Offer parsing from bech32 strings

Add common bech32 parsing for BOLT 12 messages. The encoding is similar
to bech32 only without a checksum and with support for continuing
messages across multiple parts.

Messages implementing Bech32Encode are parsed into a TLV stream, which
is converted to the desired message content while performing semantic
checks. Checking after conversion allows for more elaborate checks of
data composed of multiple TLV records and for more meaningful error
messages.

The parsed bytes are also saved to allow creating messages with mirrored
data, even if TLV records are unknown.

Author: jkczyz

lightning/src/offers/mod.rs

@@ -13,3 +13,4 @@
 //! Offers are a flexible protocol for Lightning payments.
 
 pub mod offer;
+pub mod parse;

lightning/src/offers/offer.rs

@@ -18,13 +18,15 @@
 //! extern crate core;
 //! extern crate lightning;
 //!
+//! use core::convert::TryFrom;
 //! use core::num::NonZeroU64;
 //! use core::time::Duration;
 //!
 //! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
-//! use lightning::offers::offer::{Amount, OfferBuilder, Quantity};
+//! use lightning::offers::offer::{Amount, Offer, OfferBuilder, Quantity};
+//! use lightning::offers::parse::ParseError;
+//! use lightning::util::ser::{Readable, Writeable};
 //!
-//! # use bitcoin::secp256k1;
 //! # use lightning::onion_message::BlindedPath;
 //! # #[cfg(feature = "std")]
 //! # use std::time::SystemTime;
@@ -33,9 +35,9 @@
 //! # fn create_another_blinded_path() -> BlindedPath { unimplemented!() }
 //! #
 //! # #[cfg(feature = "std")]
-//! # fn build() -> Result<(), secp256k1::Error> {
+//! # fn build() -> Result<(), ParseError> {
 //! let secp_ctx = Secp256k1::new();
-//! let keys = KeyPair::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32])?);
+//! let keys = KeyPair::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
 //! let pubkey = PublicKey::from(keys);
 //!
 //! let expiration = SystemTime::now() + Duration::from_secs(24 * 60 * 60);
@@ -48,20 +50,36 @@
 //!     .path(create_another_blinded_path())
 //!     .build()
 //!     .unwrap();
+//!
+//! // Encode as a bech32 string for use in a QR code.
+//! let encoded_offer = offer.to_string();
+//!
+//! // Parse from a bech32 string after scanning from a QR code.
+//! let offer = encoded_offer.parse::<Offer>()?;
+//!
+//! // Encode offer as raw bytes.
+//! let mut bytes = Vec::new();
+//! offer.write(&mut bytes).unwrap();
+//!
+//! // Decode raw bytes into an offer.
+//! let offer = Offer::try_from(bytes)?;
 //! # Ok(())
 //! # }
 //! ```
 
 use bitcoin::blockdata::constants::ChainHash;
 use bitcoin::network::constants::Network;
 use bitcoin::secp256k1::PublicKey;
+use core::convert::TryFrom;
 use core::num::NonZeroU64;
+use core::str::FromStr;
 use core::time::Duration;
 use crate::io;
 use crate::ln::features::OfferFeatures;
 use crate::ln::msgs::MAX_VALUE_MSAT;
+use crate::offers::parse::{Bech32Encode, ParseError, SemanticError};
 use crate::onion_message::BlindedPath;
-use crate::util::ser::{HighZeroBytesDroppedBigSize, WithoutLength, Writeable, Writer};
+use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, WithoutLength, Writeable, Writer};
 use crate::util::string::PrintableString;
 
 use crate::prelude::*;
@@ -172,11 +190,9 @@ impl OfferBuilder {
 
 	/// Builds an [`Offer`] from the builder's settings.
 	pub fn build(self) -> Result<Offer, ()> {
+		// TODO: Also check for Amount::Currency
 		if let Some(Amount::Currency { .. }) = self.offer.amount {
-			return Err(());
-		}
-
-		if self.offer.amount_msats() > MAX_VALUE_MSAT {
+		} else if self.offer.amount_msats() > MAX_VALUE_MSAT {
 			return Err(());
 		}
 
@@ -305,6 +321,12 @@ impl Offer {
 	}
 }
 
+impl AsRef<[u8]> for Offer {
+	fn as_ref(&self) -> &[u8] {
+		&self.bytes
+	}
+}
+
 impl OfferContents {
 	pub fn amount_msats(&self) -> u64 {
 		self.amount.as_ref().map(Amount::as_msats).unwrap_or(0)
@@ -343,12 +365,27 @@ impl OfferContents {
 	}
 }
 
+impl Writeable for Offer {
+	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+		WithoutLength(&self.bytes).write(writer)
+	}
+}
+
 impl Writeable for OfferContents {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 		self.as_tlv_stream().write(writer)
 	}
 }
 
