create_invoice_from_channelmanager variant with description hash support

[TheBlueMatt]

I'm not sure there's much use in description hashes in the wild today, except for lnurl/the lnpay stuff, which we'd of course like to support. We really need a variant of create_invoice_from_channelmanager which supports a description hash instead of explicit description for that, though, and will probably want something similar for create_phantom_invoice after #1199 is merged.

Tagging good first issue, but if someone does take this up, probably base it on #1199 or wait until that is merged.

[xraid]

no need for dh in lnurl one can use preimage_hash as id for what is described as dh in lnurl spec.

it is just a handle for id in roundtrips

dh is stupid . why have a description if it gets hashed and unreadable at recipient ?

[xraid]

a lnurl service could use a hash of the description not necessarily the bolt11 description_hash

[TheBlueMatt]

No, the lnurl spec requires you use the description_hash in bolt 11, so to support lnurl you need this.

[xraid]

i used hash of preimige in a lnurl service . as it is only used as id in the roundtrip, where the service can id url and hash when incoming

[xraid]

You as service can put a teddybear in that field as long as You as service can id the teddybear when it comes back, it is not used by the client, only by service ...

[xraid]

maybe i am confusing it . lnurl-withdrawal can have teddybears in description_hash field, maybe lnurl-pay can not

[TheBlueMatt]

Ah, yes, I was referring to lnurl-pay.