WIP: Offer semantic checks

Author: jkczyz

lightning/src/offers/mod.rs

@@ -15,6 +15,7 @@ use bitcoin::bech32::FromBase32;
 use bitcoin::hash_types::BlockHash;
 use bitcoin::secp256k1::{PublicKey, XOnlyPublicKey};
 use bitcoin::secp256k1::schnorr::Signature;
+use core::convert::TryFrom;
 use core::str::FromStr;
 use core::time::Duration;
 use ln::PaymentHash;
@@ -188,6 +189,25 @@ pub enum ParseError {
 	Bech32(bech32::Error),
 	/// The bech32 decoded string could not be decoded as the expected message type.
 	Decode(DecodeError),
+	/// The parsed message has invalid semantics.
+	InvalidSemantics(SemanticError),
+}
+
+#[derive(Debug, PartialEq)]
+///
+pub enum SemanticError {
+	///
+	MissingDescription,
+	///
+	MissingDestination,
+	///
+	DuplicateDestination,
+	///
+	MissingPaths,
+	///
+	InvalidQuantity,
+	///
+	UnexpectedRefund,
 }
 
 impl From<bech32::Error> for ParseError {
@@ -202,6 +222,69 @@ impl From<DecodeError> for ParseError {
 	}
 }
 
+impl From<SemanticError> for ParseError {
+	fn from(error: SemanticError) -> Self {
+		Self::InvalidSemantics(error)
+	}
+}
+
+impl FromStr for Offer {
+	type Err = ParseError;
+
+	fn from_str(s: &str) -> Result<Self, <Self as FromStr>::Err> {
+		let tlv_stream = OfferTlvStream::from_str(s)?;
+		Ok(Offer::try_from(tlv_stream)?)
+	}
+}
+
+impl TryFrom<OfferTlvStream> for Offer {
+	type Error = SemanticError;
+
+	fn try_from(tlv_stream: OfferTlvStream) -> Result<Self, Self::Error> {
+		if tlv_stream.description.is_none() {
+			return Err(SemanticError::MissingDescription);
+		}
+
+		if tlv_stream.node_id.is_none() && tlv_stream.paths.is_none() {
+			return Err(SemanticError::MissingDestination);
+		}
+
+		if tlv_stream.node_id.is_some() && tlv_stream.paths.is_some() {
+			return Err(SemanticError::DuplicateDestination);
+		}
+
+		if let Some(WithoutLength(ref paths)) = tlv_stream.paths {
+			if paths.is_empty() {
+				return Err(SemanticError::MissingPaths);
+			}
+		}
+
+		if let Some(HighZeroBytesDroppedVarInt(quantity_min)) = tlv_stream.quantity_min {
+			if quantity_min < 1 {
+				return Err(SemanticError::InvalidQuantity);
+			}
+
+			if let Some(HighZeroBytesDroppedVarInt(quantity_max)) = tlv_stream.quantity_max {
+				if quantity_min > quantity_max {
+					return Err(SemanticError::InvalidQuantity);
+				}
+			}
+		}
+
+		if let Some(HighZeroBytesDroppedVarInt(quantity_max)) = tlv_stream.quantity_max {
+			if quantity_max < 1 {
+				return Err(SemanticError::InvalidQuantity);
+			}
+		}
+
+		if tlv_stream.refund_for.is_some() && tlv_stream.send_invoice.is_none() {
+			return Err(SemanticError::UnexpectedRefund);
+		}
+
+		Ok(Offer { tlv_stream })
+	}
+}
+
 const OFFER_BECH32_HRP: &str = "lno";
 
 impl FromStr for OfferTlvStream {