First 3 bytes of files read from FatFs will be truncated

[derchr]

Hi,
I have created a repro for this bug: https://github.com/derchr/repro-fs
Just follow the instructions in the readme and the bug should show up.

Description of the bug:
What I noticed is that somehow the first 3 bytes of all files that are being read from the filesystem get truncated.
I'm almost certain that 1-2 weeks ago this bug wasn't there as I remember loading binary files (images) from the fs and this worked flawlessly. Now always 3 bytes are missing and the image does not get parsed.
I'm also not sure if this is even caused by esp-idf-sys.

My toolchain is the esp rust compiler version 1.57.0 targeting the default ESP32.
In the example I use the master branch of esp-idf, but I also encountered the issue in the stable 4.4 version.

Thanks!

EDIT:
When using a fixed size array instead of Vec or String to read in the file, it actually works! String::with_capacity on the other hand does not work.

    use std::io::Read;
    let mut lorem = std::fs::File::open("/mnt/readme.txt").unwrap();
    let mut read: usize;
    let mut buf = [0u8; 512];
    read = lorem.read(&mut buf).unwrap();
    while read != 0 {
        println!("{}", std::str::from_utf8(&buf[..read]).unwrap());
        read = lorem.read(&mut buf).unwrap();
    }

[ivmarkov]

Likely related to this issue: esp-rs/rust#96

[derchr]

Yeah, it seems like this is the same bug. Closing it here in favor of the already existing bug report.

[bugadani]

@derchr String::with_capacity only allocates memory, but does not set buffer length, i.e. you can't get a &mut [u8] for the allocated memory. Does your example work if you use vec![0; some_size] instead? In my case, I'm able to read into 0 filled vectors.

[derchr]

@derchr String::with_capacity only allocates memory, but does not set buffer length, i.e. you can't get a &mut [u8] for the allocated memory. Does your example work if you use vec![0; some_size] instead? In my case, I'm able to read into 0 filled vectors.

I remember also testing Vec::with_capacity and this did not work. Pre-filling the Vec and writing to it using &mut [u8] might actually work as it's similar to the fixed-array method that did work for me.