Refund encoding and parsing

Author: jkczyz

lightning/src/offers/invoice_request.rs

@@ -9,13 +9,14 @@
 
 //! Data structures and encoding for `invoice_request` messages.
 //!
-//! An [`InvoiceRequest`] can be either built from a parsed [`Offer`] as an "offer to be paid" or
-//! built directly as an "offer for money" (e.g., refund, ATM withdrawal). In the former case, it is
+//! An [`InvoiceRequest`] can be built from a parsed [`Offer`] as an "offer to be paid". It is
 //! typically constructed by a customer and sent to the merchant who had published the corresponding
-//! offer. In the latter case, an offer doesn't exist as a precursor to the request. Rather the
-//! merchant would typically construct the invoice request and present it to the customer.
+//! offer. The recipient of the request responds with an `Invoice`.
 //!
-//! The recipient of the request responds with an `Invoice`.
+//! For an "offer for money" (e.g., refund, ATM withdrawal), where an offer doesn't exist as a
+//! precursor, see [`Refund`].
+//!
+//! [`Refund`]: crate::offers::refund::Refund
 //!
 //! ```ignore
 //! extern crate bitcoin;
@@ -34,7 +35,6 @@
 //! let pubkey = PublicKey::from(keys);
 //! let mut buffer = Vec::new();
 //!
-//! // "offer to be paid" flow
 //! "lno1qcp4256ypq"
 //!     .parse::<Offer>()?
 //!     .request_invoice(vec![42; 64], pubkey)?

lightning/src/offers/mod.rs

@@ -17,3 +17,4 @@ mod merkle;
 pub mod offer;
 pub mod parse;
 mod payer;
+pub mod refund;

lightning/src/offers/parse.rs

@@ -127,20 +127,28 @@ pub enum SemanticError {
 	AlreadyExpired,
 	/// The provided chain hash does not correspond to a supported chain.
 	UnsupportedChain,
+	/// A chain was provided but was not expected.
+	UnexpectedChain,
 	/// An amount was expected but was missing.
 	MissingAmount,
 	/// The amount exceeded the total bitcoin supply.
 	InvalidAmount,
 	/// An amount was provided but was not sufficient in value.
 	InsufficientAmount,
+	/// An amount was provided but was not expected.
+	UnexpectedAmount,
 	/// A currency was provided that is not supported.
 	UnsupportedCurrency,
 	/// A feature was required but is unknown.
 	UnknownRequiredFeatures,
+	/// Features were provided but were not expected.
+	UnexpectedFeatures,
 	/// A required description was not provided.
 	MissingDescription,
 	/// A signing pubkey was not provided.
 	MissingSigningPubkey,
+	/// A signing pubkey was provided but was not expected.
+	UnexpectedSigningPubkey,
 	/// A quantity was expected but was missing.
 	MissingQuantity,
 	/// An unsupported quantity was provided.

