Lucas Heimberg created AVRO-3012:
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Summary: Unknown logical types are not ignored during
deserialization but lead to an exception.
Key: AVRO-3012
URL: https://issues.apache.org/jira/browse/AVRO-3012
Project: Apache Avro
Issue Type: Bug
Components: csharp
Reporter: Lucas Heimberg
By specification (see
[https://avro.apache.org/docs/current/spec.html#Logical+Types] ), unknown
logical types and logical types with invalid specification should be ignored
during deserialization and instead, the object of the underlying Avro type
should be returned.
The C# implementation of Avro however raises an exception when such a logical
type is found during parsing of a schema string. Therefore, it is not possible
to parse a schema with a logical type using a version of the C# implementation
of Avro that does not supports this logical type yet.
In particular, it is therefore as an example not possible to consume a binary
encoded Avro datum that makes use of the logical type UUID (as available in
Avro 1.10.1) with a deserializer using C# Avro 1.9.2. (by specification, the
deserializer should fall back to the underlying string representation of the
UUID).
This severly limits the downwards compability promised by the Avro
specification.
During schema parsing, a LogicalSchema instance is created using the
GetFromLogicalSchema method of the LogicalTypeFactory. This method has an
optional parameter to ignore invalid logical types, which is not used by the
caller.
It is not completely obvious to me, whether an unsupported logical type should
still be parsed as a LogicalSchema, although without a LogicalType, or whether
it should be directly parsed as the underlying Avro type (in the implementation
also called BaseSchema) - i.e., whether the downgrading to the underlying Avro
type should happen already during parsing or later during deserialization using
the schema.
For the second case, a fix to the problem would also require an update to the
ReadLogical method of the GenericReader class in order to support the case that
the LogicalType of the writer schema is null.
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