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Feature option_scid_alias separate from zero-conf #923

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Feature option_scid_alias separate from zero-conf #923

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44 changes: 41 additions & 3 deletions 02-peer-protocol.md
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Original file line number Diff line number Diff line change
Expand Up @@ -409,10 +409,23 @@ this channel will continue to use `option_static_remotekey` or `option_anchor_ou

This message indicates that the funding transaction has reached the `minimum_depth` asked for in `accept_channel`. Once both nodes have sent this, the channel enters normal operating mode.

Nodes which have funded the channel, or trust their peers to have
done, or wish to use `push_msat` from other side's opening (without
accepting incoming HTLCs) can simply send their `funding_locked` right
away. As soon as both parties have sent their `funding_locked`, the channel
can be used even if the funding transaction hasn't yet been confirmed.

1. type: 36 (`funding_locked`)
2. data:
* [`channel_id`:`channel_id`]
* [`point`:`next_per_commitment_point`]
* [`funding_locked_tlvs`:`tlvs`]

1. `tlv_stream`: `funding_locked_tlvs`
2. types:
1. type: 1 (`short_channel_id`)
2. data:
* [`short_channel_id`:`alias`]

#### Requirements

Expand All @@ -422,12 +435,26 @@ The sender MUST:
- wait until the funding transaction has reached `minimum_depth` before
sending this message.
- set `next_per_commitment_point` to the per-commitment point to be used
for the following commitment transaction, derived as specified in
for commitment transaction #1, derived as specified in
[BOLT #3](03-transactions.md#per-commitment-secret-requirements).
- if `option_scid_alias` was negotiated:
- SHOULD set `short_channel_id` `alias`.
- if it sets `alias`:
- MUST set `alias` to a value not related to the real `short_channel_id`.
- MUST NOT send the same `alias` for multiple peers.
- MUST always recognize the `alias` as a `short_channel_id` for incoming HTLCs to this channel.
- MAY send multiple `funding_locked` messages with different `alias` values.
- otherwise:
- MUST wait until the funding transaction has reached `minimum_depth` before sending this message.

The receiver:
- MAY use any of the `alias` it received in BOLT 11 `r` fields.
- if it received at least one `alias`:
- MUST NOT use the real `short_channel_id` in BOLT 11 `r` fields.

A non-funding node (fundee):
- SHOULD forget the channel if it does not see the correct funding
transaction after a timeout of 2016 blocks.
transaction after a timeout of 2016 blocks.

From the point of waiting for `funding_locked` onward, either node MAY
fail the channel if it does not receive a required response from the
Expand All @@ -445,6 +472,16 @@ to broadcast the commitment transaction to get his funds back and open a new
channel. To avoid this, the funder should ensure the funding transaction
confirms in the next 2016 blocks.

The `alias` here is both required for routing (since the real
short_channel_id is unknown until confirmation), and useful even once
there is a real `short_channel_id` for a public channel.

While a node can send multiple `alias`, it must remember all of the
ones it has sent so it can use them should they be requested by
incoming HTLCs. The recipient only need remember one, for use in
`r` route hints in BOLT 11 invoices.


## Channel Close

Nodes can negotiate a mutual close of the connection, which unlike a
Expand Down Expand Up @@ -1241,7 +1278,8 @@ A node:
sent and received:
- MUST retransmit `funding_locked`.
- otherwise:
- MUST NOT retransmit `funding_locked`.
- MUST NOT retransmit `funding_locked`, but MAY send `funding_locked` with
a different `short_channel_id` `alias` field.
- upon reconnection:
- MUST ignore any redundant `funding_locked` it receives.
- if `next_commitment_number` is equal to the commitment number of
Expand Down
2 changes: 2 additions & 0 deletions 09-features.md
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Expand Up @@ -41,6 +41,7 @@ The Context column decodes as follows:
| 20/21 | `option_anchor_outputs` | Anchor outputs | IN | `option_static_remotekey` | [BOLT #3](03-transactions.md) |
| 22/23 | `option_anchors_zero_fee_htlc_tx` | Anchor commitment type with zero fee HTLC transactions | IN | | [BOLT #3][bolt03-htlc-tx], [lightning-dev][ml-sighash-single-harmful]|
| 26/27 | `option_shutdown_anysegwit` | Future segwit versions allowed in `shutdown` | IN | | [BOLT #2][bolt02-shutdown] |
| 46/47 | `option_scid_alias`| Supports channel aliases for routing | IN | | [BOLT #2][bolt02-funding-locked] |

## Requirements

Expand Down Expand Up @@ -84,6 +85,7 @@ This work is licensed under a [Creative Commons Attribution 4.0 International Li
[bolt02-open]: 02-peer-protocol.md#the-open_channel-message
[bolt03-htlc-tx]: 03-transactions.md#htlc-timeout-and-htlc-success-transactions
[bolt02-shutdown]: 02-peer-protocol.md#closing-initiation-shutdown
[bolt02-funding-locked]: 02-peer-protocol.md#the-funding_locked-message
[bolt04]: 04-onion-routing.md
[bolt07-sync]: 07-routing-gossip.md#initial-sync
[bolt07-query]: 07-routing-gossip.md#query-messages
Expand Down