move padding to 4 bytes from CLI into library (#951)

Downstream applications needed to duplicate the padding to 4 bytes
logic that the CLI application does (although that requirement was
not documented). Otherwise flashing could fail with a RomError with
error code 0.

Author: Be-ing

CHANGELOG.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [Windows] Fixed a crash in monitor when espflash is connected via USB Serial/JTAG, and the user is typing into the monitor but the device is not reading serial input. (#943)
 - [Linux/MacOS] Fixed espflash hanging when espflash is connected via USB Serial/JTAG, and the user is typing into the monitor but the device is not reading serial input. (#944, #945)
 - Fixed ESP32-S2 flash size detection issues (#950)
+- Images are now automatically padded to 4 bytes before writing by the library (previously this was done in the CLI) (#951)
 
 ### Removed
 

espflash/src/cli/mod.rs

@@ -1139,15 +1139,9 @@ pub fn write_bin(args: WriteBinArgs, config: &Config) -> Result<()> {
     // Load the file to be flashed
     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 mut padded_bytes = 0;
-    if size % 4 != 0 {
-        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(std::iter::repeat_n(0xFF, padded_bytes as usize));
 
     let mut flasher = connect(&args.connect_args, config, false, false)?;
     print_board_info(&mut flasher)?;

espflash/src/flasher/mod.rs

@@ -1076,10 +1076,21 @@ impl Flasher {
         data: &[u8],
         progress: &mut dyn ProgressCallbacks,
     ) -> Result<(), Error> {
-        let segment = Segment {
+        let mut segment = Segment {
             addr,
             data: Cow::from(data),
         };
+
+        // If the file size is not divisible by 4, we need to pad `FF` bytes to the end
+        let size = segment.data.len();
+        if size % 4 != 0 {
+            let padded_bytes = 4 - (size % 4);
+            segment
+                .data
+                .to_mut()
+                .extend(std::iter::repeat_n(0xFF, padded_bytes));
+        }
+
         self.write_bins_to_flash(&[segment], progress)?;
 
         info!("Binary successfully written to flash!");