(CU-86b8v3uxa) Fix metadata extraction for ACK followed by MT Output (#299)

When an ACK (service 21) message has an appended MT with block 2 Output,
the metadata (identifier, direction, MIR, UUID, UETR, etc.) is now
extracted from the appended MT instead of defaulting to ACK.
For ACK followed by MT Input the existing behavior is preserved.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: zubri

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Prowide Core - CHANGELOG
 
+### 10.3.11 - SNAPSHOT
+  * Fix: `MtSwiftMessage` created from ACK (service 21) followed by MT with block 2 Output now extracts the message type and metadata from the appended MT instead of defaulting to ACK
+
 #### 10.3.10 - March 2026
   * Migrated deprecated `StringUtils` methods to `Strings.CS` equivalents (equals, startsWith, endsWith, contains, replace, indexOf, lastIndexOf, remove, removeEnd)
   * (PW-3126) Fixed DN to BIC extraction in `DistinguishedName` to include the branch code from the `ou` component

src/main/java/com/prowidesoftware/swift/model/MtSwiftMessage.java

@@ -81,8 +81,9 @@ public MtSwiftMessage(final String fin) {
      * content will be stored in the message attribute but the metadata (such as the message type) will be extracted
      * from the first message only.
      *
-     * <p>Notice that if an ACK/NAK message is used as parameter, this object will represent the ACK/NAK.
-     * Even if the original message is attached after the service 21 messages.
+     * <p>If an ACK/NAK (service 21) message is used as parameter and includes an appended MT with block 2 Output,
+     * the metadata is extracted from the appended MT. For ACK/NAK with an appended MT with block 2 Input or without
+     * an appended MT, the message is represented as ACK/NAK.
      *
      * <p>File format is set to {@link FileFormat#FIN}
      *
@@ -268,25 +269,46 @@ protected void updateFromMessage(MessageMetadataStrategy metadataStrategy) throw
      * This method extracts the metadata from the model and sets the internal attributes accordingly, using the
      * provided {@link MessageMetadataStrategy}. And on top of that, sets additional attributes such as the
      * last modified date, checksum, and MUR.
-     *
+     * <p>
+     * For ACK/NAK (service 21) messages with an appended MT that has block 2 Output, the metadata is extracted
+     * from the appended MT rather than from the ACK/NAK prefix.
      *
      * @param model            the SwiftMessage model to extract metadata from
      * @param metadataStrategy a strategy implementation to extract the metadata from the model
      */
     private void updateAttributes(final SwiftMessage model, final MessageMetadataStrategy metadataStrategy) {
-        applyStrategy(model, metadataStrategy);
+        // for ACK/NAK with an appended MT Output, use the appended MT as the effective model for metadata extraction
+        final SwiftMessage effectiveModel = resolveEffectiveModel(model);
+
+        applyStrategy(effectiveModel, metadataStrategy);
 
         setFileFormat(FileFormat.FIN);
         setLastModified(Calendar.getInstance());
-        setMur(model.getMUR());
-        setPde(model.getPDE());
-        setPdm(model.getPDM());
-        setMir(model.getMIR());
-        if (model.getBlock2() != null) {
-            setUuid(model.getUUID());
+        setMur(effectiveModel.getMUR());
+        setPde(effectiveModel.getPDE());
+        setPdm(effectiveModel.getPDM());
+        setMir(effectiveModel.getMIR());
+        if (effectiveModel.getBlock2() != null) {
+            setUuid(effectiveModel.getUUID());
+        }
+        setDirection(effectiveModel.getDirection());
+        setUetr(effectiveModel.getUETR());
+    }
+
+    /**
+     * For ACK/NAK (service 21) messages with an appended MT that has block 2 Output, returns the appended MT model.
+     * Otherwise, returns the original model unchanged.
+     */
+    private SwiftMessage resolveEffectiveModel(final SwiftMessage model) {
+        if (model.isServiceMessage21() && model.getUnparsedTextsSize() > 0) {
+            final SwiftMessage original = model.getUnparsedTexts().getTextAsMessage(0);
+            if (original != null
+                    && original.getBlock2() != null
+                    && original.getBlock2().isOutput()) {
+                return original;
+            }
         }
-        setDirection(model.getDirection());
-        setUetr(model.getUETR());
+        return model;
     }
 
