Fix #134: (protobuf) proto3 packed-default and oneof field resolution

protobuf/src/main/java/com/fasterxml/jackson/dataformat/protobuf/schema/FieldType.java

@@ -59,6 +59,15 @@ private FieldType(int wt, DataType.ScalarType... aliases) {
 
     public int getWireType() { return _wireType; }
 
+    /**
+     * Whether fields of this type may use "packed" encoding when repeated
+     * (per protobuf spec, only scalar numeric/enum/boolean types can be packed;
+     * length-delimited types like String/Bytes/Message cannot).
+     */
+    public boolean isPackable() {
+        return _wireType != WireType.LENGTH_PREFIXED;
+    }
+
     public boolean usesZigZag() {
         return (this == VINT32_Z) || (this == VINT64_Z);
     }

protobuf/src/main/java/com/fasterxml/jackson/dataformat/protobuf/schema/FileDescriptorSet.java

@@ -136,10 +136,14 @@ public static class FileDescriptorProto
 
         public ProtoFile.Syntax getSyntax()
         {
-            if (syntax == null) {
-                return ProtoFile.Syntax.PROTO_2;
+            // 01-Jul-2026, tatu: [dataformats-binary#134] Real `FileDescriptorProto.syntax`
+            //   values (as written by protoc) are lowercase ("proto2"/"proto3"), but the
+            //   enum constants are PROTO_2/PROTO_3: `valueOf(syntax)` would throw for any
+            //   proto3-origin descriptor set.
+            if ("proto3".equals(syntax)) {
+                return ProtoFile.Syntax.PROTO_3;
             }
-            return ProtoFile.Syntax.valueOf(syntax);
+            return ProtoFile.Syntax.PROTO_2;
         }
 
         public void setPackage(String p) { _package = p; }

protobuf/src/main/java/com/fasterxml/jackson/dataformat/protobuf/schema/NativeProtobufSchema.java

@@ -15,17 +15,27 @@ public class NativeProtobufSchema
     protected final String _name;
     protected final Collection<TypeElement> _nativeTypes;
 
+    /**
+     * @since 2.21.5 [dataformats-binary#134]
+     */
+    protected final boolean _isProto3;
+
     protected volatile String[] _messageNames;
 
     protected NativeProtobufSchema(ProtoFile input)
     {
-        this(input.filePath(), input.typeElements());
+        this(input.filePath(), input.typeElements(), input.syntax() == ProtoFile.Syntax.PROTO_3);
+    }
+
+    protected NativeProtobufSchema(String name, Collection<TypeElement> types) {
+        this(name, types, false);
     }
 
-    protected NativeProtobufSchema(String name, Collection<TypeElement> types)
+    protected NativeProtobufSchema(String name, Collection<TypeElement> types, boolean isProto3)
     {
         _name = name;
         _nativeTypes = types;
+        _isProto3 = isProto3;
     }
 
     public static NativeProtobufSchema construct(ProtoFile input) {
@@ -64,7 +74,7 @@ public ProtobufSchema forType(String messageTypeName)
                     +"') has no message type with name '"+messageTypeName+"': known types: "
                     +getMessageNames());
         }
-        return new ProtobufSchema(this, TypeResolver.resolve(_nativeTypes, msg));
+        return new ProtobufSchema(this, TypeResolver.resolve(_nativeTypes, msg, _isProto3));
     }
 
     /**
@@ -78,7 +88,7 @@ public ProtobufSchema forFirstType()
             throw new IllegalArgumentException("Protobuf schema definition (name '"+_name
                     +"') contains no message type definitions");
         }
-        return new ProtobufSchema(this, TypeResolver.resolve(_nativeTypes, msg));
+        return new ProtobufSchema(this, TypeResolver.resolve(_nativeTypes, msg, _isProto3));
     }
 
     public List<String> getMessageNames() {

protobuf/src/main/java/com/fasterxml/jackson/dataformat/protobuf/schema/ProtobufField.java

@@ -59,23 +59,36 @@ public class ProtobufField
     public final boolean isStdEnum;
 
     public ProtobufField(FieldElement nativeField, FieldType type) {
-        this(nativeField, type, null, null);
+        this(nativeField, type, false);
+    }
+
+    /**
+     * @param isProto3 Whether enclosing schema uses proto3 syntax: affects default
+     *    "packed" setting for repeated scalar fields when not explicitly specified
+     *    (proto3 defaults to packed, proto2 to unpacked)
+     */
+    public ProtobufField(FieldElement nativeField, FieldType type, boolean isProto3) {
+        this(nativeField, type, null, null, isProto3);
     }
 
     public ProtobufField(FieldElement nativeField, ProtobufMessage msg) {
-        this(nativeField, FieldType.MESSAGE, msg, null);
+        this(nativeField, FieldType.MESSAGE, msg, null, false);
     }
 
