Do not change writerIndex when decode DnsPtrRecord, backport netty/netty#5760

Author: slandelle

netty-bp/codec-dns/src/main/java/io/netty/handler/codec/dns/DefaultDnsRecordDecoder.java

@@ -90,10 +90,10 @@ protected DnsRecord decodeRecord(
 
         if (type == DnsRecordType.PTR) {
             in.setIndex(offset, offset + length);
-            return new DefaultDnsPtrRecord(name, dnsClass, timeToLive, decodeName0(in));
+            return new DefaultDnsPtrRecord(name, dnsClass, timeToLive, decodeName0(in.slice(offset, length)));
         }
         return new DefaultDnsRawRecord(
-                name, type, dnsClass, timeToLive, in.duplicate().setIndex(offset, offset + length).retain());
+                name, type, dnsClass, timeToLive, in.slice(offset, length).retain());
     }
 
     /**

netty-bp/codec-dns/src/test/java/io/netty/handler/codec/dns/DefaultDnsRecordDecoderTest.java

@@ -17,10 +17,10 @@
 
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
-import io.netty.util.internal.StringUtil;
-import org.junit.Assert;
 import org.junit.Test;
 
+import static org.junit.Assert.assertEquals;
+
 public class DefaultDnsRecordDecoderTest {
 
     @Test
@@ -63,7 +63,27 @@ public void testDecodeEmptyNameFromExtraZeroes() {
     private static void testDecodeName(String expected, ByteBuf buffer) {
         try {
             DefaultDnsRecordDecoder decoder = new DefaultDnsRecordDecoder();
-            Assert.assertEquals(expected, decoder.decodeName(buffer));
+            assertEquals(expected, decoder.decodeName0(buffer));
+        } finally {
+            buffer.release();
+        }
+    }
+
+    @Test
+    public void testDecodePtrRecord() throws Exception {
+        DefaultDnsRecordDecoder decoder = new DefaultDnsRecordDecoder();
+        ByteBuf buffer = Unpooled.buffer().writeByte(0);
+        int readerIndex = buffer.readerIndex();
+        int writerIndex = buffer.writerIndex();
+        try {
+            DnsPtrRecord record = (DnsPtrRecord) decoder.decodeRecord(
+                    "netty.io", DnsRecordType.PTR, DnsRecord.CLASS_IN, 60, buffer, 0, 1);
+            assertEquals("netty.io.", record.name());
+            assertEquals(DnsRecord.CLASS_IN, record.dnsClass());
+            assertEquals(60, record.timeToLive());
+            assertEquals(DnsRecordType.PTR, record.type());
+            assertEquals(readerIndex, buffer.readerIndex());
+            assertEquals(writerIndex, buffer.writerIndex());
         } finally {
             buffer.release();
         }