Add support for resolving dependencies that require a version range

annotation-processor/src/main/java/com/velocitypowered/annotationprocessor/SerializedPluginDescription.java

@@ -36,7 +36,7 @@ public final class SerializedPluginDescription {
   // @Nullable is used here to make GSON skip these in the serialized file
   private final String id;
   private final @Nullable String name;
-  private final @Nullable String version;
+  private final String version;
   private final @Nullable String description;
   private final @Nullable String url;
   private final @Nullable List<String> authors;
@@ -44,13 +44,12 @@ public final class SerializedPluginDescription {
   private final String main;
 
   private SerializedPluginDescription(String id, String name, String version, String description,
-      String url,
+      String url, List<String> authors, List<Dependency> dependencies, String main) {
-      List<String> authors, List<Dependency> dependencies, String main) {
     Preconditions.checkNotNull(id, "id");
     Preconditions.checkArgument(ID_PATTERN.matcher(id).matches(), "id is not valid");
     this.id = id;
     this.name = Strings.emptyToNull(name);
-    this.version = Strings.emptyToNull(version);
+    this.version = Preconditions.checkNotNull(version, "version");
     this.description = Strings.emptyToNull(description);
     this.url = Strings.emptyToNull(url);
     this.authors = authors == null || authors.isEmpty() ? ImmutableList.of() : authors;
@@ -62,7 +61,8 @@ public final class SerializedPluginDescription {
   static SerializedPluginDescription from(Plugin plugin, String qualifiedName) {
     List<Dependency> dependencies = new ArrayList<>();
     for (com.velocitypowered.api.plugin.Dependency dependency : plugin.dependencies()) {
-      dependencies.add(new Dependency(dependency.id(), dependency.optional()));
+      dependencies.add(new Dependency(dependency.id(), dependency.version(),
+          dependency.optional()));
     }
     return new SerializedPluginDescription(plugin.id(), plugin.name(), plugin.version(),
         plugin.description(), plugin.url(),
@@ -78,7 +78,7 @@ public final class SerializedPluginDescription {
     return name;
   }
 
-  public @Nullable String getVersion() {
+  public String getVersion() {
     return version;
   }
 
@@ -143,10 +143,12 @@ public final class SerializedPluginDescription {
   public static final class Dependency {
 
     private final String id;
+    private final String version;
     private final boolean optional;
 
-    public Dependency(String id, boolean optional) {
+    public Dependency(String id, String version, boolean optional) {
       this.id = id;
+      this.version = version;
       this.optional = optional;
     }
 
@@ -154,6 +156,10 @@ public final class SerializedPluginDescription {
       return id;
     }
 
+    public String getVersion() {
+      return version;
+    }
+
     public boolean isOptional() {
       return optional;
     }
@@ -167,19 +173,19 @@ public final class SerializedPluginDescription {
         return false;
       }
       Dependency that = (Dependency) o;
-      return optional == that.optional
+      return optional == that.optional && id.equals(that.id) && version.equals(that.version);
-          && Objects.equals(id, that.id);
     }
 
     @Override
     public int hashCode() {
-      return Objects.hash(id, optional);
+      return Objects.hash(id, version, optional);
     }
 
     @Override
     public String toString() {
       return "Dependency{"
           + "id='" + id + '\''
+          + ", version='" + version + '\''
           + ", optional=" + optional
           + '}';
     }

api/src/main/java/com/velocitypowered/api/network/NetworkEndpoint.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2018 Velocity Contributors
+ *
+ * The Velocity API is licensed under the terms of the MIT License. For more details,
+ * reference the LICENSE file in the api top-level directory.
+ */
+
+package com.velocitypowered.api.network;
+
+import java.net.SocketAddress;
+
+/**
+ * Represents a network listener for the proxy.
+ */
+public interface NetworkEndpoint {
+  /**
+   * The type.
+   *
+   * @return the type
+   */
+  ListenerType type();
+
+  /**
+   * The address the listener is listening on.
+   *
+   * @return the address
+   */
+  SocketAddress address();
+}

api/src/main/java/com/velocitypowered/api/plugin/Dependency.java

@@ -26,6 +26,15 @@ public @interface Dependency {
    */
   String id();
 
