WIP: InvoiceRequestBuilder

Author: jkczyz

lightning/src/offers/invoice_request.rs

@@ -9,18 +9,121 @@
 
 //! Data structures and encoding for `invoice_request` messages.
 
+use bitcoin::blockdata::constants::genesis_block;
 use bitcoin::hash_types::BlockHash;
-use bitcoin::secp256k1::PublicKey;
+use bitcoin::network::constants::Network;
+use bitcoin::secp256k1::{Message, PublicKey, self};
 use bitcoin::secp256k1::schnorr::Signature;
 use core::convert::TryFrom;
 use core::str::FromStr;
 use io;
 use ln::features::OfferFeatures;
 use offers::merkle::{SignatureTlvStream, self};
-use offers::offer::{Amount, OfferContents, OfferTlvStream, self};
+use offers::offer::{Offer, OfferContents, OfferTlvStream, self};
 use offers::parse::{Bech32Encode, ParseError, SemanticError};
 use offers::payer::{PayerContents, PayerTlvStream, self};
-use util::ser::{Writeable, Writer};
+use util::ser::{WithoutLength, Writeable, Writer};
+
+///
+const SIGNATURE_TAG: &'static str = concat!("lightning", "invoice_request", "signature");
+
+///
+pub struct InvoiceRequestBuilder<'a> {
+	offer: &'a Offer,
+	invoice_request: InvoiceRequestContents,
+}
+
+impl<'a> InvoiceRequestBuilder<'a> {
+	pub(super) fn new(offer: &'a Offer, payer_id: PublicKey) -> Self {
+		Self {
+			offer,
+			invoice_request: InvoiceRequestContents {
+				payer: PayerContents(None), offer: offer.contents.clone(), chain: None,
+				amount_msats: None, features: None, quantity: None, payer_id, payer_note: None,
+				signature: None,
+			},
+		}
+	}
+
+	///
+	pub fn payer_info(mut self, payer_info: Vec<u8>) -> Self {
+		self.invoice_request.payer = PayerContents(Some(payer_info));
+		self
+	}
+
+	///
+	pub fn chain(mut self, network: Network) -> Result<Self, SemanticError> {
+		let block_hash = genesis_block(network).block_hash();
+		if !self.offer.supports_chain(block_hash) {
+			return Err(SemanticError::UnsupportedChain)
+		}
+
+		self.invoice_request.chain = Some(block_hash);
+		Ok(self)
+	}
+
+	///
+	pub fn amount_msats(mut self, amount_msats: u64) -> Result<Self, SemanticError> {
+		if !self.offer.is_sufficient_amount(amount_msats) {
+			return Err(SemanticError::InsufficientAmount);
+		}
+
+		self.invoice_request.amount_msats = Some(amount_msats);
+		Ok(self)
+	}
+
+	///
+	pub fn features(mut self, features: OfferFeatures) -> Self {
+		self.invoice_request.features = Some(features);
+		self
+	}
+
+	///
+	pub fn quantity(mut self, quantity: u64) -> Result<Self, SemanticError> {
+		if !self.offer.is_valid_quantity(quantity) {
+			return Err(SemanticError::InvalidQuantity);
+		}
+
+		self.invoice_request.quantity = Some(quantity);
+		Ok(self)
+	}
+
+	///
+	pub fn payer_note(mut self, payer_note: String) -> Self {
+		self.invoice_request.payer_note = Some(payer_note);
+		self
+	}
+
+	///
+	pub fn build_signed<F>(mut self, sign: F) -> Result<InvoiceRequest, secp256k1::Error>
+	where F: FnOnce(&Message) -> Signature
+	{
+		// Use the offer bytes instead of the offer TLV stream as the offer may have contained
+		// unknown TLV records, which are not stored in `OfferContents`.
+		let (payer_tlv_stream, _offer_tlv_stream, invoice_request_tlv_stream, _) =
+			self.invoice_request.as_tlv_stream();
+		let offer_bytes = WithoutLength(&self.offer.bytes);
+		let unsigned_tlv_stream = (payer_tlv_stream, offer_bytes, invoice_request_tlv_stream);
+
+		let mut bytes = Vec::new();
+		unsigned_tlv_stream.write(&mut bytes).unwrap();
+
+		let pubkey = self.invoice_request.payer_id;
+		let signature = merkle::sign_message(sign, SIGNATURE_TAG, &bytes, pubkey)?;
+		self.invoice_request.signature = Some(signature);
+
+		// Append the signature TLV record to the bytes.
+		let signature_tlv_stream = merkle::reference::SignatureTlvStream {
+			signature: self.invoice_request.signature.as_ref(),
+		};
+		signature_tlv_stream.write(&mut bytes).unwrap();
+
+		Ok(InvoiceRequest {
+			bytes,
+			contents: self.invoice_request,
+		})
+	}
+}
 
