Graceful shutdown if serial port not available (#86)

* Graceful shutdown if serial port not available

* Formatting

src/dsmr/reader.rs

@@ -1,7 +1,7 @@
 use super::settings;
 use super::settings::ParityBitSetting;
 
-use serialport::SerialPort;
+use serialport::{Error, SerialPort};
 
 use std::io::{BufRead, BufReader};
 use std::str;
@@ -99,15 +99,16 @@ pub fn read_from_serial_port(
     }
 }
 
-pub fn connect_to_meter(serial_settings: &settings::SerialSettings) -> Box<dyn SerialPort> {
+pub fn connect_to_meter(
+    serial_settings: &settings::SerialSettings,
+) -> Result<Box<dyn SerialPort>, Error> {
     serialport::new(&serial_settings.port, serial_settings.baud_rate)
         .data_bits(to_databits(&serial_settings.byte_size))
         .flow_control(serialport::FlowControl::None)
         .parity(to_serial_port_parity_bit(&serial_settings.parity_bit))
         .stop_bits(serialport::StopBits::One)
         .timeout(Duration::from_secs(20))
         .open()
-        .expect("Failed to open port")
 }
 
 fn to_serial_port_parity_bit(input: &ParityBitSetting) -> serialport::Parity {

src/scheduler.rs

@@ -7,19 +7,35 @@ pub fn main_loop(
     serial_settings: dsmr::settings::SerialSettings,
     read_interval: f64,
 ) {
+    const FAILURE_THRESHOLD: i8 = 20;
+
     let interval = time::Duration::from_millis((read_interval * 1_000.0).round() as u64);
     let mut consumer = dsmr::sender::DelegatingConsumer::new(&api_settings.hosts);
+    let mut failure_count: i8 = 0;
 
     loop {
-        {
-            let port = dsmr::reader::connect_to_meter(&serial_settings);
-
+        let result = dsmr::reader::connect_to_meter(&serial_settings);
+        if result.is_ok() {
+            let port = result.unwrap();
             dsmr::reader::read_from_serial_port(port, &mut consumer);
+            failure_count = 0;
+        } else {
+            log::info!("failed to connect to {}", &serial_settings.port);
+            failure_count += 1;
+        }
 
-            // Close a port following the Resource Acquisition Is Initialization (RAII) paradigm
-            // by explicitly dropping the reference.
+        if failure_count >= FAILURE_THRESHOLD {
+            log::error!(
+                "failed to connect to {} for {} times, exiting...",
+                &serial_settings.port,
+                FAILURE_THRESHOLD,
+            );
+            return;
         }
 
+        // Close a port following the Resource Acquisition Is Initialization (RAII) paradigm
+        // by explicitly dropping the reference.
+
         thread::sleep(interval);
     }
 }