[rust-server] how to cope with loss of `file` type?

Created by: bjgill

Description

Swagger v2 had three types to represent binary data: {type: string, format: binary}, {type: string, format: byte}, and {type: file}. In OpenAPI v3, we lost the last of these.

In rust-server, binary and byte were treated identically - as swagger::ByteArray. File was Box<Future<Item=Option<Box<Stream<Item=Vec<u8>, Error=Error> + Send>>, Error=Error> + Send>.

I'm not sure what the correct approach for OpenAPI v3 is. Should we keep one of binary/byte as swagger::ByteArray and move the other to use the same type as file used to? Do we keep binary/byte as-is and add in some rust-server-specific workaround for those wanting to retain the old file behaviour?

openapi-generator version

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Discovered in https://github.com/OpenAPITools/openapi-generator/issues/307