Explain every byte

Profile → outer hex decode → ASCII MTI → configured bitmap → fields → display.

The supplied schema has no LengthEncoding or MTIEncoding member. The profiles are synthetic, including the legacy VisaSpec name.

Work the cursor

Binary bitmap, fields 2,3,4:

MTI [0,4), bitmap [4,12), DE2 prefix [12,14), DE2 [14,30), DE3 [30,36), DE4 [36,48).

48 wire bytes = 96 outer hex characters.

Change one representation

Hex-ASCII bitmap takes 16 wire bytes rather than 8.

The same fields now start at 20; total = 56 bytes = 112 hex characters.

Choose the profile explicitly. Do not guess from printable bytes.

Length units

BCD 05 | 01 23 45: 2 ASCII prefix bytes + 3 payload bytes.

Decoded digits: 12345. Remove the leading zero pad, not the last digit. Reject signed lengths and invalid decimal nibbles.

First unknown boundary

DE3 lacks a specification: stop at byte 30.

Return completed DE2 plus a non-nil error. Never relabel DE3 bytes as DE4. Reject trailing data after one complete message.

One display policy

Text and JSON both redact sensitive raw hex and decoded values. Masked PAN + unmasked hex still reveals the PAN.

Amounts remain in minor units until a currency exponent is available.

Independent checks

• Derive a fresh cursor table.
• Explain incomplete parse versus valid transaction.
• Search both displays for plaintext and hex disclosure.
• Reconstruct the parser without copying a full solution.