Support writing longs as strings (opt-in)

`jackson-datatype-protobuf` is a missing link in the Jackson ecosystem,
but it doesn't currently provide a canonical representation of long
integers, which poses a problem for strict parsers given the limitation
of the maximum value to
[2^53 - 1](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER)
in JavaScript, whereas this value is for instance
[2^63 - 1](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html)
in Java.

The change proposed here is to provide users who need it with an option
to activate this canonical representation, without altering the existing
default behavior.

README.md

@@ -41,7 +41,11 @@ after which functionality is available for all normal Jackson operations.
 ### Interop with Protobuf 3 Canonical JSON Representation
 
 Protobuf 3 specifies a canonical JSON representation (available [here](https://developers.google.com/protocol-buffers/docs/proto3#json)). This library conforms to that representation with a few exceptions:
-- int64, fixed64, uint64 are written as JSON numbers instead of strings
+- int64, fixed64, uint64 are written as JSON numbers instead of strings. However, you may opt for a conformal representation by means of:
+  ```java
+  ProtobufJacksonConfig config = ProtobufJacksonConfig.builder().writeLongsAsStrings(true).build();
+  new ObjectMapper().registerModules(new ProtobufModule(config));
+  ```
 - `Any` objects don't have any special handling, so the value will be a base64 string, and the type URL field name is `typeUrl` instead of `@type`
 
 ### Protobuf 2 Support

src/main/java/com/hubspot/jackson/datatype/protobuf/ProtobufJacksonConfig.java

@@ -1,14 +1,19 @@
 package com.hubspot.jackson.datatype.protobuf;
 
+import java.io.IOException;
+
+import com.fasterxml.jackson.core.JsonGenerator;
 import com.google.protobuf.ExtensionRegistry;
 
 public class ProtobufJacksonConfig {
   private final ExtensionRegistryWrapper extensionRegistry;
   private final boolean acceptLiteralFieldnames;
+  private final LongWriter longWriter;
 
-  private ProtobufJacksonConfig(ExtensionRegistryWrapper extensionRegistry, boolean acceptLiteralFieldnames) {
+  private ProtobufJacksonConfig(ExtensionRegistryWrapper extensionRegistry, boolean acceptLiteralFieldnames, LongWriter longWriter) {
     this.extensionRegistry = extensionRegistry;
     this.acceptLiteralFieldnames = acceptLiteralFieldnames;
+    this.longWriter = longWriter;
   }
 
   public static Builder builder() {
@@ -23,9 +28,14 @@ public boolean acceptLiteralFieldnames() {
     return acceptLiteralFieldnames;
   }
 
+  public LongWriter longWriter() {
+    return longWriter;
+  }
+
   public static class Builder {
     private ExtensionRegistryWrapper extensionRegistry = ExtensionRegistryWrapper.empty();
     private boolean acceptLiteralFieldnames = false;
+    private boolean writeLongsAsStrings = false;
 
     private Builder() {}
 
@@ -43,8 +53,19 @@ public Builder acceptLiteralFieldnames(boolean acceptLiteralFieldnames) {
       return this;
     }
 
+    public Builder writeLongsAsStrings(boolean writeLongsAsStrings) {
+      this.writeLongsAsStrings = writeLongsAsStrings;
+      return this;
+    }
+
     public ProtobufJacksonConfig build() {
-      return new ProtobufJacksonConfig(extensionRegistry, acceptLiteralFieldnames);
+      return new ProtobufJacksonConfig(extensionRegistry, acceptLiteralFieldnames, writeLongsAsStrings
+          ? (generator, value) -> generator.writeString(String.valueOf(value)) : JsonGenerator::writeNumber);
     }
   }
+
+  @FunctionalInterface
+  public interface LongWriter {
+    void write(JsonGenerator generator, long value) throws IOException;
+  }
 }

