Implement resource pack send event. (#625)

api/src/main/java/com/velocitypowered/api/event/player/ServerResourcePackSendEvent.java

@@ -0,0 +1,70 @@
+/*
+ * 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.event.player;
+
+import com.velocitypowered.api.event.ResultedEvent;
+import com.velocitypowered.api.event.annotation.AwaitingEvent;
+import com.velocitypowered.api.proxy.ServerConnection;
+import com.velocitypowered.api.proxy.player.ResourcePackInfo;
+
+/**
+ * This event is fired when the downstream server tries to send a player a ResourcePack packet.
+ * The proxy will wait on this event to finish before forwarding the resource pack to the user.
+ * If this event is denied, it will retroactively send a DENIED status to the downstream
+ * server in response.
+ * If the downstream server has it set to "forced" it will forcefully disconnect the user.
+ */
+@AwaitingEvent
+public class ServerResourcePackSendEvent implements ResultedEvent<ResultedEvent.GenericResult> {
+  private GenericResult result;
+  private final ResourcePackInfo receivedResourcePack;
+  private ResourcePackInfo providedResourcePack;
+  private final ServerConnection serverConnection;
+
+  /**
+   * Constructs a new ServerResourcePackSendEvent.
+   * 
+   * @param receivedResourcePack The resource pack the server sent.
+   * @param serverConnection The connection this occurred on.
+   */
+  public ServerResourcePackSendEvent(
+      ResourcePackInfo receivedResourcePack,
+      ServerConnection serverConnection
+  ) {
+    this.result = ResultedEvent.GenericResult.allowed();
+    this.receivedResourcePack = receivedResourcePack;
+    this.serverConnection = serverConnection;
+    this.providedResourcePack = receivedResourcePack;
+  }
+
+  public ServerConnection getServerConnection() {
+    return serverConnection;
+  }
+
+  public ResourcePackInfo getReceivedResourcePack() {
+    return receivedResourcePack;
+  }
+
+  public ResourcePackInfo getProvidedResourcePack() {
+    return providedResourcePack;
+  }
+
+  public void setProvidedResourcePack(ResourcePackInfo providedResourcePack) {
+    this.providedResourcePack = providedResourcePack;
+  }
+
+  @Override
+  public GenericResult getResult() {
+    return this.result;
+  }
+
+  @Override
+  public void setResult(GenericResult result) {
+    this.result = result;
+  }
+}

api/src/main/java/com/velocitypowered/api/proxy/player/ResourcePackInfo.java

@@ -46,12 +46,48 @@ public interface ResourcePackInfo {
   byte[] getHash();
 
   /**
-   * Gets the {@link Origin} of the resource-pack.
+   * Gets the {@link Origin} of this resource-pack.
    *
    * @return the origin of the resource pack
    */
   Origin getOrigin();
 
+  /**
+   * Gets the original {@link Origin} of the resource-pack.
+   * The original origin may differ if the resource pack was altered in the event
+   * {@link com.velocitypowered.api.event.player.ServerResourcePackSendEvent}.
+   *
+   * @return the origin of the resource pack
+   */
+  Origin getOriginalOrigin();
+
+  /**
+   * Returns a copy of this {@link ResourcePackInfo} instance as a builder so that it can
+   * be modified.
+   * It is <b>not</b> guaranteed that
+   * {@code resourcePackInfo.asBuilder().build().equals(resourcePackInfo)} is true. That is due to
+   * the transient {@link ResourcePackInfo#getOrigin()} and
+   * {@link ResourcePackInfo#getOriginalOrigin()} fields.
+   *
+   *
+   * @return a content-copy of this instance as a {@link ResourcePackInfo.Builder}
+   */
+  ResourcePackInfo.Builder asBuilder();
+
+  /**
+   * Returns a copy of this {@link ResourcePackInfo} instance as a builder with the new URL as the pack URL so that
+   * it can be modified.
+   * It is <b>not</b> guaranteed that
+   * {@code resourcePackInfo.asBuilder(resourcePackInfo.getUrl()).build().equals(resourcePackInfo)} is true.
+   * That is due to the transient {@link ResourcePackInfo#getOrigin()} and
+   * {@link ResourcePackInfo#getOriginalOrigin()} fields.
+   *
+   * @param newUrl The new URL to use in the updated builder.
+   *
+   * @return a content-copy of this instance as a {@link ResourcePackInfo.Builder}
+   */
+  ResourcePackInfo.Builder asBuilder(String newUrl);
+
   interface Builder {
 
