Shutdown retransmission clarifications #199
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If we've completed shutdown, you must have received revoke_and_ack, so don't require us to re-xmit in that case. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
…exmit. closing_signed means we've completed shutdown, which means the other side knows. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
pm47
reviewed
Jul 22, 2017
| @@ -980,7 +980,7 @@ last `commitment_signed` message the receiving node has sent, it | |||
| SHOULD fail the channel. | |||
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| If `next_remote_revocation_number` is equal to the commitment number of | |||
| the last `revoke_and_ack` the receiving node has sent, it MUST re-send | |||
| the last `revoke_and_ack` the receiving node has sent and the receiving node has not already received a `closing_signed`, it MUST re-send | |||
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As you state in the rationale below, the sender won't send a closing_signed until it has sent the last revoke_and_ack.
Thus I don't see how this scenario is possible?
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Yes, exactly. It shouldn't happen, thus you don't need to handle it.
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Should we mention it though? There are an infinity of other scenarii that shouldn't happen, that we don't specify. Why is this specific one more important than the others? I might be missing something but to me it isn't really different from a node sending, say, two funding_locked in a row. That sounds silly I know but my concern is consistency.
How about stating somewhere else more generally what a node should do when the counterparty violates the order of messages of the protocol, eg. always fail the channel? I think that would be a reasonable thing, since AFAICT we were careful to specify when to ignore messages.
Roasbeef
requested changes
Jul 24, 2017
| On reconnection if the node has sent a previous `shutdown` it MUST | ||
| retransmit it, and if the node has sent a previous `closing_signed` it | ||
| MUST then retransmit the last `closing_signed`. | ||
| On reconnection if the node has sent a previous `closing_signed` it |
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Why do we even require sending an identical closing_signed message? I don't see a reason to make nodes worry about an additional layer of persistence.
It seems that upon re-connect, the closing negotiation should just start from scratch (similar to a failed funding negotiation). It also could be the case the the fee preferences of either side have changed significantly since the last connection.
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Done, added new patch.
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Pierre-Marie Padiou <notifications@github.com> writes:
pm47 commented on this pull request.
> @@ -980,7 +980,7 @@ last `commitment_signed` message the receiving node has sent, it
SHOULD fail the channel.
If `next_remote_revocation_number` is equal to the commitment number of
-the last `revoke_and_ack` the receiving node has sent, it MUST re-send
+the last `revoke_and_ack` the receiving node has sent and the receiving node has not already received a `closing_signed`, it MUST re-send
Should we mention it though? There are an infinity of other scenarii that shouldn't happen, that we don't specify. Why is this specific one more important than the others? I might be missing something but to me it isn't really different from a node sending, say, two `funding_locked` in a row. That sounds silly I know but my concern is consistency.
We should be specifying the requirements in *every* case, not relying on
the reader to know that things shouldn't happen.
Here, we say you MUST re-send, but my implementation won't if we're
already in closing_signed, which I think is reasonable, but violated the
spec before this change.
How about stating somewhere else more generally what a node should do when the counterparty violates the order of messages of the protocol, eg. always fail the channel? I think that would be a reasonable thing, since AFAICT we were careful to specify when to ignore messages.
I'd prefer each requirement to be spelled out in each case. eg. you
should receive X or Y, if you receive anything else for that channel,
you SHOULD fail the channel.
That's much easier to implement, and test!
We should fix places which don't do this...
Thanks,
Rusty.
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Olaoluwa Osuntokun <notifications@github.com> writes:
Roasbeef requested changes on this pull request.
> @@ -992,9 +992,9 @@ transaction is broadcast by the other side at any time. This is
particularly important if a node does not simply retransmit the exact
same `update_` messages as previously sent.
-On reconnection if the node has sent a previous `shutdown` it MUST
-retransmit it, and if the node has sent a previous `closing_signed` it
-MUST then retransmit the last `closing_signed`.
+On reconnection if the node has sent a previous `closing_signed` it
Why do we even require sending an _identical_ `closing_signed` message? I don't see a reason to make nodes worry about an _additional_ layer of persistence.
It seems that upon re-connect, the closing negotiation should just start from scratch (similar to a failed funding negotiation). It also could be the case the the fee preferences of either side have changed significantly since the last connection.
Agreed. Let me create a patch.
Should we mark the closing tx RBF? I don't expect any implementation to
do this any time soon, but it would allow us to use a prior closing tx
with higher fee if the current one gets stuck (or even, the final
commitment tx)?
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rustyrussell
added a commit
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Jul 29, 2017
1. Change descriptions of closing tx construction to references to BOLT 3. 2. Recipient *should* check the fee offer has improved in closing_signed. 3. Therefore, sender *must* improve closing offer. 4. Offers do not persist across reconnection, so no state req'd, and also helps if fee has changed. 5. You don't need to re-send `shutdown` if you received `closing_signed` (implicit acknowledgement). 6. You don't have to accept a `channel_reestablish` which requests the last revoke_and_ack be retransmitted if you've already received `closing_signed` (which is an implicit acknowledgement). Closes: lightning#201 Closes: lightning#199 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Merged
rustyrussell
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Jul 30, 2017
1. Change descriptions of closing tx construction to references to BOLT 3. 2. Recipient *should* check the fee offer has improved in closing_signed. 3. Therefore, sender *must* improve closing offer. 4. Offers do not persist across reconnection, so no state req'd, and also helps if fee has changed. 5. You don't need to re-send `shutdown` if you received `closing_signed` (implicit acknowledgement). 6. You don't have to accept a `channel_reestablish` which requests the last revoke_and_ack be retransmitted if you've already received `closing_signed` (which is an implicit acknowledgement). Closes: lightning#201 Closes: lightning#199 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
rustyrussell
added a commit
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Aug 8, 2017
1. Change descriptions of closing tx construction to references to BOLT 3. 2. Recipient *should* check the fee offer has improved in closing_signed. 3. Therefore, sender *must* improve closing offer. 4. Offers do not persist across reconnection, so no state req'd, and also helps if fee has changed. 5. You don't need to re-send `shutdown` if you received `closing_signed` (implicit acknowledgement). 6. You don't have to accept a `channel_reestablish` which requests the last revoke_and_ack be retransmitted if you've already received `closing_signed` (which is an implicit acknowledgement). Closes: lightning#201 Closes: lightning#199 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Fairly self-explanatory, I think.