src/main/java/com/hubspot/jackson/datatype/protobuf/ProtobufModule.java

@@ -82,22 +82,22 @@ public Version version() {
   public void setupModule(SetupContext context) {
     SimpleSerializers serializers = new SimpleSerializers();
     serializers.addSerializer(new MessageSerializer(config));
-    serializers.addSerializer(new DurationSerializer());
-    serializers.addSerializer(new FieldMaskSerializer());
-    serializers.addSerializer(new ListValueSerializer());
+    serializers.addSerializer(new DurationSerializer(config));
+    serializers.addSerializer(new FieldMaskSerializer(config));
+    serializers.addSerializer(new ListValueSerializer(config));
     serializers.addSerializer(new NullValueSerializer());
-    serializers.addSerializer(new StructSerializer());
-    serializers.addSerializer(new TimestampSerializer());
-    serializers.addSerializer(new ValueSerializer());
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(DoubleValue.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(FloatValue.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(Int64Value.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(UInt64Value.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(Int32Value.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(UInt32Value.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(BoolValue.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(StringValue.class));
-    serializers.addSerializer(new WrappedPrimitiveSerializer<>(BytesValue.class));
+    serializers.addSerializer(new StructSerializer(config));
+    serializers.addSerializer(new TimestampSerializer(config));
+    serializers.addSerializer(new ValueSerializer(config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(DoubleValue.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(FloatValue.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(Int64Value.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(UInt64Value.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(Int32Value.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(UInt32Value.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(BoolValue.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(StringValue.class, config));
+    serializers.addSerializer(new WrappedPrimitiveSerializer<>(BytesValue.class, config));
 
     context.addSerializers(serializers);
 

src/main/java/com/hubspot/jackson/datatype/protobuf/ProtobufSerializer.java

@@ -20,15 +20,18 @@
 import com.google.protobuf.Message;
 import com.google.protobuf.MessageOrBuilder;
 import com.google.protobuf.NullValue;
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 
 public abstract class ProtobufSerializer<T extends MessageOrBuilder> extends StdSerializer<T> {
   private static final String NULL_VALUE_FULL_NAME = NullValue.getDescriptor().getFullName();
 
+  @SuppressFBWarnings(value="SE_BAD_FIELD")
+  protected final ProtobufJacksonConfig config;
   private final Map<Class<?>, JsonSerializer<Object>> serializerCache;
 
-  public ProtobufSerializer(Class<T> protobufType) {
+  public ProtobufSerializer(Class<T> protobufType, ProtobufJacksonConfig config) {
     super(protobufType);
-
+    this.config = config;
     this.serializerCache = new ConcurrentHashMap<>();
   }
 
@@ -64,7 +67,7 @@ protected void writeValue(
         generator.writeNumber((Integer) value);
         break;
       case LONG:
-        generator.writeNumber((Long) value);
+        config.longWriter().write(generator, (Long) value);
         break;
       case FLOAT:
         generator.writeNumber((Float) value);

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/DurationSerializer.java

@@ -6,12 +6,13 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.Duration;
 import com.google.protobuf.util.Durations;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class DurationSerializer extends ProtobufSerializer<Duration> {
 
-  public DurationSerializer() {
-    super(Duration.class);
+  public DurationSerializer(ProtobufJacksonConfig config) {
+    super(Duration.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/FieldMaskSerializer.java

@@ -6,12 +6,13 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.FieldMask;
 import com.google.protobuf.util.FieldMaskUtil;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class FieldMaskSerializer extends ProtobufSerializer<FieldMask> {
 
-  public FieldMaskSerializer() {
-    super(FieldMask.class);
+  public FieldMaskSerializer(ProtobufJacksonConfig config) {
+    super(FieldMask.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/ListValueSerializer.java

@@ -7,13 +7,14 @@
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.ListValue;
 import com.google.protobuf.Value;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class ListValueSerializer extends ProtobufSerializer<ListValue> {
   private static final FieldDescriptor VALUES_FIELD = ListValue.getDescriptor().findFieldByName("values");
 
-  public ListValueSerializer() {
-    super(ListValue.class);
+  public ListValueSerializer(ProtobufJacksonConfig config) {
+    super(ListValue.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/MessageSerializer.java

@@ -24,11 +24,7 @@
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 import com.hubspot.jackson.datatype.protobuf.internal.PropertyNamingCache;
 
-import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
-
 public class MessageSerializer extends ProtobufSerializer<MessageOrBuilder> {
-  @SuppressFBWarnings(value="SE_BAD_FIELD")
-  private final ProtobufJacksonConfig config;
   private final boolean unwrappingSerializer;
   private final Map<Descriptor, PropertyNamingCache> propertyNamingCache;
 
@@ -45,8 +41,7 @@ public MessageSerializer(ProtobufJacksonConfig config) {
   }
 
   private MessageSerializer(ProtobufJacksonConfig config, boolean unwrappingSerializer) {
-    super(MessageOrBuilder.class);
-    this.config = config;
+    super(MessageOrBuilder.class, config);
     this.unwrappingSerializer = unwrappingSerializer;
     this.propertyNamingCache = new ConcurrentHashMap<>();
   }