+impl TryFrom<Vec<u8>> for Offer {
+	type Error = ParseError;
+
+	fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
+		let tlv_stream: OfferTlvStream = Readable::read(&mut &bytes[..])?;
+		Offer::try_from((bytes, tlv_stream))
+	}
+}
+
 /// The minimum amount required for an item in an [`Offer`], denominated in either bitcoin or
 /// another currency.
 #[derive(Clone, Debug, PartialEq)]
@@ -392,6 +429,14 @@ pub enum Quantity {
 }
 
 impl Quantity {
+	fn new(quantity: Option<u64>) -> Self {
+		match quantity {
+			Some(1) | None => Quantity::One,
+			Some(0) => Quantity::Many,
+			Some(n) => Quantity::Max(NonZeroU64::new(n).unwrap()),
+		}
+	}
+
 	fn to_tlv_record(&self) -> Option<u64> {
 		match self {
 			Quantity::One => None,
@@ -415,13 +460,88 @@ tlv_stream!(OfferTlvStream, OfferTlvStreamRef, {
 	(22, node_id: PublicKey),
 });
 
+impl Bech32Encode for Offer {
+	const BECH32_HRP: &'static str = "lno";
+}
+
+type ParsedOffer = (Vec<u8>, OfferTlvStream);
+
+impl FromStr for Offer {
+	type Err = ParseError;
+
+	fn from_str(s: &str) -> Result<Self, <Self as FromStr>::Err> {
+		Self::from_bech32_str(s)
+	}
+}
+
+impl TryFrom<ParsedOffer> for Offer {
+	type Error = ParseError;
+
+	fn try_from(offer: ParsedOffer) -> Result<Self, Self::Error> {
+		let (bytes, tlv_stream) = offer;
+		let contents = OfferContents::try_from(tlv_stream)?;
+		Ok(Offer { bytes, contents })
+	}
+}
+
+impl TryFrom<OfferTlvStream> for OfferContents {
+	type Error = SemanticError;
+
+	fn try_from(tlv_stream: OfferTlvStream) -> Result<Self, Self::Error> {
+		let OfferTlvStream {
+			chains, metadata, currency, amount, description, features, absolute_expiry, paths,
+			issuer, quantity_max, node_id,
+		} = tlv_stream;
+
+		let amount = match (currency, amount) {
+			(None, None) => None,
+			(None, Some(amount_msats)) => Some(Amount::Bitcoin { amount_msats }),
+			(Some(_), None) => return Err(SemanticError::MissingAmount),
+			(Some(iso4217_code), Some(amount)) => Some(Amount::Currency { iso4217_code, amount }),
+		};
+
+		let description = match description {
+			None => return Err(SemanticError::MissingDescription),
+			Some(description) => description,
+		};
+
+		let features = features.unwrap_or_else(OfferFeatures::empty);
+
+		let absolute_expiry = absolute_expiry
+			.map(|seconds_from_epoch| Duration::from_secs(seconds_from_epoch));
+
+		let paths = match paths {
+			Some(paths) if paths.is_empty() => return Err(SemanticError::MissingPaths),
+			paths => paths,
+		};
+
+		let supported_quantity = Quantity::new(quantity_max);
+
+		if node_id.is_none() {
+			return Err(SemanticError::MissingNodeId);
+		}
+
+		Ok(OfferContents {
+			chains, metadata, amount, description, features, absolute_expiry, issuer, paths,
+			supported_quantity, signing_pubkey: node_id,
+		})
+	}
+}
+
+impl core::fmt::Display for Offer {
+	fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
+		self.fmt_bech32_str(f)
+	}
+}
+
 #[cfg(test)]
 mod tests {
-	use super::{Amount, OfferBuilder, Quantity};
+	use super::{Amount, Offer, OfferBuilder, Quantity};
 
 	use bitcoin::blockdata::constants::ChainHash;
 	use bitcoin::network::constants::Network;
 	use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
+	use core::convert::TryFrom;
 	use core::num::NonZeroU64;
 	use core::time::Duration;
 	use crate::ln::features::OfferFeatures;
@@ -444,7 +564,7 @@ mod tests {
 		let offer = OfferBuilder::new("foo".into(), pubkey(42)).build().unwrap();
 		let tlv_stream = offer.as_tlv_stream();
 		let mut buffer = Vec::new();
-		offer.contents.write(&mut buffer).unwrap();
+		offer.write(&mut buffer).unwrap();
 
 		assert_eq!(offer.bytes, buffer.as_slice());
 		assert_eq!(offer.chains(), vec![ChainHash::using_genesis_block(Network::Bitcoin)]);
@@ -471,6 +591,10 @@ mod tests {
 		assert_eq!(tlv_stream.issuer, None);
 		assert_eq!(tlv_stream.quantity_max, None);
 		assert_eq!(tlv_stream.node_id, Some(&pubkey(42)));
+
+		if let Err(e) = Offer::try_from(buffer) {
+			panic!("error parsing offer: {:?}", e);
+		}
 	}
 
