Marginally reduce allocations in `lightning-invoice`

In aa2f6b47df312f026213d0ceaaff20ffe955c377 we refactored
`lightning-invoice` de/serialization to use the new version of
`bech32`, also reducing some trivial unnecessary allocations when
we did so.

Here we drop a few additional allocations which came up in review.

diff --git a/lightning-invoice/src/de.rs b/lightning-invoice/src/de.rs
index 7c425441f4ec1f3a338f75a2a1d9c1437ca791d3..446fd5c71c0b3112018ebe7b15b9179ccd67f454 100644 (file)
--- a/lightning-invoice/src/de.rs
+++ b/lightning-invoice/src/de.rs
@@ -712,7 +712,7 @@ impl FromBase32 for PrivateRoute {
                        return Err(Bolt11ParseError::UnexpectedEndOfTaggedFields);
                }
 
-               let mut route_hops = Vec::<RouteHintHop>::new();
+               let mut route_hops = Vec::with_capacity(bytes.len() / 51);
 
                let mut bytes = bytes.as_slice();
                while !bytes.is_empty() {

diff --git a/lightning-invoice/src/ser.rs b/lightning-invoice/src/ser.rs
index 4000241f5575cf88cd1c1667d371986d80422e1d..3d79a25331499c5d69b48ad5da91a8d3060c0083 100644 (file)
--- a/lightning-invoice/src/ser.rs
+++ b/lightning-invoice/src/ser.rs
@@ -218,19 +218,20 @@ impl Display for SiPrefix {
 }
 
 /// Encode an integer to base32, big endian, without leading zeros
-fn encode_int_be_base32(int: u64) -> Vec<Fe32> {
+fn encode_int_be_base32(int: u64) -> impl ExactSizeIterator<Item=Fe32> {
        let base = 32u64;
 
        // (64 + 4) / 5 == 13
-       let mut out_vec = Vec::<Fe32>::with_capacity(13);
+       let mut out = [Fe32::Q; 13];
+       let mut out_pos = 0;
        let mut rem_int = int;
        while rem_int != 0 {
-               out_vec.push(Fe32::try_from((rem_int % base) as u8).expect("always <32"));
+               out[out_pos] = Fe32::try_from((rem_int % base) as u8).expect("always <32");
+               out_pos += 1;
                rem_int /= base;
        }
 
-       out_vec.reverse();
-       out_vec
+       out.into_iter().take(out_pos).rev()
 }
 
 /// The length of the output of `encode_int_be_base32`.
@@ -252,7 +253,7 @@ impl Base32Iterable for PositiveTimestamp {
                let fes = encode_int_be_base32(self.as_unix_timestamp());
                debug_assert!(fes.len() <= 7, "Invalid timestamp length");
                let to_pad = 7 - fes.len();
-               Box::new(core::iter::repeat(Fe32::Q).take(to_pad).chain(fes.into_iter()))
+               Box::new(core::iter::repeat(Fe32::Q).take(to_pad).chain(fes))
        }
 }
 
@@ -305,7 +306,7 @@ impl Base32Len for PayeePubKey {
 
 impl Base32Iterable for ExpiryTime {
        fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-               Box::new(encode_int_be_base32(self.as_seconds()).into_iter())
+               Box::new(encode_int_be_base32(self.as_seconds()))
        }
 }
 
@@ -317,7 +318,7 @@ impl Base32Len for ExpiryTime {
 
 impl Base32Iterable for MinFinalCltvExpiryDelta {
        fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-               Box::new(encode_int_be_base32(self.0).into_iter())
+               Box::new(encode_int_be_base32(self.0))
        }
 }
 
@@ -504,6 +505,6 @@ mod test {
                        .map(|v| Fe32::try_from(v).expect("<= 31"))
                        .collect::<Vec<Fe32>>();
 
-               assert_eq!(expected_out, encode_int_be_base32(input));
+               assert_eq!(expected_out, encode_int_be_base32(input).collect::<Vec<Fe32>>());
        }
 }