+  /**
+   * The required version of the dependency. This should be in an NPM-compatible versioning format,
+   * which you can figure from <a href="https://semver.npmjs.com/">npm's SemVer checker</a>. If
+   * not specified, this assumes any version is acceptable.
+   *
+   * @return the version requirement
+   */
+  String version() default "*";
+
   /**
    * Whether or not the dependency is not required to enable this plugin. By default this is
    * {@code false}, meaning that the dependency is required to enable this plugin.

api/src/main/java/com/velocitypowered/api/plugin/PluginDescription.java

@@ -52,8 +52,8 @@ public interface PluginDescription {
    * @return a String with the plugin version, may be null
    * @see Plugin#version()
    */
-  default @Nullable String version() {
+  default String version() {
-    return null;
+    return "";
   }
 
   /**

api/src/main/java/com/velocitypowered/api/plugin/meta/PluginDependency.java

@@ -20,7 +20,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 public final class PluginDependency {
 
   private final String id;
-  private final @Nullable String version;
+  private final String version;
 
   private final boolean optional;
 
@@ -30,10 +30,10 @@ public final class PluginDependency {
    * @param version an optional version
    * @param optional whether or not this dependency is optional
    */
-  public PluginDependency(String id, @Nullable String version, boolean optional) {
+  public PluginDependency(String id, String version, boolean optional) {
     this.id = checkNotNull(id, "id");
     checkArgument(!id.isEmpty(), "id cannot be empty");
-    this.version = emptyToNull(version);
+    this.version = checkNotNull(version, "version");
     this.optional = optional;
   }
 
@@ -47,11 +47,11 @@ public final class PluginDependency {
   }
 
   /**
-   * Returns the version this {@link PluginDependency} should match.
+   * Returns the version this {@link PluginDependency} should match in NPM SemVer range format.
    *
-   * @return a String with the plugin version, may be {@code null}
+   * @return a String with the plugin version, may be empty if no version requirement is present
    */
-  public @Nullable String version() {
+  public String version() {
     return version;
   }
 

api/src/main/java/com/velocitypowered/api/proxy/ProxyServer.java

@@ -11,6 +11,7 @@ import com.velocitypowered.api.command.CommandManager;
 import com.velocitypowered.api.command.CommandSource;
 import com.velocitypowered.api.command.ConsoleCommandSource;
 import com.velocitypowered.api.event.EventManager;
+import com.velocitypowered.api.network.NetworkEndpoint;
 import com.velocitypowered.api.plugin.PluginManager;
 import com.velocitypowered.api.proxy.config.ProxyConfig;
 import com.velocitypowered.api.proxy.connection.Player;
@@ -179,4 +180,12 @@ public interface ProxyServer extends Audience {
    * @return the proxy version
    */
   ProxyVersion version();
+
+  /**
+   * Returns all the endpoints the proxy is listening on. This collection is immutable.
+   *
+   * @return all the endpoints the proxy is listening on
+   */
+  Collection<NetworkEndpoint> endpoints();
+
 }

api/src/main/java/com/velocitypowered/api/proxy/config/ProxyConfig.java

@@ -7,6 +7,7 @@
 
 package com.velocitypowered.api.proxy.config;
 
+import com.google.common.annotations.Beta;
 import com.velocitypowered.api.proxy.ProxyServer;
 import com.velocitypowered.api.util.Favicon;
 import java.util.List;
@@ -14,8 +15,10 @@ import java.util.Map;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
- * Exposes certain proxy configuration information that plugins may use.
+ * Exposes certain proxy configuration information that plugins may use. Note that this interface
+ * is in constant flux and should never be considered stable.
  */
+@Beta
 public interface ProxyConfig {
 
   /**

api/src/main/java/com/velocitypowered/api/util/ProxyVersion.java

@@ -33,15 +33,15 @@ public final class ProxyVersion {
     this.version = Preconditions.checkNotNull(version, "version");
   }
 
-  public String getName() {
+  public String name() {
     return name;
   }
 
-  public String getVendor() {
+  public String vendor() {
     return vendor;
   }
 
