[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 a [`Bolt12Invoice`] to be paid.
//!
//! This is an [`InvoiceRequest`] produced *not* in response to an [`Offer`].
//!
//! [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
//! [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
//! [`Offer`]: crate::offers::offer::Offer
//!
//! # Example
//!
//! ```
//! 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::Bolt12ParseError;
//! use lightning::offers::refund::{Refund, RefundBuilder};
//! use lightning::util::ser::{Readable, Writeable};
//!
//! # use lightning::blinded_path::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<(), Bolt12ParseError> {
//! 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(vec![1; 32], pubkey, 20_000)?
//!     .description("coffee, large".to_string())
//!     .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(())
//! # }
//! ```
//!
//! # Note
//!
//! If constructing a [`Refund`] for use with a [`ChannelManager`], use
//! [`ChannelManager::create_refund_builder`] instead of [`RefundBuilder::new`].
//!
//! [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
//! [`ChannelManager::create_refund_builder`]: crate::ln::channelmanager::ChannelManager::create_refund_builder

use bitcoin::blockdata::constants::ChainHash;
use bitcoin::network::constants::Network;
use bitcoin::secp256k1::{PublicKey, Secp256k1, self};
use core::hash::{Hash, Hasher};
use core::ops::Deref;
use core::str::FromStr;
use core::time::Duration;
use crate::sign::EntropySource;
use crate::io;
use crate::blinded_path::BlindedPath;
use crate::ln::types::PaymentHash;
use crate::ln::channelmanager::PaymentId;
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;
use crate::offers::invoice_request::{InvoiceRequestTlvStream, InvoiceRequestTlvStreamRef};
use crate::offers::offer::{OfferTlvStream, OfferTlvStreamRef};
use crate::offers::parse::{Bech32Encode, Bolt12ParseError, Bolt12SemanticError, ParsedMessage};
use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
use crate::offers::signer::{Metadata, MetadataMaterial, self};
use crate::util::ser::{SeekReadable, WithoutLength, Writeable, Writer};
use crate::util::string::PrintableString;

#[cfg(not(c_bindings))]
use {
        crate::offers::invoice::{DerivedSigningPubkey, ExplicitSigningPubkey, InvoiceBuilder},
};
#[cfg(c_bindings)]
use {
        crate::offers::invoice::{InvoiceWithDerivedSigningPubkeyBuilder, InvoiceWithExplicitSigningPubkeyBuilder},
};

#[allow(unused_imports)]
use crate::prelude::*;

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

pub(super) const IV_BYTES: &[u8; IV_LEN] = b"LDK Refund ~~~~~";

/// Builds a [`Refund`] for the "offer for money" flow.
///
/// See [module-level documentation] for usage.
///
/// This is not exported to bindings users as builder patterns don't map outside of move semantics.
///
/// [module-level documentation]: self
pub struct RefundBuilder<'a, T: secp256k1::Signing> {
        refund: RefundContents,
        secp_ctx: Option<&'a Secp256k1<T>>,
}

/// Builds a [`Refund`] for the "offer for money" flow.
///
/// See [module-level documentation] for usage.
///
/// [module-level documentation]: self
#[cfg(c_bindings)]
#[derive(Clone)]
pub struct RefundMaybeWithDerivedMetadataBuilder<'a> {
        refund: RefundContents,
        secp_ctx: Option<&'a Secp256k1<secp256k1::All>>,
}

macro_rules! refund_explicit_metadata_builder_methods { () => {
        /// 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 (empty) [`Refund::description`], [`Refund::payer_metadata`],
        /// and [`Refund::amount_msats`].
        ///
        /// # Note
        ///
        /// If constructing a [`Refund`] for use with a [`ChannelManager`], use
        /// [`ChannelManager::create_refund_builder`] instead of [`RefundBuilder::new`].
        ///
        /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
        /// [`ChannelManager::create_refund_builder`]: crate::ln::channelmanager::ChannelManager::create_refund_builder
        pub fn new(
                metadata: Vec<u8>, payer_id: PublicKey, amount_msats: u64
        ) -> Result<Self, Bolt12SemanticError> {
                if amount_msats > MAX_VALUE_MSAT {
                        return Err(Bolt12SemanticError::InvalidAmount);
                }

