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

README.md

@@ -61,6 +61,20 @@ nix profile install "github:ulyssa/iamb"
 
 You can create a basic configuration in `$CONFIG_DIR/iamb/config.json` that looks like:
 
+```json
+{
+    "profiles": {
+        "example.com": {
+            "user_id": "@user:example.com"
+        }
+    }
+}
+```
+
+If you homeserver is located on a different domain than the server part of the
+`user_id` and you don't have a [`/.well-known`][well_known_entry] entry, then
+you can explicitly specify the homeserver URL to use:
+
 ```json
 {
     "profiles": {
@@ -122,6 +136,7 @@ iamb is released under the [Apache License, Version 2.0].
 [iamb.chat]: https://iamb.chat
 [gomuks]: https://github.com/tulir/gomuks
 [weechat-matrix]: https://github.com/poljar/weechat-matrix
+[well_known_entry]: https://spec.matrix.org/latest/client-server-api/#getwell-knownmatrixclient
 [#8]: https://github.com/ulyssa/iamb/issues/8
 [#14]: https://github.com/ulyssa/iamb/issues/14
 [#16]: https://github.com/ulyssa/iamb/issues/16

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,