lightning/src/offers/refund.rs

@@ -0,0 +1,238 @@
+// This file is Copyright its original authors, visible in version control
+// history.
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Data structures and encoding for refunds.
+//!
+//! A [`Refund`] is as an "offer for money" and is typically constructed by a merchant and presented
+//! directly to the customer. The recipient responds with an `Invoice` to be paid.
+//!
+//! This is an [`InvoiceRequest`] produced *not* in response to an [`Offer`].
+//!
+//! [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
+//! [`Offer`]: crate::offers::offer::Offer
+
+use bitcoin::blockdata::constants::ChainHash;
+use bitcoin::network::constants::Network;
+use bitcoin::secp256k1::PublicKey;
+use core::convert::TryFrom;
+use core::time::Duration;
+use crate::io;
+use crate::ln::features::InvoiceRequestFeatures;
+use crate::ln::msgs::DecodeError;
+use crate::offers::invoice_request::InvoiceRequestTlvStream;
+use crate::offers::offer::OfferTlvStream;
+use crate::offers::parse::{ParseError, ParsedMessage, SemanticError};
+use crate::offers::payer::{PayerContents, PayerTlvStream};
+use crate::onion_message::BlindedPath;
+use crate::util::ser::SeekReadable;
+use crate::util::string::PrintableString;
+
+use crate::prelude::*;
+
+#[cfg(feature = "std")]
+use std::time::SystemTime;
+
+/// A `Refund` is a request to send an `Invoice` without a preceding [`Offer`].
+///
+/// Typically, after an invoice is paid, the recipient may publish a refund allowing the sender to
+/// recoup their funds. A refund may be used more generally as an "offer for money", such as with a
+/// bitcoin ATM.
+///
+/// [`Offer`]: crate::offers::offer::Offer
+#[derive(Clone, Debug)]
+pub struct Refund {
+	bytes: Vec<u8>,
+	contents: RefundContents,
+}
+
+/// The contents of a [`Refund`], which may be shared with an `Invoice`.
+#[derive(Clone, Debug)]
+struct RefundContents {
+	payer: PayerContents,
+	// offer fields
+	metadata: Option<Vec<u8>>,
+	description: String,
+	absolute_expiry: Option<Duration>,
+	issuer: Option<String>,
+	paths: Option<Vec<BlindedPath>>,
+	// invoice_request fields
+	chain: Option<ChainHash>,
+	amount_msats: u64,
+	features: InvoiceRequestFeatures,
+	payer_id: PublicKey,
+	payer_note: Option<String>,
+}
+
+impl Refund {
+	/// A complete description of the purpose of the refund. Intended to be displayed to the user
+	/// but with the caveat that it has not been verified in any way.
+	pub fn description(&self) -> PrintableString {
+		PrintableString(&self.contents.description)
+	}
+
+	/// Duration since the Unix epoch when an invoice should no longer be sent.
+	///
+	/// If `None`, the refund does not expire.
+	pub fn absolute_expiry(&self) -> Option<Duration> {
+		self.contents.absolute_expiry
+	}
+
+	/// Whether the refund has expired.
+	#[cfg(feature = "std")]
+	pub fn is_expired(&self) -> bool {
+		match self.absolute_expiry() {
+			Some(seconds_from_epoch) => match SystemTime::UNIX_EPOCH.elapsed() {
+				Ok(elapsed) => elapsed > seconds_from_epoch,
+				Err(_) => false,
+			},
+			None => false,
+		}
+	}
+
+	/// The issuer of the refund, possibly beginning with `user@domain` or `domain`. Intended to be
+	/// displayed to the user but with the caveat that it has not been verified in any way.
+	pub fn issuer(&self) -> Option<PrintableString> {
+		self.contents.issuer.as_ref().map(|issuer| PrintableString(issuer.as_str()))
+	}
+
+	/// Paths to the sender originating from publicly reachable nodes. Blinded paths provide sender
+	/// privacy by obfuscating its node id.
+	pub fn paths(&self) -> &[BlindedPath] {
+		self.contents.paths.as_ref().map(|paths| paths.as_slice()).unwrap_or(&[])
+	}
+
+	/// An unpredictable series of bytes, typically containing information about the derivation of
+	/// [`payer_id`].
+	///
+	/// [`payer_id`]: Self::payer_id
+	pub fn metadata(&self) -> &[u8] {
+		&self.contents.payer.0
+	}
+
+	/// A chain that the refund is valid for.
+	pub fn chain(&self) -> ChainHash {
+		self.contents.chain.unwrap_or_else(|| ChainHash::using_genesis_block(Network::Bitcoin))
+	}
+
+	/// The amount to refund in msats (i.e., the minimum lightning-payable unit for [`chain`]).
+	///
+	/// [`chain`]: Self::chain
+	pub fn amount_msats(&self) -> u64 {
+		self.contents.amount_msats
+	}
+
+	/// Features for paying the invoice.
+	pub fn features(&self) -> &InvoiceRequestFeatures {
+		&self.contents.features
+	}
+
+	/// A transient pubkey used to sign the refund.
+	pub fn payer_id(&self) -> PublicKey {
+		self.contents.payer_id
+	}
+
+	/// Payer provided note to include in the invoice.
+	pub fn payer_note(&self) -> Option<PrintableString> {
+		self.contents.payer_note.as_ref().map(|payer_note| PrintableString(payer_note.as_str()))
+	}
+}
+
+type RefundTlvStream = (PayerTlvStream, OfferTlvStream, InvoiceRequestTlvStream);
+
+impl SeekReadable for RefundTlvStream {
+	fn read<R: io::Read + io::Seek>(r: &mut R) -> Result<Self, DecodeError> {
+		let payer = SeekReadable::read(r)?;
+		let offer = SeekReadable::read(r)?;
+		let invoice_request = SeekReadable::read(r)?;
+
+		Ok((payer, offer, invoice_request))
+	}
+}
+
+impl TryFrom<Vec<u8>> for Refund {
+	type Error = ParseError;
+
+	fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
+		let refund = ParsedMessage::<RefundTlvStream>::try_from(bytes)?;
+		let ParsedMessage { bytes, tlv_stream } = refund;
+		let contents = RefundContents::try_from(tlv_stream)?;
+
+		Ok(Refund { bytes, contents })
+	}
+}
+
+impl TryFrom<RefundTlvStream> for RefundContents {
+	type Error = SemanticError;
+
+	fn try_from(tlv_stream: RefundTlvStream) -> Result<Self, Self::Error> {
+		let (
+			PayerTlvStream { metadata: payer_metadata },
+			OfferTlvStream {
+				chains, metadata, currency, amount: offer_amount, description,
+				features: offer_features, absolute_expiry, paths, issuer, quantity_max, node_id,
+			},
+			InvoiceRequestTlvStream { chain, amount, features, quantity, payer_id, payer_note },
+		) = tlv_stream;
+
+		let payer = match payer_metadata {
+			None => return Err(SemanticError::MissingPayerMetadata),
+			Some(metadata) => PayerContents(metadata),
+		};
+
+		if chains.is_some() {
+			return Err(SemanticError::UnexpectedChain);
+		}
+
+		if currency.is_some() || offer_amount.is_some() {
+			return Err(SemanticError::UnexpectedAmount);
+		}
+
+		let description = match description {
+			None => return Err(SemanticError::MissingDescription),
+			Some(description) => description,
+		};
+
+		if offer_features.is_some() {
+			return Err(SemanticError::UnexpectedFeatures);
+		}
+
+		let absolute_expiry = absolute_expiry.map(Duration::from_secs);
+
+		if quantity_max.is_some() {
+			return Err(SemanticError::UnexpectedQuantity);
+		}
+
+		if node_id.is_some() {
+			return Err(SemanticError::UnexpectedSigningPubkey);
+		}
+
+		let amount_msats = match amount {
+			None => return Err(SemanticError::MissingAmount),
+			Some(amount_msats) => amount_msats,
+		};
+
+		let features = features.unwrap_or_else(InvoiceRequestFeatures::empty);
+
+		// TODO: Check why this isn't in the spec.
+		if quantity.is_some() {
+			return Err(SemanticError::UnexpectedQuantity);
+		}
+
+		let payer_id = match payer_id {
+			None => return Err(SemanticError::MissingPayerId),
+			Some(payer_id) => payer_id,
+		};
+
+		// TODO: Should metadata be included?
+		Ok(RefundContents {
+			payer, metadata, description, absolute_expiry, issuer, paths, chain, amount_msats,
+			features, payer_id, payer_note,
+		})
+	}
+}