Status

Current state: Under Discussion

Discussion thread: here

JIRA: here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Aims to add a corresponding validator to a configuration where a validator is missing.
so that the program finds these incorrect configurations during initialization.

Public Interfaces

Public classes that involve changes

1. ConfigDef
   Add a new validator NonNullAndEmptyString  to the ConfigDef class.
   
   
2. SslClientAuth
   SslClientAuth provides a static method names()  to get a list of all enumeration constant lowercase names.
   
   
3. BrokerSecurityConfigs
   Provides a new validator SaslEnabledMechanismsValidator  for validating the sasl.enabled.mechanisms  parameter.
   
   
4. CompressionType
   CompressionType provides a static method names()  to get a list of all enumeration constant lowercase names
   
   

The implementation class of AbstractConfig involved in changes

The methods and classes in bold below all need to be newly created.

1. AdminClientConfig

   config	validator
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

2. ConsumerConfig

   config	validator
   group.instance.id	new ConfigDef.NonEmptyString()
   key.deserializer	new ConfigDef.NonNullValidator()
   value.deserializer	new ConfigDef.NonNullValidator()
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

3. ProducerConfig

   config	validator
   key.serializer	new ConfigDef.NonNullValidator()
   value.serializer	new ConfigDef.NonNullValidator()
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))
   compression.type	in(CompressionType.names().toArray(new String[0]))

4. SaslConfigs

   config	validator
   sasl.mechanism	new ConfigDef.NonNullAndEmptyString()

5. MirrorClientConfig

   config	validator
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

6. MirrorConnectorConfig

   config	validator
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

7. MirrorMakerConfig

   config	validator
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

8. WorkerConfig

   config	validator
   ssl.client.auth	in(SslClientAuth.names().toArray(new String[0]))

9. DistributedConfig

   config	validator
   security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

10. KafkaConfig

    config	validator
    sasl.mechanism.controller.protocol	new ConfigDef.NonNullAndEmptyString()
    authorizer.class.name	new ConfigDef.NonNullValidator()
    security.inter.broker.protocol	in(SecurityProtocol.names().toArray(new Array[String](0)):_*)
    sasl.mechanism.inter.broker.protocol	new ConfigDef.NonNullAndEmptyString()
    sasl.enabled.mechanisms	new BrokerSecurityConfigs.SaslEnabledMechanismsValidator()
    compression.type	in(BrokerCompressionCodec.brokerCompressionOptions:_*)

11. StreamsConfig

    config	validator
    security.protocol	in(SecurityProtocol.names().toArray(new String[0]))

Proposed Changes

1.ConfigDef.NonNullAndEmptyString

public static class NonNullAndEmptyString implements Validator {

        @Override
        public void ensureValid(String name, Object o) {
            if (o == null) {
                // Pass in the string null to avoid the spotbugs warning
                throw new ConfigException(name, "null", "entry must be non null");
            }
            String s = (String) o;
            if (s.isEmpty()) {
                throw new ConfigException(name, o, "String must be non-empty");
            }
        }

        @Override
        public String toString() {
            return "non-null and non-empty string";
        }
    }

2.SslClientAuth.names()

    public static final List<SslClientAuth> VALUES;
    private static final List<String> NAMES;

    static {
        SslClientAuth[] sslClientAuths = SslClientAuth.values();
        List<String> names = new ArrayList<>(sslClientAuths.length);
        for (SslClientAuth auth : sslClientAuths) {
            names.add(auth.name().toLowerCase(Locale.ROOT));
        }
        VALUES = Collections.unmodifiableList(Arrays.asList(sslClientAuths));
        NAMES = Collections.unmodifiableList(names);
    }

    public static List<String> names() {
        return NAMES;
    }

3.BrokerSecurityConfigs.SaslEnabledMechanismsValidator

public static class SaslEnabledMechanismsValidator implements ConfigDef.Validator {
        @Override
        public void ensureValid(String name, Object value) {
            if (value == null) {
                throw new ConfigException(name, null, "entry must be non null");
            }

            @SuppressWarnings("unchecked")
            List<String> mechanismStrings = (List) value;

            if (mechanismStrings.isEmpty()) {
                throw new ConfigException(name, null, "entry must be non-empty list");
            }

            mechanismStrings.forEach(mechanism -> {
                if (mechanism == null || mechanism.isEmpty()) {
                    throw new ConfigException(name, mechanism, "enabled mechanism must be non-null or non-empty string");
                }
            });
        }

        @Override
        public String toString() {
            return "non-empty list, enabled mechanism must be non-null or non-empty string";
        }
    }

4.CompressionType.names()

    private static final List<String> NAMES;

    static {
        CompressionType[] compressionTypes = CompressionType.values();
        List<String> names = new ArrayList<>(compressionTypes.length);
        for (CompressionType compressionType : compressionTypes) {
            names.add(compressionType.name);
        }
        NAMES = Collections.unmodifiableList(names);
    }

     public static List<String> names() {
        return NAMES;
    } 

Compatibility, Deprecation, and Migration Plan

For all the configurations mentioned above, if the value set by the user is legal, the user will not perceive any changes.
If the value set by the user is invalid, the corresponding validator will throw a ConfigException  when the ConfigDef.parse(Map<?, ?> props)  method is executed. The corresponding Kafka program will fail to initialize.

Rejected Alternatives

I had hoped to add another validator for the following configuration: ValidList.in("GSSAPI", "PLAIN", "SCRAM-SHA-256", "SCRAM-SHA-512", "OAUTHBEARER") .

sasl.mechanism
sasl.enabled.mechanisms
sasl.mechanism.controller.protocol
sasl.mechanism.inter.broker.protocol

But Kafka's sasl module is highly flexible and customizable. Users can use the five sasl mechanisms supported by Kafka, or customize other mechanisms by themselves.