Introduce MessageReflector to enable alternative protobuf runtimes

src/main/java/build/buf/protovalidate/AnyEvaluator.java

@@ -19,7 +19,6 @@
 import build.buf.validate.FieldPath;
 import build.buf.validate.FieldRules;
 import com.google.protobuf.Descriptors;
-import com.google.protobuf.Message;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
@@ -78,12 +77,12 @@ final class AnyEvaluator implements Evaluator {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    Message anyValue = val.messageValue();
+    MessageReflector anyValue = val.messageValue();
     if (anyValue == null) {
       return RuleViolation.NO_VIOLATIONS;
     }
     List<RuleViolation.Builder> violationList = new ArrayList<>();
-    String typeURL = (String) anyValue.getField(typeURLDescriptor);
+    String typeURL = anyValue.getField(typeURLDescriptor).jvmValue(String.class);
     if (!in.isEmpty() && !in.contains(typeURL)) {
       RuleViolation.Builder violation =
           RuleViolation.newBuilder()

src/main/java/build/buf/protovalidate/CelPrograms.java

@@ -45,7 +45,7 @@ public boolean tautology() {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    CelVariableResolver bindings = Variable.newThisVariable(val.value(Object.class));
+    CelVariableResolver bindings = Variable.newThisVariable(val.celValue());
     List<RuleViolation.Builder> violations = new ArrayList<>();
     for (CompiledProgram program : programs) {
       RuleViolation.Builder violation = program.eval(val, bindings);

src/main/java/build/buf/protovalidate/EnumEvaluator.java

@@ -77,7 +77,7 @@ public boolean tautology() {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    Object enumValue = val.value(Object.class);
+    Long enumValue = val.jvmValue(Long.class);
     if (enumValue == null) {
       return RuleViolation.NO_VIOLATIONS;
     }

src/main/java/build/buf/protovalidate/FieldEvaluator.java

@@ -111,13 +111,17 @@ public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
     if (this.shouldIgnoreAlways()) {
       return RuleViolation.NO_VIOLATIONS;
     }
-    Message message = val.messageValue();
+    MessageReflector message = val.messageValue();
     if (message == null) {
       return RuleViolation.NO_VIOLATIONS;
     }
     boolean hasField;
     if (descriptor.isRepeated()) {
-      hasField = message.getRepeatedFieldCount(descriptor) != 0;
+      if (descriptor.isMapField()) {
+        hasField = !message.getField(descriptor).mapValue().isEmpty();
+      } else {
+        hasField = !message.getField(descriptor).repeatedValue().isEmpty();
+      }
     } else {
       hasField = message.hasField(descriptor);
     }
@@ -134,11 +138,10 @@ public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
     if (this.shouldIgnoreEmpty() && !hasField) {
       return RuleViolation.NO_VIOLATIONS;
     }
-    Object fieldValue = message.getField(descriptor);
-    if (this.shouldIgnoreDefault()
-        && Objects.equals(zero, ProtoAdapter.toCel(descriptor, fieldValue))) {
+    Value fieldValue = message.getField(descriptor);
+    if (this.shouldIgnoreDefault() && Objects.equals(zero, fieldValue.jvmValue(Object.class))) {
       return RuleViolation.NO_VIOLATIONS;
     }
-    return valueEvaluator.evaluate(new ObjectValue(descriptor, fieldValue), failFast);
+    return valueEvaluator.evaluate(fieldValue, failFast);
   }
 }

src/main/java/build/buf/protovalidate/ListElementValue.java

@@ -45,15 +45,20 @@ final class ListElementValue implements Value {
   }
 
   @Override
-  public @Nullable Message messageValue() {
+  public @Nullable MessageReflector messageValue() {
     if (fieldDescriptor.getJavaType() == Descriptors.FieldDescriptor.JavaType.MESSAGE) {
-      return (Message) value;
+      return new ProtobufMessageReflector((Message) value);
     }
     return null;
   }
 
   @Override
-  public <T> T value(Class<T> clazz) {
+  public Object celValue() {
+      return ProtoAdapter.scalarToCel(fieldDescriptor.getType(), value);
+  }
+
+  @Override
+  public <T> T jvmValue(Class<T> clazz) {
     Descriptors.FieldDescriptor.Type type = fieldDescriptor.getType();
     if (type == Descriptors.FieldDescriptor.Type.MESSAGE) {
       return clazz.cast(value);

