Refund metadata and payer id derivation

[rust-lightning] / lightning / src / offers / refund.rs

// 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 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`].
//!
//! [`Invoice`]: crate::offers::invoice::Invoice
//! [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
//! [`Offer`]: crate::offers::offer::Offer
//!
//! ```
//! extern crate bitcoin;
//! extern crate core;
//! extern crate lightning;
//!
//! use core::convert::TryFrom;
//! use core::time::Duration;
//!
//! use bitcoin::network::constants::Network;
//! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
//! use lightning::offers::parse::ParseError;
//! use lightning::offers::refund::{Refund, RefundBuilder};
//! use lightning::util::ser::{Readable, Writeable};
//!
//! # 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<(), ParseError> {
//! let secp_ctx = Secp256k1::new();
//! 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);
//! let refund = RefundBuilder::new("coffee, large".to_string(), vec![1; 32], pubkey, 20_000)?
//!     .absolute_expiry(expiration.duration_since(SystemTime::UNIX_EPOCH).unwrap())
//!     .issuer("Foo Bar".to_string())
//!     .path(create_blinded_path())
//!     .path(create_another_blinded_path())
//!     .chain(Network::Bitcoin)
//!     .payer_note("refund for order #12345".to_string())
//!     .build()?;
//!
//! // Encode as a bech32 string for use in a QR code.
//! let encoded_refund = refund.to_string();
//!
//! // Parse from a bech32 string after scanning from a QR code.
//! let refund = encoded_refund.parse::<Refund>()?;
//!
//! // Encode refund as raw bytes.
//! let mut bytes = Vec::new();
//! refund.write(&mut bytes).unwrap();
//!
//! // Decode raw bytes into an refund.
//! let refund = Refund::try_from(bytes)?;
//! # Ok(())
//! # }
//! ```

use bitcoin::blockdata::constants::ChainHash;
use bitcoin::network::constants::Network;
use bitcoin::secp256k1::{PublicKey, Secp256k1, self};
use core::convert::TryFrom;
use core::ops::Deref;
use core::str::FromStr;
use core::time::Duration;
use crate::chain::keysinterface::EntropySource;
use crate::io;
use crate::ln::PaymentHash;
use crate::ln::features::InvoiceRequestFeatures;
use crate::ln::inbound_payment::{ExpandedKey, IV_LEN, Nonce};
use crate::ln::msgs::{DecodeError, MAX_VALUE_MSAT};
use crate::offers::invoice::{BlindedPayInfo, InvoiceBuilder};
use crate::offers::invoice_request::{InvoiceRequestTlvStream, InvoiceRequestTlvStreamRef};
use crate::offers::offer::{OfferTlvStream, OfferTlvStreamRef};
use crate::offers::parse::{Bech32Encode, ParseError, ParsedMessage, SemanticError};
use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
use crate::offers::signer::{Metadata, MetadataMaterial};
use crate::onion_message::BlindedPath;
use crate::util::ser::{SeekReadable, WithoutLength, Writeable, Writer};
use crate::util::string::PrintableString;

use crate::prelude::*;

#[cfg(feature = "std")]
use std::time::SystemTime;

const IV_BYTES: &[u8; IV_LEN] = b"LDK Refund ~~~~~";

/// Builds a [`Refund`] for the "offer for money" flow.
///
/// See [module-level documentation] for usage.
///
/// [module-level documentation]: self
pub struct RefundBuilder<'a, T: secp256k1::Signing> {
        refund: RefundContents,
        secp_ctx: Option<&'a Secp256k1<T>>,
}

impl<'a> RefundBuilder<'a, secp256k1::SignOnly> {
        /// Creates a new builder for a refund using the [`Refund::payer_id`] for the public node id to
        /// send to if no [`Refund::paths`] are set. Otherwise, it may be a transient pubkey.
        ///
        /// Additionally, sets the required [`Refund::description`], [`Refund::metadata`], and
        /// [`Refund::amount_msats`].
        pub fn new(
                description: String, metadata: Vec<u8>, payer_id: PublicKey, amount_msats: u64
        ) -> Result<Self, SemanticError> {
                if amount_msats > MAX_VALUE_MSAT {
                        return Err(SemanticError::InvalidAmount);
                }