 	#[test]
@@ -537,16 +661,14 @@ mod tests {
 		assert_eq!(tlv_stream.amount, Some(1000));
 		assert_eq!(tlv_stream.currency, None);
 
-		let builder = OfferBuilder::new("foo".into(), pubkey(42))
-			.amount(currency_amount.clone());
-		let tlv_stream = builder.offer.as_tlv_stream();
-		assert_eq!(builder.offer.amount.as_ref(), Some(&currency_amount));
+		let offer = OfferBuilder::new("foo".into(), pubkey(42))
+			.amount(currency_amount.clone())
+			.build()
+			.unwrap();
+		let tlv_stream = offer.as_tlv_stream();
+		assert_eq!(offer.amount(), Some(&currency_amount));
 		assert_eq!(tlv_stream.amount, Some(10));
 		assert_eq!(tlv_stream.currency, Some(b"USD"));
-		match builder.build() {
-			Ok(_) => panic!("expected error"),
-			Err(e) => assert_eq!(e, ()),
-		}
 
 		let offer = OfferBuilder::new("foo".into(), pubkey(42))
 			.amount(currency_amount.clone())
@@ -707,3 +829,88 @@ mod tests {
 
 	}
 }
+
+#[cfg(test)]
+mod bolt12_tests {
+	use super::{Offer, ParseError};
+	use bitcoin::bech32;
+	use crate::ln::msgs::DecodeError;
+
+	// TODO: Remove once test vectors are updated.
+	#[ignore]
+	#[test]
+	fn encodes_offer_as_bech32_without_checksum() {
+		let encoded_offer = "lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy";
+		let offer = dbg!(encoded_offer.parse::<Offer>().unwrap());
+		let reencoded_offer = offer.to_string();
+		dbg!(reencoded_offer.parse::<Offer>().unwrap());
+		assert_eq!(reencoded_offer, encoded_offer);
+	}
+
+	// TODO: Remove once test vectors are updated.
+	#[ignore]
+	#[test]
+	fn parses_bech32_encoded_offers() {
+		let offers = [
+			// BOLT 12 test vectors
+			"lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+			"l+no1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+			"l+no1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+			"lno1qcp4256ypqpq+86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn0+0fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0+sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qs+y",
+			"lno1qcp4256ypqpq+ 86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn0+  0fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0+\nsqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43l+\r\nastpwuh73k29qs+\r  y",
+			// Two blinded paths
+			"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",
+		];
+		for encoded_offer in &offers {
+			if let Err(e) = encoded_offer.parse::<Offer>() {
+				panic!("Invalid offer ({:?}): {}", e, encoded_offer);
+			}
+		}
+	}
+
+	#[test]
+	fn fails_parsing_bech32_encoded_offers_with_invalid_continuations() {
+		let offers = [
+			// BOLT 12 test vectors
+			"lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy+",
+			"lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy+ ",
+			"+lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+			"+ lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+			"ln++o1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy",
+		];
+		for encoded_offer in &offers {
+			match encoded_offer.parse::<Offer>() {
+				Ok(_) => panic!("Valid offer: {}", encoded_offer),
+				Err(e) => assert_eq!(e, ParseError::InvalidContinuation),
+			}
+		}
+
+	}
+
+	#[test]
+	fn fails_parsing_bech32_encoded_offer_with_invalid_hrp() {
+		let encoded_offer = "lni1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsy";
+		match encoded_offer.parse::<Offer>() {
+			Ok(_) => panic!("Valid offer: {}", encoded_offer),
+			Err(e) => assert_eq!(e, ParseError::InvalidBech32Hrp),
+		}
+	}
+
+	#[test]
+	fn fails_parsing_bech32_encoded_offer_with_invalid_bech32_data() {
+		let encoded_offer = "lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qso";
+		match encoded_offer.parse::<Offer>() {
+			Ok(_) => panic!("Valid offer: {}", encoded_offer),
+			Err(e) => assert_eq!(e, ParseError::Bech32(bech32::Error::InvalidChar('o'))),
+		}
+	}
+
+	#[test]
+	fn fails_parsing_bech32_encoded_offer_with_invalid_tlv_data() {
+		let encoded_offer = "lno1qcp4256ypqpq86q2pucnq42ngssx2an9wfujqerp0y2pqun4wd68jtn00fkxzcnn9ehhyec6qgqsz83qfwdpl28qqmc78ymlvhmxcsywdk5wrjnj36jryg488qwlrnzyjczlqsp9nyu4phcg6dqhlhzgxagfu7zh3d9re0sqp9ts2yfugvnnm9gxkcnnnkdpa084a6t520h5zhkxsdnghvpukvd43lastpwuh73k29qsyqqqqq";
+		match encoded_offer.parse::<Offer>() {
+			Ok(_) => panic!("Valid offer: {}", encoded_offer),
+			Err(e) => assert_eq!(e, ParseError::Decode(DecodeError::InvalidValue)),
+		}
+	}
+}