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/StructSerializer.java

@@ -6,13 +6,14 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Struct;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class StructSerializer extends ProtobufSerializer<Struct> {
   private static final FieldDescriptor FIELDS_FIELD = Struct.getDescriptor().findFieldByName("fields");
 
-  public StructSerializer() {
-    super(Struct.class);
+  public StructSerializer(ProtobufJacksonConfig config) {
+    super(Struct.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/TimestampSerializer.java

@@ -6,12 +6,13 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.Timestamp;
 import com.google.protobuf.util.Timestamps;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class TimestampSerializer extends ProtobufSerializer<Timestamp> {
 
-  public TimestampSerializer() {
-    super(Timestamp.class);
+  public TimestampSerializer(ProtobufJacksonConfig config) {
+    super(Timestamp.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/ValueSerializer.java

@@ -8,12 +8,13 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Value;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class ValueSerializer extends ProtobufSerializer<Value> {
 
-  public ValueSerializer() {
-    super(Value.class);
+  public ValueSerializer(ProtobufJacksonConfig config) {
+    super(Value.class, config);
   }
 
   @Override

src/main/java/com/hubspot/jackson/datatype/protobuf/builtin/serializers/WrappedPrimitiveSerializer.java

@@ -6,12 +6,13 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.MessageOrBuilder;
+import com.hubspot.jackson.datatype.protobuf.ProtobufJacksonConfig;
 import com.hubspot.jackson.datatype.protobuf.ProtobufSerializer;
 
 public class WrappedPrimitiveSerializer<T extends MessageOrBuilder> extends ProtobufSerializer<T> {
 
-  public WrappedPrimitiveSerializer(Class<T> wrapperType) {
-    super(wrapperType);
+  public WrappedPrimitiveSerializer(Class<T> wrapperType, ProtobufJacksonConfig config) {
+    super(wrapperType, config);
   }
 
   @Override

src/test/java/com/hubspot/jackson/datatype/protobuf/WriteLongsAsStringsTest.java

@@ -0,0 +1,60 @@
+package com.hubspot.jackson.datatype.protobuf;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.hubspot.jackson.datatype.protobuf.util.TestProtobuf.AllFields;
+
+public class WriteLongsAsStringsTest {
+
+  @Test
+  public void itDoesntWriteLongsAsStringsByDefault() throws IOException {
+    ProtobufJacksonConfig config = ProtobufJacksonConfig.builder().build();
+
+    assertThat(writeSomeInt64s(config)).isEqualTo("{\"int64\":-42,\"uint64\":42}");
+  }
+
+  @Test
+  public void itDoesntWriteLongsAsStringsWhenDisabled() throws IOException {
+    ProtobufJacksonConfig config = ProtobufJacksonConfig.builder().writeLongsAsStrings(false).build();
+
+    assertThat(writeSomeInt64s(config)).isEqualTo("{\"int64\":-42,\"uint64\":42}");
+  }
+
+  @Test
+  public void itDoesntWriteLongsAsStringsWhenEnabledThenDisabled() throws IOException {
+    ProtobufJacksonConfig config = ProtobufJacksonConfig.builder()
+        .writeLongsAsStrings(true)
+        .writeLongsAsStrings(false)
+        .build();
+
+    assertThat(writeSomeInt64s(config)).isEqualTo("{\"int64\":-42,\"uint64\":42}");
+  }
+
+  @Test
+  public void itWritesLongsAsStringsWhenEnabled() throws IOException {
+    ProtobufJacksonConfig config = ProtobufJacksonConfig.builder().writeLongsAsStrings(true).build();
+
+    assertThat(writeSomeInt64s(config)).isEqualTo("{\"int64\":\"-42\",\"uint64\":\"42\"}");
+  }
+
+  @Test
+  public void itWritesLongsAsStringsWhenDisabledThenEnabled() throws IOException {
+    ProtobufJacksonConfig config = ProtobufJacksonConfig.builder()
+        .writeLongsAsStrings(false)
+        .writeLongsAsStrings(true)
+        .build();
+
+    assertThat(writeSomeInt64s(config)).isEqualTo("{\"int64\":\"-42\",\"uint64\":\"42\"}");
+  }
+
+  private static String writeSomeInt64s(final ProtobufJacksonConfig config) throws IOException {
+    ObjectMapper mapper = new ObjectMapper().registerModules(new ProtobufModule(config));
+    AllFields someInt64s = AllFields.newBuilder().setInt64(-42).setUint64(42).build();
+    return mapper.writeValueAsString(someInt64s);
+  }
+}