 ///
 pub struct InvoiceRequest {
@@ -111,8 +214,7 @@ impl FromStr for InvoiceRequest {
 		let contents = InvoiceRequestContents::try_from(tlv_stream)?;
 
 		if let Some(signature) = &contents.signature {
-			let tag = concat!("lightning", "invoice_request", "signature");
-			merkle::verify_signature(signature, tag, &bytes, contents.payer_id)?;
+			merkle::verify_signature(signature, SIGNATURE_TAG, &bytes, contents.payer_id)?;
 		}
 
 		Ok(InvoiceRequest { bytes, contents })
@@ -133,25 +235,22 @@ impl TryFrom<FullInvoiceRequestTlvStream> for InvoiceRequestContents {
 		let payer = PayerContents(payer_info.map(Into::into));
 		let offer = OfferContents::try_from(offer_tlv_stream)?;
 
-		let chain = match chain {
-			None => None,
-			Some(chain) if chain == offer.chain() => Some(chain),
-			Some(_) => return Err(SemanticError::UnsupportedChain),
-		};
+		if !offer.supports_chain(chain.unwrap_or_else(|| offer.implied_chain())) {
+			return Err(SemanticError::UnsupportedChain);
+		}
 
 		// TODO: Determine whether quantity should be accounted for
 		let amount_msats = match (offer.amount(), amount.map(Into::into)) {
 			// TODO: Handle currency case
-			(Some(Amount::Currency { .. }), _) => return Err(SemanticError::UnexpectedCurrency),
 			(Some(_), None) => return Err(SemanticError::MissingAmount),
-			(Some(Amount::Bitcoin { amount_msats: offer_amount_msats }), Some(amount_msats)) => {
-				if amount_msats < *offer_amount_msats {
+			(Some(_), Some(amount_msats)) => {
+				if !offer.is_sufficient_amount(amount_msats) {
 					return Err(SemanticError::InsufficientAmount);
 				} else {
 					Some(amount_msats)
 				}
 			},
-			(_, amount_msats) => amount_msats,
+			(None, amount_msats) => amount_msats,
 		};
 
 		if let Some(features) = &features {

lightning/src/offers/merkle.rs

@@ -20,17 +20,37 @@ tlv_stream!(struct SignatureTlvStream {
 	(240, signature: Signature),
 });
 
+pub(super) fn sign_message<F>(
+	sign: F, tag: &str, bytes: &[u8], pubkey: PublicKey,
+) -> Result<Signature, secp256k1::Error>
+where
+	F: FnOnce(&Message) -> Signature
+{
+	let digest = message_digest(tag, bytes);
+	let signature = sign(&digest);
+
+	let pubkey = pubkey.into();
+	let secp_ctx = Secp256k1::verification_only();
+	secp_ctx.verify_schnorr(&signature, &digest, &pubkey)?;
+
+	Ok(signature)
+}
+
 pub(super) fn verify_signature(
 	signature: &Signature, tag: &str, bytes: &[u8], pubkey: PublicKey,
 ) -> Result<(), secp256k1::Error> {
-	let tag = sha256::Hash::hash(tag.as_bytes());
-	let merkle_root = root_hash(bytes);
-	let digest = Message::from_slice(&tagged_hash(tag, merkle_root)).unwrap();
+	let digest = message_digest(tag, bytes);
 	let pubkey = pubkey.into();
 	let secp_ctx = Secp256k1::verification_only();
 	secp_ctx.verify_schnorr(signature, &digest, &pubkey)
 }
 
+fn message_digest(tag: &str, bytes: &[u8]) -> Message {
+	let tag = sha256::Hash::hash(tag.as_bytes());
+	let merkle_root = root_hash(bytes);
+	Message::from_slice(&tagged_hash(tag, merkle_root)).unwrap()
+}
+
 fn root_hash(data: &[u8]) -> sha256::Hash {
 	let mut tlv_stream = TlvStream::new(&data[..]).peekable();
 	let nonce_tag = tagged_hash_engine(sha256::Hash::from_engine({

lightning/src/offers/offer.rs

@@ -20,6 +20,7 @@ use core::str::FromStr;
 use core::time::Duration;
 use io;
 use ln::features::OfferFeatures;
+use offers::invoice_request::InvoiceRequestBuilder;
 use offers::parse::{Bech32Encode, ParseError, SemanticError};
 use util::ser::{WithLength, Writeable, Writer};
 
