Matrix: invite somebody into a room

Closes #74. This client could accept an invitation and decline one, and
never send one - so a room created here could never gain a second member
here, and every other member of a room was somebody who had arrived by
some other route.

It sits beside kick and ban because it is the same shape of call decided
by the same authority: a room's power levels say who may invite exactly as
they say who may remove.

A Matrix address or nothing. The server would refuse anything else anyway,
but its refusal names an endpoint rather than the thing that was typed.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/backend/matrix/moderation.rs

@@ -85,6 +85,23 @@ pub async fn kick_member(state: &AppState, account_id: &str, buffer_id: &str, ta
     Ok(())
 }
 
+/// Asks somebody into a room.
+///
+/// Lives here beside kick and ban because it is the same shape of call and
+/// the same authority decides it - a room's power levels say who may invite
+/// exactly as they say who may remove. It is the opposite action, which is
+/// why its absence was odd: a room made here could gain no second member
+/// from here.
+pub async fn invite_member(state: &AppState, account_id: &str, buffer_id: &str, target_user_id: &str) -> Result<()> {
+    let (homeserver_url, access_token, room_id) = homeserver_token_room(state, account_id, buffer_id).await?;
+    let base = homeserver_url.trim_end_matches('/');
+    let url = format!("{base}/_matrix/client/v3/rooms/{}/invite", url::form_urlencoded::byte_serialize(room_id.as_bytes()).collect::<String>());
+    http::post_json(&url, Some(&access_token), serde_json::json!({ "user_id": target_user_id }))
+        .await
+        .context("inviting member")?;
+    Ok(())
+}
+
 pub async fn ban_member(state: &AppState, account_id: &str, buffer_id: &str, target_user_id: &str, reason: Option<&str>) -> Result<()> {
     let (homeserver_url, access_token, room_id) = homeserver_token_room(state, account_id, buffer_id).await?;
     let base = homeserver_url.trim_end_matches('/');

src/rpc/methods.rs

@@ -2223,6 +2223,32 @@ pub async fn dispatch(
             }
         }
 
+        // Asking somebody into a room. Its absence was the odd one out: this
+        // client could accept an invitation and decline one, and never send
+        // one - so a room created here could never gain a second member here.
+        "inviteMatrixMember" => {
+            let (account_id, buffer_id, user_id) =
+                match (p_str_opt(params, "accountId"), p_str_opt(params, "bufferId"), p_str_opt(params, "userId")) {
+                    (Some(a), Some(b), Some(u)) => (a, b, u),
+                    _ => {
+                        return (
+                            None,
+                            Some("inviteMatrixMember requires \"accountId\", \"bufferId\" and \"userId\"".to_string()),
+                        )
+                    }
+                };
+            // A Matrix id or nothing. The server would refuse anything else
+            // anyway, but its error names an endpoint rather than the thing
+            // that was typed.
+            if !user_id.starts_with('@') || !user_id.contains(':') {
+                return (None, Some(format!("\"{user_id}\" is not a Matrix address - they look like @someone:server")));
+            }
+            match backend::matrix::moderation::invite_member(state, account_id, buffer_id, user_id).await {
+                Ok(()) => (Some(ok_node()), None),
+                Err(e) => (None, Some(format!("{e:#}"))),
+            }
+        }
+
         "banMatrixMember" => {
             let (account_id, buffer_id, user_id) =
                 match (p_str_opt(params, "accountId"), p_str_opt(params, "bufferId"), p_str_opt(params, "userId")) {