Merge pull request #1719 from jkczyz/2022-09-offer-encoding
[rust-lightning] / lightning / src / offers / offer.rs
diff --git a/lightning/src/offers/offer.rs b/lightning/src/offers/offer.rs
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+// 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 `offer` messages.
+//!
+//! An [`Offer`] represents an "offer to be paid." It is typically constructed by a merchant and
+//! published as a QR code to be scanned by a customer. The customer uses the offer to request an
+//! invoice from the merchant to be paid.
+//!
+//! ```ignore
+//! extern crate bitcoin;
+//! extern crate core;
+//! extern crate lightning;
+//!
+//! use core::num::NonZeroU64;
+//! use core::time::Duration;
+//!
+//! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
+//! use lightning::offers::offer::{OfferBuilder, Quantity};
+//!
+//! # use bitcoin::secp256k1;
+//! # use lightning::onion_message::BlindedPath;
+//! # #[cfg(feature = "std")]
+//! # use std::time::SystemTime;
+//! #
+//! # fn create_blinded_path() -> BlindedPath { unimplemented!() }
+//! # fn create_another_blinded_path() -> BlindedPath { unimplemented!() }
+//! #
+//! # #[cfg(feature = "std")]
+//! # fn build() -> Result<(), secp256k1::Error> {
+//! let secp_ctx = Secp256k1::new();
+//! let keys = KeyPair::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32])?);
+//! let pubkey = PublicKey::from(keys);
+//!
+//! let expiration = SystemTime::now() + Duration::from_secs(24 * 60 * 60);
+//! let offer = OfferBuilder::new("coffee, large".to_string(), pubkey)
+//!     .amount_msats(20_000)
+//!     .supported_quantity(Quantity::Unbounded)
+//!     .absolute_expiry(expiration.duration_since(SystemTime::UNIX_EPOCH).unwrap())
+//!     .issuer("Foo Bar".to_string())
+//!     .path(create_blinded_path())
+//!     .path(create_another_blinded_path())
+//!     .build()
+//!     .unwrap();
+//! # Ok(())
+//! # }
+//! ```
+
+use bitcoin::blockdata::constants::ChainHash;
+use bitcoin::network::constants::Network;
+use bitcoin::secp256k1::PublicKey;
+use core::num::NonZeroU64;
+use core::time::Duration;
+use crate::io;
+use crate::ln::features::OfferFeatures;
+use crate::ln::msgs::MAX_VALUE_MSAT;
+use crate::onion_message::BlindedPath;
+use crate::util::ser::{HighZeroBytesDroppedBigSize, WithoutLength, Writeable, Writer};
+use crate::util::string::PrintableString;
+
+use crate::prelude::*;
+
+#[cfg(feature = "std")]
+use std::time::SystemTime;
+
+/// Builds an [`Offer`] for the "offer to be paid" flow.
+///
+/// See [module-level documentation] for usage.
+///
+/// [module-level documentation]: self
+pub struct OfferBuilder {
+       offer: OfferContents,
+}
+
+impl OfferBuilder {
+       /// Creates a new builder for an offer setting the [`Offer::description`] and using the
+       /// [`Offer::signing_pubkey`] for signing invoices. The associated secret key must be remembered
+       /// while the offer is valid.
+       ///
+       /// Use a different pubkey per offer to avoid correlating offers.
+       pub fn new(description: String, signing_pubkey: PublicKey) -> Self {
+               let offer = OfferContents {
+                       chains: None, metadata: None, amount: None, description,
+                       features: OfferFeatures::empty(), absolute_expiry: None, issuer: None, paths: None,
+                       supported_quantity: Quantity::one(), signing_pubkey: Some(signing_pubkey),
+               };
+               OfferBuilder { offer }
+       }
+
+       /// Adds the chain hash of the given [`Network`] to [`Offer::chains`]. If not called,
+       /// the chain hash of [`Network::Bitcoin`] is assumed to be the only one supported.
+       ///
+       /// See [`Offer::chains`] on how this relates to the payment currency.