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

macro_rules! refund_builder_methods { (
        $self: ident, $self_type: ty, $return_type: ty, $return_value: expr, $secp_context: ty $(, $self_mut: tt)?
) => {
        /// Similar to [`RefundBuilder::new`] except, if [`RefundBuilder::path`] is called, the payer id
        /// is derived from the given [`ExpandedKey`] and nonce. This provides sender privacy by using a
        /// different payer id for each refund, assuming a different nonce is used.  Otherwise, the
        /// provided `node_id` is used for the payer id.
        ///
        /// Also, sets the metadata when [`RefundBuilder::build`] is called such that it can be used to
        /// verify that an [`InvoiceRequest`] was produced for the refund given an [`ExpandedKey`].
        ///
        /// The `payment_id` is encrypted in the metadata and should be unique. This ensures that only
        /// one invoice will be paid for the refund and that payments can be uniquely identified.
        ///
        /// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
        /// [`ExpandedKey`]: crate::ln::inbound_payment::ExpandedKey
        pub fn deriving_payer_id<ES: Deref>(
                node_id: PublicKey, expanded_key: &ExpandedKey, entropy_source: ES,
                secp_ctx: &'a Secp256k1<$secp_context>, amount_msats: u64, payment_id: PaymentId
        ) -> Result<Self, Bolt12SemanticError> where ES::Target: EntropySource {
                if amount_msats > MAX_VALUE_MSAT {
                        return Err(Bolt12SemanticError::InvalidAmount);
                }

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

        /// Sets the [`Refund::description`].
        ///
        /// Successive calls to this method will override the previous setting.
        pub fn description($($self_mut)* $self: $self_type, description: String) -> $return_type {
                $self.refund.description = description;
                $return_value
        }

        /// 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($($self_mut)* $self: $self_type, absolute_expiry: Duration) -> $return_type {
                $self.refund.absolute_expiry = Some(absolute_expiry);
                $return_value
        }

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

        /// 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($($self_mut)* $self: $self_type, path: BlindedPath) -> $return_type {
                $self.refund.paths.get_or_insert_with(Vec::new).push(path);
                $return_value
        }

        /// 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($self: $self_type, network: Network) -> $return_type {
                $self.chain_hash(ChainHash::using_genesis_block(network))
        }

        /// Sets the [`Refund::chain`] of the given [`ChainHash`] for paying an invoice. If not called,
        /// [`Network::Bitcoin`] is assumed.
        ///
        /// Successive calls to this method will override the previous setting.
        pub(crate) fn chain_hash($($self_mut)* $self: $self_type, chain: ChainHash) -> $return_type {
                $self.refund.chain = Some(chain);
                $return_value
        }

        /// Sets [`Refund::quantity`] of items. This is purely for informational purposes. It is useful
        /// when the refund pertains to a [`Bolt12Invoice`] 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.
        ///
        /// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
        /// [`InvoiceRequest::quantity`]: crate::offers::invoice_request::InvoiceRequest::quantity
        /// [`Offer`]: crate::offers::offer::Offer
        pub fn quantity($($self_mut)* $self: $self_type, quantity: u64) -> $return_type {
                $self.refund.quantity = Some(quantity);
                $return_value
        }

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

        /// Builds a [`Refund`] after checking for valid semantics.
        pub fn build($($self_mut)* $self: $self_type) -> Result<Refund, Bolt12SemanticError> {
                if $self.refund.chain() == $self.refund.implied_chain() {
                        $self.refund.chain = None;
                }

                // Create the metadata for stateless verification of a Bolt12Invoice.
                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_payer_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,
                        #[cfg(not(c_bindings))]
                        contents: $self.refund,
                        #[cfg(c_bindings)]
                        contents: $self.refund.clone(),
                })
        }
} }