src/main/java/build/buf/protovalidate/MapEvaluator.java

@@ -155,19 +155,19 @@ private List<RuleViolation.Builder> evalPairs(Value key, Value value, boolean fa
       case TYPE_SINT64:
       case TYPE_SFIXED32:
       case TYPE_SFIXED64:
-        fieldPathElementBuilder.setIntKey(key.value(Number.class).longValue());
+        fieldPathElementBuilder.setIntKey(key.jvmValue(Number.class).longValue());
         break;
       case TYPE_UINT32:
       case TYPE_UINT64:
       case TYPE_FIXED32:
       case TYPE_FIXED64:
-        fieldPathElementBuilder.setUintKey(key.value(Number.class).longValue());
+        fieldPathElementBuilder.setUintKey(key.jvmValue(Number.class).longValue());
         break;
       case TYPE_BOOL:
-        fieldPathElementBuilder.setBoolKey(key.value(Boolean.class));
+        fieldPathElementBuilder.setBoolKey(key.jvmValue(Boolean.class));
         break;
       case TYPE_STRING:
-        fieldPathElementBuilder.setStringKey(key.value(String.class));
+        fieldPathElementBuilder.setStringKey(key.jvmValue(String.class));
         break;
       default:
         throw new ExecutionException("Unexpected map key type");

src/main/java/build/buf/protovalidate/MessageOneofEvaluator.java

@@ -45,7 +45,7 @@ public boolean tautology() {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    Message msg = val.messageValue();
+    MessageReflector msg = val.messageValue();
     if (msg == null) {
       return RuleViolation.NO_VIOLATIONS;
     }

src/main/java/build/buf/protovalidate/MessageReflector.java

@@ -0,0 +1,43 @@
+// Copyright 2023-2025 Buf Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build.buf.protovalidate;
+
+import com.google.protobuf.Descriptors.FieldDescriptor;
+
+/**
+ * {@link MessageReflector} is a wrapper around a protobuf message that provides reflective access
+ * to the underlying message.
+ *
+ * <p>{@link MessageReflector} is a runtime-independent interface. Any protobuf runtime that
+ * implements this interface can wrap its messages and, along with their {@link
+ * com.google.protobuf.Descriptors.Descriptor}s, protovalidate-java will be able to validate them.
+ */
+public interface MessageReflector {
+  /**
+   * Whether the wrapped message has the field described by the provided field descriptor.
+   *
+   * @param field The field descriptor to check for.
+   * @return Whether the field is present.
+   */
+  boolean hasField(FieldDescriptor field);
+
+  /**
+   * Get the value described by the provided field descriptor.
+   *
+   * @param field The field descriptor for which to retrieve a value.
+   * @return The value corresponding to the field descriptor.
+   */
+  Value getField(FieldDescriptor field);
+}

src/main/java/build/buf/protovalidate/MessageValue.java

@@ -25,15 +25,15 @@
 final class MessageValue implements Value {
 
   /** Object type since the object type is inferred from the field descriptor. */
-  private final Object value;
+  private final ProtobufMessageReflector value;
 
   /**
    * Constructs a {@link MessageValue} with the provided message value.
    *
    * @param value The message value.
    */
   MessageValue(Message value) {
-    this.value = value;
+    this.value = new ProtobufMessageReflector(value);
   }
 
   @Override
@@ -42,13 +42,18 @@ final class MessageValue implements Value {
   }
 
   @Override
-  public Message messageValue() {
-    return (Message) value;
+  public MessageReflector messageValue() {
+    return value;
   }
 
   @Override
-  public <T> T value(Class<T> clazz) {
-    return clazz.cast(value);
+  public Object celValue() {
+      return value.getMessage();
+  }
+
+  @Override
+  public <T> T jvmValue(Class<T> clazz) {
+    throw new UnsupportedOperationException();
   }
 
   @Override

src/main/java/build/buf/protovalidate/ObjectValue.java

@@ -53,15 +53,23 @@ public Descriptors.FieldDescriptor fieldDescriptor() {
 
   @Nullable
   @Override
-  public Message messageValue() {
+  public MessageReflector messageValue() {
     if (fieldDescriptor.getJavaType() == Descriptors.FieldDescriptor.JavaType.MESSAGE) {
-      return (Message) value;
+      return new ProtobufMessageReflector((Message) value);
     }
     return null;
   }
 
   @Override
-  public <T> T value(Class<T> clazz) {
+  public Object celValue() {
+      return ProtoAdapter.toCel(fieldDescriptor, value);
+  }
+
+  @Override
+  public <T> T jvmValue(Class<T> clazz) {
+    if (value instanceof Descriptors.EnumValueDescriptor) {
+      return clazz.cast((long) ((Descriptors.EnumValueDescriptor) value).getNumber());
+    }
     return clazz.cast(ProtoAdapter.toCel(fieldDescriptor, value));
   }
 

src/main/java/build/buf/protovalidate/OneofEvaluator.java

@@ -17,7 +17,6 @@
 import build.buf.protovalidate.exceptions.ExecutionException;
 import build.buf.validate.FieldPathElement;
 import com.google.protobuf.Descriptors.OneofDescriptor;
-import com.google.protobuf.Message;
 import java.util.Collections;
 import java.util.List;
 
