Fix memo parsing for strings starting with 0x

[Timi16]

When a memo string starts with 0x (like an Ethereum address), the current code attempts to decode it as hexadecimal. For valid hex strings like Ethereum addresses, the decode succeeds but produces data that causes transaction failures during scanning.

Changes

• Modified interpret_memo_string in zingolib/src/wallet/utils.rs to only use hex-decoded data if it's a valid memo size (≤512 bytes)
• Added comprehensive unit tests covering:
  • Plain text memos
  • Valid hex strings
  • Ethereum addresses (valid hex but should be treated as text)
  • Invalid hex strings
  • Oversized memos

Testing

Added unit tests in zingolib/src/wallet/utils.rs:

• test_interpret_memo_string_plain_text
• test_interpret_memo_string_valid_hex
• test_interpret_memo_string_ethereum_address
• test_interpret_memo_string_invalid_hex
• test_interpret_memo_string_too_long

[Oscar-Pepper]

Hi @Timi16 thanks for looking into this. I will post in the issue #2075 to get more info as i'm struggling to understand under which conditions this bug occurs, i cant reproduce it myself. Please see this issue for more context. The changes you have made are to the parsing of an Arbitrary memo - starting with 0xFF byte as stated in zip302 - which are used internally by zingo and are not displayed to the user or intended to be human-readable. Therefore, this code needs to remain unchanged. I assume the issue we are trying to solve is when the ethereum address is inputted by the user as text. In this case, the first byte will be <= 0xF4 resulting is a memo of Text variant where the remaining 511 bytes will be parsed to a string. This string should be able to contain any valid UTF-8 and its not clear to me why any text memo starting with "0x" will be treated differently. my tests support this, here is an example:

    txid: cfd5f064237370c7d60131bdbe86a4950d206d995c06991f415a2f6bfbdd485f
    datetime: 2026-01-14 06:31:03 UTC
    status: confirmed
    blockheight: 3204220
    kind: send-to-self
    value: 0
    fee: 10000
    zec price: not available
    orchard notes:
        {
            value: 100000
            spend status: unspent
            output index: 0
            memo: 0xtest
        }

[Oscar-Pepper]

great work. thanks for your contribution!

[Oscar-Pepper]

hi @Timi16 I have pushed a commit instead of requesting changes. I hope this is ok, otherwise I can PR into your branch if you prefer. please review my commit and if all ok we can merge.

[Timi16]

hi @Timi16 I have pushed a commit instead of requesting changes. I hope this is ok, otherwise I can PR into your branch if you prefer. please review my commit and if all ok we can merge.

Yes you can all is Okay thank you

[Timi16]

great work. thanks for your contribution!

I Thank the Zingolib team for there support