                let metadata = Metadata::Bytes(metadata);
                Ok(Self {
                        refund: RefundContents {
                                payer: PayerContents(metadata), description, absolute_expiry: None, issuer: None,
                                paths: None, chain: None, amount_msats, features: InvoiceRequestFeatures::empty(),
                                quantity: None, payer_id, payer_note: None,
                        },
                        secp_ctx: None,
                })
        }
}

impl<'a, T: secp256k1::Signing> RefundBuilder<'a, T> {
        /// Similar to [`RefundBuilder::new`] except, if [`RefundBuilder::path`] is called, the payer id
        /// is derived from the given [`ExpandedKey`] and nonce. This provides sender privacy by using a
        /// different payer id for each refund, assuming a different nonce is used.  Otherwise, the
        /// provided `node_id` is used for the payer id.
        ///
        /// Also, sets the metadata when [`RefundBuilder::build`] is called such that it can be used to
        /// verify that an [`InvoiceRequest`] was produced for the refund given an [`ExpandedKey`].
        ///
        /// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
        /// [`ExpandedKey`]: crate::ln::inbound_payment::ExpandedKey
        pub fn deriving_payer_id<ES: Deref>(
                description: String, node_id: PublicKey, expanded_key: &ExpandedKey, entropy_source: ES,
                secp_ctx: &'a Secp256k1<T>, amount_msats: u64
        ) -> Result<Self, SemanticError> where ES::Target: EntropySource {
                if amount_msats > MAX_VALUE_MSAT {
                        return Err(SemanticError::InvalidAmount);
                }

                let nonce = Nonce::from_entropy_source(entropy_source);
                let derivation_material = MetadataMaterial::new(nonce, expanded_key, IV_BYTES);
                let metadata = Metadata::DerivedSigningPubkey(derivation_material);
                Ok(Self {
                        refund: RefundContents {
                                payer: PayerContents(metadata), description, absolute_expiry: None, issuer: None,
                                paths: None, chain: None, amount_msats, features: InvoiceRequestFeatures::empty(),
                                quantity: None, payer_id: node_id, payer_note: None,
                        },
                        secp_ctx: Some(secp_ctx),
                })
        }

        /// Sets the [`Refund::absolute_expiry`] as seconds since the Unix epoch. Any expiry that has
        /// already passed is valid and can be checked for using [`Refund::is_expired`].
        ///
        /// Successive calls to this method will override the previous setting.
        pub fn absolute_expiry(mut self, absolute_expiry: Duration) -> Self {
                self.refund.absolute_expiry = Some(absolute_expiry);
                self
        }

        /// Sets the [`Refund::issuer`].
        ///
        /// Successive calls to this method will override the previous setting.
        pub fn issuer(mut self, issuer: String) -> Self {
                self.refund.issuer = Some(issuer);
                self
        }

        /// Adds a blinded path to [`Refund::paths`]. Must include at least one path if only connected
        /// by private channels or if [`Refund::payer_id`] 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.refund.paths.get_or_insert_with(Vec::new).push(path);
                self
        }

        /// Sets the [`Refund::chain`] of the given [`Network`] for paying an invoice. If not
        /// called, [`Network::Bitcoin`] is assumed.
        ///
        /// Successive calls to this method will override the previous setting.
        pub fn chain(mut self, network: Network) -> Self {
                self.refund.chain = Some(ChainHash::using_genesis_block(network));
                self
        }

        /// Sets [`Refund::quantity`] of items. This is purely for informational purposes. It is useful
        /// when the refund pertains to an [`Invoice`] that paid for more than one item from an
        /// [`Offer`] as specified by [`InvoiceRequest::quantity`].
        ///
        /// Successive calls to this method will override the previous setting.
        ///
        /// [`Invoice`]: crate::offers::invoice::Invoice
        /// [`InvoiceRequest::quantity`]: crate::offers::invoice_request::InvoiceRequest::quantity
        /// [`Offer`]: crate::offers::offer::Offer
        pub fn quantity(mut self, quantity: u64) -> Self {
                self.refund.quantity = Some(quantity);
                self
        }