#[cfg(test)]
macro_rules! refund_builder_test_methods { (
        $self: ident, $self_type: ty, $return_type: ty, $return_value: expr $(, $self_mut: tt)?
) => {
        #[cfg_attr(c_bindings, allow(dead_code))]
        pub(crate) fn clear_paths($($self_mut)* $self: $self_type) -> $return_type {
                $self.refund.paths = None;
                $return_value
        }

        #[cfg_attr(c_bindings, allow(dead_code))]
        fn features_unchecked($($self_mut)* $self: $self_type, features: InvoiceRequestFeatures) -> $return_type {
                $self.refund.features = features;
                $return_value
        }
} }

impl<'a> RefundBuilder<'a, secp256k1::SignOnly> {
        refund_explicit_metadata_builder_methods!();
}

impl<'a, T: secp256k1::Signing> RefundBuilder<'a, T> {
        refund_builder_methods!(self, Self, Self, self, T, mut);

        #[cfg(test)]
        refund_builder_test_methods!(self, Self, Self, self, mut);
}

#[cfg(all(c_bindings, not(test)))]
impl<'a> RefundMaybeWithDerivedMetadataBuilder<'a> {
        refund_explicit_metadata_builder_methods!();
        refund_builder_methods!(self, &mut Self, (), (), secp256k1::All);
}

#[cfg(all(c_bindings, test))]
impl<'a> RefundMaybeWithDerivedMetadataBuilder<'a> {
        refund_explicit_metadata_builder_methods!();
        refund_builder_methods!(self, &mut Self, &mut Self, self, secp256k1::All);
        refund_builder_test_methods!(self, &mut Self, &mut Self, self);
}

#[cfg(c_bindings)]
impl<'a> From<RefundBuilder<'a, secp256k1::All>>
for RefundMaybeWithDerivedMetadataBuilder<'a> {
        fn from(builder: RefundBuilder<'a, secp256k1::All>) -> Self {
                let RefundBuilder { refund, secp_ctx } = builder;

                Self { refund, secp_ctx }
        }
}

#[cfg(c_bindings)]
impl<'a> From<RefundMaybeWithDerivedMetadataBuilder<'a>>
for RefundBuilder<'a, secp256k1::All> {
        fn from(builder: RefundMaybeWithDerivedMetadataBuilder<'a>) -> Self {
                let RefundMaybeWithDerivedMetadataBuilder { refund, secp_ctx } = builder;

                Self { refund, secp_ctx }
        }
}

/// A `Refund` is a request to send an [`Bolt12Invoice`] 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.
///
/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
/// [`Offer`]: crate::offers::offer::Offer
#[derive(Clone, Debug)]
pub struct Refund {
        pub(super) bytes: Vec<u8>,
        pub(super) contents: RefundContents,
}

/// The contents of a [`Refund`], which may be shared with an [`Bolt12Invoice`].
///
/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
#[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>,
        // invoice_request fields
        chain: Option<ChainHash>,
        amount_msats: u64,
        features: InvoiceRequestFeatures,
        quantity: Option<u64>,
        payer_id: PublicKey,
        payer_note: Option<String>,
        paths: Option<Vec<BlindedPath>>,
}

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 {
                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()
        }

        /// Whether the refund has expired given the duration since the Unix epoch.
        pub fn is_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
                self.contents.is_expired_no_std(duration_since_epoch)
        }

        /// 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()
        }

        /// 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()
        }

        /// An unpredictable series of bytes, typically containing information about the derivation of
        /// [`payer_id`].
        ///
        /// [`payer_id`]: Self::payer_id
        pub fn payer_metadata(&self) -> &[u8] {
                self.contents.metadata()
        }

