gatewayd: config, [approvals] users and socket

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/gatewayd/src/config.rs

@@ -17,6 +17,18 @@ pub struct Config {
     pub paths: Paths,
     #[serde(default)]
     pub limits: Limits,
+    #[serde(default)]
+    pub approvals: ApprovalsConfig,
+}
+
+/// `[approvals]`: who may answer approvals, and where `brokerd` brings them.
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
+#[serde(deny_unknown_fields, default)]
+pub struct ApprovalsConfig {
+    /// Mattermost user ids; empty means everyone in `[allow] users`.
+    pub users: Vec<String>,
+    /// Empty: `<home>/run/gateway/gateway.sock`.
+    pub socket: PathBuf,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
@@ -184,6 +196,13 @@ impl Config {
                 ));
             }
         }
+        for id in &self.approvals.users {
+            if !self.allow.users.contains(id) {
+                return Some(format!(
+                    "[approvals] {id:?} is not in [allow] users: an approver who is not heard could never answer"
+                ));
+            }
+        }
         if self.limits.queue == 0 {
             return Some("[limits] queue must be at least 1".to_string());
         }
@@ -221,6 +240,27 @@ impl Config {
         self.loop_.socket.clone()
     }
 
+    /// Who may answer approvals: `[approvals] users`, or `[allow] users` when that is empty.
+    pub fn approvers(&self) -> &[String] {
+        if self.approvals.users.is_empty() {
+            return &self.allow.users;
+        }
+        &self.approvals.users
+    }
+
+    /// The first approver, or `None` when there are none.
+    pub fn first_approver(&self) -> Option<&str> {
+        self.approvers().first().map(String::as_str)
+    }
+
+    /// `gateway.sock`: `[approvals] socket`, or `<home>/run/gateway/gateway.sock` when empty.
+    pub fn gateway_socket(&self) -> PathBuf {
+        if self.approvals.socket.as_os_str().is_empty() {
+            return self.paths.home.join("run/gateway/gateway.sock");
+        }
+        self.approvals.socket.clone()
+    }
+
     pub fn state_path(&self) -> PathBuf {
         // <home>/gateway/state.json.
         self.paths.home.join("gateway/state.json")

crates/gatewayd/tests/config_approvals.rs

@@ -0,0 +1,68 @@
+//! `[approvals]` in `gatewayd.toml`: who may answer, the first approver, and `gateway.sock`
+//! (M4b spec, section 3). Do not edit.
+
+use std::path::PathBuf;
+
+use gatewayd::config::Config;
+
+const KYLE: &str = "k0000000000000000000000000";
+const HERMES: &str = "h0000000000000000000000000";
+const OTHER: &str = "o0000000000000000000000000";
+
+fn text(approvals: &str) -> String {
+    format!(
+        "[mattermost]\nurl = \"https://chat.example\"\n[secrets.mattermost_token]\nenv = \"T\"\n[allow]\nusers = [\"{KYLE}\", \"{HERMES}\"]\n[paths]\nhome = \"/srv/bx\"\n{approvals}"
+    )
+}
+
+fn config(approvals: &str) -> Config {
+    let c = Config::parse(&text(approvals)).unwrap();
+    assert_eq!(c.problem(), None);
+    c
+}
+
+#[test]
+fn without_the_section_everyone_allowed_may_answer() {
+    let c = config("");
+    assert_eq!(c.approvers(), [KYLE, HERMES]);
+    assert_eq!(c.first_approver(), Some(KYLE));
+    assert_eq!(
+        c.gateway_socket(),
+        PathBuf::from("/srv/bx/run/gateway/gateway.sock")
+    );
+    assert_eq!(
+        config("[approvals]\nusers = []\n").approvers(),
+        [KYLE, HERMES]
+    );
+}
+
+#[test]
+fn a_list_narrows_who_may_answer() {
+    let c = config(&format!(
+        "[approvals]\nusers = [\"{HERMES}\"]\nsocket = \"/run/gw.sock\"\n"
+    ));
+    assert_eq!(c.approvers(), [HERMES]);
+    assert_eq!(c.first_approver(), Some(HERMES));
+    assert_eq!(c.gateway_socket(), PathBuf::from("/run/gw.sock"));
+}
+
+#[test]
+fn an_approver_must_be_heard() {
+    let c = Config::parse(&text(&format!(
+        "[approvals]\nusers = [\"{KYLE}\", \"{OTHER}\"]\n"
+    )))
+    .unwrap();
+    let why = c.problem().expect("refused");
+    assert_eq!(
+        why,
+        format!(
+            "[approvals] \"{OTHER}\" is not in [allow] users: an approver who is not heard could never answer"
+        )
+    );
+}
+
+#[test]
+fn unknown_keys_are_errors() {
+    assert!(Config::parse(&text("[approvals]\napprovers = []\n")).is_err());
+    assert!(Config::parse(&text("[approvals]\nusers = []\nttl = 5\n")).is_err());
+}