        /// Sets the [`Refund::payer_note`].
        ///
        /// Successive calls to this method will override the previous setting.
        pub fn payer_note(mut self, payer_note: String) -> Self {
                self.refund.payer_note = Some(payer_note);
                self
        }

        /// Builds a [`Refund`] after checking for valid semantics.
        pub fn build(mut self) -> Result<Refund, SemanticError> {
                if self.refund.chain() == self.refund.implied_chain() {
                        self.refund.chain = None;
                }

                // Create the metadata for stateless verification of an Invoice.
                if self.refund.payer.0.has_derivation_material() {
                        let mut metadata = core::mem::take(&mut self.refund.payer.0);

                        if self.refund.paths.is_none() {
                                metadata = metadata.without_keys();
                        }

                        let mut tlv_stream = self.refund.as_tlv_stream();
                        tlv_stream.0.metadata = None;
                        if metadata.derives_keys() {
                                tlv_stream.2.payer_id = None;
                        }

                        let (derived_metadata, keys) = metadata.derive_from(tlv_stream, self.secp_ctx);
                        metadata = derived_metadata;
                        if let Some(keys) = keys {
                                self.refund.payer_id = keys.public_key();
                        }

                        self.refund.payer.0 = metadata;
                }

                let mut bytes = Vec::new();
                self.refund.write(&mut bytes).unwrap();

                Ok(Refund { bytes, contents: self.refund })
        }
}

#[cfg(test)]
impl<'a, T: secp256k1::Signing> RefundBuilder<'a, T> {
        fn features_unchecked(mut self, features: InvoiceRequestFeatures) -> Self {
                self.refund.features = features;
                self
        }
}

/// 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.
///
/// [`Invoice`]: crate::offers::invoice::Invoice
/// [`Offer`]: crate::offers::offer::Offer
#[derive(Clone, Debug)]
#[cfg_attr(test, derive(PartialEq))]
pub struct Refund {
        pub(super) bytes: Vec<u8>,
        pub(super) contents: RefundContents,
}

/// The contents of a [`Refund`], which may be shared with an [`Invoice`].
///
/// [`Invoice`]: crate::offers::invoice::Invoice
#[derive(Clone, Debug)]
#[cfg_attr(test, derive(PartialEq))]
pub(super) struct RefundContents {
        payer: PayerContents,
        // offer fields
        description: String,
        absolute_expiry: Option<Duration>,
        issuer: Option<String>,
        paths: Option<Vec<BlindedPath>>,
        // invoice_request fields
        chain: Option<ChainHash>,
        amount_msats: u64,
        features: InvoiceRequestFeatures,
        quantity: Option<u64>,
        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 {
                self.contents.is_expired()
        }

        /// 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.as_bytes().map(|bytes| bytes.as_slice()).unwrap_or(&[])
        }

        /// A chain that the refund is valid for.
        pub fn chain(&self) -> ChainHash {
                self.contents.chain.unwrap_or_else(|| self.contents.implied_chain())
        }

        /// 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 pertaining to requesting an invoice.
        pub fn features(&self) -> &InvoiceRequestFeatures {
                &self.contents.features
        }

        /// The quantity of an item that refund is for.
        pub fn quantity(&self) -> Option<u64> {
                self.contents.quantity
        }

        /// A public node id to send to in the case where there are no [`paths`]. Otherwise, a possibly
        /// transient pubkey.
        ///
        /// [`paths`]: Self::paths
        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()))
        }

        /// Creates an [`InvoiceBuilder`] for the refund with the given required fields and using the
        /// [`Duration`] since [`std::time::SystemTime::UNIX_EPOCH`] as the creation time.
        ///
        /// See [`Refund::respond_with_no_std`] for further details where the aforementioned creation
        /// time is used for the `created_at` parameter.
        ///
        /// [`Duration`]: core::time::Duration
        #[cfg(feature = "std")]
        pub fn respond_with(
                &self, payment_paths: Vec<(BlindedPath, BlindedPayInfo)>, payment_hash: PaymentHash,
                signing_pubkey: PublicKey,
        ) -> Result<InvoiceBuilder, SemanticError> {
                let created_at = std::time::SystemTime::now()
                        .duration_since(std::time::SystemTime::UNIX_EPOCH)
                        .expect("SystemTime::now() should come after SystemTime::UNIX_EPOCH");

                self.respond_with_no_std(payment_paths, payment_hash, signing_pubkey, created_at)
        }

