brokerd: config, [gateway] socket for Mattermost approvals

crates/brokerd/src/config.rs

@@ -45,6 +45,14 @@ impl Default for Approvals {
     }
 }
 
+/// `[gateway]`: where `gatewayd` takes approvals to post in Mattermost. Without the section,
+/// Mattermost approvals are off and only `bxctl` answers. An empty path means the default.
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
+#[serde(deny_unknown_fields, default)]
+pub struct Gateway {
+    pub socket: PathBuf,
+}
+
 fn default_podman() -> PathBuf {
     PathBuf::from("podman")
 }
@@ -129,6 +137,8 @@ pub struct Config {
     pub approvals: Approvals,
     #[serde(default)]
     pub runner: Option<Runner>,
+    #[serde(default)]
+    pub gateway: Option<Gateway>,
 }
 
 /// The longest an approval may wait: a day, the longest `loopd` waits after a pending frame.
@@ -262,6 +272,15 @@ impl Config {
             self.sockets.admin.clone()
         }
     }
+    /// `gateway.sock`, when `[gateway]` is set.
+    pub fn gateway_socket(&self) -> Option<PathBuf> {
+        let gateway = self.gateway.as_ref()?;
+        if gateway.socket.as_os_str().is_empty() {
+            Some(self.paths.home.join("run/gateway/gateway.sock"))
+        } else {
+            Some(gateway.socket.clone())
+        }
+    }
     pub fn audit_dir(&self) -> PathBuf {
         self.paths.home.join("audit")
     }

crates/brokerd/tests/config_gateway.rs

@@ -0,0 +1,43 @@
+//! `[gateway]` in `brokerd.toml`: absent means Mattermost approvals are off; an empty socket is
+//! the default under `home` (M4b spec, section 3). Do not edit.
+
+use std::path::PathBuf;
+
+use brokerd::config::Config;
+
+fn parse(text: &str) -> Config {
+    Config::parse(&format!("[paths]\nhome = \"/srv/bx\"\n{text}")).unwrap()
+}
+
+#[test]
+fn without_the_section_approvals_stay_in_bxctl() {
+    let config = parse("");
+    assert_eq!(config.gateway, None);
+    assert_eq!(config.gateway_socket(), None);
+}
+
+#[test]
+fn an_empty_section_or_socket_is_the_default() {
+    let default = Some(PathBuf::from("/srv/bx/run/gateway/gateway.sock"));
+    assert_eq!(parse("[gateway]\n").gateway_socket(), default);
+    assert_eq!(
+        parse("[gateway]\nsocket = \"\"\n").gateway_socket(),
+        default
+    );
+}
+
+#[test]
+fn a_socket_path_is_used_as_given() {
+    let config = parse("[gateway]\nsocket = \"/run/bx/gw.sock\"\n");
+    assert_eq!(
+        config.gateway_socket(),
+        Some(PathBuf::from("/run/bx/gw.sock"))
+    );
+}
+
+#[test]
+fn unknown_keys_are_errors() {
+    assert!(Config::parse("[gateway]\nsockets = \"/x\"\n").is_err());
+    assert!(Config::parse("[gateway]\nsocket = \"/x\"\nenabled = true\n").is_err());
+    assert!(Config::parse("[gatewy]\nsocket = \"/x\"\n").is_err());
+}

crates/brokerd/tests/support/rig.rs

@@ -41,6 +41,7 @@ impl Rig {
             sockets: Sockets::default(),
             approvals: Approvals { ttl_ms },
             runner: None,
+            gateway: None,
         };
         Rig {
             dir,