keysend only working with other c-lightning nodes

[Fonta1n3]

I have been testing keysend and it quite reliably only seems to work with other c-lightning nodes.

This recipient for example has keysend enabled and is able to send me keysends but I am unable to return the favor and generally get an error:

error =     {
        "amount_msat" = 1000msat;
        "amount_sent_msat" = 0msat;
        code = 203;
        "created_at" = 1598181774;
        destination = 02f7dcc28e15c0b55238a0f7db02b2082b1c2fa5adf66ff96e79db8f7ae17fe7d3;
        "erring_index" = 4;
        "erring_node" = 02f7dcc28e15c0b55238a0f7db02b2082b1c2fa5adf66ff96e79db8f7ae17fe7d3;
        failcode = 16399;
        failcodename = "WIRE_INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS";
        id = 343;
        message = "failed: WIRE_INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS (reply from remote)";
        msatoshi = 1000;
        "msatoshi_sent" = 0;
        "payment_hash" = 1887be8ddb26b3336494899f0a58d068f4343ba4160c38d05ee28986426744ca;
        "raw_message" = 400f00000000000003e80009d777;
        status = pending;
    }

[ZmnSCPxj]

Hmm looks like we need to know exactly what keysend implementation the recipient is using. Do you know? Logs from the recipient implementation would be nice as well.

[Fonta1n3]

@ZmnSCPxj I know this peer is on LND v0.10.3 beta but that’s all I know right now.

Will ask around to a few others.

[Fonta1n3]

Another is on LND 0.10.4.

[rustyrussell]

Hmm. Keysend is undocumented, so perhaps we implemented it wrong? @cdecker

[cdecker]

Indeed there is no official specification for keysend, so I had to reverse engineer it. It was working for a while, but I can't guarantee it hasn't changed on the lnd side. I'll see what I can do 👍

[d4amenace]

Don't know if this is helpful, but I was trying to do a keysend to my Eclair Mobile wallet version 0.4.12 and it to is failing.

[Fonta1n3]

From my experience it literally only works c-lightning to c-lightning although i haven’t tested since latest release.

[cdecker]

The error message got me thinking that the recipient might not support keysend at all, and checking with my local gossip (which might look different now), it doesn't seem the destination supports it:

{
  "nodeid": "02f7dcc28e15c0b55238a0f7db02b2082b1c2fa5adf66ff96e79db8f7ae17fe7d3",
  "alias": "Satoshi Nakamoto",
  "color": "000000",
  "last_timestamp": 1606207493,
  "features": "02a2a1",
  "addresses": [
    {
      "type": "torv3",
      "address": "p3hv5427zr3obj2edec4uva3jvcs37jus5adpxpxy2xw4jwivfm5hvad.onion",
      "port": 9735
    }
  ]
}

(Notice that 0x02a2a1 >> 55 & 0x01 == 0x00, i.e., the keysend bit 55 is not set)

So adding the check before initiating a payment, and failing with a more informative error message, like we do in #4236 should address this issue.