gmethvin opened a new issue #2767: ClassCastException when using custom JSON schema URL: https://github.com/apache/pulsar/issues/2767 #### Expected behavior It should be possible to create a custom JSON `Schema` that's not an implementation of `JSONSchema`, so I can use schemas from libraries like https://github.com/sksamuel/pulsar4s. #### Actual behavior I used the `pulsar4s` library, which creates custom schema implementations. I wrote some very simple code like this: ``` import com.sksamuel.pulsar4s._ import com.sksamuel.pulsar4s.circe._ import io.circe.generic.auto._ case class Foo(bar: String, baz: String) val client = PulsarClient("pulsar://localhost:6650") val topic = Topic("persistent://sample/standalone/ns1/b") val producer = client.producer[Foo](ProducerConfig(topic)) ``` Because pulsar4s creates schema instances that aren't `JSONSchema`, I get a `ClassCastException`: ``` java.util.concurrent.CompletionException: java.lang.ClassCastException: com.sksamuel.pulsar4s.circe.package$$anon$1 cannot be cast to org.apache.pulsar.client.impl.schema.JSONSchema at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) at java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:659) at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:632) at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474) at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1962) at org.apache.pulsar.client.impl.ConnectionPool.lambda$null$4(ConnectionPool.java:196) at java.util.concurrent.CompletableFuture.uniRun(CompletableFuture.java:705) at java.util.concurrent.CompletableFuture$UniRun.tryFire(CompletableFuture.java:687) at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474) at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1962) at org.apache.pulsar.client.impl.ClientCnx.handleConnected(ClientCnx.java:235) at org.apache.pulsar.common.api.PulsarDecoder.channelRead(PulsarDecoder.java:148) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) at org.apache.pulsar.shade.io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:310) at org.apache.pulsar.shade.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:284) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) at org.apache.pulsar.shade.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1414) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) at org.apache.pulsar.shade.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) at org.apache.pulsar.shade.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:945) at org.apache.pulsar.shade.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:146) at org.apache.pulsar.shade.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:645) at org.apache.pulsar.shade.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:580) at org.apache.pulsar.shade.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:497) at org.apache.pulsar.shade.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:459) at org.apache.pulsar.shade.io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:886) at org.apache.pulsar.shade.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.ClassCastException: com.sksamuel.pulsar4s.circe.package$$anon$1 cannot be cast to org.apache.pulsar.client.impl.schema.JSONSchema at org.apache.pulsar.client.impl.ProducerImpl.connectionOpened(ProducerImpl.java:874) at org.apache.pulsar.client.impl.ConnectionHandler.lambda$grabCnx$0(ConnectionHandler.java:65) at java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:656) ... 30 more ``` This is due to an unsafe cast at https://github.com/apache/pulsar/blob/v2.1.1-incubating/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerImpl.java#L874 This was also reported at https://github.com/sksamuel/pulsar4s/issues/6 #### System configuration **Pulsar version**: 2.1.1
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