offers: verify invoice upon return

Cargo.toml

@@ -35,7 +35,7 @@ triggered = "0.1.2"
 bitcoincore-rpc = { package="core-rpc", version = "0.17.0" }
 bitcoind = { version = "0.30.0", features = [ "22_0" ] }
 chrono = { version = "0.4.26" }
-ldk-sample = { git = "https://github.com/lndk-org/ldk-sample", branch = "offers" }
+ldk-sample = { git = "https://github.com/lndk-org/ldk-sample", branch = "offer-handling" }
 mockall = "0.11.3"
 tempfile = "3.5.0"
 

src/lib.rs

@@ -11,11 +11,12 @@ use crate::lnd::{
 use crate::lndk_offers::{connect_to_peer, validate_amount, OfferError};
 use crate::onion_messenger::MessengerUtilities;
 use bitcoin::network::constants::Network;
-use bitcoin::secp256k1::{Error as Secp256k1Error, PublicKey};
+use bitcoin::secp256k1::{Error as Secp256k1Error, PublicKey, Secp256k1};
 use home::home_dir;
 use lightning::blinded_path::BlindedPath;
 use lightning::ln::inbound_payment::ExpandedKey;
 use lightning::ln::peer_handler::IgnoringMessageHandler;
+use lightning::offers::invoice_error::InvoiceError;
 use lightning::offers::offer::Offer;
 use lightning::onion_message::{
     DefaultMessageRouter, Destination, OffersMessage, OffersMessageHandler, OnionMessenger,
@@ -244,7 +245,7 @@ impl OfferHandler {
         let invoice_request = self
             .create_invoice_request(
                 cfg.client.clone(),
-                cfg.offer,
+                cfg.offer.clone(),
                 vec![],
                 cfg.network,
                 validated_amount,
@@ -275,7 +276,7 @@ impl OfferHandler {
         std::mem::drop(pending_messages);
 
         let mut active_offers = self.active_offers.lock().unwrap();
-        active_offers.insert(offer_id, OfferState::InvoiceRequestSent);
+        active_offers.insert(cfg.offer.to_string(), OfferState::InvoiceRequestSent);
 
         Ok(())
     }
@@ -294,7 +295,20 @@ impl OffersMessageHandler for OfferHandler {
                 log::error!("Invoice request received, payment not yet supported.");
                 None
             }
-            OffersMessage::Invoice(_invoice) => None,
+            OffersMessage::Invoice(invoice) => {
+                let secp_ctx = &Secp256k1::new();
+                // We verify that this invoice is a response to the invoice request we just sent.
+                match invoice.verify(&self.expanded_key, secp_ctx) {
+                    // TODO: Eventually when we allow for multiple payments in flight, we can use the
+                    // returned payment id below to check if we already processed an invoice for
+                    // this payment. Right now it's safe to let this be because we won't try to pay
+                    // a second invoice (if it comes through).
+                    Ok(_payment_id) => Some(OffersMessage::Invoice(invoice)),
+                    Err(()) => Some(OffersMessage::InvoiceError(InvoiceError::from_string(
+                        String::from("invoice verification failure"),
+                    ))),
+                }
+            }
             OffersMessage::InvoiceError(_error) => None,
         }
     }