How to set a payment in Ripple without specifying currency issuers?

Question

I want to send IOUs from one of my accounts to another through the use of the API. Both of the accounts trust the same IOU issuer, which is a separate address. According to the Transaction Format, I would set the Amount issuer to the receiving account, and the SendMax issuer to the sending account. However, trying this, I get a "path dry" error:

{
  "id": 6,
  "status": "success",
  "type": "response",
  "result": {
    "engine_result": "tecPATH_DRY",
    "engine_result_code": 128,
    "engine_result_message": "Path could not send partial amount.",
    "tx_blob": "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",
    "tx_json": {
      "Account": "rL2ZJ8iTF9w5UGr8MzQSt8GpedNmutpEEQ",
      "Amount": {
        "currency": "TBC",
        "issuer": "rLJZHsAbNZu264dWnPCGgpqePAYfNZR1Zk",
        "value": "0.123"
      },
      "Destination": "rLJZHsAbNZu264dWnPCGgpqePAYfNZR1Zk",
      "Fee": "10",
      "Flags": 2147483648,
      "InvoiceID": "000000323031342D30392D32335430313A34373A34303A393838343836353030",
      "SendMax": {
        "currency": "TBC",
        "issuer": "rL2ZJ8iTF9w5UGr8MzQSt8GpedNmutpEEQ",
        "value": "0.12423"
      },
      "Sequence": 14,
      "SigningPubKey": "0220AFA84AEEE2DD794576E98411946D671F8E1F80E6C432B5ABAAAB2957651CD6",
      "TransactionType": "Payment",
      "TxnSignature": "3045022100FD0F2FECF958294BEA74876A4E5FE4192EA10EFC55C9B166F9F427861D5CBC42022067AA4B5CDA1BEB1D400937888C7819A412B238C79423A3DDB6F4FC8F45D45D61",
      "hash": "6CDB694DF36F4BD3AB928A9D761A9F60C285557B3C1136749DF7BC56A46ED641"
    }
  }
}

Despite rLJZHsAbNZu264dWnPCGgpqePAYfNZR1Zk and rL2ZJ8iTF9w5UGr8MzQSt8GpedNmutpEEQ trusting the same issuer (rTJdjjQ5wWAMh8TL1ToXXD2mZzesa6DSX) and having enough IOUs to cover the transaction.

How can I fix this issue? What am I doing wrong?

Answer 1

Ripple won't search for paths while processing transactions. The paths must be found first, using pathfinding, and specified in the transaction. You're getting a path dry error because you're not specifying any paths, so the only path you're getting is the default path.

A simple solution is to change the issuer of the SendMax amount to be the gateway. This will implicitly insert the gateway's account node before each path, including the default path. Alternatively, specify the gateway's account node as an explicit path or use pathfinding.