+       ///
+       /// Successive calls to this method will add another chain hash.
+       pub fn chain(mut self, network: Network) -> Self {
+               let chains = self.offer.chains.get_or_insert_with(Vec::new);
+               let chain = ChainHash::using_genesis_block(network);
+               if !chains.contains(&chain) {
+                       chains.push(chain);
+               }
+
+               self
+       }
+
+       /// Sets the [`Offer::metadata`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       pub fn metadata(mut self, metadata: Vec<u8>) -> Self {
+               self.offer.metadata = Some(metadata);
+               self
+       }
+
+       /// Sets the [`Offer::amount`] as an [`Amount::Bitcoin`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       pub fn amount_msats(mut self, amount_msats: u64) -> Self {
+               self.amount(Amount::Bitcoin { amount_msats })
+       }
+
+       /// Sets the [`Offer::amount`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       fn amount(mut self, amount: Amount) -> Self {
+               self.offer.amount = Some(amount);
+               self
+       }
+
+       /// Sets the [`Offer::features`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       #[cfg(test)]
+       pub fn features(mut self, features: OfferFeatures) -> Self {
+               self.offer.features = features;
+               self
+       }
+
+       /// Sets the [`Offer::absolute_expiry`] as seconds since the Unix epoch. Any expiry that has
+       /// already passed is valid and can be checked for using [`Offer::is_expired`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       pub fn absolute_expiry(mut self, absolute_expiry: Duration) -> Self {
+               self.offer.absolute_expiry = Some(absolute_expiry);
+               self
+       }
+
+       /// Sets the [`Offer::issuer`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       pub fn issuer(mut self, issuer: String) -> Self {
+               self.offer.issuer = Some(issuer);
+               self
+       }
+
+       /// Adds a blinded path to [`Offer::paths`]. Must include at least one path if only connected by
+       /// private channels or if [`Offer::signing_pubkey`] is not a public node id.
+       ///
+       /// Successive calls to this method will add another blinded path. Caller is responsible for not
+       /// adding duplicate paths.
+       pub fn path(mut self, path: BlindedPath) -> Self {
+               self.offer.paths.get_or_insert_with(Vec::new).push(path);
+               self
+       }
+
+       /// Sets the quantity of items for [`Offer::supported_quantity`].
+       ///
+       /// Successive calls to this method will override the previous setting.
+       pub fn supported_quantity(mut self, quantity: Quantity) -> Self {
+               self.offer.supported_quantity = quantity;
+               self
+       }
+
+       /// Builds an [`Offer`] from the builder's settings.
+       pub fn build(mut self) -> Result<Offer, ()> {
+               match self.offer.amount {
+                       Some(Amount::Bitcoin { amount_msats }) => {
+                               if amount_msats > MAX_VALUE_MSAT {
+                                       return Err(());
+                               }
+                       },
+                       Some(Amount::Currency { .. }) => unreachable!(),
+                       None => {},
+               }
+
+               if let Some(chains) = &self.offer.chains {
+                       if chains.len() == 1 && chains[0] == self.offer.implied_chain() {
+                               self.offer.chains = None;
+                       }
+               }
+
+               let mut bytes = Vec::new();
+               self.offer.write(&mut bytes).unwrap();
+
+               Ok(Offer {
+                       bytes,
+                       contents: self.offer,
+               })
+       }
+}
+
+/// An `Offer` is a potentially long-lived proposal for payment of a good or service.
+///
+/// An offer is a precursor to an `InvoiceRequest`. A merchant publishes an offer from which a
+/// customer may request an `Invoice` for a specific quantity and using an amount sufficient to
+/// cover that quantity (i.e., at least `quantity * amount`). See [`Offer::amount`].
+///
+/// Offers may be denominated in currency other than bitcoin but are ultimately paid using the
+/// latter.
+///
+/// Through the use of [`BlindedPath`]s, offers provide recipient privacy.
+#[derive(Clone, Debug)]
+pub struct Offer {
+       // The serialized offer. Needed when creating an `InvoiceRequest` if the offer contains unknown
+       // fields.
