Add a commitment feerate parameter to multifundchannel
#4139
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darosior
suggested changes
Oct 19, 2020
| size_t bitcoin_tx_input_sig_weight(void) | ||
| { | ||
| return 1 + 71 + 1; | ||
| return 1 + 71; |
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I think you overlooked the length prefix.
length prefix + sig + sighash_flag
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sighash_flag is included in the 71 count, see commit message
Technically there *are* two feerates that we need to know: - the feerate to use for the funding transaction, and - the feerate to tell our peer to use for our commitment txs/htlc txs As written, `multifundchannel` uses the same feerate for both. This optional parameter will allow us to differentiate between the two, which will be exceedingly handy for anchor output worlds. ;) FIXME: test this Changelog-Added: JSON API: `multifundchannel` has a new optional argument, 'commitment_feerate', which can be used to differentiate between the funding feerate and the channel's initial commitment feerate
reduce, reuse, recycle for a greener world
71-bytes for a signature already includes the sighash byte. 2-bytes 30 44 (DER- prefix thing) 34-bytes 02 20 6e29c8df67fffdda1613cef1413eb1a9ef3627f1fc5e4d910837274eafcc7b2a (r) 34-bytes 02 20 4b8563d79b92fdd830a546862439f80b24132d09318af2c7220c791067067e29 (s) 1-byte 01 (sighash) == 71-bytes
Liquid is excluded because the mempool entry doesn't contain a 'weight' field.
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This lets a caller of
multifundchannelspecify a separate feerate for the channel's initial commitment transaction. This separates it from the feerate used for the funding transaction.Writing the test for this uncovered an off by one in how we were calculating signature lengths.
Note that this conforms with the interface for
openchannel_init, the new RPC that will initiate a v2 channel open (which contains two separate feerates, one for the funding tx and another for the commitment txs)