Introduce SendingParameters struct

`SendingParameters` allows users to override opinionated values while
routing a payment such as `max_total_routing_fees`, `max_path_count`
`max_total_cltv_delta`, and `max_channel_saturation_power_of_half`

Updated docs for `max_channel_saturation_power_of_half` for
clarity.

Author: slanesuke

bindings/ldk_node.udl

@@ -319,6 +319,13 @@ dictionary PaymentDetails {
 	u64 latest_update_timestamp;
 };
 
+dictionary SendingParameters {
+    u64? max_total_routing_fee_msat;
+    u32? max_total_cltv_expiry_delta;
+    u8? max_path_count;
+    u8? max_channel_saturation_power_of_half;
+};
+
 [NonExhaustive]
 enum Network {
 	"Bitcoin",

src/payment/mod.rs

@@ -13,3 +13,52 @@ pub use onchain::OnchainPayment;
 pub use spontaneous::SpontaneousPayment;
 pub use store::{LSPFeeLimits, PaymentDetails, PaymentDirection, PaymentKind, PaymentStatus};
 pub use unified_qr::{QrPaymentResult, UnifiedQrPayment};
+
+/// Represents information used to route a payment.
+#[derive(Clone, Debug, PartialEq)]
+pub struct SendingParameters {
+	/// The maximum total fees, in millisatoshi, that may accrue during route finding.
+	///
+	/// This limit also applies to the total fees that may arise while retrying failed payment
+	/// paths.
+	///
+	/// Note that values below a few sats may result in some paths being spuriously ignored.
+	pub max_total_routing_fee_msat: Option<u64>,
+
+	/// The maximum total CLTV delta we accept for the route.
+	///
+	/// Defaults to [`DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA`].
+	///
+	/// [`DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA`]: lightning::routing::router::DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA
+	pub max_total_cltv_expiry_delta: Option<u32>,
+
+	/// The maximum number of paths that may be used by (MPP) payments.
+	///
+	/// Defaults to [`DEFAULT_MAX_PATH_COUNT`].
+	///
+	/// [`DEFAULT_MAX_PATH_COUNT`]: lightning::routing::router::DEFAULT_MAX_PATH_COUNT
+	pub max_path_count: Option<u8>,
+
+	/// Selects the maximum share of a channel's total capacity which will be sent over a channel,
+	/// as a power of 1/2.
+	///
+	/// A higher value prefers to send the payment using more MPP parts whereas
+	/// a lower value prefers to send larger MPP parts, potentially saturating channels and
+	/// increasing failure probability for those paths.
+	///
+	/// Note that this restriction will be relaxed during pathfinding after paths which meet this
+	/// restriction have been found. While paths which meet this criteria will be searched for, it
+	/// is ultimately up to the scorer to select them over other paths.
+	///
+	/// Examples:
+	///
+	/// | Value | Max Proportion of Channel Capacity Used |
+	/// |-------|-----------------------------------------|
+	/// | 0     | Up to 100% of the channel’s capacity    |
+	/// | 1     | Up to 50% of the channel’s capacity     |
+	/// | 2     | Up to 25% of the channel’s capacity     |
+	/// | 3     | Up to 12.5% of the channel’s capacity   |
+	///
+	/// Default value: 2
+	pub max_channel_saturation_power_of_half: Option<u8>,
+}

src/uniffi_types.rs

@@ -5,7 +5,7 @@
 
 pub use crate::graph::{ChannelInfo, ChannelUpdateInfo, NodeAnnouncementInfo, NodeInfo};
 pub use crate::payment::store::{LSPFeeLimits, PaymentDirection, PaymentKind, PaymentStatus};
-pub use crate::payment::QrPaymentResult;
+pub use crate::payment::{QrPaymentResult, SendingParameters};
 
 pub use lightning::events::{ClosureReason, PaymentFailureReason};
 pub use lightning::ln::{ChannelId, PaymentHash, PaymentPreimage, PaymentSecret};