pubsub: Add a PubSubPayload trait.

src/avatar.rs

@@ -5,6 +5,7 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 use crate::hashes::Sha1HexAttribute;
+use crate::pubsub::PubSubPayload;
 use crate::util::helpers::WhitespaceAwareBase64;
 
 generate_element!(
@@ -16,6 +17,8 @@ generate_element!(
     ]
 );
 
+impl PubSubPayload for Metadata {}
+
 generate_element!(
     /// Communicates avatar metadata.
     Info, "info", AVATAR_METADATA,
@@ -49,6 +52,8 @@ generate_element!(
     )
 );
 
+impl PubSubPayload for Data {}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/pubsub/event.rs

@@ -8,7 +8,7 @@ use crate::data_forms::DataForm;
 use crate::date::DateTime;
 use crate::util::error::Error;
 use crate::ns;
-use crate::pubsub::{ItemId, NodeName, Subscription, SubscriptionId};
+use crate::pubsub::{ItemId, NodeName, Subscription, SubscriptionId, PubSubPayload};
 use jid::Jid;
 use minidom::Element;
 use try_from::TryFrom;
@@ -58,6 +58,17 @@ impl From<Item> for Element {
     }
 }
 
+impl Item {
+    /// Create a new item event, accepting only payloads implementing `PubSubPayload`.
+    pub fn new<P: PubSubPayload>(id: Option<ItemId>, publisher: Option<Jid>, payload: Option<P>) -> Item {
+        Item {
+            id,
+            publisher,
+            payload: payload.map(|payload| payload.into()),
+        }
+    }
+}
+
 /// Represents an event happening to a PubSub node.
 #[derive(Debug, Clone)]
 pub enum PubSubEvent {

src/pubsub/mod.rs

@@ -45,3 +45,6 @@ generate_attribute!(
         Unconfigured => "unconfigured",
     }, Default = None
 );
+
+/// This trait should be implemented on any element which can be included as a PubSub payload.
+pub trait PubSubPayload: crate::TryFrom<crate::Element> + Into<crate::Element> {}