[Doc] add explanations for broker entry metadata (apache#13336)

* [Doc] add explanations for broker entry metadata

* update

* update

(cherry picked from commit 1f80634)

site2/docs/developing-binary-protocol.md

@@ -63,6 +63,14 @@ It is created by the broker when the message arrived at the broker and passed wi
 | `broker_timestamp` | Optional        | The timestamp when a message arrived at the broker (`id est` as the number of milliseconds since January 1st, 1970 in UTC)      |
 | `index`            | Optional        | The index of the message. It is assigned by the broker.
 
+If you want to use broker entry metadata for **brokers**, configure the [`brokerEntryMetadataInterceptors`](reference-configuration.md#broker) parameter in the `broker.conf` file.
+
+If you want to use broker entry metadata for **consumers**:
+
+1. Use the client protocol version [18 or later](https://github.com/apache/pulsar/blob/ca37e67211feda4f7e0984e6414e707f1c1dfd07/pulsar-common/src/main/proto/PulsarApi.proto#L259).
+
+2. Configure the [`brokerEntryMetadataInterceptors`](reference-configuration.md#broker) parameter and set the [`enableExposingBrokerEntryMetadataToClient`](reference-configuration.md#broker) parameter to `true` in the `broker.conf` file.
+
 ## Message metadata
 
 Message metadata is stored alongside the application-specified payload as a serialized protobuf message. Metadata is created by the producer and passed without changes to the consumer.

site2/docs/reference-configuration.md

@@ -352,6 +352,8 @@ brokerServiceCompactionThresholdInBytes|If the estimated backlog size is greater
 #### Configuration Override For Clients Internal to Broker
 
 It's possible to configure some clients by using the appropriate prefix.
+| brokerEntryMetadataInterceptors | Set broker entry metadata interceptors.<br /><br />Multiple interceptors should be separated by commas. <br /><br />Available values:<li>org.apache.pulsar.common.intercept.AppendBrokerTimestampMetadataInterceptor</li><li>org.apache.pulsar.common.intercept.AppendIndexMetadataInterceptor</li> <br /><br />Example<br />brokerEntryMetadataInterceptors=org.apache.pulsar.common.intercept.AppendBrokerTimestampMetadataInterceptor, org.apache.pulsar.common.intercept.AppendIndexMetadataInterceptor|N/A |
+| enableExposingBrokerEntryMetadataToClient|Whether to expose broker entry metadata to client or not.<br /><br />Available values:<li>true</li><li>false</li><br />Example<br />enableExposingBrokerEntryMetadataToClient=true  | false |
 
 |Prefix|Description|
 |brokerClient_| Configure **all** the broker's Pulsar Clients and Pulsar Admin Clients. These configurations are applied after hard coded configuration and before the above brokerClient configurations named above.|