Extract constants and add config loader + example appsettings for niom-signaling; wire main to config

.gitignore

@@ -19,4 +19,4 @@ target
 #  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
-#.idea/
+.idea/

appsettings.example.json

@@ -0,0 +1,5 @@
+{
+  "server": {
+    "bind": "127.0.0.1:3478"
+  }
+}

src/config.rs

@@ -0,0 +1,24 @@
+use serde::Deserialize;
+use std::path::Path;
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct ServerOptions {
+    pub bind: String,
+}
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct Config {
+    pub server: ServerOptions,
+}
+
+impl Config {
+    pub fn from_file<P: AsRef<Path>>(p: P) -> Result<Self, Box<dyn std::error::Error>> {
+        let s = std::fs::read_to_string(p)?;
+        let cfg: Config = serde_json::from_str(&s)?;
+        Ok(cfg)
+    }
+
+    pub fn load_default() -> Result<Self, Box<dyn std::error::Error>> {
+        Self::from_file("appsettings.json")
+    }
+}

src/constants.rs

@@ -0,0 +1,3 @@
+// Central constants for niom-signaling
+pub const DEFAULT_BIND: &str = "127.0.0.1:3478";
+pub const DEFAULT_HOST_URL: &str = "http://localhost:3478";

src/main.rs

@@ -3,6 +3,10 @@ use futures_util::StreamExt;
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 use tokio::sync::broadcast;
+mod constants;
+mod config;
+use crate::config::Config;
+use crate::constants::*;
 
 #[derive(Clone)]
 struct AppState {
@@ -25,15 +29,26 @@ async fn main() -> std::io::Result<()> {
     let app_state = AppState {
         broadcaster: Arc::new(tx)
     };
+    // Try to load config, otherwise fall back to defaults
+    let cfg = match Config::load_default() {
+        Ok(c) => {
+            println!("Loaded config from appsettings.json");
+            c
+        }
+        Err(_) => {
+            println!("No config found, using defaults");
+            Config { server: crate::config::ServerOptions { bind: DEFAULT_BIND.to_string() } }
+        }
+    };
 
-    println!("Server is running on http://localhost:3478");
+    println!("Server is running on {}", DEFAULT_HOST_URL);
 
     HttpServer::new(move || {
         App::new()
             .app_data(web::Data::new(app_state.clone()))
             .route("/ws", web::get().to(websocket_handler))
     })
-    .bind("127.0.0.1:3478")?
+    .bind(&cfg.server.bind)?
     .run()
     .await
 }