Expose min_funding_satoshis via Config

[vincenzopalazzo]

Summary

• Add min_funding_sats field to Config that maps to LDK's ChannelHandshakeLimits::min_funding_satoshis
• Server operators can now enforce a higher minimum channel funding amount for inbound channels (default remains 1000 sats)
• Updated UniFFI bindings

Fixes #842

Test plan

• cargo check passes
• cargo test --lib config passes
• CI passes

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com
AI-assisted-by: OpenAI Codex

cc @tankyleo

[ldk-reviews-bot]

👋 Hi! This PR is now in draft status.
I'll wait to assign reviewers until you mark it as ready for review.
Just convert it out of draft status when you're ready for review!

[tankyleo]

I would have cleaned it up like this; I don't think it's worth adding the Option there, the config setting logically is just a single number.

diff --git a/src/config.rs b/src/config.rs
index ffd9d134..d6402257 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -28,6 +28,7 @@ const DEFAULT_LDK_WALLET_SYNC_INTERVAL_SECS: u64 = 30;
 const DEFAULT_FEE_RATE_CACHE_UPDATE_INTERVAL_SECS: u64 = 60 * 10;
 const DEFAULT_PROBING_LIQUIDITY_LIMIT_MULTIPLIER: u64 = 3;
 const DEFAULT_ANCHOR_PER_CHANNEL_RESERVE_SATS: u64 = 25_000;
+const DEFAULT_MIN_FUNDING_SATS: u64 = 1000;

 // The default timeout after which we abort a wallet syncing operation.
 const DEFAULT_BDK_WALLET_SYNC_TIMEOUT_SECS: u64 = 60;
@@ -125,7 +126,7 @@ pub(crate) const LNURL_AUTH_TIMEOUT_SECS: u64 = 15;
 /// | `node_alias`                           | None               |
 /// | `trusted_peers_0conf`                  | []                 |
 /// | `probing_liquidity_limit_multiplier`   | 3                  |
-/// | `min_funding_sats`                     | None               |
+/// | `min_funding_sats`                     | 1000               |
 /// | `anchor_channels_config`               | Some(..)           |
 /// | `route_parameters`                     | None               |
 /// | `tor_config`                           | None               |
@@ -172,13 +173,7 @@ pub struct Config {
        /// they open inbound channels to us.
        ///
        /// Channels with funding below this value will be rejected.
-       ///
-       /// If unset, the `rust-lightning` default of `1000` sats will be used.
-       ///
-       /// Please refer to [`ChannelHandshakeLimits::min_funding_satoshis`] for further details.
-       ///
-       /// [`ChannelHandshakeLimits::min_funding_satoshis`]: lightning::util::config::ChannelHandshakeLimits::min_funding_satoshis
-       pub min_funding_sats: Option<u64>,
+       pub min_funding_sats: u64,
        /// Configuration options pertaining to Anchor channels, i.e., channels for which the
        /// `option_anchors_zero_fee_htlc_tx` channel type is negotiated.
        ///
@@ -222,7 +217,7 @@ impl Default for Config {
                        announcement_addresses: None,
                        trusted_peers_0conf: Vec::new(),
                        probing_liquidity_limit_multiplier: DEFAULT_PROBING_LIQUIDITY_LIMIT_MULTIPLIER,
-                       min_funding_sats: None,
+                       min_funding_sats: DEFAULT_MIN_FUNDING_SATS,
                        anchor_channels_config: Some(AnchorChannelsConfig::default()),
                        tor_config: None,
                        route_parameters: None,
@@ -352,9 +347,7 @@ pub(crate) fn default_user_config(config: &Config) -> UserConfig {
        // will mostly be relevant for inbound channels.
        let mut user_config = UserConfig::default();
        user_config.channel_handshake_limits.force_announced_channel_preference = false;
-       if let Some(min_funding_sats) = config.min_funding_sats {
-               user_config.channel_handshake_limits.min_funding_satoshis = min_funding_sats;
-       }
+       user_config.channel_handshake_limits.min_funding_satoshis = config.min_funding_sats;
        user_config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx =
                config.anchor_channels_config.is_some();
        user_config.reject_inbound_splices = false;

[vincenzopalazzo]

@tankyleo Fixed in e2113b3. Switched Config::min_funding_sats to a plain u64 with an explicit 1000-sat default, removed the conditional assignment into the LDK user config, and added a unit test covering both the default and override path.

[tnull]

Thanks, but see #842 (comment)

For all values we'd also still want to fill them from LDK's defaults, not define our own default values in LDK Node as far as possible, as that would risk them getting out-of-sync at some point.

[vincenzopalazzo]

Moving the discussion on the issue #842 (comment) and moving the PR as a draft while we have the discussion going