# Specification: Flexible Byte Layout

Status: Prescriptive - Draft

Flexible Byte Layout is an advanced layout for representing binary data.

It is flexible enough to support very small and very large (multi-block) binary data.

type FlexibleByteLayout union {
  | Bytes bytes
  | NestedByteList list
  | &FlexibleByteLayout link
} representation kinded

type NestedByteList [ NestedByte ]

type NestedByte union {
  | Bytes bytes
  | NestedFBL list
} representation kinded

type NestedFBL struct {
  length Int
  part FlexibleByteLayout
} representation tuple

FlexibleByteLayout is the entrypoint/root of the data structure and uses a potentially recursive union type. This allows you to build very large nested dags via NestedByteList that can themselves contain additional NestedByteLists or actual Bytes (via Links to FlexibleByteLayout in NestedByte).

An implementation must define a custom function for reading ranges of binary data but once implemented, you can read data regardless of the layout algorithm used.

Since readers only need to concern themselves with implementing the read method, they do not need to understand the algorithms used to generate the layouts. This gives a lot of flexibility in the future to define new layout algorithms as necessary without needing to worry about updating prior impelementations.

The length property must be encoded with the proper byte length. If not encoded properly, readers will not be able to read properly. However, the property is not secure and a malicious encoder could write it as whatever they please. As such, it should not be relied upon when calculating usage against a quota or any similar calculation where there may be an incentive for an encoder to alter the length.