Add workaround for Netty issue which will be fixed by Netty PR 14071

pulsar-common/src/main/java/org/apache/pulsar/common/protocol/ByteBufPair.java

@@ -133,12 +133,23 @@ public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise)
             }
         }
 
-        // .asReadOnly() is needed to prevent SslHandler from modifying the input buffers.
+        // readonly buffer is needed to prevent SslHandler from modifying the input buffers.
         private static ByteBuf readOnlyRetainedDuplicate(ByteBuf buf) {
-            // If the buffer is already read-only, .asReadOnly() will return the same buffer.
-            // That's why the additional .retainedDuplicate() is needed to ensure that the returned buffer
-            // has independent readIndex and writeIndex.
-            return buf.asReadOnly().retainedDuplicate();
+            if (buf.readableBytes() == 0) {
+                return Unpooled.EMPTY_BUFFER;
+            }
+
+            // using "buf.asReadOnly().retainedDuplicate()" would be preferred here, however it's not supported
+            // by SslHandler until the fix https://github.com/netty/netty/pull/14071 is released.
+            // There's a need to use ".retainedDuplicate()" together with ".asReadOnly()".
+            // If the buffer is already read-only, .asReadOnly() will return the current buffer. This would be a problem
+            // since a duplicate is needed so that the buffer has independent readIndex and writeIndex state.
+            //
+            // The alternative workaround is to use "Unpooled.unmodifiableBuffer(buf).retain()". This is a deprecated
+            // method, but it will achieve the same result with the additional detail that it won't require the PR 14071
+            // in SslHandler to be released. The reason for this is that isWritable methods return false for an
+            // unwrapped ReadOnlyByteBuf instance.
+            return Unpooled.unmodifiableBuffer(buf).retain();
         }
     }
 }