Support Vec serialization that include element length prefix

We add new macro alternatives to
impl_writeable_for_vec/impl_readable_for_vec that add a length prefix to
each element in the `Vec`. This is intended to be used over the existing
macros when attempting to serialize a `Vec` with elements of variable
lengths.

diff --git a/lightning/src/util/ser.rs b/lightning/src/util/ser.rs
index f333fa2bac27f5182e4122a5321e684fc83a08ab..f6af5ce53d74f52b94039362a95154360f890114 100644 (file)
--- a/lightning/src/util/ser.rs
+++ b/lightning/src/util/ser.rs
@@ -820,6 +820,49 @@ macro_rules! impl_for_vec {
        }
 }
 
+// Alternatives to impl_writeable_for_vec/impl_readable_for_vec that add a length prefix to each
+// element in the Vec. Intended to be used when elements have variable lengths.
+macro_rules! impl_writeable_for_vec_with_element_length_prefix {
+       ($ty: ty $(, $name: ident)*) => {
+               impl<$($name : Writeable),*> Writeable for Vec<$ty> {
+                       #[inline]
+                       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+                               CollectionLength(self.len() as u64).write(w)?;
+                               for elem in self.iter() {
+                                       CollectionLength(elem.serialized_length() as u64).write(w)?;
+                                       elem.write(w)?;
+                               }
+                               Ok(())
+                       }
+               }
+       }
+}
+macro_rules! impl_readable_for_vec_with_element_length_prefix {
+       ($ty: ty $(, $name: ident)*) => {
+               impl<$($name : Readable),*> Readable for Vec<$ty> {
+                       #[inline]
+                       fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+                               let len: CollectionLength = Readable::read(r)?;
+                               let mut ret = Vec::with_capacity(cmp::min(len.0 as usize, MAX_BUF_SIZE / core::mem::size_of::<$ty>()));
+                               for _ in 0..len.0 {
+                                       let elem_len: CollectionLength = Readable::read(r)?;
+                                       let mut elem_reader = FixedLengthReader::new(r, elem_len.0);
+                                       if let Some(val) = MaybeReadable::read(&mut elem_reader)? {
+                                               ret.push(val);
+                                       }
+                               }
+                               Ok(ret)
+                       }
+               }
+       }
+}
+macro_rules! impl_for_vec_with_element_length_prefix {
+       ($ty: ty $(, $name: ident)*) => {
+               impl_writeable_for_vec_with_element_length_prefix!($ty $(, $name)*);
+               impl_readable_for_vec_with_element_length_prefix!($ty $(, $name)*);
+       }
+}
+
 impl Writeable for Vec<u8> {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {