[bencode/ser] Implement serializing Options in maps

src/bencode/error.rs

@@ -20,6 +20,7 @@ pub enum Error {
     ExpectedListEnd,
     ExpectedDict,
     ExpectedDictEnd,
+    OptionNone,
     TrailingCharacters,
 }
 
@@ -58,7 +59,8 @@ impl Display for Error {
             Error::ExpectedListEnd => formatter.write_str("expected list end char 'e'"),
             Error::ExpectedDict => formatter.write_str("expected dict start char 'd'"),
             Error::ExpectedDictEnd => formatter.write_str("expected dict end char 'e'"),
-            Error::TrailingCharacters => formatter.write_str("trailing characters")
+            Error::OptionNone => formatter.write_str("cannot serialize standalone none values of options"),
+            Error::TrailingCharacters => formatter.write_str("trailing characters"),
         }
     }
 }

src/bencode/ser.rs

@@ -132,14 +132,14 @@ impl<'a> ser::Serializer for &'a mut Serializer
     }
 
     fn serialize_none(self) -> Result<()> {
-        todo!()
+        Err(Error::OptionNone)
     }
 
     fn serialize_some<T>(self, value: &T) -> Result<()>
     where
         T: ?Sized + Serialize
     {
-        todo!()
+        value.serialize(self)
     }
 
     fn serialize_unit(self) -> Result<()> {
@@ -290,12 +290,24 @@ impl <'a> ser::SerializeMap for MapSerializer<'a> {
     where
         T: ?Sized + Serialize
     {
-        value.serialize(&mut self.value_serializer)?;
-        let mut value_to_insert = Vec::new();
-        swap(&mut self.value_serializer.output, &mut value_to_insert);
-        let Some(x) = self.sorted_map.get_mut(&self.last_inserted_key)
-            else { unreachable!() };
-        *x = value_to_insert;
+        let value_none = match value.serialize(&mut self.value_serializer) {
+            Ok(_) => false,
+            Err(e) =>
+                match e {
+                    Error::OptionNone => true,
+                    _ => return Err(e),
+                },
+        };
+        if !value_none {
+            let mut value_to_insert = Vec::new();
+            swap(&mut self.value_serializer.output, &mut value_to_insert);
+            let Some(x) = self.sorted_map.get_mut(&self.last_inserted_key)
+                else { unreachable!() };
+            *x = value_to_insert;
+        } else {
+            self.sorted_map.remove(&self.last_inserted_key);
+            self.value_serializer.output.clear();
+        }
         self.last_inserted_key.clear();
         Ok(())
     }
@@ -388,5 +400,11 @@ mod test {
         ])).unwrap(),
             "d3:bar4:🙈3:foo4:💩e"
         );
+        assert_eq!(to_string(&HashMap::from([
+            ("foo", Some("💩")),
+            ("bar", None),
+        ])).unwrap(),
+            "d3:foo4:💩e"
+        );
     }
 }