     public ProtobufField(FieldElement nativeField, ProtobufEnum et) {
-        this(nativeField, FieldType.ENUM, null, et);
+        this(nativeField, FieldType.ENUM, null, et, false);
+    }
+
+    public ProtobufField(FieldElement nativeField, ProtobufEnum et, boolean isProto3) {
+        this(nativeField, FieldType.ENUM, null, et, isProto3);
     }
 
     public static ProtobufField unknownField() {
-        return new ProtobufField(null, FieldType.MESSAGE, null, null);
+        return new ProtobufField(null, FieldType.MESSAGE, null, null, false);
     }
 
     protected ProtobufField(FieldElement nativeField, FieldType type,
-            ProtobufMessage msg, ProtobufEnum et)
+            ProtobufMessage msg, ProtobufEnum et, boolean isProto3)
     {
         this.type = type;
         wireType = type.getWireType();
@@ -113,8 +126,15 @@ protected ProtobufField(FieldElement nativeField, FieldType type,
              *   we can't use 'isPacked()' in 3.1.5 (and probably deprecated has same issue);
              *   let's add a temporary workaround.
              */
-            packed = _findBooleanOption(nativeField, "packed");
-            deprecated = _findBooleanOption(nativeField, "deprecated");
+            Boolean explicitPacked = _findBooleanOptionValue(nativeField, "packed");
+            if (explicitPacked != null) {
+                packed = explicitPacked.booleanValue();
+            } else {
+                // 01-Jul-2026: [dataformats-binary#134] proto3 defaults repeated
+                //   scalar/enum fields to packed encoding unless overridden
+                packed = repeated && isProto3 && type.isPackable();
+            }
+            deprecated = Boolean.TRUE.equals(_findBooleanOptionValue(nativeField, "deprecated"));
 
             // 13-Apr-2017, tatu: [databind#79] Need to write length-prefixed for packed arrays
             if (repeated && packed) {
@@ -127,18 +147,18 @@ protected ProtobufField(FieldElement nativeField, FieldType type,
         isObject = (type == FieldType.MESSAGE);
     }
 
-    private static boolean _findBooleanOption(FieldElement f, String key)
+    private static Boolean _findBooleanOptionValue(FieldElement f, String key)
     {
         for (OptionElement opt : f.options()) {
             if (key.equals(opt.name())) {
                 Object val = opt.value();
                 if (val instanceof Boolean) {
-                    return ((Boolean) val).booleanValue();
+                    return (Boolean) val;
                 }
-                return "true".equals(String.valueOf(val).trim());
+                return Boolean.valueOf("true".equals(String.valueOf(val).trim()));
             }
         }
-        return false;
+        return null;
     }
 
     public void assignMessageType(ProtobufMessage msgType) {

protobuf/src/main/java/com/fasterxml/jackson/dataformat/protobuf/schema/TypeResolver.java

@@ -40,12 +40,21 @@ public class TypeResolver
      */
     private Map<String,ProtobufMessage> _resolvedMessageTypes;
 
+    /**
+     * Whether enclosing schema (single .proto file) uses proto3 syntax: affects
+     * default "packed" setting for repeated scalar/enum fields.
+     *
+     * @since 2.21.5 [dataformats-binary#134]
+     */
+    private final boolean _isProto3;
+
     protected TypeResolver(TypeResolver p, String name, Map<String,MessageElement> declaredMsgs,
-            Map<String,ProtobufEnum> enums)
+            Map<String,ProtobufEnum> enums, boolean isProto3)
     {
         _parent = p;
         _contextName = name;
         _enumTypes = enums;
+        _isProto3 = isProto3;
         if (declaredMsgs == null) {
             declaredMsgs = Collections.emptyMap();
         }
@@ -58,21 +67,29 @@ protected TypeResolver(TypeResolver p, String name, Map<String,MessageElement> d
      * types it depends on.
      */
     public static ProtobufMessage resolve(Collection<TypeElement> nativeTypes, MessageElement rawType) {
-        final TypeResolver rootR  = construct(null, null, nativeTypes);
+        return resolve(nativeTypes, rawType, false);
+    }
+
+    /**
+     * @since 2.21.5 [dataformats-binary#134]
+     */
+    public static ProtobufMessage resolve(Collection<TypeElement> nativeTypes, MessageElement rawType,
+            boolean isProto3) {
+        final TypeResolver rootR  = construct(null, null, nativeTypes, isProto3);
         // Important: parent context for "root types", but child context for nested; further,
         // resolution happens in "child" context to allow proper referencing
-        return TypeResolver.construct(rootR, rawType.name(), rawType.nestedElements())
+        return TypeResolver.construct(rootR, rawType.name(), rawType.nestedElements(), isProto3)
                 ._resolve(rawType);
     }
 
     protected ProtobufMessage resolve(TypeResolver parent, MessageElement rawType)
     {
-        return TypeResolver.construct(this, rawType.name(), rawType.nestedElements())
+        return TypeResolver.construct(this, rawType.name(), rawType.nestedElements(), _isProto3)
                 ._resolve(rawType);
     }
 
