From 9a97f8c154dfc84e69d494a1a72bfdc00041de5a Mon Sep 17 00:00:00 2001
From: Christian Decker <decker.christian@gmail.com>
Date: Wed, 8 Jun 2022 13:54:18 +0200
Subject: [PATCH] plugin: Add `reserve` to `openchannel` hook result

Changelog-Added: plugin: The `openchannel` hook may return a custom absolute `reserve` value that the peer must not dip below.
---
 doc/PLUGINS.md               | 18 +++++++++++++++++-
 lightningd/opening_control.c | 11 +++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/doc/PLUGINS.md b/doc/PLUGINS.md
index 563e34fe0..6152bed95 100644
--- a/doc/PLUGINS.md
+++ b/doc/PLUGINS.md
@@ -1198,13 +1198,29 @@ e.g.
 {
     "result": "continue",
     "close_to": "bc1qlq8srqnz64wgklmqvurv7qnr4rvtq2u96hhfg2"
+	"mindepth": 0,
+	"reserve": "1234sat"
 }
 ```
 
 Note that `close_to` must be a valid address for the current chain,
 an invalid address will cause the node to exit with an error.
 
-Note that `openchannel` is a chained hook. Therefore `close_to` will only be
+ - `mindepth` is the number of confirmations to require before making
+   the channel usable. Notice that setting this to 0 (`zeroconf`) or
+   some other low value might expose you to double-spending issues, so
+   only lower this value from the default if you trust the peer not to
+   double-spend, or you reject incoming payments, including forwards,
+   until the funding is confirmed.
+
+ - `reserve` is an absolute value for the amount in the channel that
+   the peer must keep on their side. This ensures that they always
+   have something to lose, so only lower this below the 1% of funding
+   amount if you trust the peer. The protocol requires this to be
+   larger than the dust limit, hence it will be adjusted to be the
+   dust limit if the specified value is below.
+
+Note that `openchannel` is a chained hook. Therefore `close_to`, `reserve` will only be
 evaluated for the first plugin that sets it. If more than one plugin tries to
 set a `close_to` address an error will be logged.
 
diff --git a/lightningd/opening_control.c b/lightningd/opening_control.c
index a82959a53..bbdcf7745 100644
--- a/lightningd/opening_control.c
+++ b/lightningd/opening_control.c
@@ -732,6 +732,7 @@ openchannel_hook_deserialize(struct openchannel_hook_payload *payload,
 	const jsmntok_t *t_errmsg  = json_get_member(buffer, toks, "error_message");
 	const jsmntok_t *t_closeto = json_get_member(buffer, toks, "close_to");
 	const jsmntok_t *t_mindepth = json_get_member(buffer, toks, "mindepth");
+	const jsmntok_t *t_reserve = json_get_member(buffer, toks, "reserve");
 
 	if (!t_result)
 		fatal("Plugin returned an invalid response to the"
@@ -793,6 +794,16 @@ openchannel_hook_deserialize(struct openchannel_hook_payload *payload,
 		    payload->uc->minimum_depth);
 	}
 
+	if (t_reserve != NULL) {
+		payload->uc->reserve = tal(payload->uc, struct amount_sat);
+		json_to_sat(buffer, t_reserve, payload->uc->reserve);
+		log_debug(openingd->ld->log,
+			  "Setting reserve=%s for this channel as requested by "
+			  "the openchannel hook",
+			  type_to_string(tmpctx, struct amount_sat,
+					 payload->uc->reserve));
+	}
+
 	return true;
 }