-  public String getVersion() {
+  public String version() {
     return version;
   }
 

proxy/build.gradle

@@ -25,10 +25,14 @@ test {
 
 jar {
     manifest {
-        def buildNumber = System.getenv("BUILD_NUMBER") ?: "unknown"
+        def buildNumber = System.getenv("BUILD_NUMBER")
         def version
         if (project.version.endsWith("-SNAPSHOT")) {
-            version = "${project.version} (git-${project.ext.getCurrentShortRevision()}-b${buildNumber})"
+            if (buildNumber != null) {
+                version = "${project.version}+g${project.ext.getCurrentShortRevision()}-b${buildNumber}"
+            } else {
+                version = "${project.version}+g${project.ext.getCurrentShortRevision()}"
+            }
         } else {
             version = "${project.version}"
         }
@@ -86,6 +90,7 @@ dependencies {
     implementation 'org.lanternpowered:lmbda:2.0.0-SNAPSHOT'
 
     implementation 'com.github.ben-manes.caffeine:caffeine:2.8.8'
+    implementation 'com.vdurmont:semver4j:3.1.0'
 
     compileOnly 'com.github.spotbugs:spotbugs-annotations:4.1.2'
 

proxy/src/main/java/com/velocitypowered/proxy/Metrics.java

@@ -118,7 +118,7 @@ public class Metrics {
               () -> server.configuration().isOnlineMode() ? "online" : "offline")
       );
       metrics.addCustomChart(new SimplePie("velocity_version",
-          () -> server.version().getVersion()));
+          () -> server.version().version()));
 
       metrics.addCustomChart(new DrilldownPie("java_version", () -> {
         Map<String, Map<String, Integer>> map = new HashMap<>();

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -26,6 +26,7 @@ import com.velocitypowered.api.event.EventManager;
 import com.velocitypowered.api.event.lifecycle.ProxyInitializeEventImpl;
 import com.velocitypowered.api.event.lifecycle.ProxyReloadEventImpl;
 import com.velocitypowered.api.event.lifecycle.ProxyShutdownEventImpl;
+import com.velocitypowered.api.network.NetworkEndpoint;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.plugin.PluginContainer;
 import com.velocitypowered.api.plugin.PluginManager;
@@ -184,6 +185,11 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     return new ProxyVersion(implName, implVendor, implVersion);
   }
 
+  @Override
+  public Collection<NetworkEndpoint> endpoints() {
+    return this.cm.endpoints();
+  }
+
   @Override
   public VelocityCommandManager commandManager() {
     return commandManager;
@@ -195,7 +201,7 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
 
   @EnsuresNonNull({"serverKeyPair", "eventManager", "console", "cm", "configuration"})
   void start() {
-    logger.info("Booting up {} {}...", version().getName(), version().getVersion());
+    logger.info("Booting up {} {}...", version().name(), version().version());
     console.setupStreams();
 
     registerTranslations();

proxy/src/main/java/com/velocitypowered/proxy/command/builtin/VelocityCommand.java

@@ -217,19 +217,19 @@ public class VelocityCommand implements SimpleCommand {
 
       ProxyVersion version = server.version();
 
-      Component velocity = Component.text().content(version.getName() + " ")
+      Component velocity = Component.text().content(version.name() + " ")
           .decoration(TextDecoration.BOLD, true)
           .color(VELOCITY_COLOR)
-          .append(Component.text(version.getVersion()).decoration(TextDecoration.BOLD, false))
+          .append(Component.text(version.version()).decoration(TextDecoration.BOLD, false))
           .build();
       Component copyright = Component
           .translatable("velocity.command.version-copyright",
-              Component.text(version.getVendor()),
+              Component.text(version.vendor()),
-              Component.text(version.getName()));
+              Component.text(version.name()));
       source.sendMessage(velocity);
       source.sendMessage(copyright);
 
