Protobuf

Glue supports protobuf as a code generation target, allowing you to generate .proto schemas from Glue models, enums, and services.

Simply run:

#Configuration

You can configure the emitted protobuf package name:

#Example

For this Glue spec:

...generating protobuf...

...will produce:

Enum constants are generated in CONSTANT_CASE from the Glue string values. Values that normalize to the same Protobuf identifier are rejected because Protobuf enum value names share the package scope.

Integer primitives map to Protobuf scalar integer types where available. i64 and u64 emit int64 and uint64; uint, u8, u16, and u32 emit uint32; other signed integer primitives emit int32.

#Field tags

By default, Glue assigns Protobuf field tags from field declaration order, starting at 1. You do not need to annotate fields for simple or early schemas.

Use @field(proto_tag=<number>) when you need stable Protobuf wire compatibility across field reordering:

If one field in a message has proto_tag, every field in that message must have one. Untagged messages keep source-order numbering.

proto_tag can use folded int constant expressions, including model-scoped constants:

#Optional fields

Optional Glue fields generate optional Protobuf fields:

Protobuf does not track field presence for repeated or map fields, so optional repeated/map Glue fields are emitted as regular repeated and map fields.

#Services

Glue services generate Protobuf service definitions:

#Notes

• Endpoint declarations are ignored by the Protobuf generator.

#Current limitations

• Record<K, V> is emitted as map<K, V> for supported Protobuf key/value types.
• Homogeneous tuples are downcast to repeated T; heterogeneous tuples are rejected because Protobuf has no positional tuple type.
• Anonymous structs are emitted as generated messages named from the owning field path.
• Unions are emitted as oneof only when every member is valid inside a Protobuf oneof; repeated fields, maps, optional members, and explicit proto_tag unions are rejected with an error.
• RPC body and returns must be message types.