RawBolt11Invoice serialization utilities

[devrandom]

for remote signing of invoices

[TheBlueMatt]

Gah we need to make the HRP decoder support mixed-case strings...allocating a new string just to lower-case it before parsing it is absurd...Doesn't have to happen here, but the over-allocations in this crate irritate me.

[TheBlueMatt]

I kinda prefer we call this from_bytes or something. The fact that its a string is a bit weird to expose in the API - there's no string serialization for an unsigned invoice, we're just supporting serializing them to bytes for programatic use.

[devrandom]

so there are no low-level utilities to ser/de the data part to bytes, so this would add significant amount of code. I changed this to be [Fe32] for the data part, and str for the hrp. see what you think.

[TheBlueMatt]

This is super trivial and I would land it, but rustfmt is sad, so you'll need to apply this (+squash):

+ rustfmt +1.63.0 --edition 2021 --check lightning-invoice/src/lib.rs
Diff in /home/runner/work/rust-lightning/rust-lightning/lightning-invoice/src/lib.rs at line 79:
 /// Re-export serialization traits
 #[cfg(fuzzing)]
 pub use crate::de::FromBase32;
+#[cfg(not(fuzzing))]
+use crate::de::FromBase32;
 #[cfg(fuzzing)]
 pub use crate::ser::Base32Iterable;
 #[cfg(not(fuzzing))]
Diff in /home/runner/work/rust-lightning/rust-lightning/lightning-invoice/src/lib.rs at line 85:
-use crate::de::FromBase32;
-#[cfg(not(fuzzing))]
 use crate::ser::Base32Iterable;
 
 /// Errors that indicate what is wrong with the invoice. They have some granularity for debug
Diff in /home/runner/work/rust-lightning/rust-lightning/lightning-invoice/src/lib.rs at line 1207:
 		let raw_hrp: RawHrp = RawHrp::from_str(hrp)?;
 		let data_part = RawDataPart::from_base32(data)?;
 
-		Ok(Self {
-			hrp: raw_hrp,
-			data: data_part,
-		})
+		Ok(Self { hrp: raw_hrp, data: data_part })
 	}
 }

[devrandom]

done

[TheBlueMatt]

Thanks

[TheBlueMatt]

Backported in #3567