Fix Jackson being unable to deserialize neural network config (#2232)

## Description

#2224 removed the custom deserializers for `Path`, but we still need one
to be able to deserialize the `Path` key in
`NeuralNetworkPropertyManager`. Additionally, Jackson seems to
auto-convert the `Path` key to a `String` using `toString` instead of
its own serializers, so a custom key serializer is also needed to
consistently use the same format for paths. This also removes unused
serde methods in `JacksonUtils` to minimize potential future churn, and
tacks an `@JsonIgnore` on `getModels` to prevent Jackson from
serializing a `ModelProperty` array into the database.

## Meta

Merge checklist:
- [x] Pull Request title is [short, imperative
summary](https://cbea.ms/git-commit/) of proposed changes
- [x] The description documents the _what_ and _why_
- [ ] If this PR changes behavior or adds a feature, user documentation
is updated
- [ ] If this PR touches photon-serde, all messages have been
regenerated and hashes have not changed unexpectedly
- [ ] If this PR touches configuration, this is backwards compatible
with settings back to v2025.3.2
- [ ] If this PR touches pipeline settings or anything related to data
exchange, the frontend typing is updated
- [x] If this PR addresses a bug, a regression test for it is added

photon-core/src/main/java/org/photonvision/common/configuration/NeuralNetworkPropertyManager.java

@@ -18,6 +18,7 @@
 package org.photonvision.common.configuration;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import java.nio.file.Path;
 import java.util.HashMap;
@@ -125,6 +126,7 @@ public class NeuralNetworkPropertyManager {
      *
      * @return A list of all models
      */
+    @JsonIgnore
     public ModelProperties[] getModels() {
         return modelPathToProperties.values().toArray(new ModelProperties[0]);
     }

photon-core/src/main/java/org/photonvision/common/util/file/JacksonUtils.java

@@ -17,20 +17,25 @@
 
 package org.photonvision.common.util.file;
 
+import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.json.JsonReadFeature;
+import com.fasterxml.jackson.databind.DeserializationContext;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ext.NioPathDeserializer;
+import com.fasterxml.jackson.databind.ext.NioPathSerializer;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 import com.fasterxml.jackson.databind.jsontype.BasicPolymorphicTypeValidator;
 import com.fasterxml.jackson.databind.jsontype.PolymorphicTypeValidator;
 import com.fasterxml.jackson.databind.module.SimpleModule;
-import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 import java.io.File;
 import java.io.FileDescriptor;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.net.URI;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.HashMap;
 import java.util.Map;
 import org.eclipse.jetty.io.EofException;
@@ -38,41 +43,67 @@ import org.eclipse.jetty.io.EofException;
 public class JacksonUtils {
     public static class UIMap extends HashMap<String, Object> {}
 
+    // Custom Path key deserializer for Maps with Path keys
+    public static class PathKeySerializer
+            extends com.fasterxml.jackson.databind.JsonSerializer<Path> {
+        @Override
+        public void serialize(Path value, JsonGenerator gen, SerializerProvider serializers)
+                throws IOException {
+            if (value == null) {
+                gen.writeNull();
+            } else {
+                gen.writeFieldName(value.toUri().toString());
+            }
+        }
+    }
+
+    // Custom Path key deserializer for Maps with Path keys
+    public static class PathKeyDeserializer extends com.fasterxml.jackson.databind.KeyDeserializer {
+        @Override
+        public Object deserializeKey(String key, DeserializationContext ctxt) throws IOException {
+            if (key == null || key.isEmpty()) {
+                return null;
+            }
+            return Paths.get(URI.create(key));
+        }
+    }
+
+    // Helper method to create ObjectMapper with Path serialization support
+    private static ObjectMapper createObjectMapperWithPathSupport(Class<?> baseType) {
+        PolymorphicTypeValidator ptv =
+                BasicPolymorphicTypeValidator.builder().allowIfBaseType(baseType).build();
+
+        SimpleModule pathModule = new SimpleModule();
+        pathModule.addSerializer(Path.class, new NioPathSerializer());
+        pathModule.addKeySerializer(Path.class, new PathKeySerializer());
+        pathModule.addDeserializer(Path.class, new NioPathDeserializer());
+        pathModule.addKeyDeserializer(Path.class, new PathKeyDeserializer());
+
+        return JsonMapper.builder()
+                .configure(JsonReadFeature.ALLOW_JAVA_COMMENTS, true)
+                .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
+                .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
+                .addModule(pathModule)
+                .build();
+    }
+
     public static <T> void serialize(Path path, T object) throws IOException {
         serialize(path, object, true);
     }
 
     public static <T> String serializeToString(T object) throws IOException {
-        PolymorphicTypeValidator ptv =
-                BasicPolymorphicTypeValidator.builder().allowIfBaseType(object.getClass()).build();
-        ObjectMapper objectMapper =
-                JsonMapper.builder()
-                        .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
-                        .build();
+        ObjectMapper objectMapper = createObjectMapperWithPathSupport(object.getClass());
         return objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(object);
     }
 