-      if (version.getName().equals("Velocity")) {
+      if (version.name().equals("Velocity")) {
         TextComponent embellishment = Component.text()
             .append(Component.text().content("velocitypowered.com")
                 .color(NamedTextColor.GREEN)
@@ -383,8 +383,8 @@ public class VelocityCommand implements SimpleCommand {
       BoundRequestBuilder request =
               httpClient.preparePost("https://dump.velocitypowered.com/documents");
       request.setHeader("Content-Type", "text/plain");
-      request.addHeader("User-Agent", server.version().getName() + "/"
+      request.addHeader("User-Agent", server.version().name() + "/"
-              + server.version().getVersion());
+              + server.version().version());
       request.setBody(
               InformationUtils.toHumanReadableString(dump).getBytes(StandardCharsets.UTF_8));
 

proxy/src/main/java/com/velocitypowered/proxy/connection/client/StatusSessionHandler.java

@@ -25,6 +25,7 @@ import com.velocitypowered.api.proxy.connection.InboundConnection;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.proxy.server.ServerPing;
 import com.velocitypowered.api.util.ModInfo;
+import com.velocitypowered.api.util.ProxyVersion;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.config.PingPassthroughMode;
 import com.velocitypowered.proxy.config.VelocityConfiguration;
@@ -75,9 +76,10 @@ public class StatusSessionHandler implements MinecraftSessionHandler {
 
   private ServerPing constructLocalPing(ProtocolVersion version) {
     VelocityConfiguration configuration = server.configuration();
+    ProxyVersion proxyVersion = server.version();
     return new ServerPing(
         new ServerPing.Version(version.protocol(),
-            "Velocity " + ProtocolVersion.SUPPORTED_VERSION_STRING),
+            proxyVersion.name() + " " + ProtocolVersion.SUPPORTED_VERSION_STRING),
         new ServerPing.Players(server.countConnectedPlayers(), configuration.getShowMaxPlayers(),
             ImmutableList.of()),
         configuration.getMotd(),

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -24,6 +24,7 @@ import com.google.common.base.Preconditions;
 import com.velocitypowered.api.event.lifecycle.network.ListenerBoundEventImpl;
 import com.velocitypowered.api.event.lifecycle.network.ListenerClosedEventImpl;
 import com.velocitypowered.api.network.ListenerType;
+import com.velocitypowered.api.network.NetworkEndpoint;
 import com.velocitypowered.natives.util.Natives;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.network.pipeline.GS4QueryHandler;
@@ -39,7 +40,9 @@ import io.netty.channel.epoll.EpollChannelOption;
 import io.netty.util.concurrent.GlobalEventExecutor;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
+import java.util.Collection;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -87,7 +90,7 @@ public final class ConnectionManager {
     this.resolver = new SeparatePoolInetNameResolver(GlobalEventExecutor.INSTANCE);
     this.httpClient = asyncHttpClient(config()
         .setEventLoopGroup(this.workerGroup)
-        .setUserAgent(server.version().getName() + "/" + server.version().getVersion())
+        .setUserAgent(server.version().name() + "/" + server.version().version())
         .addRequestFilter(new RequestFilter() {
           @Override
           public <T> FilterContext<T> filter(FilterContext<T> ctx) {
@@ -205,7 +208,7 @@ public final class ConnectionManager {
 
     // Fire proxy close event to notify plugins of socket close. We block since plugins
     // should have a chance to be notified before the server stops accepting connections.
-    server.eventManager().fire(new ListenerClosedEventImpl(oldBind, endpoint.getType())).join();
+    server.eventManager().fire(new ListenerClosedEventImpl(oldBind, endpoint.type())).join();
 
     Channel serverChannel = endpoint.getChannel();
 
@@ -224,7 +227,7 @@ public final class ConnectionManager {
 
       // Fire proxy close event to notify plugins of socket close. We block since plugins
       // should have a chance to be notified before the server stops accepting connections.
-      server.eventManager().fire(new ListenerClosedEventImpl(address, endpoint.getType())).join();
+      server.eventManager().fire(new ListenerClosedEventImpl(address, endpoint.type())).join();
 
       try {
         LOGGER.info("Closing endpoint {}", address);
@@ -253,4 +256,8 @@ public final class ConnectionManager {
   public ChannelInitializerHolder<Channel> getBackendChannelInitializer() {
     return this.backendChannelInitializer;
   }
+
+  public Collection<NetworkEndpoint> endpoints() {
+    return List.copyOf(this.endpoints.values());
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/network/Endpoint.java

@@ -19,12 +19,14 @@ package com.velocitypowered.proxy.network;
 
