Fix crash with dual opening when we cannot estimate fees

[enaples]

Important

26.04 FREEZE March 11th: Non-bugfix PRs not ready by this date will wait for 26.06.

RC1 is scheduled on March 23rd

The final release is scheduled for April 15th.

Checklist

Before submitting the PR, ensure the following tasks are completed. If an item is not applicable to your PR, please mark it as checked:

• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.
• Important All PRs must consider how to reverse any persistent changes for tools/lightning-downgrade

Additional info

Test to reproduce #8847

uv run python -m pytest -vvvv tests/test_opening.py::test_opening_dualfund_with_unknown_feerates

Unfortunately I cannot continue the test after BROKEN message. I was able to reproduce the issue on signet and I can can confirm that the error message after crash are the same pointed out in the issue.

I report logs for completeness:

lightningd: common/fee_states.c:175: marginal_feerate: Assertion `current_feerate >= minfeerate' failed.

lightningd: FATAL SIGNAL 6 (version v25.12)

0xaaaad9c1a477 send_backtrace
	common/daemon.c:38

0xaaaad9c1a523 crashdump

	common/daemon.c:83

0xffff9dbed7cf ???

	???:0

0xffff9d717608 __pthread_kill_implementation

	./nptl/pthread_kill.c:44

0xffff9d6ccb3b __GI_raise

	../sysdeps/posix/raise.c:26

0xffff9d6b7dff __GI_abort

	./stdlib/abort.c:79

0xffff9d6c5cbf __assert_fail_base

	./assert/assert.c:96

0xffff9d6c5d2f __assert_fail

	./assert/assert.c:105

0xaaaad9c1c8a7 marginal_feerate

	common/fee_states.c:175

0xaaaad9ba149b commit_txfee

	lightningd/peer_control.c:747

0xaaaad9ba5d9b channel_amount_spendable

	lightningd/peer_control.c:814

0xaaaad9ba6997 json_add_channel

	lightningd/peer_control.c:1222

0xaaaad9ba6fe3 json_add_peerchannels

	lightningd/peer_control.c:2621

0xaaaad9ba71bf json_listpeerchannels

	lightningd/peer_control.c:2662

0xaaaad9b802d3 command_exec

	lightningd/jsonrpc.c:769
0xaaaac3972517 rpc_command_hook_final

	lightningd/jsonrpc.c:910

0xaaaac39a7b7b hook_done

	lightningd/plugin_hook.c:243

0xaaaac39a7caf plugin_hook_call_next

	lightningd/plugin_hook.c:343

0xaaaac39a8983 plugin_hook_call_

	lightningd/plugin_hook.c:395

0xaaaac3972c4b plugin_hook_call_rpc_command

	lightningd/jsonrpc.c:998

0xaaaac3972c4b parse_request

	lightningd/jsonrpc.c:1122

0xaaaac3972fcb read_json

	lightningd/jsonrpc.c:1216

0xaaaac3a51d47 next_plan

	ccan/ccan/io/io.c:60

0xaaaac3a5231b do_plan

	ccan/ccan/io/io.c:422

0xaaaac3a523f3 io_ready

	ccan/ccan/io/io.c:439

0xaaaac3a543bf io_loop

	ccan/ccan/io/poll.c:470

0xaaaac39701d3 io_loop_with_timers

	lightningd/io_loop_with_timers.c:22

0xaaaac39a5837 plugins_config

	lightningd/plugin.c:2237

0xaaaac3975e6f main

	lightningd/lightningd.c:1396

0xffff7fea84c3 __libc_start_call_main

	../sysdeps/nptl/libc_start_call_main.h:58

0xffff7fea8597 __libc_start_main_impl

	../csu/libc-start.c:360

0xaaaac39431ef ???

	_start+0x2f:0

0xffffffffffffffff ???

	???:0

Lost connection to the RPC socket.Reading sync lightningd: Connection reset by peerReading sync lightningd: Connection reset by peer

From crash.log I get:

+8983.404577377 lightningdDEBUG: Unable to estimate any fees
+9012.664302501 jsonrpc#50IO_IN: 7b226a736f6e727063223a22322e30222c226964223a2274696d65722f7265636f7665723a6c697374706565726368616e6e656c73233237222c226d6574686f64223a226c697374706565726368616e6e656c73222c22706172616d73223a7b7d7d0a0a
+9012.664657543 jsonrpc#50IO_IN: "timer/recover:listpeerchannels#27"
+9012.781892001 lightningdBROKEN: FATAL SIGNAL 6 (version v25.12)
+9012.782006793 lightningdBROKEN: backtrace: common/daemon.c:46 (send_backtrace) 0xaaaacc08a4c3
+9012.782011335 lightningdBROKEN: backtrace: common/daemon.c:83 (crashdump) 0xaaaacc08a523
+9012.782013460 lightningdBROKEN: backtrace: (null):0 ((null)) 0xffff8a8177cf
+9012.782015626 lightningdBROKEN: backtrace: ./nptl/pthread_kill.c:44 (__pthread_kill_implementation) 0xffff8a347608
+9012.782017335 lightningdBROKEN: backtrace: ../sysdeps/posix/raise.c:26 (__GI_raise) 0xffff8a2fcb3b
+9012.782018876 lightningdBROKEN: backtrace: ./stdlib/abort.c:79 (__GI_abort) 0xffff8a2e7dff
+9012.782020585 lightningdBROKEN: backtrace: ./assert/assert.c:96 (__assert_fail_base) 0xffff8a2f5cbf
+9012.782021918 lightningdBROKEN: backtrace: ./assert/assert.c:105 (__assert_fail) 0xffff8a2f5d2f
+9012.782023501 lightningdBROKEN: backtrace: common/fee_states.c:175 (marginal_feerate) 0xaaaacc08c8a7
+9012.782025293 lightningdBROKEN: backtrace: lightningd/peer_control.c:747 (commit_txfee) 0xaaaacc01149b
+9012.782027501 lightningdBROKEN: backtrace: lightningd/peer_control.c:814 (channel_amount_spendable) 0xaaaacc015d9b
+9012.782029918 lightningdBROKEN: backtrace: lightningd/peer_control.c:1222 (json_add_channel) 0xaaaacc016997
+9012.782031168 lightningdBROKEN: backtrace: lightningd/peer_control.c:2621 (json_add_peerchannels) 0xaaaacc016fe3
+9012.782047793 lightningdBROKEN: backtrace: lightningd/peer_control.c:2662 (json_listpeerchannels) 0xaaaacc0171bf
+9012.782050168 lightningdBROKEN: backtrace: lightningd/jsonrpc.c:769 (command_exec) 0xaaaacbff02d3
+9012.782051918 lightningdBROKEN: backtrace: lightningd/jsonrpc.c:910 (rpc_command_hook_final) 0xaaaacbff2517
+9012.782053293 lightningdBROKEN: backtrace: lightningd/plugin_hook.c:243 (hook_done) 0xaaaacc027b7b
+9012.782054376 lightningdBROKEN: backtrace: lightningd/plugin_hook.c:343 (plugin_hook_call_next) 0xaaaacc027caf
+9012.782055501 lightningdBROKEN: backtrace: lightningd/plugin_hook.c:395 (plugin_hook_call_) 0xaaaacc028983
+9012.782057168 lightningdBROKEN: backtrace: lightningd/jsonrpc.c:998 (plugin_hook_call_rpc_command) 0xaaaacbff2c4b
+9012.782058001 lightningdBROKEN: backtrace: lightningd/jsonrpc.c:1122 (parse_request) 0xaaaacbff2c4b
+9012.782059418 lightningdBROKEN: backtrace: lightningd/jsonrpc.c:1216 (read_json) 0xaaaacbff2fcb
+9012.782060668 lightningdBROKEN: backtrace: ccan/ccan/io/io.c:60 (next_plan) 0xaaaacc0d1d47
+9012.782061751 lightningdBROKEN: backtrace: ccan/ccan/io/io.c:422 (do_plan) 0xaaaacc0d231b
+9012.782064460 lightningdBROKEN: backtrace: ccan/ccan/io/io.c:439 (io_ready) 0xaaaacc0d23f3
+9012.782067585 lightningdBROKEN: backtrace: ccan/ccan/io/poll.c:470 (io_loop) 0xaaaacc0d43bf
+9012.782068751 lightningdBROKEN: backtrace: lightningd/io_loop_with_timers.c:22 (io_loop_with_timers) 0xaaaacbff01d3
+9012.782070043 lightningdBROKEN: backtrace: lightningd/lightningd.c:1492 (main) 0xaaaacbff6217
+9012.782071210 lightningdBROKEN: backtrace: ../sysdeps/nptl/libc_start_call_main.h:58 (__libc_start_call_main) 0xffff8a2e84c3
+9012.782072418 lightningdBROKEN: backtrace: ../csu/libc-start.c:360 (__libc_start_main_impl) 0xffff8a2e8597
+9012.782073460 lightningdBROKEN: backtrace: (null):0 ((null)) 0xaaaacbfc31ef
+9012.782074460 lightningdBROKEN: backtrace: (null):0 ((null)) 0xffffffffffffffff

[rustyrussell]

This is awesome! I cleaned up the test a little, and proceeded with the fix. Please review!

[enaples]

Since there is the general case test_opening_dualfund_with_unknown_feerates, I think that the previous test (test_opening_dualfund_with_unknown_feerates) can be deleted from PR.

Just to make sure, the channel opening should be successful if every node is able to autonomously compute fees, is it correct? If a node specify the feerate but the other one is not able to compute the fees, the fundchannel will fail, isn't it?

If we specify the feerate on fundchannel in the last line, it shall match the RpcError, correct?

def test_opening_incoming_unknown_feerates(node_factory, bitcoind):
    """
    Don't allow incoming channels if we can't estimate feerates.
    """
    nofee_opts = {'ignore-fee-limits': True,
                  'feerates': None,
                  'dev-no-fake-fees': True,
                  'experimental-dual-fund': None}

    l1, l2 = node_factory.get_nodes(2, opts=[{}, nofee_opts])

    l1.fundwallet(FUNDAMOUNT)

    # Connect peers
    l1.rpc.connect(l2.info['id'], 'localhost', l2.port)

    # Verify fee estimation is failing
    l2.daemon.wait_for_log('Unable to estimate any fees')

    # Open channel l1 <-> l2: l2 should refuse!
    with pytest.raises(RpcError, match=r'They sent.*Cannot accept channel: feerates unknown'):
        l1.rpc.fundchannel(l2.info['id'], 100000, "253perkw")

[enaples]

See comment above