objecttrouve opened a new issue #11562:
URL: https://github.com/apache/pulsar/issues/11562


   ### Describe the bug
   
   I'm trying to configure a `CryptoKeyReader` with a 
[`FlinkPulsarSource`](https://github.com/streamnative/pulsar-flink#source).
   
   The [Pulsar 
docs](https://pulsar.apache.org/docs/en/client-libraries-java/#configure-reader)
 suggest you can configure such a crypto key reader by passing a value for 
property called `cryptoKeyReader`.
        
[Here's](https://github.com/streamnative/pulsar-flink/blob/a38b8095d3bd96470af07f4fd20d830983c0a07c/pulsar-flink-connector/src/main/java/org/apache/flink/streaming/connectors/pulsar/internal/ReaderThread.java#L126)
 where those properties are used (on creating the Flink Pulsar source).
   
   The evaluating code tries to _deserialize_ a config object from the property 
map.  
   But what would be the value in such a map? It's  _not_  the class name, as I 
naively assumed. 
   
   If I understand the code correctly, the value doesn't even matter, because 
the object mapper tries to instantiate an  _interface_. Resulting in the 
following error:  
   
    ```com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot 
construct instance of `org.apache.pulsar.client.api.CryptoKeyReader` (no 
Creators, like default constructor, exist): abstract types either need to be 
mapped to concrete types, have custom deserializer, or contain additional type 
information```
   
   [I also asked about this in the `flink-connector` channel on 
Slack.](https://apache-pulsar.slack.com/archives/CA678TN9G/p1627910055002100?thread_ts=1627909730.002000&cid=CA678TN9G)
 But unless I'm missing something, I think it's a bug in Pulsar. Or at least a 
misleading documentation. Raising this issue to clarify.
   
   (If the calling code was under my control, I could, of course, just use the 
[setter for the crypto key 
reader](https://github.com/apache/pulsar/blob/ce9a6d2392fdf9f3b50afa37f4d871d5360362ca/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ReaderBuilderImpl.java#L153).
 I might do a PR about it here or in the [`pulsar-flink` 
project](https://github.com/streamnative/pulsar-flink). However, I want to 
clarify the intended usage first.) 
   
   
   ### To Reproduce
   
   
[Here](https://github.com/objecttrouve/pulsar/blob/90f35be79735a9a53add4093d0a403e326761403/pulsar-client/src/test/java/org/apache/pulsar/client/impl/BuildersTest.java#L121)'s
 a unit test illustrating what I was trying to do: 
   ```
   @SuppressWarnings("unused")
   public static class MyCryptoKeyReader implements CryptoKeyReader {
   
        @Override
        public EncryptionKeyInfo getPublicKey(String keyName, Map<String, 
String> metadata) {
                return null;
        }
   
        @Override
        public EncryptionKeyInfo getPrivateKey(String keyName, Map<String, 
String> metadata) {
                return null;
        }
   }
   
        @Ignore("Illustrates wrong usage.")
        @Test
        public void readerBuilderLoadConfWithCryptoKeyReaderClassValueTest() 
throws Exception {
   
                @Cleanup
                PulsarClient client = 
PulsarClient.builder().serviceUrl("pulsar://localhost:6650").build();
   
                Map<String, Object> config = new HashMap<>();
   
                /*
                * This is what I first assumed.
                * This ISN'T how it works!
                * The `loadConf` method expects a _serialized_ 
`CryptoKeyReader` at this point.
                */
   
                config.put("cryptoKeyReader", 
"org.apache.pulsar.client.impl.BuildersTest.MyCryptoKeyReader");
   
                ReaderBuilderImpl<byte[]> builder = (ReaderBuilderImpl<byte[]>) 
client.newReader()
                .loadConf(config);
   
                Class<?> clazz = builder.getClass();
                Field conf = clazz.getDeclaredField("conf");
                conf.setAccessible(true);
                Object obj = conf.get(builder);
                assertTrue(obj instanceof ReaderConfigurationData);
                //noinspection rawtypes
                assertTrue(((ReaderConfigurationData)obj).getCryptoKeyReader() 
instanceof MyCryptoKeyReader);
   
   }
   ```
   
   It reproduces the error mentioned above.
   
   
   ### Expected behavior
   
   I inspected a property where I could pass a class name of a 
`CryptoKeyReader` implementation with a no-arg constructor, which would be 
instantiated on loading the config.
   
   
   ### Desktop (please complete the following information):
   ```
   uname -a
   Linux otto 5.4.0-80-generic #90-Ubuntu SMP Fri Jul 9 22:49:44 UTC 2021 
x86_64 x86_64 x86_64 GNU/Linux
   ```
   
   ### Additional context
   
   [Same question in the Pulsar 
Slack.](https://apache-pulsar.slack.com/archives/CA678TN9G/p1627910055002100?thread_ts=1627909730.002000&cid=CA678TN9G)
   


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