        /// Creates an [`InvoiceBuilder`] for the refund with the given required fields.
        ///
        /// Unless [`InvoiceBuilder::relative_expiry`] is set, the invoice will expire two hours after
        /// `created_at`, which is used to set [`Invoice::created_at`]. Useful for `no-std` builds where
        /// [`std::time::SystemTime`] is not available.
        ///
        /// The caller is expected to remember the preimage of `payment_hash` in order to
        /// claim a payment for the invoice.
        ///
        /// The `signing_pubkey` is required to sign the invoice since refunds are not in response to an
        /// offer, which does have a `signing_pubkey`.
        ///
        /// The `payment_paths` parameter is useful for maintaining the payment recipient's privacy. It
        /// must contain one or more elements ordered from most-preferred to least-preferred, if there's
        /// a preference. Note, however, that any privacy is lost if a public node id is used for
        /// `signing_pubkey`.
        ///
        /// Errors if the request contains unknown required features.
        ///
        /// [`Invoice::created_at`]: crate::offers::invoice::Invoice::created_at
        pub fn respond_with_no_std(
                &self, payment_paths: Vec<(BlindedPath, BlindedPayInfo)>, payment_hash: PaymentHash,
                signing_pubkey: PublicKey, created_at: Duration
        ) -> Result<InvoiceBuilder, SemanticError> {
                if self.features().requires_unknown_bits() {
                        return Err(SemanticError::UnknownRequiredFeatures);
                }

                InvoiceBuilder::for_refund(self, payment_paths, created_at, payment_hash, signing_pubkey)
        }

        #[cfg(test)]
        fn as_tlv_stream(&self) -> RefundTlvStreamRef {
                self.contents.as_tlv_stream()
        }
}

impl AsRef<[u8]> for Refund {
        fn as_ref(&self) -> &[u8] {
                &self.bytes
        }
}

impl RefundContents {
        #[cfg(feature = "std")]
        pub(super) 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,
                }
        }

        pub(super) fn chain(&self) -> ChainHash {
                self.chain.unwrap_or_else(|| self.implied_chain())
        }

        pub fn implied_chain(&self) -> ChainHash {
                ChainHash::using_genesis_block(Network::Bitcoin)
        }

        pub(super) fn as_tlv_stream(&self) -> RefundTlvStreamRef {
                let payer = PayerTlvStreamRef {
                        metadata: self.payer.0.as_bytes(),
                };

                let offer = OfferTlvStreamRef {
                        chains: None,
                        metadata: None,
                        currency: None,
                        amount: None,
                        description: Some(&self.description),
                        features: None,
                        absolute_expiry: self.absolute_expiry.map(|duration| duration.as_secs()),
                        paths: self.paths.as_ref(),
                        issuer: self.issuer.as_ref(),
                        quantity_max: None,
                        node_id: None,
                };

                let features = {
                        if self.features == InvoiceRequestFeatures::empty() { None }
                        else { Some(&self.features) }
                };

                let invoice_request = InvoiceRequestTlvStreamRef {
                        chain: self.chain.as_ref(),
                        amount: Some(self.amount_msats),
                        features,
                        quantity: self.quantity,
                        payer_id: Some(&self.payer_id),
                        payer_note: self.payer_note.as_ref(),
                };

                (payer, offer, invoice_request)
        }
}

impl Writeable for Refund {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                WithoutLength(&self.bytes).write(writer)
        }
}

impl Writeable for RefundContents {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                self.as_tlv_stream().write(writer)
        }
}

type RefundTlvStream = (PayerTlvStream, OfferTlvStream, InvoiceRequestTlvStream);

type RefundTlvStreamRef<'a> = (
        PayerTlvStreamRef<'a>,
        OfferTlvStreamRef<'a>,
        InvoiceRequestTlvStreamRef<'a>,
);

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 Bech32Encode for Refund {
        const BECH32_HRP: &'static str = "lnr";
}

impl FromStr for Refund {
        type Err = ParseError;

        fn from_str(s: &str) -> Result<Self, <Self as FromStr>::Err> {
                Refund::from_bech32_str(s)
        }
}

