Make DeviceId a newtype rather than an alias

ruma-events/src/key/verification/start.rs

@@ -288,7 +288,7 @@ mod tests {
                 key_agreement_protocols,
                 message_authentication_codes,
                 short_authentication_string,
-            }) if from_device.as_ref() == "123"
+            }) if from_device.as_str() == "123"
                 && transaction_id == "456"
                 && hashes == vec![HashAlgorithm::Sha256]
                 && key_agreement_protocols == vec![KeyAgreementProtocol::Curve25519]
@@ -323,7 +323,7 @@ mod tests {
                     message_authentication_codes,
                     short_authentication_string,
                 })
-            } if from_device.as_ref() == "123"
+            } if from_device.as_str() == "123"
                 && transaction_id == "456"
                 && hashes == vec![HashAlgorithm::Sha256]
                 && key_agreement_protocols == vec![KeyAgreementProtocol::Curve25519]

ruma-events/src/room/encrypted.rs

@@ -161,7 +161,7 @@ mod tests {
                 session_id,
             }) if ciphertext == "ciphertext"
                 && sender_key == "sender_key"
-                && device_id.as_ref() == "device_id"
+                && device_id.as_str() == "device_id"
                 && session_id == "session_id"
         );
     }

ruma-identifiers/CHANGELOG.md

@@ -32,9 +32,9 @@ Breaking changes:
     ```rust
     fn server_name() -> &ServerName
     ```
-* Change `DeviceId` from being an alias for `String` to being an alias for `str`
-  * This means any string slice or string literal is a valid `&DeviceId` now
-  * But to store one, you need to box it: `Box<DeviceId>`
+* Change `DeviceId` from being an alias for `String` to being a newtype around `str`
+
+  This means owned device IDs are now `Box<DeviceId>`.
 * Change `RoomVersionId` from being an opaque struct to a non-exhaustive enum
   * The constructor functions and `is_` predicates are now deprecated
 

ruma-identifiers/src/device_id.rs

@@ -1,5 +1,10 @@
 //! Matrix device identifiers.
 
+use std::{
+    fmt::{self, Display},
+    mem,
+};
+
 #[cfg(feature = "rand")]
 use crate::generate_localpart;
 
@@ -7,21 +12,142 @@ use crate::generate_localpart;
 ///
 /// Device identifiers in Matrix are completely opaque character sequences. This type alias is
 /// provided simply for its semantic value.
-pub type DeviceId = str;
+#[repr(transparent)]
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize), serde(transparent))]
+pub struct DeviceId(str);
+
+impl DeviceId {
+    #[allow(clippy::transmute_ptr_to_ptr)]
+    fn from_borrowed(s: &str) -> &Self {
+        unsafe { mem::transmute(s) }
+    }
+
+    fn from_owned(s: Box<str>) -> Box<Self> {
+        unsafe { mem::transmute(s) }
+    }
+
+    fn into_owned(self: Box<Self>) -> Box<str> {
+        unsafe { mem::transmute(self) }
+    }
 
     /// Generates a random `DeviceId`, suitable for assignment to a new device.
     #[cfg(feature = "rand")]
     #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+    pub fn new() -> Box<Self> {
+        Self::from_owned(generate_localpart(8))
+    }
+
+    /// Creates a string slice from this `DeviceId`.
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+impl Clone for Box<DeviceId> {
+    fn clone(&self) -> Self {
+        (**self).to_owned()
+    }
+}
+
+impl ToOwned for DeviceId {
+    type Owned = Box<DeviceId>;
+
+    fn to_owned(&self) -> Self::Owned {
+        Self::from_owned(self.0.to_owned().into_boxed_str())
+    }
+}
+
+impl AsRef<str> for DeviceId {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+
+impl AsRef<str> for Box<DeviceId> {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+
+impl<'a> From<&'a str> for &'a DeviceId {
+    fn from(s: &'a str) -> Self {
+        DeviceId::from_borrowed(s)
+    }
+}
+
+impl From<&str> for Box<DeviceId> {
+    fn from(s: &str) -> Self {
+        DeviceId::from_owned(s.into())
+    }
+}
+
+impl From<String> for Box<DeviceId> {
+    fn from(s: String) -> Self {
+        DeviceId::from_owned(s.into())
+    }
+}
+
+impl From<Box<DeviceId>> for String {
+    fn from(id: Box<DeviceId>) -> Self {
+        id.into_owned().into()
+    }
+}
+
+impl Display for DeviceId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for Box<DeviceId> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        crate::deserialize_id(deserializer, "An IP address or hostname")
+    }
+}
+
+impl PartialEq<str> for DeviceId {
+    fn eq(&self, other: &str) -> bool {
+        self.as_str() == other
+    }
+}
+
+impl PartialEq<DeviceId> for str {
+    fn eq(&self, other: &DeviceId) -> bool {
+        self == other.as_str()
+    }
+}
+
+impl PartialEq<String> for DeviceId {
+    fn eq(&self, other: &String) -> bool {
+        self.as_str() == other.as_str()
+    }
+}
+
+impl PartialEq<DeviceId> for String {
+    fn eq(&self, other: &DeviceId) -> bool {
+        self.as_str() == other.as_str()
+    }
+}
+
+/// Generates a random `DeviceId`, suitable for assignment to a new device.
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+#[deprecated = "use DeviceId::new instead"]
 pub fn generate() -> Box<DeviceId> {
-    generate_localpart(8)
+    DeviceId::new()
 }
 
 #[cfg(all(test, feature = "rand"))]
 mod tests {
-    use super::generate;
+    use super::DeviceId;
 
     #[test]
     fn generate_device_id() {
-        assert_eq!(generate().len(), 8);
+        assert_eq!(DeviceId::new().as_str().len(), 8);
     }
 }

ruma-identifiers/src/device_key_id.rs

@@ -18,7 +18,7 @@ impl DeviceKeyId {
 
     /// Returns device ID of the device key ID.
     pub fn device_id(&self) -> &DeviceId {
-        &self.full_id[self.colon_idx.get() as usize + 1..]
+        (&self.full_id[self.colon_idx.get() as usize + 1..]).into()
     }
 }