Expose methods for ChannelManager-less phantom invoice generation

Author: valentinewallace

lightning-invoice/src/utils.rs

@@ -38,16 +38,20 @@ use sync::Mutex;
 ///   may be too long for QR code scanning. To fix this, `PhantomRouteHints::channels` may be pared
 ///   down
 ///
-/// `payment_hash` and `payment_secret` come from [`ChannelManager::create_inbound_payment`] or
+/// `payment_hash` and `payment_secret` can come from [`ChannelManager::create_inbound_payment`] or
 /// [`ChannelManager::create_inbound_payment_for_hash`]. These values can be retrieved from any
-/// participating node.
+/// participating node. Alternatively, [`inbound_payment::create`] or
+/// [`inbound_payment::create_from_hash`] may be used to retrieve these values without a
+/// `ChannelManager`.
 ///
 /// Note that the provided `keys_manager`'s `KeysInterface` implementation must support phantom
 /// invoices in its `sign_invoice` implementation ([`PhantomKeysManager`] satisfies this
 /// requirement).
 ///
 /// [`PhantomKeysManager`]: lightning::chain::keysinterface::PhantomKeysManager
 /// [`ChannelManager::get_phantom_route_hints`]: lightning::ln::channelmanager::ChannelManager::get_phantom_route_hints
+/// [`inbound_payment::create`]: lightning::ln::inbound_payment::create
+/// [`inbound_payment::create_from_hash`]: lightning::ln::inbound_payment::create_from_hash
 /// [`PhantomRouteHints::channels`]: lightning::ln::channelmanager::PhantomRouteHints::channels
 pub fn create_phantom_invoice<Signer: Sign, K: Deref>(
 	amt_msat: Option<u64>, description: String, payment_hash: PaymentHash, payment_secret: PaymentSecret,
@@ -76,16 +80,20 @@ pub fn create_phantom_invoice<Signer: Sign, K: Deref>(
 ///
 /// `description_hash` is a SHA-256 hash of the description text
 ///
-/// `payment_hash` and `payment_secret` come from [`ChannelManager::create_inbound_payment`] or
+/// `payment_hash` and `payment_secret` can come from [`ChannelManager::create_inbound_payment`] or
 /// [`ChannelManager::create_inbound_payment_for_hash`]. These values can be retrieved from any
-/// participating node.
+/// participating node. Alternatively, [`inbound_payment::create`] or
+/// [`inbound_payment::create_from_hash`] may be used to retrieve these values without a
+/// `ChannelManager`.
 ///
 /// Note that the provided `keys_manager`'s `KeysInterface` implementation must support phantom
 /// invoices in its `sign_invoice` implementation ([`PhantomKeysManager`] satisfies this
 /// requirement).
 ///
 /// [`PhantomKeysManager`]: lightning::chain::keysinterface::PhantomKeysManager
 /// [`ChannelManager::get_phantom_route_hints`]: lightning::ln::channelmanager::ChannelManager::get_phantom_route_hints
+/// [`inbound_payment::create`]: lightning::ln::inbound_payment::create
+/// [`inbound_payment::create_from_hash`]: lightning::ln::inbound_payment::create_from_hash
 /// [`PhantomRouteHints::channels`]: lightning::ln::channelmanager::PhantomRouteHints::channels
 pub fn create_phantom_invoice_with_description_hash<Signer: Sign, K: Deref>(
 	amt_msat: Option<u64>, description_hash: Sha256, payment_hash: PaymentHash,

lightning/src/ln/inbound_payment.rs

@@ -38,7 +38,7 @@ const METHOD_TYPE_OFFSET: usize = 5;
 /// [`KeysInterface::get_inbound_payment_key_material`].
 ///
 /// [`KeysInterface::get_inbound_payment_key_material`]: crate::chain::keysinterface::KeysInterface::get_inbound_payment_key_material
-pub(super) struct ExpandedKey {
+pub struct ExpandedKey {
 	/// The key used to encrypt the bytes containing the payment metadata (i.e. the amount and
 	/// expiry, included for payment verification on decryption).
 	metadata_key: [u8; 32],
@@ -51,7 +51,10 @@ pub(super) struct ExpandedKey {
 }
 