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::Bytes(metadata)),
                };

                if metadata.is_some() {
                        return Err(SemanticError::UnexpectedMetadata);
                }

                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) if amount_msats > MAX_VALUE_MSAT => {
                                return Err(SemanticError::InvalidAmount);
                        },
                        Some(amount_msats) => amount_msats,
                };

                let features = features.unwrap_or_else(InvoiceRequestFeatures::empty);

                let payer_id = match payer_id {
                        None => return Err(SemanticError::MissingPayerId),
                        Some(payer_id) => payer_id,
                };

                Ok(RefundContents {
                        payer, description, absolute_expiry, issuer, paths, chain, amount_msats, features,
                        quantity, payer_id, payer_note,
                })
        }
}

impl core::fmt::Display for Refund {
        fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
                self.fmt_bech32_str(f)
        }
}

#[cfg(test)]
mod tests {
        use super::{Refund, RefundBuilder, RefundTlvStreamRef};

        use bitcoin::blockdata::constants::ChainHash;
        use bitcoin::network::constants::Network;
        use bitcoin::secp256k1::{KeyPair, Secp256k1, SecretKey};
        use core::convert::TryFrom;
        use core::time::Duration;
        use crate::ln::features::{InvoiceRequestFeatures, OfferFeatures};
        use crate::ln::msgs::{DecodeError, MAX_VALUE_MSAT};
        use crate::offers::invoice_request::InvoiceRequestTlvStreamRef;
        use crate::offers::offer::OfferTlvStreamRef;
        use crate::offers::parse::{ParseError, SemanticError};
        use crate::offers::payer::PayerTlvStreamRef;
        use crate::offers::test_utils::*;
        use crate::onion_message::{BlindedHop, BlindedPath};
        use crate::util::ser::{BigSize, Writeable};
        use crate::util::string::PrintableString;

        trait ToBytes {
                fn to_bytes(&self) -> Vec<u8>;
        }

        impl<'a> ToBytes for RefundTlvStreamRef<'a> {
                fn to_bytes(&self) -> Vec<u8> {
                        let mut buffer = Vec::new();
                        self.write(&mut buffer).unwrap();
                        buffer
                }
        }

        #[test]
        fn builds_refund_with_defaults() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();

                let mut buffer = Vec::new();
                refund.write(&mut buffer).unwrap();

                assert_eq!(refund.bytes, buffer.as_slice());
                assert_eq!(refund.metadata(), &[1; 32]);
                assert_eq!(refund.description(), PrintableString("foo"));
                assert_eq!(refund.absolute_expiry(), None);
                #[cfg(feature = "std")]
                assert!(!refund.is_expired());
                assert_eq!(refund.paths(), &[]);
                assert_eq!(refund.issuer(), None);
                assert_eq!(refund.chain(), ChainHash::using_genesis_block(Network::Bitcoin));
                assert_eq!(refund.amount_msats(), 1000);
                assert_eq!(refund.features(), &InvoiceRequestFeatures::empty());
                assert_eq!(refund.payer_id(), payer_pubkey());
                assert_eq!(refund.payer_note(), None);

                assert_eq!(
                        refund.as_tlv_stream(),
                        (
                                PayerTlvStreamRef { metadata: Some(&vec![1; 32]) },
                                OfferTlvStreamRef {
                                        chains: None,
                                        metadata: None,
                                        currency: None,
                                        amount: None,
                                        description: Some(&String::from("foo")),
                                        features: None,
                                        absolute_expiry: None,
                                        paths: None,
                                        issuer: None,
                                        quantity_max: None,
                                        node_id: None,
                                },
                                InvoiceRequestTlvStreamRef {
                                        chain: None,
                                        amount: Some(1000),
                                        features: None,
                                        quantity: None,
                                        payer_id: Some(&payer_pubkey()),
                                        payer_note: None,
                                },
                        ),
                );

                if let Err(e) = Refund::try_from(buffer) {
                        panic!("error parsing refund: {:?}", e);
                }
        }

        #[test]
        fn fails_building_refund_with_invalid_amount() {
                match RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), MAX_VALUE_MSAT + 1) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => assert_eq!(e, SemanticError::InvalidAmount),
                }
        }