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

macro_rules! respond_with_explicit_signing_pubkey_methods { ($self: ident, $builder: ty) => {
        /// Creates an [`InvoiceBuilder`] for the refund with the given required fields and using the
        /// [`Duration`] since [`std::time::SystemTime::UNIX_EPOCH`] as the creation time.
        ///
        /// See [`Refund::respond_with_no_std`] for further details where the aforementioned creation
        /// time is used for the `created_at` parameter.
        ///
        /// This is not exported to bindings users as builder patterns don't map outside of move semantics.
        ///
        /// [`Duration`]: core::time::Duration
        #[cfg(feature = "std")]
        pub fn respond_with(
                &$self, payment_paths: Vec<(BlindedPayInfo, BlindedPath)>, payment_hash: PaymentHash,
                signing_pubkey: PublicKey,
        ) -> Result<$builder, Bolt12SemanticError> {
                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 [`Bolt12Invoice::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.
        ///
        /// This is not exported to bindings users as builder patterns don't map outside of move semantics.
        ///
        /// [`Bolt12Invoice::created_at`]: crate::offers::invoice::Bolt12Invoice::created_at
        pub fn respond_with_no_std(
                &$self, payment_paths: Vec<(BlindedPayInfo, BlindedPath)>, payment_hash: PaymentHash,
                signing_pubkey: PublicKey, created_at: Duration
        ) -> Result<$builder, Bolt12SemanticError> {
                if $self.features().requires_unknown_bits() {
                        return Err(Bolt12SemanticError::UnknownRequiredFeatures);
                }

                <$builder>::for_refund($self, payment_paths, created_at, payment_hash, signing_pubkey)
        }
} }

macro_rules! respond_with_derived_signing_pubkey_methods { ($self: ident, $builder: ty) => {
        /// Creates an [`InvoiceBuilder`] for the refund using the given required fields and that uses
        /// derived signing keys to sign the [`Bolt12Invoice`].
        ///
        /// See [`Refund::respond_with`] for further details.
        ///
        /// This is not exported to bindings users as builder patterns don't map outside of move semantics.
        ///
        /// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
        #[cfg(feature = "std")]
        pub fn respond_using_derived_keys<ES: Deref>(
                &$self, payment_paths: Vec<(BlindedPayInfo, BlindedPath)>, payment_hash: PaymentHash,
                expanded_key: &ExpandedKey, entropy_source: ES
        ) -> Result<$builder, Bolt12SemanticError>
        where
                ES::Target: EntropySource,
        {
                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_using_derived_keys_no_std(
                        payment_paths, payment_hash, created_at, expanded_key, entropy_source
                )
        }

        /// Creates an [`InvoiceBuilder`] for the refund using the given required fields and that uses
        /// derived signing keys to sign the [`Bolt12Invoice`].
        ///
        /// See [`Refund::respond_with_no_std`] for further details.
        ///
        /// This is not exported to bindings users as builder patterns don't map outside of move semantics.
        ///
        /// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
        pub fn respond_using_derived_keys_no_std<ES: Deref>(
                &$self, payment_paths: Vec<(BlindedPayInfo, BlindedPath)>, payment_hash: PaymentHash,
                created_at: core::time::Duration, expanded_key: &ExpandedKey, entropy_source: ES
        ) -> Result<$builder, Bolt12SemanticError>
        where
                ES::Target: EntropySource,
        {
                if $self.features().requires_unknown_bits() {
                        return Err(Bolt12SemanticError::UnknownRequiredFeatures);
                }

                let nonce = Nonce::from_entropy_source(entropy_source);
                let keys = signer::derive_keys(nonce, expanded_key);
                <$builder>::for_refund_using_keys($self, payment_paths, created_at, payment_hash, keys)
        }
} }

#[cfg(not(c_bindings))]
impl Refund {
        respond_with_explicit_signing_pubkey_methods!(self, InvoiceBuilder<ExplicitSigningPubkey>);
        respond_with_derived_signing_pubkey_methods!(self, InvoiceBuilder<DerivedSigningPubkey>);
}

#[cfg(c_bindings)]
impl Refund {
        respond_with_explicit_signing_pubkey_methods!(self, InvoiceWithExplicitSigningPubkeyBuilder);
        respond_with_derived_signing_pubkey_methods!(self, InvoiceWithDerivedSigningPubkeyBuilder);
}

