overview.md

Data Types Overview

This section describes the data-type model used for eBUS payload decoding and encoding.

Interface Shape

Each data type exposes a common interface:

type Value struct {
    Value any
    Valid bool
}

type DataType interface {
    Decode([]byte) (Value, error)
    Encode(any) ([]byte, error)
    Size() int
    ReplacementValue() []byte
}

Value / Valid Model

• Value.Valid == true means the payload represented a concrete value.
• Value.Valid == false means the payload is not a usable value for the type, either because it matched the replacement value or because the type-specific decoder rejected it (e.g., NaN/Inf or out-of-range for EXP).

Replacement values are defined per type and are used by devices to indicate “unknown” or “not available.”

Replacement Value Semantics

Each type defines a byte sequence returned by ReplacementValue(). When decoding:

• If the payload equals the replacement value, Valid is false and Value is unset.
• Otherwise, the decoder may still set Valid to false if the decoded value is invalid for that type (for example, EXP treats NaN/Inf as invalid).
• If the value is acceptable, Valid is true and Value contains the decoded value.

When encoding:

• Values that would encode to the replacement value are rejected.
• Inputs outside the valid range are rejected.

This keeps “unknown” distinct from legitimate numeric values without using sentinel numbers in application code.

See Also

• types/ebusd-csv.md – common ebusd CSV type spec strings and selector conventions (observed).