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lightning-sendonion -- Send a payment with a custom onion packet

SYNOPSIS

sendonion onion first_hop payment_hash [label] [shared_secrets]

DESCRIPTION

The sendonion RPC command can be used to initiate a payment attempt with a custom onion packet. The onion packet is used to deliver instructions for hops along the route on how to behave. Normally these instructions are indications on where to forward a payment and what parameters to use, or contain details of the payment for the final hop. However, it is possible to add arbitrary information for hops in the custom onion, allowing for custom extensions that are not directly supported by c-lightning.

The onion is specific to the route that is being used and the payment_hash used to construct, and therefore cannot be reused for other payments or to attempt a separate route. The custom onion can generally be created using the devtools/onion CLI tool, or the createonion RPC command.

The onion parameter is a hex-encoded 1366 bytes long blob that was returned by either of the tools that can generate onions. It contains the payloads destined for each hop and some metadata. Please refer to BOLT 04 for further details.

The first_hop parameter instructs c-lightning which peer to send the onion to. It is a JSON dictionary that corresponds to the first element of the route array returned by getroute. The following is a minimal example telling c-lightning to use channel 103x1x1 to add an HTLC for 1002 millisatoshis and a delay of 21 blocks on top of the current blockheight:

{
  "channel": "103x1x1",
  "direction": 1,
  "amount_msat": "1002msat",
  "delay": 21,
}

The payment_hash parameter specifies the 32 byte hex-encoded hash to use as a challenge to the HTLC that we are sending. It is specific to the onion and has to match the one the onion was created with.

The label parameter can be used to provide a human readable reference to retrieve the payment at a later time.

The shared_secrets parameter is a JSON list of 32 byte hex-encoded secrets that were used when creating the onion. c-lightning can send a payment with a custom onion without the knowledge of these secrets, however it will not be able to parse an eventual error message since that is encrypted with the shared secrets used in the onion. If shared_secrets is provided c-lightning will decrypt the error, act accordingly, e.g., add a channel_update included in the error to its network view, and set the details in listsendpays correctly. If it is not provided c-lightning will store the encrypted onion, and expose it in listsendpays allowing the caller to decrypt it externally. The following is an example of a 3 hop onion:

[
	"298606954e9de3e9d938d18a74fed794c440e8eda82e52dc08600953c8acf9c4",
	"2dc094de72adb03b90894192edf9f67919cb2691b37b1f7d4a2f4f31c108b087",
	"a7b82b240dbd77a4ac8ea07709b1395d8c510c73c17b4b392bb1f0605d989c85"
]

If shared_secrets is not provided the c-lightning node does not know how long the route is, which channels or nodes are involved, and what an eventual error could have been. It can therefore be used for oblivious payments.

RETURN VALUE

On success, an object similar to the output of sendpay will be returned. This object will have a status field that is typically the string "pending", but may be "complete" if the payment was already performed successfully.

If shared_secrets was provided and an error was returned by one of the intermediate nodes the error details are decrypted and presented here. Otherwise the error code is 202 for an unparseable onion.

AUTHOR

Christian Decker <decker.christian@gmail.com> is mainly responsible.

RESOURCES

Main web site: https://github.com/ElementsProject/lightning

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