From 194de936c56375345d4677b0c9063517bdec6a79 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vilius=20Panev=C4=97=C5=BEys?= <vilius@elitnet.lt>
Date: Thu, 30 Oct 2025 14:37:13 +0200
Subject: [PATCH] Add support for extensible enum decoding

---
 .../java/net/gcdc/asn1/uper/EnumCoder.java    | 40 +++++++++++--------
 .../net/gcdc/asn1/uper/EnumCoderTest.java     | 37 +++++++++++++++++
 2 files changed, 61 insertions(+), 16 deletions(-)
 create mode 100644 asn1-uper/src/test/java/net/gcdc/asn1/uper/EnumCoderTest.java

diff --git a/asn1-uper/src/main/java/net/gcdc/asn1/uper/EnumCoder.java b/asn1-uper/src/main/java/net/gcdc/asn1/uper/EnumCoder.java
index fb30cef..8a3f6dd 100644
--- a/asn1-uper/src/main/java/net/gcdc/asn1/uper/EnumCoder.java
+++ b/asn1-uper/src/main/java/net/gcdc/asn1/uper/EnumCoder.java
@@ -64,23 +64,31 @@ class EnumCoder implements Decoder, Encoder {
         AnnotationStore annotations = new AnnotationStore(classOfT.getAnnotations(),
                 extraAnnotations);
         UperEncoder.logger.debug("ENUM");
-        if (UperEncoder.hasExtensionMarker(annotations)) {
-            boolean extensionPresent = bitbuffer.get();
-            UperEncoder.logger.debug("with extension marker, {}", extensionPresent ? "present" : "absent");
-            if (extensionPresent) {
-                throw new UnsupportedOperationException(
-                        "choice extension is not implemented yet");
+        T value = null;
+        if (UperEncoder.hasExtensionMarker(annotations)
+                && bitbuffer.get()) {   // extension present
+            UperEncoder.logger.debug("with extension marker, extension present");
+            boolean isGreaterThan64 = bitbuffer.get();
+            // The decoded value is discarded - no way to return an undefined enum value, just consuming the bits.
+            if (!isGreaterThan64) {
+                UperEncoder.decodeConstrainedInt(bitbuffer, UperEncoder.newRange(0, uintMax(6), false));
             } else {
-                // We already consumed the bit, keep processing as if there were no extension.
+                int numOctets = (int) UperEncoder.decodeLengthDeterminant(bitbuffer);
+                UperEncoder.decodeConstrainedInt(bitbuffer, UperEncoder.newRange(0, uintMax(numOctets * 8), false));
             }
+        } else {
+            T[] enumValues = classOfT.getEnumConstants();
+            int index = (int) UperEncoder.decodeConstrainedInt(bitbuffer,
+                    UperEncoder.newRange(0, enumValues.length - 1, false));
+            if (index > enumValues.length - 1) { throw new IllegalArgumentException(
+                    "decoded enum index " + index + " is larger than number of elements (0.."
+                            + enumValues.length + ") in " + classOfT.getName()); }
+            value = enumValues[index];
         }
-        T[] enumValues = classOfT.getEnumConstants();
-        int index = (int) UperEncoder.decodeConstrainedInt(bitbuffer,
-                UperEncoder.newRange(0, enumValues.length - 1, false));
-        if (index > enumValues.length - 1) { throw new IllegalArgumentException(
-                "decoded enum index " + index + " is larger then number of elements (0.."
-                        + enumValues.length + ") in " + classOfT.getName()); }
-        T value = enumValues[index];
-        return value;        }
+        return value;
+    }
 
-}
\ No newline at end of file
+    private static int uintMax(int bits) {
+        return (int) Math.pow(2, bits) - 1;
+    }
+}
diff --git a/asn1-uper/src/test/java/net/gcdc/asn1/uper/EnumCoderTest.java b/asn1-uper/src/test/java/net/gcdc/asn1/uper/EnumCoderTest.java
new file mode 100644
index 0000000..0f147df
--- /dev/null
+++ b/asn1-uper/src/test/java/net/gcdc/asn1/uper/EnumCoderTest.java
@@ -0,0 +1,37 @@
+package net.gcdc.asn1.uper;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+import org.junit.Test;
+
+import net.gcdc.asn1.datatypes.HasExtensionMarker;
+
+public class EnumCoderTest {
+    @HasExtensionMarker
+    private enum ConstructedType {
+        CHOICE(1), SEQUENCE(2), SET(3), SEQUENCE_OF(4), SET_OF(5);
+
+        private final int value;
+
+        private ConstructedType(int value) {
+            this.value = value;
+        }
+    }
+
+    @Test
+    public void extensibleNoExt() {
+        assertEquals(ConstructedType.SEQUENCE,
+                UperEncoder.decode(new byte[] {0x10}, ConstructedType.class));
+    }
+
+    @Test
+    public void extensibleExtSmall() {
+        assertNull(UperEncoder.decode(new byte[] {(byte) 0xA9}, ConstructedType.class));
+    }
+
+    @Test
+    public void extensibleWithLength() {
+        assertNull(UperEncoder.decode(new byte[] {(byte) 0xC0, 0x50, 0x00}, ConstructedType.class));
+    }
+}