Value to Bytes Encoder

This document outlines the creation of a JSON schema for constructing custom byte arrays (packets or payloads). A schema dictates the sequential assembly of bytes. The system parses the schema sequentially to construct the final byte array.

Schema Fundamentals

The schema is a JSON array containing specific “fields”. Three field types are supported for payload construction:

1. Static: Fixed, hardcoded bytes.
2. Dynamic: Live input data.
3. Metadata Length: Automated byte calculation for referenced fields.

General structure:

[
  { "type": "...", ... },
  { "type": "...", ... }
]

1. Static Fields

Used for fixed byte sequences (e.g., headers, footers).

Data formats accepted:

• Numbers: Integer values between 0 and 255 (1 byte).
• Hexadecimal Strings: Strings prefixed with "0x" (e.g., "0xA1", "0xFF").

Example:

{
    "type": "static",
    "id": "header_field",
    "data": ["0xAA", "0xBB", 255, 0]
}

• id: Unique identifier.
• data: Array of bytes to output. The example outputs AA BB FF 00.

2. Dynamic Fields

Used for integrating live data streams. Requires defining the data size and byte order.

Example:

{
    "type": "dynamic",
    "id": "sensor_payload",
    "key": "temperature_input",
    "data_type": "I32",
    "endian": "be"
}

• id: Unique identifier.
• key: Target data channel name.
• data_type: Target format configuration. Supported values:
  • Numeric: "U8", "I8", "U16", "I16", "U32", "I32", "U64", "I64", "F32", "F64"
  • Non-numeric: "STRING", "BYTES", "BOOL"
• endian: Byte order for multi-byte numbers.
  • "be": Big-Endian (most significant byte first).
  • "le": Little-Endian (least significant byte first).

3. Metadata Length Fields

Calculates the total byte size of specified fields. Required for dynamic payload sizing.

Example:

{
    "type": "metadata_length",
    "id": "payload_size",
    "ids": ["sensor_payload", "extra_data"],
    "data_type": "U8",
    "endian": "be"
}

• id: Unique identifier.
• ids: Array of field IDs to measure. The total byte size of all referenced fields is summed.
• data_type: Output format for the length value (e.g., "U8", "U16").
• endian: Byte order ("be" or "le").

Complete Example

Objective: Construct a packet with the following structure:

1. 2-byte Header (0xAA 0xBB).
2. 1-byte Length indicator.
3. Dynamic payload (I32 from speed_sensor channel).
4. 1-byte Footer (0xFF).

JSON Schema:

[
    {
        "type": "static",
        "id": "header",
        "data": ["0xAA", "0xBB"]
    },
    {
        "type": "metadata_length",
        "id": "length_byte",
        "ids": ["live_speed"],
        "data_type": "U8",
        "endian": "be"
    },
    {
        "type": "dynamic",
        "id": "live_speed",
        "key": "speed_sensor",
        "data_type": "I32",
        "endian": "be"
    },
    {
        "type": "static",
        "id": "footer",
        "data": ["0xFF"]
    }
]

Execution Flow: Given an incoming speed_sensor integer reading of 1000:

1. Static header is evaluated: AA BB
2. Dynamic field converts 1000 to a 4-byte I32: 00 00 03 E8
3. Metadata Length evaluates the payload size (4 bytes) and outputs as U8: 04
4. Static footer is evaluated: FF

Final Byte Array Output: AA BB 04 00 00 03 E8 FF