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.network.ListenerType;
+import com.velocitypowered.api.network.NetworkEndpoint;
 import io.netty.channel.Channel;
+import java.net.SocketAddress;
 
 /**
  * Represents a listener endpoint.
  */
-public final class Endpoint {
+public final class Endpoint implements NetworkEndpoint {
   private final Channel channel;
   private final ListenerType type;
 
@@ -37,7 +39,13 @@ public final class Endpoint {
     return channel;
   }
 
-  public ListenerType getType() {
+  @Override
+  public ListenerType type() {
     return type;
   }
+
+  @Override
+  public SocketAddress address() {
+    return this.channel.localAddress();
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/network/PluginMessageUtil.java

@@ -153,7 +153,7 @@ public final class PluginMessageUtil {
     checkArgument(isMcBrand(message), "message is not a brand plugin message");
 
     String currentBrand = readBrandMessage(message.content());
-    String rewrittenBrand = String.format("%s (%s)", currentBrand, version.getName());
+    String rewrittenBrand = String.format("%s (%s)", currentBrand, version.name());
 
     ByteBuf rewrittenBuf = Unpooled.buffer();
     if (protocolVersion.gte(ProtocolVersion.MINECRAFT_1_8)) {

proxy/src/main/java/com/velocitypowered/proxy/plugin/PluginClassLoader.java

@@ -17,6 +17,7 @@
 
 package com.velocitypowered.proxy.plugin;
 
+import com.velocitypowered.api.plugin.PluginDescription;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URL;
@@ -33,8 +34,11 @@ public class PluginClassLoader extends URLClassLoader {
     ClassLoader.registerAsParallelCapable();
   }
 
-  public PluginClassLoader(URL[] urls) {
+  private final PluginDescription description;
+
+  public PluginClassLoader(URL[] urls, PluginDescription description) {
     super(urls);
+    this.description = description;
   }
 
   public void addToClassloaders() {
@@ -82,4 +86,9 @@ public class PluginClassLoader extends URLClassLoader {
 
     throw new ClassNotFoundException(name);
   }
+
+  @Override
+  public String toString() {
+    return "plugin " + this.description.name();
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java

@@ -25,6 +25,9 @@ import com.google.common.base.MoreObjects;
 import com.google.inject.AbstractModule;
 import com.google.inject.Module;
 import com.google.inject.name.Names;
+import com.vdurmont.semver4j.Semver;
+import com.vdurmont.semver4j.Semver.SemverType;
+import com.vdurmont.semver4j.SemverException;
 import com.velocitypowered.api.command.CommandManager;
 import com.velocitypowered.api.event.EventManager;
 import com.velocitypowered.api.plugin.PluginContainer;
@@ -36,6 +39,7 @@ import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.plugin.loader.VelocityPluginContainer;
 import com.velocitypowered.proxy.plugin.loader.java.JavaPluginLoader;
 import com.velocitypowered.proxy.plugin.util.PluginDependencyUtils;
+import com.velocitypowered.proxy.plugin.util.ProxyPluginContainer;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.IOException;
 import java.nio.file.DirectoryStream;
@@ -44,6 +48,7 @@ import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
 import java.util.LinkedHashMap;
@@ -64,6 +69,9 @@ public class VelocityPluginManager implements PluginManager {
 
   public VelocityPluginManager(VelocityServer server) {
     this.server = checkNotNull(server, "server");
+
+    // Register ourselves as a plugin
+    this.registerPlugin(ProxyPluginContainer.VELOCITY);
   }
 
   private void registerPlugin(PluginContainer plugin) {
@@ -106,17 +114,48 @@ public class VelocityPluginManager implements PluginManager {
 
     List<PluginDescription> sortedPlugins = PluginDependencyUtils.sortCandidates(found);
 
