Message IDs can be strings or numbers

Author: jkschneider

src/main/java/io/moderne/jsonrpc/JsonRpc.java

@@ -31,7 +31,7 @@ public class JsonRpc {
     private volatile boolean shutdown = false;
 
     private final MessageHandler messageHandler;
-    private final Map<String, CompletableFuture<JsonRpcSuccess>> openRequests = new ConcurrentHashMap<>();
+    private final Map<Object, CompletableFuture<JsonRpcSuccess>> openRequests = new ConcurrentHashMap<>();
 
     public <P> JsonRpc rpc(String name, JsonRpcMethod<P> method) {
         methods.put(name, method);
@@ -55,12 +55,12 @@ public JsonRpc bind() {
             @Override
             protected void compute() {
                 while (!shutdown) {
-                    String requestId = null;
+                    Object requestId = null;
                     try {
                         JsonRpcMessage msg = messageHandler.receive();
                         if (msg instanceof JsonRpcResponse) {
                             JsonRpcResponse response = (JsonRpcResponse) msg;
-                            String id = response.getId();
+                            Object id = response.getId();
                             if (id != null) {
                                 CompletableFuture<JsonRpcSuccess> responseFuture = openRequests.remove(id);
                                 if (response instanceof JsonRpcError) {

src/main/java/io/moderne/jsonrpc/JsonRpcError.java

@@ -15,6 +15,7 @@
  */
 package io.moderne.jsonrpc;
 
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import lombok.EqualsAndHashCode;
 import lombok.Value;
 import org.jspecify.annotations.Nullable;
@@ -25,7 +26,9 @@
 @Value
 @EqualsAndHashCode(callSuper = false)
 public class JsonRpcError extends JsonRpcResponse {
-    String id;
+    @JsonDeserialize(using = JsonRpcIdDeserializer.class)
+    Object id;
+
     Detail error;
 
     @Value
@@ -37,27 +40,27 @@ public static class Detail {
         String data;
     }
 
-    public static JsonRpcError parseError(String id) {
+    public static JsonRpcError parseError(Object id) {
         return new JsonRpcError(id, new Detail(-32700, "Parse error", null));
     }
 
-    public static JsonRpcError invalidRequest(String id, String message) {
+    public static JsonRpcError invalidRequest(Object id, String message) {
         return new JsonRpcError(id, new Detail(-32600, "Invalid Request: " + message, null));
     }
 
-    public static JsonRpcError methodNotFound(String id, String method) {
+    public static JsonRpcError methodNotFound(Object id, String method) {
         return new JsonRpcError(id, new Detail(-32601, "Method not found: " + method, null));
     }
 
-    public static JsonRpcError invalidParams(String id) {
+    public static JsonRpcError invalidParams(Object id) {
         return new JsonRpcError(id, new Detail(-32602, "Invalid params", null));
     }
 
-    public static JsonRpcError internalError(String id, String message) {
+    public static JsonRpcError internalError(Object id, String message) {
         return new JsonRpcError(id, new Detail(-32603, "Internal error: " + message, null));
     }
 
-    public static JsonRpcError internalError(String id, Throwable t) {
+    public static JsonRpcError internalError(Object id, Throwable t) {
         StringWriter sw = new StringWriter();
         t.printStackTrace(new PrintWriter(sw));
         return new JsonRpcError(id, new Detail(-32603, "Internal error: " + t.getMessage(), sw.toString()));