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

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

impl PartialEq for Refund {
        fn eq(&self, other: &Self) -> bool {
                self.bytes.eq(&other.bytes)
        }
}

impl Eq for Refund {}

impl Hash for Refund {
        fn hash<H: Hasher>(&self, state: &mut H) {
                self.bytes.hash(state);
        }
}

impl RefundContents {
        pub fn description(&self) -> PrintableString {
                PrintableString(&self.description)
        }

        pub fn absolute_expiry(&self) -> Option<Duration> {
                self.absolute_expiry
        }

        #[cfg(feature = "std")]
        pub(super) fn is_expired(&self) -> bool {
                SystemTime::UNIX_EPOCH
                        .elapsed()
                        .map(|duration_since_epoch| self.is_expired_no_std(duration_since_epoch))
                        .unwrap_or(false)
        }

        pub(super) fn is_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
                self.absolute_expiry
                        .map(|absolute_expiry| duration_since_epoch > absolute_expiry)
                        .unwrap_or(false)
        }

        pub fn issuer(&self) -> Option<PrintableString> {
                self.issuer.as_ref().map(|issuer| PrintableString(issuer.as_str()))
        }

        pub fn paths(&self) -> &[BlindedPath] {
                self.paths.as_ref().map(|paths| paths.as_slice()).unwrap_or(&[])
        }

        pub(super) fn metadata(&self) -> &[u8] {
                self.payer.0.as_bytes().map(|bytes| bytes.as_slice()).unwrap_or(&[])
        }

        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 fn amount_msats(&self) -> u64 {
                self.amount_msats
        }

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

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

        /// Payer provided note to include in the invoice.
        pub fn payer_note(&self) -> Option<PrintableString> {
                self.payer_note.as_ref().map(|payer_note| PrintableString(payer_note.as_str()))
        }

        pub(super) fn derives_keys(&self) -> bool {
                self.payer.0.derives_payer_keys()
        }

        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: None,
                        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(),
                        paths: self.paths.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 = Bolt12ParseError;

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

impl TryFrom<Vec<u8>> for Refund {
        type Error = Bolt12ParseError;

        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 = Bolt12SemanticError;

        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: offer_paths, issuer, quantity_max,
                                node_id,
                        },
                        InvoiceRequestTlvStream {
                                chain, amount, features, quantity, payer_id, payer_note, paths
                        },
                ) = tlv_stream;

                let payer = match payer_metadata {
                        None => return Err(Bolt12SemanticError::MissingPayerMetadata),
                        Some(metadata) => PayerContents(Metadata::Bytes(metadata)),
                };

                if metadata.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedMetadata);
                }

                if chains.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedChain);
                }

                if currency.is_some() || offer_amount.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedAmount);
                }

                let description = match description {
                        None => return Err(Bolt12SemanticError::MissingDescription),
                        Some(description) => description,
                };

                if offer_features.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedFeatures);
                }

                let absolute_expiry = absolute_expiry.map(Duration::from_secs);

                if offer_paths.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedPaths);
                }

                if quantity_max.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedQuantity);
                }

                if node_id.is_some() {
                        return Err(Bolt12SemanticError::UnexpectedSigningPubkey);
                }

                let amount_msats = match amount {
                        None => return Err(Bolt12SemanticError::MissingAmount),
                        Some(amount_msats) if amount_msats > MAX_VALUE_MSAT => {
                                return Err(Bolt12SemanticError::InvalidAmount);
                        },
                        Some(amount_msats) => amount_msats,
                };

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

                let payer_id = match payer_id {
                        None => return Err(Bolt12SemanticError::MissingPayerId),
                        Some(payer_id) => payer_id,
                };