@@ -150,8 +151,8 @@ impl OfferBuilder {
 ///
 #[derive(Clone, Debug)]
 pub struct Offer {
-	bytes: Vec<u8>,
-	contents: OfferContents,
+	pub(super) bytes: Vec<u8>,
+	pub(super) contents: OfferContents,
 }
 
 ///
@@ -176,6 +177,11 @@ impl Offer {
 		self.contents.chain()
 	}
 
+	///
+	pub fn supports_chain(&self, chain: BlockHash) -> bool {
+		self.contents.supports_chain(chain)
+	}
+
 	///
 	pub fn metadata(&self) -> Option<&Vec<u8>> {
 		self.contents.metadata.as_ref()
@@ -186,6 +192,11 @@ impl Offer {
 		self.contents.amount()
 	}
 
+	///
+	pub fn is_sufficient_amount(&self, amount_msats: u64) -> bool {
+		self.contents.is_sufficient_amount(amount_msats)
+	}
+
 	///
 	pub fn description(&self) -> &String {
 		&self.contents.description
@@ -243,6 +254,11 @@ impl Offer {
 		self.contents.node_id.unwrap()
 	}
 
+	///
+	pub fn request_invoice(&self, payer_id: PublicKey) -> InvoiceRequestBuilder {
+		InvoiceRequestBuilder::new(self, payer_id)
+	}
+
 	#[cfg(test)]
 	fn as_bytes(&self) -> &[u8] {
 		&self.bytes
@@ -273,13 +289,34 @@ impl OfferContents {
 		self.chains
 			.as_ref()
 			.and_then(|chains| chains.first().copied())
-			.unwrap_or_else(|| genesis_block(Network::Bitcoin).block_hash())
+			.unwrap_or_else(|| self.implied_chain())
+	}
+
+	///
+	pub fn supports_chain(&self, chain: BlockHash) -> bool {
+		self.chains
+			.as_ref()
+			.map(|chains| chains.contains(&chain))
+			.unwrap_or_else(||chain == self.implied_chain())
+	}
+
+	pub(super) fn implied_chain(&self) -> BlockHash {
+		genesis_block(Network::Bitcoin).block_hash()
 	}
 
 	pub fn amount(&self) -> Option<&Amount> {
 		self.amount.as_ref()
 	}
 
+	pub fn is_sufficient_amount(&self, amount_msats: u64) -> bool {
+		match self.amount {
+			Some(Amount::Currency { .. }) => unimplemented!(),
+			Some(Amount::Bitcoin { amount_msats: offer_amount_msats }) => {
+				amount_msats >= offer_amount_msats
+			},
+			None => true,
+		}
+	}
 	pub fn quantity_min(&self) -> u64 {
 		self.quantity_min.unwrap_or(1)
 	}
@@ -519,6 +556,7 @@ mod tests {
 
 		assert_eq!(offer.as_bytes(), &offer.to_bytes()[..]);
 		assert_eq!(offer.chain(), genesis_block(Network::Bitcoin).block_hash());
+		assert!(offer.supports_chain(genesis_block(Network::Bitcoin).block_hash()));
 		assert_eq!(offer.metadata(), None);
 		assert_eq!(offer.amount(), None);
 		assert_eq!(offer.description(), "foo");
@@ -556,6 +594,7 @@ mod tests {
 		let offer = OfferBuilder::new("foo".into(), pubkey())
 			.chain(Network::Bitcoin)
 			.build();
+		assert!(offer.supports_chain(block_hash));
 		assert_eq!(offer.chain(), block_hash);
 		assert_eq!(offer.as_tlv_stream().chains, Some((&vec![block_hash]).into()));
 
@@ -570,6 +609,8 @@ mod tests {
 			.chain(Network::Bitcoin)
 			.chain(Network::Testnet)
 			.build();
+		assert!(offer.supports_chain(block_hashes[0]));
+		assert!(offer.supports_chain(block_hashes[1]));
 		assert_eq!(offer.chain(), block_hashes[0]);
 		assert_eq!(offer.as_tlv_stream().chains, Some((&block_hashes).into()));
 	}