        #[test]
        fn builds_refund_with_absolute_expiry() {
                let future_expiry = Duration::from_secs(u64::max_value());
                let past_expiry = Duration::from_secs(0);

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .absolute_expiry(future_expiry)
                        .build()
                        .unwrap();
                let (_, tlv_stream, _) = refund.as_tlv_stream();
                #[cfg(feature = "std")]
                assert!(!refund.is_expired());
                assert_eq!(refund.absolute_expiry(), Some(future_expiry));
                assert_eq!(tlv_stream.absolute_expiry, Some(future_expiry.as_secs()));

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .absolute_expiry(future_expiry)
                        .absolute_expiry(past_expiry)
                        .build()
                        .unwrap();
                let (_, tlv_stream, _) = refund.as_tlv_stream();
                #[cfg(feature = "std")]
                assert!(refund.is_expired());
                assert_eq!(refund.absolute_expiry(), Some(past_expiry));
                assert_eq!(tlv_stream.absolute_expiry, Some(past_expiry.as_secs()));
        }

        #[test]
        fn builds_refund_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 refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .path(paths[0].clone())
                        .path(paths[1].clone())
                        .build()
                        .unwrap();
                let (_, offer_tlv_stream, invoice_request_tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.paths(), paths.as_slice());
                assert_eq!(refund.payer_id(), pubkey(42));
                assert_ne!(pubkey(42), pubkey(44));
                assert_eq!(offer_tlv_stream.paths, Some(&paths));
                assert_eq!(invoice_request_tlv_stream.payer_id, Some(&pubkey(42)));
        }

        #[test]
        fn builds_refund_with_issuer() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .issuer("bar".into())
                        .build()
                        .unwrap();
                let (_, tlv_stream, _) = refund.as_tlv_stream();
                assert_eq!(refund.issuer(), Some(PrintableString("bar")));
                assert_eq!(tlv_stream.issuer, Some(&String::from("bar")));

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .issuer("bar".into())
                        .issuer("baz".into())
                        .build()
                        .unwrap();
                let (_, tlv_stream, _) = refund.as_tlv_stream();
                assert_eq!(refund.issuer(), Some(PrintableString("baz")));
                assert_eq!(tlv_stream.issuer, Some(&String::from("baz")));
        }

        #[test]
        fn builds_refund_with_chain() {
                let mainnet = ChainHash::using_genesis_block(Network::Bitcoin);
                let testnet = ChainHash::using_genesis_block(Network::Testnet);

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .chain(Network::Bitcoin)
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.chain(), mainnet);
                assert_eq!(tlv_stream.chain, None);

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .chain(Network::Testnet)
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.chain(), testnet);
                assert_eq!(tlv_stream.chain, Some(&testnet));

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .chain(Network::Regtest)
                        .chain(Network::Testnet)
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.chain(), testnet);
                assert_eq!(tlv_stream.chain, Some(&testnet));
        }

        #[test]
        fn builds_refund_with_quantity() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .quantity(10)
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.quantity(), Some(10));
                assert_eq!(tlv_stream.quantity, Some(10));

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .quantity(10)
                        .quantity(1)
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.quantity(), Some(1));
                assert_eq!(tlv_stream.quantity, Some(1));
        }

        #[test]
        fn builds_refund_with_payer_note() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .payer_note("bar".into())
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.payer_note(), Some(PrintableString("bar")));
                assert_eq!(tlv_stream.payer_note, Some(&String::from("bar")));

                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .payer_note("bar".into())
                        .payer_note("baz".into())
                        .build().unwrap();
                let (_, _, tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.payer_note(), Some(PrintableString("baz")));
                assert_eq!(tlv_stream.payer_note, Some(&String::from("baz")));
        }

        #[test]
        fn fails_responding_with_unknown_required_features() {
                match RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .features_unchecked(InvoiceRequestFeatures::unknown())
                        .build().unwrap()
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                {
                        Ok(_) => panic!("expected error"),
                        Err(e) => assert_eq!(e, SemanticError::UnknownRequiredFeatures),
                }
        }

