Utility to extract the localpart from a MXID

Cargo.lock

@@ -3527,6 +3527,7 @@ version = "0.13.0-rc.1"
 dependencies = [
  "anyhow",
  "async-trait",
+ "ruma-common",
  "tokio",
 ]
 

Cargo.toml

@@ -248,6 +248,10 @@ version = "0.12.12"
 default-features = false
 features = ["http2", "rustls-tls-manual-roots", "charset", "json", "socks"]
 
+# Matrix-related types
+[workspace.dependencies.ruma-common]
+version = "0.15.0"
+
 # TLS stack
 [workspace.dependencies.rustls]
 version = "0.23.21"

crates/data-model/Cargo.toml

@@ -24,7 +24,7 @@ rand.workspace = true
 rand_chacha = "0.3.1"
 regex = "1.11.1"
 woothee = "0.13.0"
-ruma-common = "0.15.0"
+ruma-common.workspace = true
 
 mas-iana.workspace = true
 mas-jose.workspace = true

crates/matrix/Cargo.toml

@@ -15,3 +15,4 @@ workspace = true
 anyhow.workspace = true
 async-trait.workspace = true
 tokio.workspace = true
+ruma-common.workspace = true

crates/matrix/src/lib.rs

@@ -8,6 +8,8 @@ mod mock;
 
 use std::{collections::HashSet, sync::Arc};
 
+use ruma_common::UserId;
+
 pub use self::mock::HomeserverConnection as MockHomeserverConnection;
 
 // TODO: this should probably be another error type by default
@@ -193,6 +195,22 @@ pub trait HomeserverConnection: Send + Sync {
         format!("@{}:{}", localpart, self.homeserver())
     }
 
+    /// Get the localpart of a Matrix ID if it has the right server name
+    ///
+    /// Returns [`None`] if the input isn't a valid MXID, or if the server name
+    /// doesn't match
+    ///
+    /// # Parameters
+    ///
+    /// * `mxid` - The MXID of the user
+    fn localpart<'a>(&self, mxid: &'a str) -> Option<&'a str> {
+        let mxid = <&UserId>::try_from(mxid).ok()?;
+        if mxid.server_name() != self.homeserver() {
+            return None;
+        }
+        Some(mxid.localpart())
+    }
+
     /// Query the state of a user on the homeserver.
     ///
     /// # Parameters