sim-all: Allow running the simulator without it writing on disk

It is rather annoying to run the simulator and having to delete the output files
when we are doing testing/dev. This allows us to do so without the file being created.

I've approached this by making the simulator to write the results to "/dev/null" to
minimized the code diff, but I'm happy to change the approach if this feels to hacky
(it is worth to keep in mind this is for dev only).

sim-cli/src/main.rs

@@ -28,6 +28,10 @@ struct Cli {
     expected_pmt_amt: Option<u64>,
     #[clap(long, short)]
     capacity_multiplier: Option<f64>,
+    // DEV-ONLY args, set hide = true so they are not logged
+    /// Do not an output file including the simulations results
+    #[clap(long, short, hide = true, default_value = "false")]
+    no_results: bool,
 }
 
 #[tokio::main]
@@ -149,6 +153,7 @@ async fn main() -> anyhow::Result<()> {
         cli.print_batch_size,
         cli.expected_pmt_amt,
         cli.capacity_multiplier,
+        cli.no_results,
     );
     let sim2 = sim.clone();
 

sim-lib/src/lib.rs

@@ -334,6 +334,8 @@ pub struct Simulation {
     /// The number of times that the network sends its total capacity in a month of operation when generating random
     /// activity.
     activity_multiplier: f64,
+    /// Wether we want the simulation not to produce and result file. Useful for developing, defaults to false.
+    no_results: bool,
 }
 
 const DEFAULT_PRINT_BATCH_SIZE: u32 = 500;
@@ -346,6 +348,7 @@ impl Simulation {
         print_batch_size: Option<u32>,
         expected_payment_amount: Option<u64>,
         activity_multiplier: Option<f64>,
+        no_results: bool,
     ) -> Self {
         let (shutdown_trigger, shutdown_listener) = triggered::trigger();
         Self {
@@ -357,6 +360,7 @@ impl Simulation {
             print_batch_size: print_batch_size.unwrap_or(DEFAULT_PRINT_BATCH_SIZE),
             expected_payment_msat: expected_payment_amount.unwrap_or(EXPECTED_PAYMENT_AMOUNT),
             activity_multiplier: activity_multiplier.unwrap_or(ACTIVITY_MULTIPLIER),
+            no_results,
         }
     }
 
@@ -536,7 +540,6 @@ impl Simulation {
         tasks: &mut JoinSet<()>,
     ) {
         let listener = self.shutdown_listener.clone();
-        let print_batch_size = self.print_batch_size;
         log::debug!("Setting up simulator data collection.");
 
         // Create a sender/receiver pair that will be used to report final results of simulation.
@@ -552,7 +555,8 @@ impl Simulation {
         tasks.spawn(consume_simulation_results(
             results_receiver,
             listener,
-            print_batch_size,
+            self.print_batch_size,
+            self.no_results,
         ));
         log::debug!("Simulator data collection set up.");
     }
@@ -872,10 +876,11 @@ async fn consume_simulation_results(
     receiver: Receiver<(Payment, PaymentResult)>,
     listener: Listener,
     print_batch_size: u32,
+    no_results: bool,
 ) {
     log::debug!("Simulation results consumer started.");
 
-    if let Err(e) = write_payment_results(receiver, listener, print_batch_size).await {
+    if let Err(e) = write_payment_results(receiver, listener, print_batch_size, no_results).await {
         log::error!("Error while reporting payment results: {:?}.", e);
     }
 
@@ -886,14 +891,19 @@ async fn write_payment_results(
     mut receiver: Receiver<(Payment, PaymentResult)>,
     listener: Listener,
     print_batch_size: u32,
+    no_results: bool,
 ) -> Result<(), SimulationError> {
-    let mut writer = WriterBuilder::new().from_path(format!(
-        "simulation_{:?}.csv",
-        SystemTime::now()
-            .duration_since(SystemTime::UNIX_EPOCH)
-            .unwrap()
-            .as_secs()
-    ))?;
+    let mut writer = if no_results {
+        WriterBuilder::new().from_path("/dev/null")?
+    } else {
+        WriterBuilder::new().from_path(format!(
+            "simulation_{:?}.csv",
+            SystemTime::now()
+                .duration_since(SystemTime::UNIX_EPOCH)
+                .unwrap()
+                .as_secs()
+        ))?
+    };
 
     let mut result_logger = PaymentResultLogger::new();