Set up a logger crate

To see debug messages from zenoh.

runtime/Cargo.toml

@@ -18,3 +18,5 @@ tokio = { version = "1.17.0", features = ["full"] }
 tokio-stream = "0.1.8"
 zenoh = { git = "https://github.com/eclipse-zenoh/zenoh.git" }
 zenoh-config = { git = "https://github.com/eclipse-zenoh/zenoh.git" }
+log = "0.4.17"
+fern = "0.6.1"

runtime/src/main.rs

@@ -22,6 +22,8 @@ mod operator;
 
 #[tokio::main]
 async fn main() -> eyre::Result<()> {
+    set_up_logger()?;
+
     let node_id = {
         let raw =
             std::env::var("DORA_NODE_ID").wrap_err("env variable DORA_NODE_ID must be set")?;
@@ -270,3 +272,20 @@ struct OperatorInput {
     pub id: DataId,
     pub data: Vec<u8>,
 }
+
+fn set_up_logger() -> Result<(), fern::InitError> {
+    fern::Dispatch::new()
+        .format(|out, message, record| {
+            out.finish(format_args!(
+                "    [{}][{}] {}",
+                record.target(),
+                record.level(),
+                message
+            ))
+        })
+        .level(log::LevelFilter::Debug)
+        .chain(std::io::stdout())
+        .chain(fern::log_file("runtime.log")?)
+        .apply()?;
+    Ok(())
+}