     protected static TypeResolver construct(TypeResolver parent, String localName,
-            Collection<TypeElement> nativeTypes)
+            Collection<TypeElement> nativeTypes, boolean isProto3)
     {
         Map<String,MessageElement> declaredMsgs = null;
         Map<String,ProtobufEnum> declaredEnums = new LinkedHashMap<>();
@@ -92,7 +109,7 @@ protected static TypeResolver construct(TypeResolver parent, String localName,
                 }
             } // no other known types?
         }
-        return new TypeResolver(parent, localName, declaredMsgs, declaredEnums);
+        return new TypeResolver(parent, localName, declaredMsgs, declaredEnums, isProto3);
     }
 
     protected void addEnumType(String name, ProtobufEnum enumType) {
@@ -125,6 +142,17 @@ protected static ProtobufEnum constructEnum(EnumElement nativeEnum)
     protected ProtobufMessage _resolve(MessageElement rawType)
     {
         List<FieldElement> rawFields = rawType.fields();
+        List<OneOfElement> oneOfs = rawType.oneOfs();
+        // 01-Jul-2026, tatu: [dataformats-binary#134] Fields declared inside a
+        //   `oneof` block live in a separate list from regular fields and were
+        //   silently dropped during resolution; merge them in so they're not lost.
+        if (!oneOfs.isEmpty()) {
+            List<FieldElement> merged = new ArrayList<FieldElement>(rawFields);
+            for (OneOfElement oneOf : oneOfs) {
+                merged.addAll(oneOf.fields());
+            }
+            rawFields = merged;
+        }
         ProtobufField[] resolvedFields = new ProtobufField[rawFields.size()];
 
         ProtobufMessage message = new ProtobufMessage(rawType.name(), resolvedFields);
@@ -142,7 +170,7 @@ protected ProtobufMessage _resolve(MessageElement rawType)
             ProtobufField pbf;
 
             if (type != null) { // simple type
-                pbf = new ProtobufField(f, type);
+                pbf = new ProtobufField(f, type, _isProto3);
             } else if (fieldType instanceof DataType.NamedType) {
                 final String typeStr = ((DataType.NamedType) fieldType).name();
 
@@ -260,7 +288,7 @@ private ProtobufField _findLocalResolved(FieldElement nativeField, String typeSt
         }
         ProtobufEnum et = _enumTypes.get(typeStr);
         if (et != null) {
-            return new ProtobufField(nativeField, et);
+            return new ProtobufField(nativeField, et, _isProto3);
         }
         return null;
     }

protobuf/src/test/java/com/fasterxml/jackson/dataformat/protobuf/OneofFieldResolutionTest.java

@@ -0,0 +1,56 @@
+package com.fasterxml.jackson.dataformat.protobuf;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.fasterxml.jackson.dataformat.protobuf.schema.ProtobufSchema;
+import com.fasterxml.jackson.dataformat.protobuf.schema.ProtobufSchemaLoader;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+// [dataformats-binary#134]: fields declared inside a `oneof` block live in a
+// separate list (`MessageElement.oneOfs()`) from regular fields
+// (`MessageElement.fields()`); TypeResolver only ever resolved the latter,
+// so `oneof` member fields were silently dropped from the schema -- no
+// error, they simply couldn't be read or written.
+public class OneofFieldResolutionTest extends ProtobufTestBase
+{
+    private final ProtobufMapper MAPPER = newObjectMapper();
+
+    private final static String SCHEMA_STR = "message t {\n"
+            + "  oneof choice {\n"
+            + "    string a = 1;\n"
+            + "    int32 b = 2;\n"
+            + "  }\n"
+            + "  optional string other = 3;\n"
+            + "}\n";
+
+    @Test
+    public void testOneofFieldsAreResolved() throws Exception
+    {
+        ProtobufSchema schema = ProtobufSchemaLoader.std.parse(SCHEMA_STR);
+
+        assertEquals(3, schema.getRootType().getFieldCount());
+        assertNotNull(schema.getRootType().field("a"));
+        assertNotNull(schema.getRootType().field("b"));
+        assertNotNull(schema.getRootType().field("other"));
+    }
+
+    @Test
+    public void testOneofFieldsRoundTrip() throws Exception
+    {
+        ProtobufSchema schema = ProtobufSchemaLoader.std.parse(SCHEMA_STR);
+
+        ObjectNode input = MAPPER.createObjectNode();
+        input.put("a", "value-for-a");
+        input.put("other", "other-value");
+
+        byte[] bytes = MAPPER.writer(schema).writeValueAsBytes(input);
+        JsonNode result = MAPPER.readerFor(JsonNode.class).with(schema).readValue(bytes);
+
+        assertEquals("value-for-a", result.get("a").asText());
+        assertEquals("other-value", result.get("other").asText());
+    }
+}