RPC exception serialization

runtime/src/main/java/org/capnproto/RpcException.java

@@ -0,0 +1,52 @@
+package org.capnproto;
+
+public final class RpcException extends java.lang.Exception {
+
+    public enum Type {
+        UNKNOWN,
+        UNIMPLEMENTED,
+        FAILED
+    }
+
+    private Type type;
+
+    public RpcException(Type type, String message) {
+        super(message);
+        this.type = type;
+    }
+
+    public final Type getType() {
+        return type;
+    }
+
+    public static RpcException unimplemented(String message) {
+        return new RpcException(Type.UNIMPLEMENTED, message);
+    }
+
+    public static RpcException failed(String message) {
+        return new RpcException(Type.FAILED, message);
+    }
+
+    static void fromException(Throwable exc, RpcProtocol.Exception.Builder builder) {
+        builder.setReason(exc.getMessage());
+        builder.setType(RpcProtocol.Exception.Type.FAILED);
+    }
+
+    static RpcException toException(RpcProtocol.Exception.Reader reader) {
+        var type = RpcException.Type.UNKNOWN;
+
+        switch (reader.getType()) {
+            case UNIMPLEMENTED:
+                type = RpcException.Type.UNIMPLEMENTED;
+                break;
+            case FAILED:
+                type = RpcException.Type.FAILED;
+                break;
+            case DISCONNECTED:
+            case OVERLOADED:
+            default:
+                break;
+        }
+        return new RpcException(type, reader.getReason().toString());
+    }
+}