From 8af808ca64779bf722e196fa04e29a4180bad845 Mon Sep 17 00:00:00 2001
From: Zach Bray <zachbray@googlemail.com>
Date: Wed, 27 Nov 2024 13:07:37 +0000
Subject: [PATCH] [Java] Preserve byte order throughout IR transformations.

Previously, the IrDecoder looked at the message header's BEGIN_COMPOSITE
token to determine byte order; however, IrEncoder does not write the
schema's byte order on tokens like these. Now, the IrDecoder finds the
first real ENCODING token and reads the byte order from that.
---
 .../uk/co/real_logic/sbe/ir/IrDecoder.java    | 11 ++++++-
 .../sbe/ir/BasicXmlIrGenerationTest.java      | 30 ++++++++++++++++++-
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/sbe-tool/src/main/java/uk/co/real_logic/sbe/ir/IrDecoder.java b/sbe-tool/src/main/java/uk/co/real_logic/sbe/ir/IrDecoder.java
index b7da2ead1c..4db9e04a99 100644
--- a/sbe-tool/src/main/java/uk/co/real_logic/sbe/ir/IrDecoder.java
+++ b/sbe-tool/src/main/java/uk/co/real_logic/sbe/ir/IrDecoder.java
@@ -126,7 +126,16 @@ public Ir decode()
             i = captureHeader(tokens);
         }
 
-        final ByteOrder byteOrder = !tokens.isEmpty() ? tokens.get(0).encoding().byteOrder() : null;
+        ByteOrder byteOrder = null;
+        for (int j = 0; j < tokens.size(); j++)
+        {
+            if (tokens.get(j).signal() == Signal.ENCODING)
+            {
+                byteOrder = tokens.get(j).encoding().byteOrder();
+                break;
+            }
+        }
+
         final Ir ir = new Ir(
             irPackageName, irNamespaceName, irId, irVersion, null, semanticVersion, byteOrder, irHeader);
 
diff --git a/sbe-tool/src/test/java/uk/co/real_logic/sbe/ir/BasicXmlIrGenerationTest.java b/sbe-tool/src/test/java/uk/co/real_logic/sbe/ir/BasicXmlIrGenerationTest.java
index 7f89f2e18d..f3509f7d97 100644
--- a/sbe-tool/src/test/java/uk/co/real_logic/sbe/ir/BasicXmlIrGenerationTest.java
+++ b/sbe-tool/src/test/java/uk/co/real_logic/sbe/ir/BasicXmlIrGenerationTest.java
@@ -13,15 +13,17 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package uk.co.real_logic.sbe.ir;
 
-import org.junit.jupiter.api.Test;
 import uk.co.real_logic.sbe.PrimitiveType;
 import uk.co.real_logic.sbe.xml.IrGenerator;
 import uk.co.real_logic.sbe.xml.MessageSchema;
 import uk.co.real_logic.sbe.xml.ParserOptions;
+import org.junit.jupiter.api.Test;
 
 import java.io.InputStream;
+import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.util.List;
 
@@ -308,4 +310,30 @@ void shouldGenerateIrForMessageWithVariableLengthFieldWithEmbeddedLength() throw
             assertThat(tokens.get(dataEncIdx).encoding().primitiveType(), is(PrimitiveType.CHAR));
         }
     }
+
+    @Test
+    void shouldRegenerateIrWithSameByteOrder() throws Exception
+    {
+        try (InputStream in = getLocalResource("example-bigendian-test-schema.xml"))
+        {
+            final MessageSchema schema = parse(in, ParserOptions.DEFAULT);
+            final IrGenerator generator = new IrGenerator();
+            final Ir firstIr = generator.generate(schema);
+            final ByteBuffer firstIrOutputBuffer = ByteBuffer.allocate(8 * 1024);
+
+            final int length;
+            try (IrEncoder firstIrEncoder = new IrEncoder(firstIrOutputBuffer, firstIr))
+            {
+                length = firstIrEncoder.encode();
+            }
+
+            final Ir secondIr;
+            try (IrDecoder firstIrDecoder = new IrDecoder(firstIrOutputBuffer.slice(0, length)))
+            {
+                secondIr = firstIrDecoder.decode();
+            }
+
+            assertThat(secondIr.byteOrder(), is(firstIr.byteOrder()));
+        }
+    }
 }