     /**

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -21,12 +21,12 @@ import static com.velocitypowered.proxy.connection.backend.BungeeCordMessageResp
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
-import com.mojang.brigadier.builder.ArgumentBuilder;
-import com.mojang.brigadier.tree.CommandNode;
 import com.mojang.brigadier.tree.RootCommandNode;
 import com.velocitypowered.api.command.CommandSource;
 import com.velocitypowered.api.event.command.PlayerAvailableCommandsEvent;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
+import com.velocitypowered.api.event.player.PlayerResourcePackStatusEvent;
+import com.velocitypowered.api.event.player.ServerResourcePackSendEvent;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.api.proxy.player.ResourcePackInfo;
@@ -45,6 +45,7 @@ import com.velocitypowered.proxy.protocol.packet.KeepAlive;
 import com.velocitypowered.proxy.protocol.packet.PlayerListItem;
 import com.velocitypowered.proxy.protocol.packet.PluginMessage;
 import com.velocitypowered.proxy.protocol.packet.ResourcePackRequest;
+import com.velocitypowered.proxy.protocol.packet.ResourcePackResponse;
 import com.velocitypowered.proxy.protocol.packet.TabCompleteResponse;
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import io.netty.buffer.ByteBuf;
@@ -52,7 +53,7 @@ import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
 import io.netty.handler.timeout.ReadTimeoutException;
-import java.util.Collection;
+
 import java.util.regex.Pattern;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -138,17 +139,50 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
   @Override
   public boolean handle(ResourcePackRequest packet) {
     ResourcePackInfo.Builder builder = new VelocityResourcePackInfo.BuilderImpl(
-        Preconditions.checkNotNull(packet.getUrl()))
-        .setPrompt(packet.getPrompt())
-        .setShouldForce(packet.isRequired());
-    // Why SpotBugs decides that this is unsafe I have no idea;
-    if (packet.getHash() != null && !Preconditions.checkNotNull(packet.getHash()).isEmpty()) {
-      if (PLAUSIBLE_SHA1_HASH.matcher(packet.getHash()).matches()) {
-        builder.setHash(ByteBufUtil.decodeHexDump(packet.getHash()));
+            Preconditions.checkNotNull(packet.getUrl()))
+            .setPrompt(packet.getPrompt())
+            .setShouldForce(packet.isRequired())
+            .setOrigin(ResourcePackInfo.Origin.DOWNSTREAM_SERVER);
+
+    String hash = packet.getHash();
+    if (hash != null && !hash.isEmpty()) {
+      if (PLAUSIBLE_SHA1_HASH.matcher(hash).matches()) {
+        builder.setHash(ByteBufUtil.decodeHexDump(hash));
       }
     }
 