+       bytes: Vec<u8>,
+       contents: OfferContents,
+}
+
+/// The contents of an [`Offer`], which may be shared with an `InvoiceRequest` or an `Invoice`.
+#[derive(Clone, Debug)]
+pub(crate) struct OfferContents {
+       chains: Option<Vec<ChainHash>>,
+       metadata: Option<Vec<u8>>,
+       amount: Option<Amount>,
+       description: String,
+       features: OfferFeatures,
+       absolute_expiry: Option<Duration>,
+       issuer: Option<String>,
+       paths: Option<Vec<BlindedPath>>,
+       supported_quantity: Quantity,
+       signing_pubkey: Option<PublicKey>,
+}
+
+impl Offer {
+       // TODO: Return a slice once ChainHash has constants.
+       // - https://github.com/rust-bitcoin/rust-bitcoin/pull/1283
+       // - https://github.com/rust-bitcoin/rust-bitcoin/pull/1286
+       /// The chains that may be used when paying a requested invoice (e.g., bitcoin mainnet).
+       /// Payments must be denominated in units of the minimal lightning-payable unit (e.g., msats)
+       /// for the selected chain.
+       pub fn chains(&self) -> Vec<ChainHash> {
+               self.contents.chains
+                       .as_ref()
+                       .cloned()
+                       .unwrap_or_else(|| vec![self.contents.implied_chain()])
+       }
+
+       // TODO: Link to corresponding method in `InvoiceRequest`.
+       /// Opaque bytes set by the originator. Useful for authentication and validating fields since it
+       /// is reflected in `invoice_request` messages along with all the other fields from the `offer`.
+       pub fn metadata(&self) -> Option<&Vec<u8>> {
+               self.contents.metadata.as_ref()
+       }
+
+       /// The minimum amount required for a successful payment of a single item.
+       pub fn amount(&self) -> Option<&Amount> {
+               self.contents.amount.as_ref()
+       }
+
+       /// A complete description of the purpose of the payment. 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)
+       }
+
+       /// Features pertaining to the offer.
+       pub fn features(&self) -> &OfferFeatures {
+               &self.contents.features
+       }
+
+       /// Duration since the Unix epoch when an invoice should no longer be requested.
+       ///
+       /// If `None`, the offer does not expire.
+       pub fn absolute_expiry(&self) -> Option<Duration> {
+               self.contents.absolute_expiry
+       }
+
+       /// Whether the offer 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 offer, 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 recipient originating from publicly reachable nodes. Blinded paths provide
+       /// recipient privacy by obfuscating its node id.
+       pub fn paths(&self) -> &[BlindedPath] {
+               self.contents.paths.as_ref().map(|paths| paths.as_slice()).unwrap_or(&[])
+       }
+
+       /// The quantity of items supported.
+       pub fn supported_quantity(&self) -> Quantity {
+               self.contents.supported_quantity()
+       }
+
+       /// The public key used by the recipient to sign invoices.
+       pub fn signing_pubkey(&self) -> PublicKey {
+               self.contents.signing_pubkey.unwrap()
+       }
+
+       #[cfg(test)]
+       fn as_tlv_stream(&self) -> OfferTlvStreamRef {
+               self.contents.as_tlv_stream()
+       }
+}
+
+impl OfferContents {
+       pub fn implied_chain(&self) -> ChainHash {
+               ChainHash::using_genesis_block(Network::Bitcoin)
+       }
+
+       pub fn supported_quantity(&self) -> Quantity {
+               self.supported_quantity
+       }
+
+       fn as_tlv_stream(&self) -> OfferTlvStreamRef {
+               let (currency, amount) = match &self.amount {
+                       None => (None, None),
+                       Some(Amount::Bitcoin { amount_msats }) => (None, Some(*amount_msats)),
+                       Some(Amount::Currency { iso4217_code, amount }) => (
+                               Some(iso4217_code), Some(*amount)
+                       ),
+               };
+
+               let features = {
+                       if self.features == OfferFeatures::empty() { None } else { Some(&self.features) }
+               };
+
+               OfferTlvStreamRef {
+                       chains: self.chains.as_ref(),
+                       metadata: self.metadata.as_ref(),
+                       currency,
+                       amount,
+                       description: Some(&self.description),
+                       features,
+                       absolute_expiry: self.absolute_expiry.map(|duration| duration.as_secs()),
+                       paths: self.paths.as_ref(),
+                       issuer: self.issuer.as_ref(),
+                       quantity_max: self.supported_quantity.to_tlv_record(),
+                       node_id: self.signing_pubkey.as_ref(),
+               }
+       }
+}
+
+impl Writeable for OfferContents {
+       fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+               self.as_tlv_stream().write(writer)
+       }
+}
+
+/// The minimum amount required for an item in an [`Offer`], denominated in either bitcoin or
+/// another currency.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Amount {
+       /// An amount of bitcoin.
