Support get the SchemaInfo from a topic and the schema version #257
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BewareMyPower
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RobertIndie,
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shibd
### Motivation Currently there is no public API to get the SchemaInfo from the broker. However, when a consumer tries to decode a message of Avro schema, the writer schema that was stored in the broker is required. The C++ client is not responsible to decode the message, but the extended library like the Python client needs the ability to get the writer schema from the broker. There is a workaround that we can send a REST request to query the schema, but it requires the admin permission. ### Modification - Add the `Client::getSchemaInfoAsync` method to get the schema info asynchronously. When the schema of the given version does not exist, the `SchemaInfo` whose type is `NONE` will be returned. - Add the `Message::getLongSchemaVersion` method to get the schema version of a message. The existing `getSchemaVersion` method is hard to use because it returns a byte array, which users need to know how to decode. - Provide `fromBigEndianBytes` and `toBigEndianBytes` functions to perform conversion between a byte array and the long value of the schema version. Add `Int64SerDes` to test them. - Fix the `LookupServiceTest` that initializes `client_` only once (even with the `GetParam()` method) so the HTTP URL was never tested. - Add `testGetSchemaByVersion` to test `getSchemaInfoAsync`.
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RobertIndie
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Apr 26, 2023
shibd
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BewareMyPower
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May 22, 2023
Fixes apache#108 ### Motivation Currently the Python client uses the reader schema, which is the schema of the consumer, to decode Avro messages. However, when the writer schema is different from the reader schema, the decode will fail. ### Modifications Add `attach_client` method to `Schema` and call it when creating consumers and readers. This method stores a reference to a `_pulsar.Client` instance, which leverages the C++ APIs added in apache/pulsar-client-cpp#257 to fetch schema info. The `AvroSchema` class fetches and caches the writer schema if it is not cached, then use both the writer schema and reader schema to decode messages. Add `test_schema_evolve` to test consumers or readers can decode any message whose writer schema is different with the reader schema.
shibd
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May 25, 2023
Fixes #108 ### Motivation Currently the Python client uses the reader schema, which is the schema of the consumer, to decode Avro messages. However, when the writer schema is different from the reader schema, the decode will fail. ### Modifications Add `attach_client` method to `Schema` and call it when creating consumers and readers. This method stores a reference to a `_pulsar.Client` instance, which leverages the C++ APIs added in apache/pulsar-client-cpp#257 to fetch schema info. The `AvroSchema` class fetches and caches the writer schema if it is not cached, then use both the writer schema and reader schema to decode messages. Add `test_schema_evolve` to test consumers or readers can decode any message whose writer schema is different with the reader schema.
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@BewareMyPower : Can this PR be back merged to Pulsar 2.10 CPP client? |
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@armanjupriya-er The Pulsar CPP client version is no longer associated with the Pulsar version. So there is no need to "back merged". Just use the latest client |
Thank you @BewareMyPower of the quick reply. |
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Motivation
Currently there is no public API to get the SchemaInfo from the broker. However, when a consumer tries to decode a message of Avro schema, the writer schema that was stored in the broker is required. The C++ client is not responsible to decode the message, but the extended library like the Python client needs the ability to get the writer schema from the broker. There is a workaround that we can send a REST request to query the schema, but it requires the admin permission.
Modification
Client::getSchemaInfoAsyncmethod to get the schema info asynchronously. When the schema of the given version does not exist, theSchemaInfowhose type isNONEwill be returned.Message::getLongSchemaVersionmethod to get the schema version of a message. The existinggetSchemaVersionmethod is hard to use because it returns a byte array, which users need to know how to decode.fromBigEndianBytesandtoBigEndianBytesfunctions to perform conversion between a byte array and the long value of the schema version. AddInt64SerDesto test them.LookupServiceTestthat initializesclient_only once (even with theGetParam()method) so the HTTP URL was never tested.testGetSchemaByVersionto testgetSchemaInfoAsync.Documentation
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