Standardize lighting invoice amount rounding

[vindard]

Background

The Lightning Network is denominated in millisatoshis but amounts in our system are usually presented as a rounded version of satoshis.

Within lnd there are usually two types of token amounts quoted:

• tokens: a rounded down version of millitokens
• safe_tokens: a rounded up version of millitokens

In our own domain we express this distinction with the roundedUp- and roundedDown- prefixs, and you will see types defined as things like roundedUpAmount or roundedDownFees

Issue

There's a discrepancy in the amount we present in a fee probe and the amount we write to the ledger. These two values are usually off by exactly 1 satoshi and the issue may be coming from inconsistent rounding.

To observe the issue someone can:

• call our lnInvoiceFeeProbe mutation with an invoice and note the fee returned
• call our lnInvoicePaymentSend mutation with the same invoice and make sure it returns SUCCESS
• fetch the last transaction via our me query and compare the fee recorded in the transaction

Suggested Task

This issue has two potential tiers to solve:

1. Investigate and fix the immediate discrepancy

2. Look at how we use roundedUp/roundedDown values across the codebase to see if there are any other potential discrepancies. My initial instinct is that we can probably standardize on using one of these (roundedUp- maybe) consistently and phase out our roundedDown- usage but this would need to be investigated.

[AustinKelsay]

Hey @vindard I started working on this but am having trouble initiating lnInvoiceCreate to get a paymentRequest to start investigating lnInvoiceFeeProbe Do I need to be using a testnet invoice when mocking these API calls locally, or am I missing something else?

[vindard]

Hey @vindard I started working on this but am having trouble initiating lnInvoiceCreate to get a paymentRequest to start investigating lnInvoiceFeeProbe Do I need to be using a testnet invoice when mocking these API calls locally, or am I missing something else?

Hey awesome, are you in our Slack yet?

With the dev setup it's testnet format yea. That one runs in regtest mode.

[AustinKelsay]

Ahh ok that makes sense Not yet but I would love to join!

[vindard]

Ahh ok that makes sense Not yet but I would love to join!

Can join here