-    Set<String> loadedPluginsById = new HashSet<>();
+    Map<String, PluginContainer> loadedPluginsById = new HashMap<>(this.plugins);
     Map<PluginContainer, Module> pluginContainers = new LinkedHashMap<>();
     // Now load the plugins
     pluginLoad:
     for (PluginDescription candidate : sortedPlugins) {
       // Verify dependencies
       for (PluginDependency dependency : candidate.dependencies()) {
-        if (!dependency.optional() && !loadedPluginsById.contains(dependency.id())) {
+        final PluginContainer dependencyContainer = loadedPluginsById.get(dependency.id());
-          logger.error("Can't load plugin {} due to missing dependency {}", candidate.id(),
+        if (dependencyContainer == null) {
-              dependency.id());
+          if (dependency.optional()) {
-          continue pluginLoad;
+            logger.warn("Plugin {} has an optional dependency {} that is not available",
+                candidate.id(), dependency.id());
+          } else {
+            logger.error("Can't load plugin {} due to missing dependency {}",
+                candidate.id(), dependency.id());
+            continue pluginLoad;
+          }
+        } else {
+          String requiredRange = dependency.version();
+          if (!requiredRange.isEmpty()) {
+            try {
+              Semver dependencyCandidateVersion = new Semver(
+                  dependencyContainer.description().version(), SemverType.NPM);
+              if (!dependencyCandidateVersion.satisfies(requiredRange)) {
+                if (dependency.optional()) {
+                  logger.error(
+                      "Can't load plugin {} due to incompatible dependency {} {} (you have {})",
+                      candidate.id(), dependency.id(), requiredRange,
+                      dependencyContainer.description().version());
+                  continue pluginLoad;
+                } else {
+                  logger.warn(
+                      "Plugin {} has an optional dependency on {} {}, but you have {}",
+                      candidate.id(), dependency.id(), requiredRange,
+                      dependencyContainer.description().version());
+                }
+              }
+            } catch (SemverException exception) {
+              logger.warn("Can't check dependency of {} for the proper version of {},"
+                      + " assuming they are compatible", candidate.id(), dependency.id());
+            }
+          }
         }
       }
 
@@ -124,7 +163,7 @@ public class VelocityPluginManager implements PluginManager {
         PluginDescription realPlugin = loader.loadPlugin(candidate);
         VelocityPluginContainer container = new VelocityPluginContainer(realPlugin);
         pluginContainers.put(container, loader.createModule(container));
-        loadedPluginsById.add(realPlugin.id());
+        loadedPluginsById.put(candidate.id(), container);
       } catch (Exception e) {
         logger.error("Can't create module for plugin {}", candidate.id(), e);
       }

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/VelocityPluginDescription.java

@@ -34,7 +34,7 @@ public class VelocityPluginDescription implements PluginDescription {
 
   private final String id;
   private final @Nullable String name;
-  private final @Nullable String version;
+  private final String version;
   private final @Nullable String description;
   private final @Nullable String url;
   private final List<String> authors;
@@ -52,13 +52,13 @@ public class VelocityPluginDescription implements PluginDescription {
    * @param dependencies the dependencies for this plugin
    * @param source the original source for the plugin
    */
-  public VelocityPluginDescription(String id, @Nullable String name, @Nullable String version,
+  public VelocityPluginDescription(String id, @Nullable String name, String version,
       @Nullable String description, @Nullable String url,
       @Nullable List<String> authors, Collection<PluginDependency> dependencies,
       @Nullable Path source) {
     this.id = checkNotNull(id, "id");
     this.name = Strings.emptyToNull(name);
-    this.version = Strings.emptyToNull(version);
+    this.version = checkNotNull(version, "version");
     this.description = Strings.emptyToNull(description);
     this.url = Strings.emptyToNull(url);
     this.authors = authors == null ? ImmutableList.of() : ImmutableList.copyOf(authors);
@@ -77,7 +77,7 @@ public class VelocityPluginDescription implements PluginDescription {
   }
 
   @Override
-  public @Nullable String version() {
+  public String version() {
     return version;
   }
 

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/java/JavaPluginLoader.java

@@ -81,7 +81,8 @@ public class JavaPluginLoader implements PluginLoader {
 
     URL pluginJarUrl = jarFilePath.toUri().toURL();
     PluginClassLoader loader = AccessController.doPrivileged(
-        (PrivilegedAction<PluginClassLoader>) () -> new PluginClassLoader(new URL[]{pluginJarUrl}));
+        (PrivilegedAction<PluginClassLoader>) () -> new PluginClassLoader(new URL[]{pluginJarUrl},
+            source));
     loader.addToClassloaders();
 