+       Bitcoin {
+               /// The amount in millisatoshi.
+               amount_msats: u64,
+       },
+       /// An amount of currency specified using ISO 4712.
+       Currency {
+               /// The currency that the amount is denominated in.
+               iso4217_code: CurrencyCode,
+               /// The amount in the currency unit adjusted by the ISO 4712 exponent (e.g., USD cents).
+               amount: u64,
+       },
+}
+
+/// An ISO 4712 three-letter currency code (e.g., USD).
+pub type CurrencyCode = [u8; 3];
+
+/// Quantity of items supported by an [`Offer`].
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Quantity {
+       /// Up to a specific number of items (inclusive).
+       Bounded(NonZeroU64),
+       /// One or more items.
+       Unbounded,
+}
+
+impl Quantity {
+       fn one() -> Self {
+               Quantity::Bounded(NonZeroU64::new(1).unwrap())
+       }
+
+       fn to_tlv_record(&self) -> Option<u64> {
+               match self {
+                       Quantity::Bounded(n) => {
+                               let n = n.get();
+                               if n == 1 { None } else { Some(n) }
+                       },
+                       Quantity::Unbounded => Some(0),
+               }
+       }
+}
+
+tlv_stream!(OfferTlvStream, OfferTlvStreamRef, {
+       (2, chains: (Vec<ChainHash>, WithoutLength)),
+       (4, metadata: (Vec<u8>, WithoutLength)),
+       (6, currency: CurrencyCode),
+       (8, amount: (u64, HighZeroBytesDroppedBigSize)),
+       (10, description: (String, WithoutLength)),
+       (12, features: OfferFeatures),
+       (14, absolute_expiry: (u64, HighZeroBytesDroppedBigSize)),
+       (16, paths: (Vec<BlindedPath>, WithoutLength)),
+       (18, issuer: (String, WithoutLength)),
+       (20, quantity_max: (u64, HighZeroBytesDroppedBigSize)),
+       (22, node_id: PublicKey),
+});
+
+#[cfg(test)]
+mod tests {
+       use super::{Amount, OfferBuilder, Quantity};
+
+       use bitcoin::blockdata::constants::ChainHash;
+       use bitcoin::network::constants::Network;
+       use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
+       use core::num::NonZeroU64;
+       use core::time::Duration;
+       use crate::ln::features::OfferFeatures;
+       use crate::ln::msgs::MAX_VALUE_MSAT;
+       use crate::onion_message::{BlindedHop, BlindedPath};
+       use crate::util::ser::Writeable;
+       use crate::util::string::PrintableString;
+
+       fn pubkey(byte: u8) -> PublicKey {
+               let secp_ctx = Secp256k1::new();
+               PublicKey::from_secret_key(&secp_ctx, &privkey(byte))
+       }
+
+       fn privkey(byte: u8) -> SecretKey {
+               SecretKey::from_slice(&[byte; 32]).unwrap()
+       }
+
+       #[test]
+       fn builds_offer_with_defaults() {
+               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();
+
+               assert_eq!(offer.bytes, buffer.as_slice());
+               assert_eq!(offer.chains(), vec![ChainHash::using_genesis_block(Network::Bitcoin)]);
+               assert_eq!(offer.metadata(), None);
+               assert_eq!(offer.amount(), None);
+               assert_eq!(offer.description(), PrintableString("foo"));
+               assert_eq!(offer.features(), &OfferFeatures::empty());
+               assert_eq!(offer.absolute_expiry(), None);
+               #[cfg(feature = "std")]
+               assert!(!offer.is_expired());
+               assert_eq!(offer.paths(), &[]);
+               assert_eq!(offer.issuer(), None);
+               assert_eq!(offer.supported_quantity(), Quantity::one());
+               assert_eq!(offer.signing_pubkey(), pubkey(42));
+
+               assert_eq!(tlv_stream.chains, None);
+               assert_eq!(tlv_stream.metadata, None);
+               assert_eq!(tlv_stream.currency, None);
+               assert_eq!(tlv_stream.amount, None);
+               assert_eq!(tlv_stream.description, Some(&String::from("foo")));
+               assert_eq!(tlv_stream.features, None);
+               assert_eq!(tlv_stream.absolute_expiry, None);
+               assert_eq!(tlv_stream.paths, None);
+               assert_eq!(tlv_stream.issuer, None);