     public static <T> void serialize(Path path, T object, boolean forceSync) throws IOException {
-        PolymorphicTypeValidator ptv =
-                BasicPolymorphicTypeValidator.builder().allowIfBaseType(object.getClass()).build();
-        ObjectMapper objectMapper =
-                JsonMapper.builder()
-                        .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
-                        .build();
+        ObjectMapper objectMapper = createObjectMapperWithPathSupport(object.getClass());
         String json = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(object);
         saveJsonString(json, path, forceSync);
     }
 
     public static <T> T deserialize(Map<?, ?> s, Class<T> ref) throws IOException {
-        PolymorphicTypeValidator ptv =
-                BasicPolymorphicTypeValidator.builder().allowIfBaseType(ref).build();
-        ObjectMapper objectMapper =
-                JsonMapper.builder()
-                        .configure(JsonReadFeature.ALLOW_JAVA_COMMENTS, true)
-                        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
-                        .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
-                        .build();
-
+        ObjectMapper objectMapper = createObjectMapperWithPathSupport(ref);
         return objectMapper.convertValue(s, ref);
     }
 
@@ -81,28 +112,14 @@ public class JacksonUtils {
             throw new EofException("Provided empty string for class " + ref.getName());
         }
 
-        PolymorphicTypeValidator ptv =
-                BasicPolymorphicTypeValidator.builder().allowIfBaseType(ref).build();
-        ObjectMapper objectMapper =
-                JsonMapper.builder()
-                        .configure(JsonReadFeature.ALLOW_JAVA_COMMENTS, true)
-                        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
-                        .enable(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL)
-                        .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
-                        .build();
+        ObjectMapper objectMapper = createObjectMapperWithPathSupport(ref);
+        objectMapper.enable(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL);
 
         return objectMapper.readValue(s, ref);
     }
 
     public static <T> T deserialize(Path path, Class<T> ref) throws IOException {
-        PolymorphicTypeValidator ptv =
-                BasicPolymorphicTypeValidator.builder().allowIfBaseType(ref).build();
-        ObjectMapper objectMapper =
-                JsonMapper.builder()
-                        .configure(JsonReadFeature.ALLOW_JAVA_COMMENTS, true)
-                        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
-                        .activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT)
-                        .build();
+        ObjectMapper objectMapper = createObjectMapperWithPathSupport(ref);
         File jsonFile = new File(path.toString());
         if (jsonFile.exists() && jsonFile.length() > 0) {
             return objectMapper.readValue(jsonFile, ref);
@@ -110,36 +127,6 @@ public class JacksonUtils {
         return null;
     }
 
-    public static <T> T deserialize(Path path, Class<T> ref, StdDeserializer<T> deserializer)
-            throws IOException {
-        ObjectMapper objectMapper = new ObjectMapper();
-        SimpleModule module = new SimpleModule();
-        module.addDeserializer(ref, deserializer);
-        objectMapper.registerModule(module);
-
-        File jsonFile = new File(path.toString());
-        if (jsonFile.exists() && jsonFile.length() > 0) {
-            return objectMapper.readValue(jsonFile, ref);
-        }
-        return null;
-    }
-
-    public static <T> void serialize(Path path, T object, Class<T> ref, StdSerializer<T> serializer)
-            throws IOException {
-        serialize(path, object, ref, serializer, true);
-    }
-
-    public static <T> void serialize(
-            Path path, T object, Class<T> ref, StdSerializer<T> serializer, boolean forceSync)
-            throws IOException {
-        ObjectMapper objectMapper = new ObjectMapper();
-        SimpleModule module = new SimpleModule();
-        module.addSerializer(ref, serializer);
-        objectMapper.registerModule(module);
-        String json = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(object);
-        saveJsonString(json, path, forceSync);
-    }
-
     private static void saveJsonString(String json, Path path, boolean forceSync) throws IOException {
         var file = path.toFile();
         if (file.getParentFile() != null && !file.getParentFile().exists()) {

photon-core/src/test/java/org/photonvision/common/configuration/NeuralNetworkPropertyManagerTest.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) Photon Vision.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.photonvision.common.configuration;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.file.Path;
+import java.util.LinkedList;
+import org.junit.jupiter.api.Test;
+import org.photonvision.common.configuration.NeuralNetworkModelManager.Family;
+import org.photonvision.common.configuration.NeuralNetworkModelManager.Version;
+import org.photonvision.common.configuration.NeuralNetworkPropertyManager.ModelProperties;
+import org.photonvision.common.util.file.JacksonUtils;
+
+public class NeuralNetworkPropertyManagerTest {
+    @Test
+    void testSerialization() {
+        var nnpm = new NeuralNetworkPropertyManager();
+        // Path is always serialized as absolute; for the test to pass, this must also be made absolute
+        nnpm.addModelProperties(
+                new ModelProperties(
+                        Path.of("test", "yolov8nCOCO.rknn").toAbsolutePath(),
+                        "COCO",
+                        new LinkedList<>(),
+                        640,
+                        640,
+                        Family.RKNN,
+                        Version.YOLOV8));
+        String result = assertDoesNotThrow(() -> JacksonUtils.serializeToString(nnpm));
+        var deserializedNnpm =
+                assertDoesNotThrow(
+                        () -> JacksonUtils.deserialize(result, NeuralNetworkPropertyManager.class));
+        assertEquals(nnpm.getModels()[0], deserializedNnpm.getModels()[0]);
+    }
+}