Offer raw byte encoding and decoding

Offers are typically encoded as bech32 strings for use in QR codes.
However, a more compact encoding is useful when storing offers
long-term. Implement Writeable for Offer and have a corresponding
TryFrom implementation for decoding the raw bytes.

Author: jkczyz

lightning/src/offers/offer.rs

@@ -18,12 +18,14 @@
 //! extern crate core;
 //! extern crate lightning;
 //!
+//! use core::convert::TryFrom;
 //! use core::num::NonZeroU64;
 //! use core::time::Duration;
 //!
 //! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
 //! use lightning::offers::offer::{Amount, Offer, OfferBuilder};
 //! use lightning::offers::parse::ParseError;
+//! use lightning::util::ser::{Readable, Writeable};
 //!
 //! # use lightning::onion_message::BlindedPath;
 //! # #[cfg(feature = "std")]
@@ -54,6 +56,13 @@
 //!
 //! // Parse from a bech32 string after scanning from a QR code.
 //! let offer = encoded_offer.parse::<Offer>()?;
+//!
+//! // Encode offer as raw bytes.
+//! let mut bytes = Vec::new();
+//! offer.write(&mut bytes).unwrap();
+//!
+//! // Decode raw bytes into an offer.
+//! let offer = Offer::try_from(bytes)?;
 //! # Ok(())
 //! # }
 //! ```
@@ -70,7 +79,7 @@ use io;
 use ln::features::OfferFeatures;
 use offers::parse::{Bech32Encode, ParseError, SemanticError};
 use onion_message::BlindedPath;
-use util::ser::{Writeable, Writer};
+use util::ser::{Readable, Writeable, Writer};
 
 use prelude::*;
 
@@ -383,12 +392,27 @@ impl OfferContents {
 	}
 }
 
+impl Writeable for Offer {
+	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+		self.bytes.write(writer)
+	}
+}
+
 impl Writeable for OfferContents {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
 		self.as_tlv_stream().write(writer)
 	}
 }
 
+impl TryFrom<Vec<u8>> for Offer {
+	type Error = ParseError;
+
+	fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
+		let tlv_stream: OfferTlvStream = Readable::read(&mut &bytes[..])?;
+		Offer::try_from((bytes, tlv_stream))
+	}
+}
+
 /// The amount required for an item in an [`Offer`] denominated in either bitcoin or another
 /// currency.
 #[derive(Clone, Debug, PartialEq)]
@@ -431,6 +455,8 @@ impl Bech32Encode for Offer {
 	const BECH32_HRP: &'static str = "lno";
 }
 
+type ParsedOffer = (Vec<u8>, OfferTlvStream);
+
 impl FromStr for Offer {
 	type Err = ParseError;
 
@@ -441,6 +467,16 @@ impl FromStr for Offer {
 	}
 }
 
+impl TryFrom<ParsedOffer> for Offer {
+	type Error = ParseError;
+
+	fn try_from(offer: ParsedOffer) -> Result<Self, Self::Error> {
+		let (bytes, tlv_stream) = offer;
+		let contents = OfferContents::try_from(tlv_stream)?;
+		Ok(Offer { bytes, contents })
+	}
+}
+
 impl TryFrom<OfferTlvStream> for OfferContents {
 	type Error = SemanticError;