        #[test]
        fn parses_refund_with_metadata() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();
                if let Err(e) = refund.to_string().parse::<Refund>() {
                        panic!("error parsing refund: {:?}", e);
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.0.metadata = None;

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::MissingPayerMetadata));
                        },
                }
        }

        #[test]
        fn parses_refund_with_description() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();
                if let Err(e) = refund.to_string().parse::<Refund>() {
                        panic!("error parsing refund: {:?}", e);
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.description = None;

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::MissingDescription));
                        },
                }
        }

        #[test]
        fn parses_refund_with_amount() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();
                if let Err(e) = refund.to_string().parse::<Refund>() {
                        panic!("error parsing refund: {:?}", e);
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.2.amount = None;

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::MissingAmount));
                        },
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.2.amount = Some(MAX_VALUE_MSAT + 1);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::InvalidAmount));
                        },
                }
        }

        #[test]
        fn parses_refund_with_payer_id() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();
                if let Err(e) = refund.to_string().parse::<Refund>() {
                        panic!("error parsing refund: {:?}", e);
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.2.payer_id = None;

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::MissingPayerId));
                        },
                }
        }

        #[test]
        fn parses_refund_with_optional_fields() {
                let past_expiry = Duration::from_secs(0);
                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 refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .absolute_expiry(past_expiry)
                        .issuer("bar".into())
                        .path(paths[0].clone())
                        .path(paths[1].clone())
                        .chain(Network::Testnet)
                        .features_unchecked(InvoiceRequestFeatures::unknown())
                        .quantity(10)
                        .payer_note("baz".into())
                        .build()
                        .unwrap();
                match refund.to_string().parse::<Refund>() {
                        Ok(refund) => {
                                assert_eq!(refund.absolute_expiry(), Some(past_expiry));
                                #[cfg(feature = "std")]
                                assert!(refund.is_expired());
                                assert_eq!(refund.paths(), &paths[..]);
                                assert_eq!(refund.issuer(), Some(PrintableString("bar")));
                                assert_eq!(refund.chain(), ChainHash::using_genesis_block(Network::Testnet));
                                assert_eq!(refund.features(), &InvoiceRequestFeatures::unknown());
                                assert_eq!(refund.quantity(), Some(10));
                                assert_eq!(refund.payer_note(), Some(PrintableString("baz")));
                        },
                        Err(e) => panic!("error parsing refund: {:?}", e),
                }
        }

        #[test]
        fn fails_parsing_refund_with_unexpected_fields() {
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .build().unwrap();
                if let Err(e) = refund.to_string().parse::<Refund>() {
                        panic!("error parsing refund: {:?}", e);
                }

                let metadata = vec![42; 32];
                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.metadata = Some(&metadata);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedMetadata));
                        },
                }

                let chains = vec![ChainHash::using_genesis_block(Network::Testnet)];
                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.chains = Some(&chains);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedChain));
                        },
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.currency = Some(&b"USD");
                tlv_stream.1.amount = Some(1000);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedAmount));
                        },
                }

                let features = OfferFeatures::unknown();
                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.features = Some(&features);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedFeatures));
                        },
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.quantity_max = Some(10);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedQuantity));
                        },
                }

                let node_id = payer_pubkey();
                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.1.node_id = Some(&node_id);

                match Refund::try_from(tlv_stream.to_bytes()) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => {
                                assert_eq!(e, ParseError::InvalidSemantics(SemanticError::UnexpectedSigningPubkey));
                        },
                }
        }

        #[test]
        fn fails_parsing_refund_with_extra_tlv_records() {
                let secp_ctx = Secp256k1::new();
                let keys = KeyPair::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap());
                let refund = RefundBuilder::new("foo".into(), vec![1; 32], keys.public_key(), 1000).unwrap()
                        .build().unwrap();

                let mut encoded_refund = Vec::new();
                refund.write(&mut encoded_refund).unwrap();
                BigSize(1002).write(&mut encoded_refund).unwrap();
                BigSize(32).write(&mut encoded_refund).unwrap();
                [42u8; 32].write(&mut encoded_refund).unwrap();

                match Refund::try_from(encoded_refund) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => assert_eq!(e, ParseError::Decode(DecodeError::InvalidValue)),
                }
        }
}