+               assert_eq!(tlv_stream.quantity_max, None);
+               assert_eq!(tlv_stream.node_id, Some(&pubkey(42)));
+       }
+
+       #[test]
+       fn builds_offer_with_chains() {
+               let mainnet = ChainHash::using_genesis_block(Network::Bitcoin);
+               let testnet = ChainHash::using_genesis_block(Network::Testnet);
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .chain(Network::Bitcoin)
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.chains(), vec![mainnet]);
+               assert_eq!(offer.as_tlv_stream().chains, None);
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .chain(Network::Testnet)
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.chains(), vec![testnet]);
+               assert_eq!(offer.as_tlv_stream().chains, Some(&vec![testnet]));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .chain(Network::Testnet)
+                       .chain(Network::Testnet)
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.chains(), vec![testnet]);
+               assert_eq!(offer.as_tlv_stream().chains, Some(&vec![testnet]));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .chain(Network::Bitcoin)
+                       .chain(Network::Testnet)
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.chains(), vec![mainnet, testnet]);
+               assert_eq!(offer.as_tlv_stream().chains, Some(&vec![mainnet, testnet]));
+       }
+
+       #[test]
+       fn builds_offer_with_metadata() {
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .metadata(vec![42; 32])
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.metadata(), Some(&vec![42; 32]));
+               assert_eq!(offer.as_tlv_stream().metadata, Some(&vec![42; 32]));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .metadata(vec![42; 32])
+                       .metadata(vec![43; 32])
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.metadata(), Some(&vec![43; 32]));
+               assert_eq!(offer.as_tlv_stream().metadata, Some(&vec![43; 32]));
+       }
+
+       #[test]
+       fn builds_offer_with_amount() {
+               let bitcoin_amount = Amount::Bitcoin { amount_msats: 1000 };
+               let currency_amount = Amount::Currency { iso4217_code: *b"USD", amount: 10 };
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .amount_msats(1000)
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.amount(), Some(&bitcoin_amount));
+               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, Some(currency_amount.clone()));
+               assert_eq!(tlv_stream.amount, Some(10));
+               assert_eq!(tlv_stream.currency, Some(b"USD"));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .amount(currency_amount.clone())
+                       .amount(bitcoin_amount.clone())
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(tlv_stream.amount, Some(1000));
+               assert_eq!(tlv_stream.currency, None);
+
+               let invalid_amount = Amount::Bitcoin { amount_msats: MAX_VALUE_MSAT + 1 };
+               match OfferBuilder::new("foo".into(), pubkey(42)).amount(invalid_amount).build() {
+                       Ok(_) => panic!("expected error"),
+                       Err(e) => assert_eq!(e, ()),
+               }
+       }
+
+       #[test]
+       fn builds_offer_with_features() {
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .features(OfferFeatures::unknown())
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.features(), &OfferFeatures::unknown());
+               assert_eq!(offer.as_tlv_stream().features, Some(&OfferFeatures::unknown()));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .features(OfferFeatures::unknown())
+                       .features(OfferFeatures::empty())
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.features(), &OfferFeatures::empty());
+               assert_eq!(offer.as_tlv_stream().features, None);
+       }
+
+       #[test]
+       fn builds_offer_with_absolute_expiry() {
+               let future_expiry = Duration::from_secs(u64::max_value());
+               let past_expiry = Duration::from_secs(0);
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .absolute_expiry(future_expiry)
+                       .build()
+                       .unwrap();
