lostluck commented on a change in pull request #12426:
URL: https://github.com/apache/beam/pull/12426#discussion_r465202931
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File path: model/pipeline/src/main/proto/beam_runner_api.proto
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@@ -855,10 +855,21 @@ message StandardCoders {
// BOOLEAN: beam:coder:bool:v1
// BYTES: beam:coder:bytes:v1
// ArrayType: beam:coder:iterable:v1 (always has a known length)
- // MapType: not yet a standard coder (BEAM-7996)
+ // MapType: not a standard coder, specification defined below.
// RowType: beam:coder:row:v1
// LogicalType: Uses the coder for its representation.
//
+ // The MapType is encoded by:
+ // - An INT32 representing the size of the map (N)
+ // - Followed by N interleaved keys and values, encoded with their
+ // corresponding coder.
+ //
+ // Nullable types in container types (ArrayType, MapType) are encoded by:
+ // - A one byte null indicator, 0x00 for null values, or 0x01 for present
+ // values.
+ // - For present values the null indicator is followed by the value
+ // encoded with it's corresponding coder.
+ //
Review comment:
Also, this requirement means that *all* values must be pointers (or
reference types) in Go as ordinary primitives cannot be nullable. That feels
very strange.
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