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

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, RefundTlvStreamRef};
        #[cfg(not(c_bindings))]
        use {
                super::RefundBuilder,
        };
        #[cfg(c_bindings)]
        use {
                super::RefundMaybeWithDerivedMetadataBuilder as RefundBuilder,
        };

        use bitcoin::blockdata::constants::ChainHash;
        use bitcoin::network::constants::Network;
        use bitcoin::secp256k1::{KeyPair, Secp256k1, SecretKey};

        use core::time::Duration;

        use crate::blinded_path::{BlindedHop, BlindedPath, IntroductionNode};
        use crate::sign::KeyMaterial;
        use crate::ln::channelmanager::PaymentId;
        use crate::ln::features::{InvoiceRequestFeatures, OfferFeatures};
        use crate::ln::inbound_payment::ExpandedKey;
        use crate::ln::msgs::{DecodeError, MAX_VALUE_MSAT};
        use crate::offers::invoice_request::InvoiceRequestTlvStreamRef;
        use crate::offers::offer::OfferTlvStreamRef;
        use crate::offers::parse::{Bolt12ParseError, Bolt12SemanticError};
        use crate::offers::payer::PayerTlvStreamRef;
        use crate::offers::test_utils::*;
        use crate::util::ser::{BigSize, Writeable};
        use crate::util::string::PrintableString;
        use crate::prelude::*;

        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(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.payer_metadata(), &[1; 32]);
                assert_eq!(refund.description(), PrintableString(""));
                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("")),
                                        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,
                                        paths: 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(vec![1; 32], payer_pubkey(), MAX_VALUE_MSAT + 1) {
                        Ok(_) => panic!("expected error"),
                        Err(e) => assert_eq!(e, Bolt12SemanticError::InvalidAmount),
                }
        }

        #[test]
        fn builds_refund_with_metadata_derived() {
                let node_id = payer_pubkey();
                let expanded_key = ExpandedKey::new(&KeyMaterial([42; 32]));
                let entropy = FixedEntropy {};
                let secp_ctx = Secp256k1::new();
                let payment_id = PaymentId([1; 32]);

                let refund = RefundBuilder
                        ::deriving_payer_id(node_id, &expanded_key, &entropy, &secp_ctx, 1000, payment_id)
                        .unwrap()
                        .build().unwrap();
                assert_eq!(refund.payer_id(), node_id);

                // Fails verification with altered fields
                let invoice = refund
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                match invoice.verify(&expanded_key, &secp_ctx) {
                        Ok(payment_id) => assert_eq!(payment_id, PaymentId([1; 32])),
                        Err(()) => panic!("verification failed"),
                }

                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.2.amount = Some(2000);

                let mut encoded_refund = Vec::new();
                tlv_stream.write(&mut encoded_refund).unwrap();

                let invoice = Refund::try_from(encoded_refund).unwrap()
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                assert!(invoice.verify(&expanded_key, &secp_ctx).is_err());

                // Fails verification with altered metadata
                let mut tlv_stream = refund.as_tlv_stream();
                let metadata = tlv_stream.0.metadata.unwrap().iter().copied().rev().collect();
                tlv_stream.0.metadata = Some(&metadata);

                let mut encoded_refund = Vec::new();
                tlv_stream.write(&mut encoded_refund).unwrap();

                let invoice = Refund::try_from(encoded_refund).unwrap()
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                assert!(invoice.verify(&expanded_key, &secp_ctx).is_err());
        }

        #[test]
        fn builds_refund_with_derived_payer_id() {
                let node_id = payer_pubkey();
                let expanded_key = ExpandedKey::new(&KeyMaterial([42; 32]));
                let entropy = FixedEntropy {};
                let secp_ctx = Secp256k1::new();
                let payment_id = PaymentId([1; 32]);

                let blinded_path = BlindedPath {
                        introduction_node: IntroductionNode::NodeId(pubkey(40)),
                        blinding_point: pubkey(41),
                        blinded_hops: vec![
                                BlindedHop { blinded_node_id: pubkey(43), encrypted_payload: vec![0; 43] },
                                BlindedHop { blinded_node_id: node_id, encrypted_payload: vec![0; 44] },
                        ],
                };

                let refund = RefundBuilder
                        ::deriving_payer_id(node_id, &expanded_key, &entropy, &secp_ctx, 1000, payment_id)
                        .unwrap()
                        .path(blinded_path)
                        .build().unwrap();
                assert_ne!(refund.payer_id(), node_id);

                let invoice = refund
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                match invoice.verify(&expanded_key, &secp_ctx) {
                        Ok(payment_id) => assert_eq!(payment_id, PaymentId([1; 32])),
                        Err(()) => panic!("verification failed"),
                }

