fix unconfirmed change note tracking in transactions

[borngraced]

This fixes the issue where change outputs weren't being tracked properly in the unconfirmed state, which could cause incorrect balance calculations and note availability issues KomodoPlatform/komodo-defi-framework#2273

[dimxy]

As I can see, the change output is added in KDF code. I hope this won't affect that code.
Maybe some test is needed in KDF to ensure that the change is calculated correctly

[borngraced]

I see. Thanks a lot..

[dimxy]

Without this code we would need to wait until the block is scanned, right?

[borngraced]

right

[borngraced]

with the case above, we need this fix in kdf directly after building txs..

[dimxy]

Looks like this store_sent_tx call stores the created transaction output in the walletdb.
Wouldn't the decrypt_and_store_transaction call do a similar thing?

[borngraced]

store_sent_tx - stores notes we created to send value to others, while decrypt_and_store_transaction calls store_received_tx(stores notes we can spend) internally

librustzcash/zcash_extras/src/wallet.rs

Lines 24 to 60 in d78f4df

	/// Scans a [`Transaction`] for any information that can be decrypted by the accounts in
	/// the wallet, and saves it to the wallet.
	pub async fn decrypt_and_store_transaction<N, E, P, D>(
	params: &P,
	data: &mut D,
	tx: &Transaction,
	) -> Result<(), E>
	where
	E: From<Error<N>>,
	P: consensus::Parameters,
	D: WalletWrite<Error = E>,
	{
	// Fetch the ExtendedFullViewingKeys we are tracking
	let extfvks = data.get_extended_full_viewing_keys().await?;
	let max_height = data.block_height_extrema().await?.map(|(_, max)| max + 1);
	let height = data
	.get_tx_height(tx.txid())
	.await?
	.or(max_height)
	.or_else(|| params.activation_height(NetworkUpgrade::Sapling))
	.ok_or(Error::SaplingNotActive)?;
	let outputs = decrypt_transaction(params, height, tx, &extfvks);
	if outputs.is_empty() {
	Ok(())
	} else {
	data.store_received_tx(&ReceivedTransaction {
	tx,
	outputs: &outputs,
	})
	.await?;
	Ok(())
	}
	}

[dimxy]

Aha, we need to add the change as a received output, to fix the balance