support configuration file

src/settings.default.toml

@@ -0,0 +1,7 @@
+slack_token = "<TOKEN>"
+slack_channel_id = "<CHANNEL_ID>"
+# see https://api.slack.com/reference/surfaces/formatting
+open_session_message = """🕵️ ▶️▶️▶️ IP `{addr}` logged in `{hostname}` as `{user}` using `{auth_info}` at `{when}`"""
+close_session_message = """🕵️ 🛑🛑🛑 IP `{addr}` logout from `{hostname}` (is was `{user}` using `{auth_info}`) at `{when}`"""
+# could be "America/Sao_Paulo" or "America/Los_Angeles" or "Europe/Oslo"
+timezone = "UTC"

src/settings.rs

@@ -0,0 +1,52 @@
+use config::{Config, ConfigError, File, FileFormat};
+use serde::Deserialize;
+use std::env;
+
+#[derive(Debug, Deserialize)]
+pub struct Settings {
+    pub slack_token: String,
+    pub slack_channel_id: String,
+    pub open_session_message: String,
+    pub close_session_message: String,
+    pub timezone: String,
+}
+
+impl Settings {
+    pub fn new(system_config_file: &str) -> Result<Self, ConfigError> {
+        let mut s = Config::default();
+
+        // Start off by merging in the "default" configuration file
+        s.merge(File::from_str(
+            include_str!("settings.default.toml").into(),
+            FileFormat::Toml,
+        ))?;
+
+        // Add some settings from environment variables
+        match env::var("SLACK_TOKEN") {
+            Ok(token) => {
+                s.set("slack_token", token)?;
+            }
+            Err(_) => {}
+        };
+
+        match env::var("SLACK_TOKEN") {
+            Ok(token) => {
+                s.set("slack_token", token)?;
+            }
+            Err(_) => {}
+        };
+
+        match env::var("SLACK_CHANNEL_ID") {
+            Ok(channel_id) => {
+                s.set("slack_channel_id", channel_id)?;
+            }
+            Err(_) => {}
+        };
+
+        // Add in system configuration file
+        s.merge(File::new(system_config_file, FileFormat::Toml).required(false))?;
+
+        // You can deserialize (and thus freeze) the entire configuration as
+        s.try_into()
+    }
+}