 impl ExpandedKey {
-	pub(super) fn new(key_material: &KeyMaterial) -> ExpandedKey {
+	/// Create a  new [`ExpandedKey`] for generating an inbound payment hash and secret.
+	///
+	/// It is recommended to cache this value and not regenerate it for each new inbound payment.
+	pub fn new(key_material: &KeyMaterial) -> ExpandedKey {
 		let (metadata_key, ldk_pmt_hash_key, user_pmt_hash_key) =
 			hkdf_extract_expand_thrice(b"LDK Inbound Payment Key Expansion", &key_material.0);
 		Self {
@@ -77,10 +80,21 @@ impl Method {
 	}
 }
 
-pub(super) fn create<Signer: Sign, K: Deref>(keys: &ExpandedKey, min_value_msat: Option<u64>, invoice_expiry_delta_secs: u32, keys_manager: &K, highest_seen_timestamp: u64) -> Result<(PaymentHash, PaymentSecret), ()>
+/// Equivalent to [`crate::ln::channelmanager::ChannelManager::create_inbound_payment`], but no
+/// `ChannelManager` is required. Useful for generating invoices for [phantom node payments] without
+/// a `ChannelManager`.
+///
+/// `keys` is generated by calling [`KeysInterface::get_inbound_payment_key_material`] and then
+/// calling [`ExpandedKey::new`] with its result. It is recommended to cache this value and not
+/// regenerate it for each new inbound payment.
+///
+/// `current_time` is a Unix timestamp representing the current time.
+///
+/// [phantom node payments]: crate::chain::keysinterface::PhantomKeysManager
+pub fn create<Signer: Sign, K: Deref>(keys: &ExpandedKey, min_value_msat: Option<u64>, invoice_expiry_delta_secs: u32, keys_manager: &K, current_time: u64) -> Result<(PaymentHash, PaymentSecret), ()>
 	where K::Target: KeysInterface<Signer = Signer>
 {
-	let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::LdkPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
+	let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::LdkPaymentHash, invoice_expiry_delta_secs, current_time)?;
 
 	let mut iv_bytes = [0 as u8; IV_LEN];
 	let rand_bytes = keys_manager.get_secure_random_bytes();
@@ -96,8 +110,15 @@ pub(super) fn create<Signer: Sign, K: Deref>(keys: &ExpandedKey, min_value_msat:
 	Ok((ldk_pmt_hash, payment_secret))
 }
 
-pub(super) fn create_from_hash(keys: &ExpandedKey, min_value_msat: Option<u64>, payment_hash: PaymentHash, invoice_expiry_delta_secs: u32, highest_seen_timestamp: u64) -> Result<PaymentSecret, ()> {
-	let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::UserPaymentHash, invoice_expiry_delta_secs, highest_seen_timestamp)?;
+/// Equivalent to [`crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash`],
+/// but no `ChannelManager` is required. Useful for generating invoices for [phantom node payments]
+/// without a `ChannelManager`.
+///
+/// See [`create`] for information on the `keys` and `current_time` parameters.
+///
+/// [phantom node payments]: crate::chain::keysinterface::PhantomKeysManager
+pub fn create_from_hash(keys: &ExpandedKey, min_value_msat: Option<u64>, payment_hash: PaymentHash, invoice_expiry_delta_secs: u32, current_time: u64) -> Result<PaymentSecret, ()> {
+	let metadata_bytes = construct_metadata_bytes(min_value_msat, Method::UserPaymentHash, invoice_expiry_delta_secs, current_time)?;
 
 	let mut hmac = HmacEngine::<Sha256>::new(&keys.user_pmt_hash_key);
 	hmac.input(&metadata_bytes);