Channel establishment v2 (dual funding) - #239
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BOLT 2 derives both the temporary_channel_id and the channel_id of a dual-funded channel from revocation basepoints rather than from the funding outpoint.
Channel establishment v2 needs the previous transaction bytes for tx_add_input and our own witnesses for tx_signatures, which the wallet can only produce as a partial signing of the shared transaction.
A dual-funded funding transaction holds whatever the program negotiated: no inputs, inputs the wallet cannot sign, a lock time in the future or an output that breaks a consensus rule. None of these is a harness failure. Classify sendrawtransaction rejections, and keep a policy-rejected transaction for mining later only if a block would accept it.
SharedTransaction accumulates the inputs and outputs both peers add and remove by serial_id and assembles the BOLT 2 shared transaction, with the initiator's fee computed per BOLT 3 Appendix G.
TxExchange drives a SharedTransaction from the messages sent and received, queuing unanswered sends so a program that sends several messages before reading a reply still settles which tx_complete concluded the exchange.
Negotiations are keyed by temporary_channel_id and addressable by the derived channel_id every later message carries.
BOLT 2 makes the two channel establishment flows mutually exclusive on one connection, so the v2 flow needs its own post-init snapshot that keeps option_dual_fund, and CLN and Eclair need to advertise it.
Each tx_add_input locks the coin it selects, so a program contributing several inputs needs several mature coinbase outputs.
The first half of the channel establishment v2 flow: build and send open_channel2, receive accept_channel2 and extract its fields, and derive the temporary_channel_id and channel_id BOLT 2 computes from the revocation basepoints. New variants are appended to Operation: it is postcard-encoded by declaration index, so inserting mid-enum would make existing corpus entries decode as different operations.
Contribute inputs and outputs to the shared transaction, remove them, send tx_complete and read the peer's replies, then rebuild the funding transaction from the negotiation. A receive reads only while the peer owes a reply, and building from the negotiation settles the owed replies first, so what is built is what the peer agreed to.
Exchange the initial commitment_signed over the negotiated funding transaction, then tx_signatures in the order BOLT 2 prescribes: the peer that contributed less signs first, ties broken by node_id. The peer's witnesses are applied when the funding transaction is broadcast, since our wallet cannot sign its inputs.
One linear script from open_channel2 through channel_ready, with every interactive tx send paired with a receive.
BOLT 2 makes the two channel establishment flows mutually exclusive on one connection, so a campaign only wants the generators its snapshot can act on. SMITE_IR_GENERATORS picks v1, v2 or all, and smitebot sets it from the scenario name.
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Adds fuzzing support for the BOLT 2 v2 channel establishment flow: open_channel2, interactive transaction construction, v2 commitment signatures and tx_signatures.
Protocol and transaction primitives
IR and generators
Scenarios
Depends on #222 , #221 and #240
For follow ups: