Fix empty seq (#58)

* fix serialization of empty sequences.

* add a test for empty sequences.

* update changelog + fmt

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Fixed serialization of empty sequences ([#58](https://github.com/monero-rs/monero-epee-bin-serde/pull/58))
 - No longer panic on unknown fields ([#46](https://github.com/monero-rs/monero-epee-bin-serde/pull/46))
 - Deserialization of nested structs ([#37](https://github.com/monero-rs/monero-epee-bin-serde/pull/37)).
 

src/ser.rs

@@ -216,9 +216,12 @@ impl<'a, 'b> serde::Serializer for &'a mut Serializer<'b> {
     }
 
     fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
-        self.state = State::First {
-            length: len.ok_or_else(Error::no_length)?,
-        };
+        let len = len.ok_or_else(Error::no_length)?;
+        self.state = State::First { length: len };
+
+        if len == 0 {
+            self.write_marker(Marker::Sequence { element: 255 })?;
+        }
 
         Ok(self)
     }

tests/other.rs

@@ -0,0 +1,14 @@
+use monero_epee_bin_serde::{from_bytes, to_bytes};
+use serde::{Deserialize, Serialize};
+
+#[derive(Default, Deserialize, Serialize, PartialEq, Debug)]
+struct TestStruct {
+    seq: Vec<u32>,
+}
+
+#[test]
+fn empty_sequence() {
+    let obj = TestStruct::default();
+    let data = to_bytes(&obj).unwrap();
+    assert_eq!(obj, from_bytes(data).unwrap());
+}