+                final Integer protocol = servers.get(serverName);
                 if (protocol != null && protocol == serverPing.getVersion().getProtocol()) {
                     return;
                 }
+
                 // Ensure we're the only ones writing to the config
                 synchronized (Via.getPlatform().getConfigurationProvider()) {
-                        servers.put(key, serverPing.getVersion().getProtocol());
+                    servers.put(serverName, serverPing.getVersion().getProtocol());
                 }
-                    // Save
                 Via.getPlatform().getConfigurationProvider().saveConfig();
             }
-            }
         });
     }
 
-    public static Map<String, Integer> getDetectedIds() {
-        return new HashMap<>(detectedProtocolIds);
+    @Override
+    protected Map<String, Integer> configuredServers() {
+        return ((VelocityViaConfig) Via.getConfig()).getVelocityServerProtocols();
     }
 
-    public static ProtocolDetectorService getInstance() {
-        return instance;
+    @Override
+    protected int lowestSupportedProtocolVersion() {
+        try {
+            return ProtocolVersion.getProtocol(Via.getManager().getInjector().getServerProtocolVersion()).getVersion();
+        } catch (final Exception e) {
+            e.printStackTrace();
+            return ProtocolVersion.v1_8.getVersion();
+        }
     }
 }