Better error when port is inaccessible

Author: zachfeldman

inputmodule-control/src/inputmodule.rs

@@ -388,12 +388,17 @@ fn simple_cmd_multiple(serialdevs: &Vec<String>, command: Command, args: &[u8])
 }
 
 fn simple_cmd(serialdev: &str, command: Command, args: &[u8]) {
-    let mut port = serialport::new(serialdev, 115_200)
+    let port_result = serialport::new(serialdev, 115_200)
         .timeout(SERIAL_TIMEOUT)
-        .open()
-        .expect("Failed to open port");
+        .open();
 
-    simple_cmd_port(&mut port, command, args);
+    match port_result {
+        Ok(mut port) => simple_cmd_port(&mut port, command, args),
+        Err(error) => match error.kind {
+            serialport::ErrorKind::Io(std::io::ErrorKind::PermissionDenied) => panic!("Permission denied, couldn't access input module port. Ensure that udev rule is installed or the port the module is on is otherwise accessible."),
+            other_error => panic!("Couldn't open port: {:?}", other_error)
+        }
+    };
 }
 
 fn open_serialport(serialdev: &str) -> Box<dyn SerialPort> {