Add DeviceId.

src/device_id.rs

@@ -0,0 +1,24 @@
+//! Matrix device identifiers.
+
+use crate::generate_localpart;
+
+///  A Matrix device ID.
+///
+///  Device identifiers in Matrix are completely opaque character sequences. This type alias is
+///  provided simply for its semantic value.
+pub type DeviceId = String;
+
+/// Generates a random `DeviceId`, suitable for assignment to a new device.
+pub fn generate() -> DeviceId {
+    generate_localpart(8).to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::generate;
+
+    #[test]
+    fn generate_device_id() {
+        assert_eq!(generate().len(), 8);
+    }
+}

src/lib.rs

@@ -38,11 +38,14 @@ use url::Url;
 
 pub use url::Host;
 
+#[doc(inline)]
+pub use crate::device_id::DeviceId;
 pub use crate::{
     error::Error, event_id::EventId, room_alias_id::RoomAliasId, room_id::RoomId,
     room_id_or_room_alias_id::RoomIdOrAliasId, room_version_id::RoomVersionId, user_id::UserId,
 };
 
+pub mod device_id;
 #[cfg(feature = "diesel")]
 mod diesel_integration;
 mod error;