feat: Add basic API for server links

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

@@ -21,6 +21,7 @@
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.api.util.ModInfo;
+import com.velocitypowered.api.util.ServerLink;
 import java.net.InetSocketAddress;
 import java.util.Collection;
 import java.util.List;
@@ -461,4 +462,14 @@ default void openBook(@NotNull Book book) {
    * @sinceMinecraft 1.20.5
    */
   void requestCookie(Key key);
+
+  /**
+   * Send the player a list of custom links to display in their client's pause menu.
+   *
+   * @param links an ordered list of {@link ServerLink}s to send to the player
+   * @throws IllegalArgumentException if the player is from a version lower than 1.21
+   * @since 3.3.0
+   * @sinceMinecraft 1.21
+   */
+  void setServerLinks(@NotNull List<ServerLink> links);
 }

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

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2021-2024 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.util;
+
+import com.google.common.base.Preconditions;
+import java.net.URI;
+import java.util.Optional;
+import net.kyori.adventure.text.Component;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Represents a custom URL servers can show in player pause menus.
+ * Links can be of a built-in type or use a custom component text label.
+ */
+public final class ServerLink {
+
+  private @Nullable Type type;
+  private @Nullable Component label;
+  private final String link;
+
+  /**
+   * Construct a server link with a custom component label.
+   *
+   * @param label a custom component label to display
+   * @param link  the URL to open when clicked
+   */
+  public ServerLink(Component label, String link) {
+    this.label = Preconditions.checkNotNull(label, "label");
+    this.link = URI.create(link).toString();
+  }
+
+  /**
+   * Construct a server link with a built-in type.
+   *
+   * @param type the {@link Type built-in type} of link
+   * @param link the URL to open when clicked
+   */
+  public ServerLink(Type type, String link) {
+    this.type = Preconditions.checkNotNull(type, "type");
+    this.link = URI.create(link).toString();
+  }
+
+  /**
+   * Get the type of the server link.
+   *
+   * @return the type of the server link
+   */
+  public Optional<Type> getBuiltInType() {
+    return Optional.ofNullable(type);
+  }
+
+  /**
+   * Get the custom component label of the server link.
+   *
+   * @return the custom component label of the server link
+   */
+  public Optional<Component> getCustomLabel() {
+    return Optional.ofNullable(label);
+  }
+
+  /**
+   * Get the link URL.
+   *
+   * @return the link URL
+   */
+  public String getLink() {
+    return link;
+  }
+
+  /**
+   * Built-in types of server links.
+   *
+   * @apiNote {@link Type#BUG_REPORT} links are shown on the connection error screen
+   */
+  public enum Type {
+    BUG_REPORT,
+    COMMUNITY_GUIDELINES,
+    SUPPORT,
+    STATUS,
+    FEEDBACK,
+    COMMUNITY,
+    WEBSITE,
+    FORUMS,
+    NEWS,
+    ANNOUNCEMENTS
+  }
+
+}

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

@@ -23,6 +23,7 @@
 import static java.util.concurrent.CompletableFuture.completedFuture;
 
 import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
 import com.google.gson.JsonObject;
 import com.velocitypowered.api.event.connection.DisconnectEvent;
 import com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus;
@@ -54,6 +55,7 @@
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.api.util.ModInfo;
+import com.velocitypowered.api.util.ServerLink;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.adventure.VelocityBossBarImplementation;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
@@ -81,6 +83,7 @@
 import com.velocitypowered.proxy.protocol.packet.chat.PlayerChatCompletionPacket;
 import com.velocitypowered.proxy.protocol.packet.chat.builder.ChatBuilderFactory;
 import com.velocitypowered.proxy.protocol.packet.chat.legacy.LegacyChatPacket;
+import com.velocitypowered.proxy.protocol.packet.config.ClientboundServerLinksPacket;
 import com.velocitypowered.proxy.protocol.packet.config.StartUpdatePacket;
 import com.velocitypowered.proxy.protocol.packet.title.GenericTitlePacket;
 import com.velocitypowered.proxy.protocol.util.ByteBufDataOutput;
@@ -1057,6 +1060,25 @@ public void requestCookie(final Key key) {
         }, connection.eventLoop());
   }
 
+  @Override
+  public void setServerLinks(final @NotNull List<ServerLink> links) {
+    Preconditions.checkNotNull(links, "links");
+    Preconditions.checkArgument(
+        this.getProtocolVersion().noLessThan(ProtocolVersion.MINECRAFT_1_21),
+        "Player version must be at least 1.21 to be able to set server links");
+
+    if (connection.getState() != StateRegistry.PLAY
+        && connection.getState() != StateRegistry.CONFIG) {
+      throw new IllegalStateException("Can only send server links in CONFIGURATION or PLAY protocol");
+    }
+
+    connection.write(new ClientboundServerLinksPacket(ImmutableList.copyOf(links).stream()
+        .map(l -> new ClientboundServerLinksPacket.ServerLink(
+            l.getBuiltInType().map(Enum::ordinal).orElse(-1),
+            l.getCustomLabel().map(c -> new ComponentHolder(getProtocolVersion(), c)).orElse(null),
+            l.getLink())).toList()));
+  }
+
   @Override
   public void addCustomChatCompletions(@NotNull Collection<String> completions) {
     Preconditions.checkNotNull(completions, "completions");