                // Fails verification with altered fields
                let mut tlv_stream = refund.as_tlv_stream();
                tlv_stream.2.amount = Some(2000);

                let mut encoded_refund = Vec::new();
                tlv_stream.write(&mut encoded_refund).unwrap();

                let invoice = Refund::try_from(encoded_refund).unwrap()
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                assert!(invoice.verify(&expanded_key, &secp_ctx).is_err());

                // Fails verification with altered payer_id
                let mut tlv_stream = refund.as_tlv_stream();
                let payer_id = pubkey(1);
                tlv_stream.2.payer_id = Some(&payer_id);

                let mut encoded_refund = Vec::new();
                tlv_stream.write(&mut encoded_refund).unwrap();

                let invoice = Refund::try_from(encoded_refund).unwrap()
                        .respond_with_no_std(payment_paths(), payment_hash(), recipient_pubkey(), now())
                        .unwrap()
                        .build().unwrap()
                        .sign(recipient_sign).unwrap();
                assert!(invoice.verify(&expanded_key, &secp_ctx).is_err());
        }

        #[test]
        fn builds_refund_with_absolute_expiry() {
                let future_expiry = Duration::from_secs(u64::max_value());
                let past_expiry = Duration::from_secs(0);
                let now = future_expiry - Duration::from_secs(1_000);

                let refund = RefundBuilder::new(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!(!refund.is_expired_no_std(now));
                assert_eq!(refund.absolute_expiry(), Some(future_expiry));
                assert_eq!(tlv_stream.absolute_expiry, Some(future_expiry.as_secs()));

                let refund = RefundBuilder::new(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!(refund.is_expired_no_std(now));
                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: IntroductionNode::NodeId(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: IntroductionNode::NodeId(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(vec![1; 32], payer_pubkey(), 1000).unwrap()
                        .path(paths[0].clone())
                        .path(paths[1].clone())
                        .build()
                        .unwrap();
                let (_, _, invoice_request_tlv_stream) = refund.as_tlv_stream();
                assert_eq!(refund.payer_id(), pubkey(42));
                assert_eq!(refund.paths(), paths.as_slice());
                assert_ne!(pubkey(42), pubkey(44));
                assert_eq!(invoice_request_tlv_stream.payer_id, Some(&pubkey(42)));
                assert_eq!(invoice_request_tlv_stream.paths, Some(&paths));
        }

        #[test]
        fn builds_refund_with_issuer() {
                let refund = RefundBuilder::new(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(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(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(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(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(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(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(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(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(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, Bolt12SemanticError::UnknownRequiredFeatures),
                }
        }

        #[test]
        fn parses_refund_with_metadata() {
                let refund = RefundBuilder::new(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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::MissingPayerMetadata));
                        },
                }
        }

        #[test]
        fn parses_refund_with_description() {
                let refund = RefundBuilder::new(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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::MissingDescription));
                        },
                }
        }

        #[test]
        fn parses_refund_with_amount() {
                let refund = RefundBuilder::new(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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::InvalidAmount));
                        },
                }
        }

        #[test]
        fn parses_refund_with_payer_id() {
                let refund = RefundBuilder::new(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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::MissingPayerId));
                        },
                }
        }

        #[test]
        fn parses_refund_with_optional_fields() {
                let past_expiry = Duration::from_secs(0);
                let paths = vec![
                        BlindedPath {
                                introduction_node: IntroductionNode::NodeId(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: IntroductionNode::NodeId(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(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(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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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, Bolt12ParseError::InvalidSemantics(Bolt12SemanticError::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(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, Bolt12ParseError::Decode(DecodeError::InvalidValue)),
                }
        }
}