     /**

src/main/java/com/prowidesoftware/swift/model/SwiftMessageUtils.java

@@ -357,7 +357,9 @@ public static String receiver(final SwiftMessage m) {
      * Get a string in the form of businessprocess.messagetype.variant
      *
      * <p>
-     * For acknowledges and negative acknowledges, the identifier is fixed to "ACK" and "NAK" respectively.
+     * For acknowledges and negative acknowledges with an appended MT with block 2 Input, the identifier is fixed
+     * to "ACK" and "NAK" respectively. However, if the appended MT has block 2 Output, the identifier is extracted
+     * from the appended MT message type.
      *
      * @return a string with the MT message type identification
      * @since 9.3.19
@@ -366,8 +368,16 @@ public static String identifier(final SwiftMessage m) {
         if (m == null) {
             return null;
         }
-        // for ACK/NAK messages, we return the fixed identifiers
+        // for ACK/NAK messages with an appended MT with block 2 Output, we extract the identifier from the MT
         if (m.isServiceMessage21()) {
+            if (m.getUnparsedTextsSize() > 0) {
+                final SwiftMessage original = m.getUnparsedTexts().getTextAsMessage(0);
+                if (original != null
+                        && original.getBlock2() != null
+                        && original.getBlock2().isOutput()) {
+                    return identifier(original);
+                }
+            }
             if (m.isAck()) {
                 return MtSwiftMessage.IDENTIFIER_ACK;
             } else if (m.isNack()) {

src/test/java/com/prowidesoftware/swift/model/MtSwiftMessageTest.java

@@ -70,7 +70,8 @@ public void testParseAck() {
     }
 
     @Test
-    public void testParseAckWithOriginalMessageCopy() {
+    public void testParseAckWithOriginalMessageCopyInput() {
+        // ACK followed by MT with block 2 Input -> identifier should be ACK
         String fin =
                 "{1:F21AAAALT2XAXXX0000000000}{4:{177:1903250612}{451:0}}{1:F01AAAALT2XAXXX1012000002}{2:I103BBBBARZZXXXXN}{4:\n"
                         + ":20:TEST\n"
@@ -101,6 +102,40 @@ public void testParseAckWithOriginalMessageCopy() {
         // the original message has an amount, we extract it
         assertEquals(new BigDecimal("23453"), mt.getAmount());
         assertEquals("USD", mt.getCurrency());
+
+        // ACK followed by MT Input keeps the ACK identifier
+        assertEquals("ACK", mt.getIdentifier());
+    }
+
+    @Test
+    public void testParseAckWithOriginalMessageCopyOutput() {
+        // ACK followed by MT with block 2 Output -> metadata should be extracted from the appended MT
+        String fin =
+                "{1:F21AAAALT2XAXXX0000000000}{4:{177:1903250612}{451:0}}{1:F01BBBBARZZAXXX1012000002}{2:O1031200190903AAAALT2XAXXX00000000001903250612N}{3:{121:d]8b27e4-5891-4649-b1b8-22a3c0985ab2}}{4:\n"
+                        + ":20:TEST-OUT\n"
+                        + ":32A:190903EUR12345,\n"
+                        + "-}";
+        MtSwiftMessage mt = MtSwiftMessage.parse(fin);
+
+        // identifier and message type are extracted from the appended MT, not "ACK"
+        assertEquals("fin.103", mt.getIdentifier());
+        assertEquals("103", mt.getMessageType());
+
+        // reference is extracted from the appended MT
+        assertEquals("TEST-OUT", mt.getReference());
+
+        // direction is resolved from the appended MT's block 2 Output (incoming)
+        assertEquals(MessageIOType.incoming, mt.getDirection());
+
+        // value date from the appended MT
+        Calendar valueDate = mt.getValueDate();
+        assertEquals(2019, valueDate.get(Calendar.YEAR));
+        assertEquals(Calendar.SEPTEMBER, valueDate.get(Calendar.MONTH));
+        assertEquals(3, valueDate.get(Calendar.DAY_OF_MONTH));
+
+        // amount from the appended MT
+        assertEquals(new BigDecimal("12345"), mt.getAmount());
+        assertEquals("EUR", mt.getCurrency());
     }
 
     @Test