src/main/java/io/moderne/jsonrpc/JsonRpcIdDeserializer.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * 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
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 io.moderne.jsonrpc;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.ObjectCodec;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.io.IOException;
+
+public class JsonRpcIdDeserializer extends JsonDeserializer<Object> {
+
+    @Override
+    public Object deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
+        ObjectCodec codec = jsonParser.getCodec();
+        JsonNode jsonNode = codec.readTree(jsonParser);
+        if (jsonNode.isNumber()) {
+            // The assumption here is that the id is either a String or an Integer, and likely
+            // an Integer that is no larger than JavaScripts `Number.MAX_SAFE_INTEGER` since
+            // any JSON-RPC client interacting with a JavaScript peer wouldn't be able to send
+            // integer values larger than that without JavaScript converting that integer to a
+            // float, losing precision, and therefore not being able to associate requests/responses
+            // with the correct id.
+            return jsonNode.asInt();
+        } else if (jsonNode.isTextual()) {
+            return jsonNode.asText();
+        } else if (jsonNode.isNull()) {
+            return null;
+        } else {
+            throw new IOException("A JSON-RPC ID according to the spec \"MUST contain a String, Number, or NULL value if included\". See §4 of https://www.jsonrpc.org/specification.");
+        }
+    }
+}

src/main/java/io/moderne/jsonrpc/JsonRpcMessage.java

@@ -21,5 +21,5 @@
 public abstract class JsonRpcMessage {
     private final String jsonrpc = "2.0";
 
-    public abstract String getId();
+    public abstract Object getId();
 }

src/main/java/io/moderne/jsonrpc/JsonRpcRequest.java

@@ -15,6 +15,7 @@
  */
 package io.moderne.jsonrpc;
 
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import io.moderne.jsonrpc.internal.SnowflakeId;
 import lombok.EqualsAndHashCode;
 import lombok.Value;
@@ -23,7 +24,9 @@
 @Value
 @EqualsAndHashCode(callSuper = false)
 public class JsonRpcRequest extends JsonRpcMessage {
-    String id;
+    @JsonDeserialize(using = JsonRpcIdDeserializer.class)
+    Object id;
+
     String method;
 
     /**

src/main/java/io/moderne/jsonrpc/JsonRpcSuccess.java

@@ -18,6 +18,7 @@
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.fasterxml.jackson.databind.cfg.ConstructorDetector;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
@@ -38,7 +39,11 @@ public class JsonRpcSuccess extends JsonRpcResponse {
             .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
             .setSerializationInclusion(JsonInclude.Include.NON_NULL);
 
-    String id;
+    /**
+     * String or Integer
+     */
+    @JsonDeserialize(using = JsonRpcIdDeserializer.class)
+    Object id;
 
     /**
      * No need for polymorphic deserialization here, since the result type will

src/test/java/io/moderne/jsonrpc/formatter/JsonMessageFormatterTest.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * 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
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 io.moderne.jsonrpc.formatter;
+
+import io.moderne.jsonrpc.JsonRpcMessage;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class JsonMessageFormatterTest {
+    JsonMessageFormatter formatter = new JsonMessageFormatter();
+
+    @Test
+    void idAsString() throws IOException {
+        assertThat(message("{\"jsonrpc\":\"2.0\",\"id\":\"1\"}").getId()).isEqualTo("1");
+    }
+
+    @Test
+    void idAsNumber() throws IOException {
+        assertThat(message("{\"jsonrpc\":\"2.0\",\"id\":1}").getId()).isEqualTo(1);
+    }
+
+    @Test
+    void idAsNull() throws IOException {
+        assertThat(message("{\"jsonrpc\":\"2.0\",\"id\":null}").getId()).isNull();
+    }
+
+    @Test
+    void idNotIncluded() throws IOException {
+        assertThat(message("{\"jsonrpc\":\"2.0\"}").getId()).isNull();
+    }
+
+    @Disabled
+    @Test
+    void idAsObjectFails() {
+        assertThatThrownBy(() -> message("{\"jsonrpc\":\"2.0\",\"id\":[]}").getId())
+                .hasMessageContaining("MUST");
+    }
+
+    private JsonRpcMessage message(String x) throws IOException {
+        return formatter.deserialize(new ByteArrayInputStream(
+                x.getBytes(formatter.getEncoding())
+        ));
+    }
+}