feat: Update the way we pad bins

Author: SergioGasquez

espflash/src/bin/espflash.rs

@@ -1,6 +1,6 @@
 use std::{
-    fs::{self, File, OpenOptions},
-    io::{Read, Seek, SeekFrom, Write},
+    fs::{self, File},
+    io::Read,
     path::PathBuf,
 };
 
@@ -342,38 +342,18 @@ fn save_image(args: SaveImageArgs, config: &Config) -> Result<()> {
     Ok(())
 }
 
-fn pad_to(file: &mut File, alignment: u64, pad_character: u8) -> Result<()> {
-    let current_size = file.metadata().into_diagnostic()?.len();
-    let pad_mod = current_size % alignment;
-
-    if pad_mod != 0 {
-        let pad_size = alignment - pad_mod;
-
-        // Move the file cursor to the end of the file
-        file.seek(SeekFrom::End(0)).into_diagnostic()?;
-
-        file.write_all(&vec![pad_character; pad_size as usize])
-            .into_diagnostic()?;
-    }
-
-    Ok(())
-}
-
 fn write_bin(args: WriteBinArgs, config: &Config) -> Result<()> {
     let mut flasher = connect(&args.connect_args, config, false, false)?;
     print_board_info(&mut flasher)?;
 
-    // if the file size is not divisible by 4, we need to pad FF bytes to the end of
-    // the file, that's why we need `write` permission as well
-    let mut f = OpenOptions::new()
-        .read(true)
-        .write(true)
-        .open(&args.file)
-        .into_diagnostic()?;
-    pad_to(&mut f, 4, 0xFF)?;
+    let mut f = File::open(&args.file).into_diagnostic()?;
+
+    // If the file size is not divisible by 4, we need to pad `FF` bytes to the end
     let size = f.metadata().into_diagnostic()?.len();
+    let padded_bytes = 4 - (size % 4);
     let mut buffer = Vec::with_capacity(size.try_into().into_diagnostic()?);
     f.read_to_end(&mut buffer).into_diagnostic()?;
+    buffer.extend_from_slice(&vec![0xFF; padded_bytes as usize]);
 
     flasher.write_bin_to_flash(
         args.address,