Sending Cashu Token

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Send Cashu Token

This is not complete, but gives a general overview of sending a token and the process of swap proofs for new proofs needed to send.

The process of sending a Cashu token involves swapping proofs from a user's balance for the correct denomination, then encoding them as a token.

1. User chooses the account to send from and how much.
2. Validate send amount: make sure the selected account has a sufficient balance.
3. Coin selection: select proofs where the sum of the proof amounts is >= the amount to send
4. If the proof amount does not exactly match the send amount, then we must swap with the mint to get the exact send amount (see swap to send below)
5. Put these proofs to send in a pending state so that the user can reclaim them or resend the token
6. Once we have the correct amount of proofs, encode them into a token

• const token = getEncodedToken({ proofs, mint, unit, memo })

7. Display the token to copy or scan

Swap to Send

1. Select the proofs to swap.
2. Determine the output amounts where there should be amounts that sum to the send amount exactly, and then amounts that sum to the remaining difference of the total proof amount and the send amount. For example:

• Total proof amount: 8
• Send amount: 7
• send output amounts: [1,2,4]
• change/keep output amounts: [1]

3. Create deterministic output data for the output amounts
4. Create a swap_cashu_proofs_draft in our DB:

{
   amount: number; // amount to send
   counter: number;
   output_amounts: number[];
   keyset_id: <keyset_id_for_outputs>;
   inputs: Proof[];
}

9. Swap by calling POST /v1/swap with a payload of

{
  "inputs": <Array[Proof]>,
  "outputs": <Array[BlindedMessage]>,
}

10. Unblind the returned blinded signatures to get our proofs to send and proofs to keep
11. Store the proofs to keep and use the proof to send to proceed with sending.