+               #[cfg(feature = "std")]
+               assert!(!offer.is_expired());
+               assert_eq!(offer.absolute_expiry(), Some(future_expiry));
+               assert_eq!(offer.as_tlv_stream().absolute_expiry, Some(future_expiry.as_secs()));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .absolute_expiry(future_expiry)
+                       .absolute_expiry(past_expiry)
+                       .build()
+                       .unwrap();
+               #[cfg(feature = "std")]
+               assert!(offer.is_expired());
+               assert_eq!(offer.absolute_expiry(), Some(past_expiry));
+               assert_eq!(offer.as_tlv_stream().absolute_expiry, Some(past_expiry.as_secs()));
+       }
+
+       #[test]
+       fn builds_offer_with_paths() {
+               let paths = vec![
+                       BlindedPath {
+                               introduction_node_id: pubkey(40),
+                               blinding_point: pubkey(41),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: pubkey(43), encrypted_payload: vec![0; 43] },
+                                       BlindedHop { blinded_node_id: pubkey(44), encrypted_payload: vec![0; 44] },
+                               ],
+                       },
+                       BlindedPath {
+                               introduction_node_id: pubkey(40),
+                               blinding_point: pubkey(41),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: pubkey(45), encrypted_payload: vec![0; 45] },
+                                       BlindedHop { blinded_node_id: pubkey(46), encrypted_payload: vec![0; 46] },
+                               ],
+                       },
+               ];
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .path(paths[0].clone())
+                       .path(paths[1].clone())
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.paths(), paths.as_slice());
+               assert_eq!(offer.signing_pubkey(), pubkey(42));
+               assert_ne!(pubkey(42), pubkey(44));
+               assert_eq!(tlv_stream.paths, Some(&paths));
+               assert_eq!(tlv_stream.node_id, Some(&pubkey(42)));
+       }
+
+       #[test]
+       fn builds_offer_with_issuer() {
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .issuer("bar".into())
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.issuer(), Some(PrintableString("bar")));
+               assert_eq!(offer.as_tlv_stream().issuer, Some(&String::from("bar")));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .issuer("bar".into())
+                       .issuer("baz".into())
+                       .build()
+                       .unwrap();
+               assert_eq!(offer.issuer(), Some(PrintableString("baz")));
+               assert_eq!(offer.as_tlv_stream().issuer, Some(&String::from("baz")));
+       }
+
+       #[test]
+       fn builds_offer_with_supported_quantity() {
+               let ten = NonZeroU64::new(10).unwrap();
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .supported_quantity(Quantity::one())
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.supported_quantity(), Quantity::one());
+               assert_eq!(tlv_stream.quantity_max, None);
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .supported_quantity(Quantity::Unbounded)
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.supported_quantity(), Quantity::Unbounded);
+               assert_eq!(tlv_stream.quantity_max, Some(0));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .supported_quantity(Quantity::Bounded(ten))
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.supported_quantity(), Quantity::Bounded(ten));
+               assert_eq!(tlv_stream.quantity_max, Some(10));
+
+               let offer = OfferBuilder::new("foo".into(), pubkey(42))
+                       .supported_quantity(Quantity::Bounded(ten))
+                       .supported_quantity(Quantity::one())
+                       .build()
+                       .unwrap();
+               let tlv_stream = offer.as_tlv_stream();
+               assert_eq!(offer.supported_quantity(), Quantity::one());
+               assert_eq!(tlv_stream.quantity_max, None);
+       }
+}