     JavaVelocityPluginDescriptionCandidate candidate =
@@ -200,7 +201,7 @@ public class JavaPluginLoader implements PluginLoader {
       SerializedPluginDescription.Dependency dependency) {
     return new PluginDependency(
         dependency.getId(),
-        null, // TODO Implement version matching in dependency annotation
+        dependency.getVersion(),
         dependency.isOptional()
     );
   }

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/java/JavaVelocityPluginDescription.java

@@ -30,7 +30,7 @@ class JavaVelocityPluginDescription extends VelocityPluginDescription {
 
   private final Class<?> mainClass;
 
-  JavaVelocityPluginDescription(String id, @Nullable String name, @Nullable String version,
+  JavaVelocityPluginDescription(String id, @Nullable String name, String version,
       @Nullable String description, @Nullable String url,
       @Nullable List<String> authors, Collection<PluginDependency> dependencies,
       @Nullable Path source, Class<?> mainClass) {

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/java/JavaVelocityPluginDescriptionCandidate.java

@@ -30,7 +30,7 @@ class JavaVelocityPluginDescriptionCandidate extends VelocityPluginDescription {
 
   private final String mainClass;
 
-  JavaVelocityPluginDescriptionCandidate(String id, @Nullable String name, @Nullable String version,
+  JavaVelocityPluginDescriptionCandidate(String id, @Nullable String name, String version,
       @Nullable String description, @Nullable String url,
       @Nullable List<String> authors, Collection<PluginDependency> dependencies, Path source,
       String mainClass) {

proxy/src/main/java/com/velocitypowered/proxy/plugin/util/ProxyPluginContainer.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2018 Velocity 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.plugin.util;
+
+import com.google.common.base.MoreObjects;
+import com.velocitypowered.api.plugin.PluginContainer;
+import com.velocitypowered.api.plugin.PluginDescription;
+import com.velocitypowered.proxy.VelocityServer;
+import java.util.List;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public class ProxyPluginContainer implements PluginContainer {
+
+  public static final PluginContainer VELOCITY = new ProxyPluginContainer();
+
+  private final PluginDescription description = new PluginDescription() {
+    @Override
+    public String id() {
+      return "velocity";
+    }
+
+    @Override
+    public String name() {
+      final Package pkg = VelocityServer.class.getPackage();
+      return MoreObjects.firstNonNull(pkg.getImplementationTitle(), "Velocity");
+    }
+
+    @Override
+    public String version() {
+      final Package pkg = VelocityServer.class.getPackage();
+      return MoreObjects.firstNonNull(pkg.getImplementationVersion(), "<unknown>");
+    }
+
+    @Override
+    public List<String> authors() {
+      final Package pkg = VelocityServer.class.getPackage();
+      final String vendor = MoreObjects.firstNonNull(pkg.getImplementationVendor(),
+          "Velocity Contributors");
+      return List.of(vendor);
+    }
+  };
+
+  @Override
+  public PluginDescription description() {
+    return this.description;
+  }
+
+  @Override
+  public @Nullable Object instance() {
+    return null;
+  }
+}

proxy/src/test/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtilsTest.java

@@ -33,11 +33,11 @@ class PluginDependencyUtilsTest {
   private static final PluginDescription NO_DEPENDENCY = testDescription("trivial");
   private static final PluginDescription NO_DEPENDENCY_2 = testDescription("trivial2");
   private static final PluginDescription HAS_DEPENDENCY_1 = testDescription("dependent1",
-      new PluginDependency("trivial", null, false));
+      new PluginDependency("trivial", "", false));
   private static final PluginDescription HAS_DEPENDENCY_2 = testDescription("dependent2",
-      new PluginDependency("dependent1", null, false));
+      new PluginDependency("dependent1", "", false));
   private static final PluginDescription HAS_DEPENDENCY_3 = testDescription("dependent3",
-      new PluginDependency("trivial", null, false));
+      new PluginDependency("trivial", "", false));
 
   private static final PluginDescription CIRCULAR_DEPENDENCY_1 = testDescription("circle",
       new PluginDependency("oval", "", false));