Support base64 encoded data (type: string + format: byte)

[apple]

Support base64 encoded data (type: string + format: byte)

[czechboy0]

Note that since this isn't a content type, but a way to encode and decode any schema, including a nested one, this'll likely justify creating a type looking like this in the runtime library:

struct Base64EncodedData: Sendable, Codable, Hashable {
    var data: Foundation.Data // or [UInt8] or ArraySlice<UInt8>
    init(data: Foundation.Data) {
        self.data = data
    }
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let base64EncodedString = try container.decode(String.self)
        guard let data = Data(base64Encoded: base64EncodedString) else {
            throw RuntimeError.invalidBase64String(base64EncodedString)
        }
        self.init(data: data)
    }
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        let base64String = data.base64EncodedString()
        try container.encode(base64String)
    }
}

And then for e.g. the following JSON Schema snippet

MyObj:
  type: object
  properties:
    stuff:
      type: string
      format: byte
  required: [stuff]

generate a struct like:

struct MyObj: Sendable, Codable, Hashable {
  var stuff: OpenAPIRuntime.Base64EncodedData
  // ...
}

[czechboy0]

Shipped in https://github.com/apple/swift-openapi-generator/releases/tag/0.3.1.