Support following the .well-known entries for a username's domain (#209)

src/config.rs

@@ -505,7 +505,7 @@ pub enum Layout {
 #[derive(Clone, Deserialize)]
 pub struct ProfileConfig {
     pub user_id: OwnedUserId,
-    pub url: Url,
+    pub url: Option<Url>,
     pub settings: Option<Tunables>,
     pub dirs: Option<Directories>,
     pub layout: Option<Layout>,

src/tests.rs

@@ -209,7 +209,7 @@ pub fn mock_settings() -> ApplicationSettings {
         profile_name: "test".into(),
         profile: ProfileConfig {
             user_id: user_id!("@user:example.com").to_owned(),
-            url: Url::parse("https://example.com").unwrap(),
+            url: None,
             settings: None,
             dirs: None,
             layout: None,

src/worker.rs

@@ -738,15 +738,21 @@ impl ClientWorker {
         let req_config = RequestConfig::new().timeout(req_timeout).retry_timeout(req_timeout);
 
         // Set up the Matrix client for the selected profile.
-        let client = Client::builder()
+        let builder = Client::builder()
             .http_client(Arc::new(http))
-            .homeserver_url(account.url.clone())
             .sled_store(settings.matrix_dir.as_path(), None)
             .expect("Failed to setup up sled store for Matrix SDK")
-            .request_config(req_config)
-            .build()
-            .await
-            .expect("Failed to instantiate Matrix client");
+            .request_config(req_config);
+
+        let builder = if let Some(url) = account.url.as_ref() {
+            // Use the explicitly specified homeserver.
+            builder.homeserver_url(url.as_str())
+        } else {
+            // Try to discover the homeserver from the user ID.
+            builder.server_name(account.user_id.server_name())
+        };
+
+        let client = builder.build().await.expect("Failed to instantiate Matrix client");
 
         let mut worker = ClientWorker {
             initialized: false,