Check permissions before providing suggestions (#430)

proxy/src/main/java/com/velocitypowered/proxy/command/CommandNodeFactory.java

@@ -46,6 +46,10 @@ public interface CommandNodeFactory<T extends Command> {
         },
         (context, builder) -> {
           String[] args = BrigadierUtils.getSplitArguments(context);
+          if (!command.hasPermission(context.getSource(), args)) {
+              return builder.buildFuture();
+          }
+
           return command.suggestAsync(context.getSource(), args).thenApply(values -> {
             for (String value : values) {
               builder.suggest(value);
@@ -82,6 +86,9 @@ public interface CommandNodeFactory<T extends Command> {
           (context, builder) -> {
             I invocation = createInvocation(context);
 
+            if (!command.hasPermission(invocation)) {
+                return builder.buildFuture();
+            }
             return command.suggestAsync(invocation).thenApply(values -> {
               for (String value : values) {
                 builder.suggest(value);

proxy/src/test/java/com/velocitypowered/proxy/command/CommandManagerTests.java

@@ -25,6 +25,7 @@ import com.velocitypowered.api.command.SimpleCommand;
 import com.velocitypowered.proxy.plugin.MockEventManager;
 import com.velocitypowered.proxy.plugin.VelocityEventManager;
 import java.util.List;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 import org.checkerframework.checker.nullness.qual.NonNull;
@@ -487,6 +488,54 @@ public class CommandManagerTests {
             manager.offerSuggestions(MockCommandSource.INSTANCE, "foo2 baz ").join());
   }
 
+  @Test
+  void testSuggestionPermissions() throws ExecutionException, InterruptedException {
+    VelocityCommandManager manager = createManager();
+    RawCommand rawCommand = new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail("The Command should not be executed while testing suggestions");
+      }
+
+      @Override
+      public boolean hasPermission(Invocation invocation) {
+        return invocation.arguments().length() > 0;
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return ImmutableList.of("suggestion");
+      }
+    };
+
+    manager.register(rawCommand, "foo");
+
+    assertTrue(manager.offerSuggestions(MockCommandSource.INSTANCE, "foo").get().isEmpty());
+    assertFalse(manager.offerSuggestions(MockCommandSource.INSTANCE, "foo bar").get().isEmpty());
+
+    Command oldCommand = new Command() {
+      @Override
+      public void execute(CommandSource source, String @NonNull [] args) {
+        fail("The Command should not be executed while testing suggestions");
+      }
+
+      @Override
+      public boolean hasPermission(CommandSource source, String @NonNull [] args) {
+        return args.length > 0;
+      }
+
+      @Override
+      public List<String> suggest(CommandSource source, String @NonNull [] currentArgs) {
+        return ImmutableList.of("suggestion");
+      }
+    };
+
+    manager.register(oldCommand, "bar");
+
+    assertTrue(manager.offerSuggestions(MockCommandSource.INSTANCE, "bar").get().isEmpty());
+    assertFalse(manager.offerSuggestions(MockCommandSource.INSTANCE, "bar foo").get().isEmpty());
+  }
+
   static class NoopSimpleCommand implements SimpleCommand {
     @Override
     public void execute(final Invocation invocation) {