Implement Serialize and Deserialize for SessionDescriptionType.

src/call/mod.rs

@@ -2,6 +2,12 @@
 //!
 //! This module also contains types shared by events in its child namespaces.
 
+use std::fmt::{Display, Formatter, Error as FmtError};
+use std::str::FromStr;
+
+use serde::{Deserialize, Deserializer, Error as SerdeError, Serialize, Serializer};
+use serde::de::Visitor;
+
 pub mod answer;
 pub mod candidates;
 pub mod hangup;
@@ -17,10 +23,88 @@ pub struct SessionDescription {
 }
 
 /// The type of VoIP session description.
-#[derive(Debug, Deserialize, Serialize)]
+#[derive(Debug, PartialEq)]
 pub enum SessionDescriptionType {
     /// An answer.
     Answer,
     /// An offer.
     Offer,
 }
+
+/// An error when attempting to parse an invalid `SessionDescriptionType` from a string.
+pub struct SessionDescriptionTypeParseError;
+
+impl Display for SessionDescriptionType {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), FmtError> {
+        let session_description_type_str = match *self {
+            SessionDescriptionType::Answer => "answer",
+            SessionDescriptionType::Offer => "offer",
+        };
+
+        write!(f, "{}", session_description_type_str)
+    }
+}
+
+impl FromStr for SessionDescriptionType {
+    type Err = SessionDescriptionTypeParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "answer" => Ok(SessionDescriptionType::Answer),
+            "offer" => Ok(SessionDescriptionType::Offer),
+            _ => Err(SessionDescriptionTypeParseError),
+        }
+    }
+}
+
+impl Serialize for SessionDescriptionType {
+    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error> where S: Serializer {
+        serializer.serialize_str(&self.to_string())
+    }
+}
+
+impl Deserialize for SessionDescriptionType {
+    fn deserialize<D>(deserializer: &mut D) -> Result<Self, D::Error> where D: Deserializer {
+        struct SessionDescriptionTypeVisitor;
+
+        impl Visitor for SessionDescriptionTypeVisitor {
+            type Value = SessionDescriptionType;
+
+            fn visit_str<E>(&mut self, v: &str) -> Result<Self::Value, E> where E: SerdeError {
+                v.parse().map_err(|_| {
+                    E::invalid_value(v)
+                })
+            }
+        }
+
+        deserializer.deserialize_str(SessionDescriptionTypeVisitor)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::{from_str, to_string};
+
+    use super::SessionDescriptionType;
+
+    #[test]
+    fn session_description_types_serialize_to_display_form() {
+        assert_eq!(
+            to_string(&SessionDescriptionType::Answer).unwrap(),
+            r#""answer""#
+        );
+    }
+
+    #[test]
+    fn session_description_types_deserialize_from_display_form() {
+        assert_eq!(
+            from_str::<SessionDescriptionType>(r#""answer""#).unwrap(),
+            SessionDescriptionType::Answer
+        );
+    }
+
+    #[test]
+    fn invalid_session_description_types_fail_deserialization() {
+        assert!(from_str::<SessionDescriptionType>(r#""bad""#).is_err());
+    }
+}

src/lib.rs

@@ -227,8 +227,7 @@ impl Deserialize for EventType {
         impl Visitor for EventTypeVisitor {
             type Value = EventType;
 
-            fn visit_str<E>(&mut self, v: &str) -> Result<Self::Value, E>
+            fn visit_str<E>(&mut self, v: &str) -> Result<Self::Value, E> where E: SerdeError {
-            where E: SerdeError {
                 Ok(EventType::from(v))
             }
         }