@@ -48,8 +47,12 @@ public boolean tautology() {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    Message message = val.messageValue();
-    if (message == null || !required || (message.getOneofFieldDescriptor(descriptor) != null)) {
+    MessageReflector message = val.messageValue();
+    if (message == null) {
+        return RuleViolation.NO_VIOLATIONS;
+    }
+    boolean hasField = descriptor.getFields().stream().anyMatch(message::hasField);
+    if (!required || hasField) {
       return RuleViolation.NO_VIOLATIONS;
     }
     return Collections.singletonList(

src/main/java/build/buf/protovalidate/ProtobufMessageReflector.java

@@ -0,0 +1,40 @@
+// Copyright 2023-2025 Buf Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build.buf.protovalidate;
+
+import com.google.protobuf.Descriptors.FieldDescriptor;
+import com.google.protobuf.Message;
+
+class ProtobufMessageReflector implements MessageReflector {
+  private final Message message;
+
+  ProtobufMessageReflector(Message message) {
+    this.message = message;
+  }
+
+  public Message getMessage() {
+    return message;
+  }
+
+  @Override
+  public boolean hasField(FieldDescriptor field) {
+    return message.hasField(field);
+  }
+
+  @Override
+  public Value getField(FieldDescriptor field) {
+    return new ObjectValue(field, message.getField(field));
+  }
+}

src/main/java/build/buf/protovalidate/RuleViolation.java

@@ -55,7 +55,7 @@ static class FieldValue implements Violation.FieldValue {
      * @param value A {@link Value} to create this {@link FieldValue} from.
      */
     FieldValue(Value value) {
-      this.value = value.value(Object.class);
+      this.value = value.jvmValue(Object.class);
       this.descriptor = Objects.requireNonNull(value.fieldDescriptor());
     }
 

src/main/java/build/buf/protovalidate/Value.java

@@ -15,7 +15,6 @@
 package build.buf.protovalidate;
 
 import com.google.protobuf.Descriptors;
-import com.google.protobuf.Message;
 import java.util.List;
 import java.util.Map;
 import org.jspecify.annotations.Nullable;
@@ -24,7 +23,7 @@
  * {@link Value} is a wrapper around a protobuf value that provides helper methods for accessing the
  * value.
  */
-interface Value {
+public interface Value {
   /**
    * Get the field descriptor that corresponds to the underlying Value, if it is a message field.
    *
@@ -34,21 +33,12 @@ interface Value {
   Descriptors.@Nullable FieldDescriptor fieldDescriptor();
 
   /**
-   * Get the underlying value as a {@link Message} type.
+   * Get the underlying value as a {@link MessageReflector} type.
    *
-   * @return The underlying {@link Message} value. null if the underlying value is not a {@link
-   *     Message} type.
+   * @return The underlying {@link MessageReflector} value. null if the underlying value is not a {@link
+   *     MessageReflector} type.
    */
-  @Nullable Message messageValue();
-
-  /**
-   * Get the underlying value and cast it to the class type.
-   *
-   * @param clazz The inferred class.
-   * @return The value casted to the inferred class type.
-   * @param <T> The class type.
-   */
-  <T> T value(Class<T> clazz);
+  @Nullable MessageReflector messageValue();
 
   /**
    * Get the underlying value as a list.
@@ -65,4 +55,21 @@ interface Value {
    *     list.
    */
   Map<Value, Value> mapValue();
+
+  /**
+   * Get the underlying value as it should be provided to CEL.
+   *
+   * @return The underlying value as a CEL-compatible type.
+   */
+  Object celValue();
+
+  /**
+   * Get the underlying value and cast it to the class type, which will be a type checkable
+   * internally by protovalidate-java.
+   *
+   * @param clazz The inferred class.
+   * @return The value cast to the inferred class type.
+   * @param <T> The class type.
+   */
+  <T> T jvmValue(Class<T> clazz);
 }

src/main/java/build/buf/protovalidate/ValueEvaluator.java

@@ -71,7 +71,7 @@ public boolean tautology() {
   @Override
   public List<RuleViolation.Builder> evaluate(Value val, boolean failFast)
       throws ExecutionException {
-    if (this.shouldIgnore(val.value(Object.class))) {
+    if (this.shouldIgnore(val.jvmValue(Object.class))) {
       return RuleViolation.NO_VIOLATIONS;
     }
     List<RuleViolation.Builder> allViolations = new ArrayList<>();