-    serverConn.getPlayer().queueResourcePack(builder.build());
+    ServerResourcePackSendEvent event = new ServerResourcePackSendEvent(
+            builder.build(), this.serverConn);
+
+    server.getEventManager().fire(event).thenAcceptAsync(serverResourcePackSendEvent -> {
+      if (playerConnection.isClosed()) {
+        return;
+      }
+      if (serverResourcePackSendEvent.getResult().isAllowed()) {
+        ResourcePackInfo toSend = serverResourcePackSendEvent.getProvidedResourcePack();
+        if (toSend != serverResourcePackSendEvent.getReceivedResourcePack()) {
+          ((VelocityResourcePackInfo) toSend)
+                  .setOriginalOrigin(ResourcePackInfo.Origin.DOWNSTREAM_SERVER);
+        }
+
+        serverConn.getPlayer().queueResourcePack(builder.build());
+      } else if (serverConn.getConnection() != null) {
+        serverConn.getConnection().write(new ResourcePackResponse(
+            packet.getHash(),
+            PlayerResourcePackStatusEvent.Status.DECLINED
+        ));
+      }
+    }, playerConnection.eventLoop()).exceptionally((ex) -> {
+      if (serverConn.getConnection() != null) {
+        serverConn.getConnection().write(new ResourcePackResponse(
+                packet.getHash(),
+                PlayerResourcePackStatusEvent.Status.DECLINED
+        ));
+      }
+      logger.error("Exception while handling resource pack send for {}", playerConnection, ex);
+      return null;
+    });
+
     return true;
   }
 

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

@@ -985,7 +985,8 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
       connection.eventLoop().execute(this::tickResourcePackQueue);
     }
 
-    return queued != null && queued.getOrigin() == ResourcePackInfo.Origin.DOWNSTREAM_SERVER;
+    return queued != null
+            && queued.getOriginalOrigin() == ResourcePackInfo.Origin.DOWNSTREAM_SERVER;
   }
 
   /**

proxy/src/main/java/com/velocitypowered/proxy/connection/player/VelocityResourcePackInfo.java

@@ -28,6 +28,7 @@ public final class VelocityResourcePackInfo implements ResourcePackInfo {
   private final boolean shouldForce;
   private final @Nullable Component prompt; // 1.17+ only
   private final Origin origin;
+  private Origin originalOrigin;
 
   private VelocityResourcePackInfo(String url, @Nullable byte[] hash, boolean shouldForce,
                                   @Nullable Component prompt, Origin origin) {
@@ -36,6 +37,7 @@ public final class VelocityResourcePackInfo implements ResourcePackInfo {
     this.shouldForce = shouldForce;
     this.prompt = prompt;
     this.origin = origin;
+    this.originalOrigin = origin;
   }
 
   @Override
@@ -63,6 +65,31 @@ public final class VelocityResourcePackInfo implements ResourcePackInfo {
     return origin;
   }
 
+  public void setOriginalOrigin(Origin originalOrigin) {
+    this.originalOrigin = originalOrigin;
+  }
+
+  @Override
+  public Origin getOriginalOrigin() {
+    return originalOrigin;
+  }
+
+  @Override
+  public Builder asBuilder() {
+    return new BuilderImpl(url)
+            .setShouldForce(shouldForce)
+            .setHash(hash)
+            .setPrompt(prompt);
+  }
+
+  @Override
+  public Builder asBuilder(String newUrl) {
+    return new BuilderImpl(newUrl)
+            .setShouldForce(shouldForce)
+            .setHash(hash)
+            .setPrompt(prompt);
+  }
+
   public static final class BuilderImpl implements ResourcePackInfo.Builder {
     private final String url;
     private boolean shouldForce;
@@ -102,8 +129,9 @@ public final class VelocityResourcePackInfo implements ResourcePackInfo {
       return new VelocityResourcePackInfo(url, hash, shouldForce, prompt, origin);
     }
 
-    public void setOrigin(Origin origin) {
+    public BuilderImpl setOrigin(Origin origin) {
       this.origin = origin;
+      return this;
     }
   }
 

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/ResourcePackResponse.java

@@ -31,6 +31,14 @@ public class ResourcePackResponse implements MinecraftPacket {
   private String hash = "";
   private @MonotonicNonNull Status status;
 
+  public ResourcePackResponse() {
+  }
+
+  public ResourcePackResponse(String hash, @MonotonicNonNull Status status) {
+    this.hash = hash;
+    this.status = status;
+  }
+
   public Status getStatus() {
     if (status == null) {
       throw new IllegalStateException("Packet not yet deserialized");