Serialization macro for TLV streams

BOLT 12's offer message is encoded as a TLV stream (i.e., a sequence of
TLV records). impl_writeable_tlv_based can't be used because it writes
the overall length of the struct, whereas TLV streams only include the
length of each TLV record.

Author: jkczyz

lightning/src/util/ser_macros.rs

@@ -427,6 +427,37 @@ macro_rules! impl_writeable_tlv_based {
 	}
 }
 
+/// Implements [`Readable`]/[`Writeable`] for TLV streams (i.e., a sequence of TLV records).
+///
+///
+/// This is like [`impl_writeable_tlv_based`] only without a length prefix for the entire TLV
+/// stream.
+macro_rules! impl_writeable_tlv_stream {
+	($st: ident, {$(($type: expr, $field: ident, $fieldty: tt)),* $(,)*}) => {
+		impl ::util::ser::Writeable for $st {
+			fn write<W: ::util::ser::Writer>(&self, writer: &mut W) -> Result<(), $crate::io::Error> {
+				encode_tlv_stream!(writer, { $(($type, self.$field, $fieldty)),* });
+				Ok(())
+			}
+		}
+
+		impl ::util::ser::Readable for $st {
+			fn read<R: $crate::io::Read>(reader: &mut R) -> Result<Self, ::ln::msgs::DecodeError> {
+				$(
+					init_tlv_field_var!($field, $fieldty);
+				)*
+				decode_tlv_stream!(reader, {$(($type, $field, $fieldty)),*});
+
+					Ok(Self {
+						$(
+							$field: init_tlv_based_struct_field!($field, $fieldty)
+						),*
+					})
+			}
+		}
+	}
+}
+
 macro_rules! _impl_writeable_tlv_based_enum_common {
 	($st: ident, $(($variant_id: expr, $variant_name: ident) =>
 		{$(($type: expr, $field: ident, $fieldty: tt)),* $(,)*}