Add error for cases when we cant read the serial monitor trying to decode the bootmode

espflash/src/connection/mod.rs

@@ -7,6 +7,7 @@
 use std::{
     io::{BufWriter, Write},
     iter::zip,
+    str::from_utf8,
     thread::sleep,
     time::Duration,
 };
@@ -132,9 +133,14 @@ impl Connection {
                 Ok(_) => {
                     return Ok(());
                 }
-                Err(e) => {
-                    debug!("Failed to reset, error {:#?}, retrying", e);
-                }
+                Err(e) => match e {
+                    Error::InvalidSerialRead => {
+                        return Err(Error::InvalidSerialRead);
+                    }
+                    _ => {
+                        debug!("Failed to reset, error {:#?}, retrying", e);
+                    }
+                },
             }
         }
 
@@ -168,7 +174,10 @@ impl Connection {
                 )));
             }
 
-            let read_slice = std::str::from_utf8(&buff[..read_bytes as usize]).unwrap();
+            let read_slice = from_utf8(&buff[..read_bytes as usize]).map_err(|err| {
+                debug!("Error: {}", err);
+                Error::InvalidSerialRead
+            })?;
 
             let pattern = Regex::new(r"boot:(0x[0-9a-fA-F]+)(.*waiting for download)?").unwrap();
 

espflash/src/error.rs

@@ -96,6 +96,10 @@ pub enum Error {
     #[error("The provided bootloader binary is invalid")]
     InvalidBootloader,
 
+    #[error("Invalid byte sequence read from the serial port while trying to detect Boot Mode")]
+    #[diagnostic(code(espflash::invalid_serial_read))]
+    InvalidSerialRead,
+
     #[error("Specified bootloader path is not a .bin file")]
     #[diagnostic(code(espflash::invalid_bootloader_path))]
     InvalidBootloaderPath,