Add input validation, fix forms with inputs not having labels

core/src/main/java/org/geysermc/geyser/session/dialog/Dialog.java

@@ -67,6 +67,8 @@ public abstract class Dialog {
     private final AfterAction afterAction;
     private final List<String> labels;
     private final List<DialogInput<?>> inputs = new ArrayList<>();
+    @Getter
+    private final ParsedInputs defaultInputs;
 
     protected Dialog(GeyserSession session, NbtMap map) {
         title = MessageTranslator.convertFromNullableNbtTag(session, map.get("title"));
@@ -96,6 +98,7 @@ public abstract class Dialog {
         for (NbtMap input : inputTag) {
             inputs.add(DialogInput.read(session, input));
         }
+        defaultInputs = inputs.isEmpty() ? ParsedInputs.EMPTY : new ParsedInputs(inputs);
     }
 
     private static Optional<String> readBody(GeyserSession session, NbtMap tag) {
@@ -123,6 +126,9 @@ public abstract class Dialog {
             CustomForm.Builder builder = CustomForm.builder()
                 .translator(MinecraftLocale::getLocaleString, session.locale())
                 .title(title);
+            for (String label : labels) {
+                builder.label(label);
+            }
 
             restored.ifPresentOrElse(last -> last.restore(builder), () -> inputs.forEach(input -> input.addComponent(builder)));
             builder.closedOrInvalidResultHandler(response -> holder.closeDialog(onCancel()));
@@ -143,8 +149,13 @@ public abstract class Dialog {
         session.sendDialogForm(createForm(session, Optional.of(inputs), holder).build());
     }
 
-    protected ParsedInputs parseInput(CustomFormResponse response) {
-        return new ParsedInputs(inputs, response);
+    protected Optional<ParsedInputs> parseInput(GeyserSession session, CustomFormResponse response, DialogHolder holder) {
+        ParsedInputs parsed = new ParsedInputs(inputs, response);
+        if (parsed.hasErrors()) {
+            restoreForm(session, parsed, holder);
+            return Optional.empty();
+        }
+        return Optional.of(parsed);
     }
 
     public static Dialog readDialog(RegistryEntryContext context) {

core/src/main/java/org/geysermc/geyser/session/dialog/DialogHolder.java

@@ -146,7 +146,7 @@ public class DialogHolder {
         // Don't run close functionality if we're asking for command confirmation
         if (dialog.canCloseWithEscape()) {
             shouldClose = true;
-            if (runAction(onCancel, lastInputs == null ? ParsedInputs.EMPTY : lastInputs)) {
+            if (runAction(onCancel, lastInputs == null ? dialog.defaultInputs() : lastInputs)) {
                 manager.close();
             }
             return;
@@ -216,7 +216,7 @@ public class DialogHolder {
             .translator(MinecraftLocale::getLocaleString, manager.session().locale())
             .title("gui.waitingForResponse.title")
             .content(content)
-            .optionalButton("Back", sendBackButton)
+            .optionalButton("gui.back", sendBackButton)
             .closedOrInvalidResultHandler(() -> {
                 if (stillValid()) { // If still waiting on a new dialog
                     waitForResponse();
@@ -229,7 +229,7 @@ public class DialogHolder {
     /**
      * This method runs the given action, if present, with the given inputs.
      *
-     * <p>These inputs can be {@link ParsedInputs#EMPTY} when the dialog has no inputs, or the dialog was closed without entering anything, but can never be {@code null}.
+     * <p>These inputs can be {@link ParsedInputs#EMPTY} when the dialog has no inputs, but can never be {@code null}.
      * The method returns {@code true} if the dialog's after action can be executed, and {@code false} if not. The latter is the case when the action opened a new
      * dialog or screen, in which case the after action will not be handled or be handled by the screen, respectively.</p>
      *

core/src/main/java/org/geysermc/geyser/session/dialog/DialogWithButtons.java

@@ -58,13 +58,14 @@ public abstract class DialogWithButtons extends Dialog {
         builder.dropdown(dropdown);
 
         builder.validResultHandler(response -> {
-            ParsedInputs inputs = parseInput(response);
-            int selection = response.asDropdown();
-            if (selection == buttons.size()) {
-                holder.runButton(exitAction, inputs);
-            } else {
-                holder.runButton(Optional.of(buttons.get(selection)), inputs);
-            }
+            parseInput(session, response, holder).ifPresent(inputs -> {
+                int selection = response.asDropdown();
+                if (selection == buttons.size()) {
+                    holder.runButton(exitAction, inputs);
+                } else {
+                    holder.runButton(Optional.of(buttons.get(selection)), inputs);
+                }
+            });
         });
     }
 
@@ -79,7 +80,6 @@ public abstract class DialogWithButtons extends Dialog {
             if (response.clickedButtonId() == buttons.size()) {
                 holder.runButton(exitAction, ParsedInputs.EMPTY);
             } else {
-
                 holder.runButton(Optional.of(buttons.get(response.clickedButtonId())), ParsedInputs.EMPTY);
             }
         });

core/src/main/java/org/geysermc/geyser/session/dialog/NoticeDialog.java

@@ -53,7 +53,7 @@ public class NoticeDialog extends Dialog {
 
     @Override
     protected void addCustomComponents(GeyserSession session, CustomForm.Builder builder, DialogHolder holder) {
-        builder.validResultHandler(response -> holder.runButton(button, parseInput(response)));
+        builder.validResultHandler(response -> parseInput(session, response, holder).ifPresent(inputs -> holder.runButton(button, inputs)));
     }
 
