Add error codes to distinguish invalid requests and server errors

API:ADDITION

Signed-off-by: Trumeet <yuuta@yuuta.moe>

4 files changed, 35 insertions, 8 deletions

diff --git a/README.md b/README.md
index c68122f..e1284a6 100644
--- a/README.md
+++ b/README.md
@@ -219,10 +219,16 @@ codes, all faulty WebSocket requests will receive error in the following format:
 {
   "type": "error",
   "id": 1,
+  "code": 500,
   "message": "Error message. Not machine-readable."
 }
 ```
 
+Parameters:
+
+* `.code` (int, HTTP status codes, always present): The machine-readable error code (e. g. 400 for Bad Request).
+* `.message` (string, any, always present): The human-readable error message.
+
 **`.type` and `.id` are included in every request / response, except for further noticed. Thus,
 this document excludes them from the parameter lists.**
 
diff --git a/src/main/java/moe/ymc/acron/net/WSFrameHandler.java b/src/main/java/moe/ymc/acron/net/WSFrameHandler.java
index c578f2e..713d433 100644
--- a/src/main/java/moe/ymc/acron/net/WSFrameHandler.java
+++ b/src/main/java/moe/ymc/acron/net/WSFrameHandler.java
@@ -1,5 +1,6 @@
 package moe.ymc.acron.net;
 
+import com.google.gson.JsonParseException;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.SimpleChannelInboundHandler;
 import io.netty.handler.codec.http.websocketx.*;
@@ -57,10 +58,18 @@ public class WSFrameHandler extends SimpleChannelInboundHandler<WebSocketFrame>
 
         final ClientIdentification identification = ctx.channel().attr(Attributes.ID).get();
         final ClientConfiguration configuration = ctx.channel().attr(Attributes.CONFIGURATION).get();
-        int id = -2;
+        int id;
+        final Request request;
         try {
-            final Request request = Serializer.deserialize(frame);
+            request = Serializer.deserialize(frame);
             id = request.getId();
+        } catch (JsonParseException | IllegalArgumentException | IllegalStateException e) {
+            ctx.channel().writeAndFlush(
+                    Serializer.serialize(new EventError(-2, EventError.Code.BAD_REQUEST.value, e.getMessage()))
+            );
+            return;
+        }
+        try {
             if (request instanceof final ReqCmd reqCmd) {
                 LOGGER.info("Client {} executed a command: `{}`.",
                         identification.client().id(),
@@ -90,7 +99,9 @@ public class WSFrameHandler extends SimpleChannelInboundHandler<WebSocketFrame>
                             "This may just be a malformed request. " +
                             "It is reported to the client.",
                     e);
-            ctx.channel().writeAndFlush(Serializer.serialize(new EventError(id, e.getMessage())));
+            ctx.channel().writeAndFlush(
+                    Serializer.serialize(new EventError(id, EventError.Code.SERVER_ERROR.value, e.getMessage()))
+            );
         }
     }
 
diff --git a/src/main/java/moe/ymc/acron/s2c/response/EventError.java b/src/main/java/moe/ymc/acron/s2c/response/EventError.java
index 48d2683..d2a03c3 100644
--- a/src/main/java/moe/ymc/acron/s2c/response/EventError.java
+++ b/src/main/java/moe/ymc/acron/s2c/response/EventError.java
@@ -5,6 +5,16 @@ import moe.ymc.acron.s2c.Event;
 import org.jetbrains.annotations.Nullable;
 
 public record EventError(@SerializedName("id") int id,
+                         @SerializedName("code") int code,
                          @SerializedName("message") @Nullable String message)
         implements Event {
+    public enum Code {
+        SERVER_ERROR(500),
+        BAD_REQUEST(400);
+
+        public final int value;
+        Code(int value) {
+            this.value = value;
+        }
+    }
 }
diff --git a/src/main/java/moe/ymc/acron/serialization/Serializer.java b/src/main/java/moe/ymc/acron/serialization/Serializer.java
index 900d6fc..6d06388 100644
--- a/src/main/java/moe/ymc/acron/serialization/Serializer.java
+++ b/src/main/java/moe/ymc/acron/serialization/Serializer.java
@@ -2,6 +2,7 @@ package moe.ymc.acron.serialization;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonParseException;
 import com.google.gson.typeadapters.RuntimeTypeAdapterFactory;
 import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
 import moe.ymc.acron.c2s.ReqCmd;
@@ -14,13 +15,13 @@ import org.jetbrains.annotations.NotNull;
 
 public class Serializer {
     @NotNull
-    public static Request deserialize(@NotNull TextWebSocketFrame frame) {
+    public static Request deserialize(@NotNull TextWebSocketFrame frame)
+            throws JsonParseException, IllegalArgumentException, IllegalStateException {
         final String text = frame.text();
         final RuntimeTypeAdapterFactory<Request> adapter =
                 RuntimeTypeAdapterFactory.of(Request.class, "type")
                         .registerSubtype(ReqSetConfig.class, "set_config")
-                        .registerSubtype(ReqCmd.class, "cmd")
-                ;
+                        .registerSubtype(ReqCmd.class, "cmd");
         final Gson gson = new GsonBuilder()
                 .registerTypeAdapter(ReqSetConfig.class, new ReqSetConfig.ReqSetConfigDeserializer())
                 .registerTypeAdapter(ReqSetConfig.Vec3d.class, new ReqSetConfig.Vec3d.Vec3dDeserializer())
@@ -46,8 +47,7 @@ public class Serializer {
                         .registerSubtype(EventLagging.class, "lagging")
                         .registerSubtype(EventCmdDenied.class, "cmd_denied")
                         .registerSubtype(EventError.class, "error")
-                        .registerSubtype(EventOk.class, "ok")
-                ;
+                        .registerSubtype(EventOk.class, "ok");
         final Gson gson = new GsonBuilder()
                 .registerTypeAdapterFactory(adapter)
                 .create();