Only generate non-constant header fields in wrapAndApply method. Fixes #602 for java only

Author: Kyle D Kavanagh

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -2272,19 +2272,42 @@ private CharSequence generateEncoderFlyweightCode(final String className, final
             "    }\n\n",
             className,
             mutableBuffer);
-
-        final String wrapAndApplyHeaderMethod = String.format(
+        final String indent = "            ";
+        String wrapAndApplyHeaderMethodFmtString =
             "    public %1$s wrapAndApplyHeader(\n" +
             "        final %2$s buffer, final int offset, final %3$s headerEncoder)\n" +
             "    {\n" +
             "        headerEncoder\n" +
-            "            .wrap(buffer, offset)\n" +
-            "            .blockLength(BLOCK_LENGTH)\n" +
-            "            .templateId(TEMPLATE_ID)\n" +
-            "            .schemaId(SCHEMA_ID)\n" +
-            "            .version(SCHEMA_VERSION);\n\n" +
+            "            .wrap(buffer, offset)";
+        for (final Token headerToken : ir.headerStructure().tokens())
+        {
+            if (!headerToken.isConstantEncoding())
+            {
+                final String fieldName = headerToken.name();
+                switch (fieldName)
+                {
+                    case "blockLength":
+                        wrapAndApplyHeaderMethodFmtString += '\n' + indent + ".blockLength(BLOCK_LENGTH)";
+                        break;
+                    case "templateId":
+                        wrapAndApplyHeaderMethodFmtString += '\n' + indent + ".templateId(TEMPLATE_ID)";
+                        break;
+                    case "schemaId":
+                        wrapAndApplyHeaderMethodFmtString += '\n' + indent + ".schemaId(SCHEMA_ID)";
+                        break;
+                    case "version":
+                        wrapAndApplyHeaderMethodFmtString += '\n' + indent + ".version(SCHEMA_VERSION)";
+                        break;
+                }
+            }
+        }
+
+
+        wrapAndApplyHeaderMethodFmtString += ";\n" +
             "        return wrap(buffer, offset + %3$s.ENCODED_LENGTH);\n" +
-            "    }\n\n",
+            "    }\n\n";
+        final String wrapAndApplyHeaderMethod = String.format(
+            wrapAndApplyHeaderMethodFmtString,
             className,
             mutableBuffer,
             formatClassName(ir.headerStructure().tokens().get(0).applicableTypeName() + "Encoder"));

sbe-tool/src/test/java/uk/co/real_logic/sbe/xml/BasicSchemaFileTest.java

@@ -33,6 +33,13 @@ public void shouldHandleBasicFile()
         parse(TestUtil.getLocalResource("basic-schema.xml"), ParserOptions.DEFAULT);
     }
 
+    @Test
+    public void shouldHandleConstantHeaderField()
+        throws Exception
+    {
+        parse(TestUtil.getLocalResource("basic-schema-constant-header-field.xml"), ParserOptions.DEFAULT);
+    }
+
     @Test
     public void shouldHandleBasicFileWithGroup()
         throws Exception

sbe-tool/src/test/resources/basic-schema-constant-header-field.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<messageSchema package="SBE tests"
+               id="2"
+               semanticVersion="5.2"
+               description="Unit Test"
+               byteOrder="littleEndian">
+    <types>
+        <type name="Symbol" description="Symbol" length="20" primitiveType="char" semanticType="char"/>
+        <composite name="messageHeader" description="Message identifiers and length of message root">
+            <type name="blockLength" primitiveType="uint16"/>
+            <type name="templateId" primitiveType="uint16"/>
+            <type name="schemaId" primitiveType="uint16" presence="constant">1</type>
+            <type name="version" primitiveType="uint16"/>
+        </composite>
+    </types>
+    <message name="TestMessage50001" id="50001" description="TestMessage" blockLength="16">
+        <field name="Tag40001" id="40001" type="uint32" semanticType="int"/>
+    </message>
+</messageSchema>