     @Override

core/src/main/java/org/geysermc/geyser/session/dialog/input/BooleanInput.java

@@ -56,7 +56,7 @@ public class BooleanInput extends DialogInput<Boolean> {
     }
 
     @Override
-    public Boolean read(CustomFormResponse response) {
+    public Boolean read(CustomFormResponse response) throws DialogInputParseException {
         return response.asToggle();
     }
 

core/src/main/java/org/geysermc/geyser/session/dialog/input/DialogInput.java

@@ -51,7 +51,7 @@ public abstract class DialogInput<T> {
 
     public abstract void addComponent(CustomForm.Builder builder, Optional<T> restored);
 
-    public abstract T read(CustomFormResponse response);
+    public abstract T read(CustomFormResponse response) throws DialogInputParseException;
 
     public abstract String asSubstitution(T value);
 

core/src/main/java/org/geysermc/geyser/session/dialog/input/DialogInputParseException.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2025 GeyserMC. http://geysermc.org
+ *
+ * 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.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.session.dialog.input;
+
+import lombok.Getter;
+
+public class DialogInputParseException extends Exception {
+
+    // Exceptions don't work with generics, so we have to do a bit of unsafe casting and assume the object is of the input type :(
+    @Getter
+    private final Object partial;
+
+    public DialogInputParseException(String message, Object partial) {
+        super(message);
+        this.partial = partial;
+    }
+}

core/src/main/java/org/geysermc/geyser/session/dialog/input/NumberRangeInput.java

@@ -59,7 +59,7 @@ public class NumberRangeInput extends DialogInput<Float> {
     }
 
     @Override
-    public Float read(CustomFormResponse response) {
+    public Float read(CustomFormResponse response) throws DialogInputParseException {
         return response.asSlider();
     }
 

core/src/main/java/org/geysermc/geyser/session/dialog/input/ParsedInputs.java

@@ -30,19 +30,26 @@ import org.cloudburstmc.nbt.NbtMapBuilder;
 import org.geysermc.cumulus.form.CustomForm;
 import org.geysermc.cumulus.response.CustomFormResponse;
 
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
 public class ParsedInputs {
-    public static final ParsedInputs EMPTY = new ParsedInputs(List.of(), null);
+    public static final ParsedInputs EMPTY = new ParsedInputs(List.of());
 
     private final Map<DialogInput<?>, Object> values = new LinkedHashMap<>();
+    private final Map<DialogInput<?>, String> errors = new HashMap<>();
 
     public ParsedInputs(List<DialogInput<?>> inputs, CustomFormResponse response) {
         for (DialogInput<?> input : inputs) {
-            values.put(input, input.read(response));
+            try {
+                values.put(input, input.read(response));
+            } catch (DialogInputParseException exception) {
+                values.put(input, exception.getPartial());
+                errors.put(input, exception.getMessage());
+            }
         }
     }
 
@@ -54,6 +61,11 @@ public class ParsedInputs {
 
     public void restore(CustomForm.Builder builder) {
         for (Map.Entry<DialogInput<?>, Object> entry : values.entrySet()) {
+            String error = errors.get(entry.getKey());
+            if (error != null) {
+                builder.label("§cError parsing input data: " + error + ".");
+                builder.label("§cPlease adjust!");
+            }
             // Can't be a Geyser update without eclipse dealing with generics
             ((DialogInput) entry.getKey()).addComponent(builder, Optional.of(entry.getValue()));
         }
@@ -75,4 +87,8 @@ public class ParsedInputs {
         }
         return builder.build();
     }
+
+    public boolean hasErrors() {
+        return !errors.isEmpty();
+    }
 }

core/src/main/java/org/geysermc/geyser/session/dialog/input/SingleOptionInput.java

@@ -78,7 +78,7 @@ public class SingleOptionInput extends DialogInput<String> {
     }
 
     @Override
-    public String read(CustomFormResponse response) {
+    public String read(CustomFormResponse response) throws DialogInputParseException {
         return entries.get(response.asDropdown()).id();
     }
 

core/src/main/java/org/geysermc/geyser/session/dialog/input/TextInput.java

@@ -56,11 +56,13 @@ public class TextInput extends DialogInput<String> {
     }
 
     @Override
-    public String read(CustomFormResponse response) {
-        String raw = response.asInput();
-        assert raw != null;
-        // Bedrock doesn't support setting a max length, so we just cut it off to not have the server complain
-        return raw.substring(0, Math.min(raw.length(), maxLength));
+    public String read(CustomFormResponse response) throws DialogInputParseException {
+        String text = response.asInput();
+        assert text != null;
+        if (text.length() > maxLength) {
+            throw new DialogInputParseException("length of text cannot be above " + maxLength, text);
+        }
+        return text;
     }
 
     @Override