loop/docs/faqs.md

Frequently Asked Questions

How does Loop recover from a crash?

When loopd is terminated (or killed) for whatever reason, it will pickup pending swaps after a restart.

Information about pending swaps is stored persistently in the swap database. Its location is ~/.loopd/<network>/loop.db.

Can Loop handle multiple simultaneous swaps?

It is possible to execute multiple swaps simultaneously. Just keep loopd running.

What are the fees?

You can pass the --verbose flag when using Loop to get a detailed fee breakdown

Loop Out Fees

An explanation of each fee:

• Estimated on-chain fee: The estimated cost to sweep the HTLC in case of success, calculated based on the current on-chain fees. This value is called miner_fee in the gRPC/REST responses.
• Max on-chain fee: The maximum on-chain fee the daemon is going to allow for sweeping the HTLC in case of success. A fee estimation based on the --conf_target flag is always performed before sweeping. The factor of 100 times the estimated fee is applied in case the fees spike between the time the swap is initiated and the time the HTLC can be swept. But that is the absolute worst-case fee that will be paid. If there is no fee spike, a normal, much lower fee will be used.
• Max off-chain swap routing fee: The maximum off-chain routing fee that the daemon should pay when finding a route to pay the Lightning invoice. This is a hard limit. If no route with a lower or equal fee is found, the payment (and the swap) is aborted. This value is calculated statically based on the swap amount (see maxRoutingFeeBase and maxRoutingFeeRate in cmd/loop/main.go).
• Max off-chain prepay routing fee: The maximum off-chain routing fee that the daemon should pay when finding a route to pay the prepay fee. This is a hard limit. If no route with a lower or equal fee is found, the payment (and the swap) is aborted. This value is calculated statically based on the prepay amount (see maxRoutingFeeBase and maxRoutingFeeRate in cmd/loop/main.go).
• No show penalty (prepay): This is the amount that has to be pre-paid (off-chain) before the server publishes the HTLC on-chain. This is necessary to ensure the server's on-chain fees are paid if the client aborts and never completes the swap after the HTLC has been published on-chain. If the swap completes normally, this amount is counted towards the full swap amount and therefore is actually a pre-payment and not a fee. This value is called prepay_amt in the gRPC/REST responses.

Loop In Fees

An explanation of each fee:

• Estimated on-chain fee: The estimated on-chain fee that the daemon has to pay to publish the HTLC. This is an estimation from lnd's wallet based on the available UTXOs and current network fees. This value is called miner_fee in the gRPC/REST responses.