How to save TaggedFile to Vec<u8> ?

[jerry7536]

I am new to Rust and want to build a wasm version of this awesome project, see #289

I am facing a problem of how to save TaggedFile to Vec<u8>, so that I can send the modified file buffer from wasm to js.

Any help is highly appreciated!

[Serial-ATA]

It's a WIP, see #290.

I looked into WASM after you submitted #289. I had no experience with it prior and did not know it doesn't have access to std::io.

[jerry7536]

Thanks for explaination!

[jerry7536]

Hey👋
I upgrade lofty to 0.19 and finally write a demo for wasm, but I encountered a question and all the GPT/coplite cannot help, so I'm here asking for help 🙏.

Is there any way to save without cloning the original buffer?

#[wasm_bindgen]
pub struct MetaFile {
    buffer: Vec<u8>,
    tag: Tag,
}

#[wasm_bindgen]
impl MetaFile {
    #[wasm_bindgen(constructor)]
    pub fn new(buf: Vec<u8>) -> Self {
        set_panic_hook();
        let tagged_file = Probe::new(Cursor::new(buf.clone()))
            .guess_file_type()
            .expect("fail to guess file type")
            .read()
            .expect("fail to read file");

        MetaFile {
            buffer: buf,
            tag: tagged_file.primary_tag().cloned().unwrap_or_else(|| {
                tagged_file
                    .first_tag()
                    .cloned()
                    .expect("ERROR: No tags found!")
            }),
        }
    }

    // other tags...

    #[wasm_bindgen]
    pub fn save(&mut self) -> () {
        // is .clone Avoidable?
        let mut buf = Cursor::new(self.buffer.clone());

        let _ = self.tag.save_to(&mut buf, WriteOptions::default());
        self.buffer = buf.into_inner();
    }
}

the suggested solution is below, but errors the trait bound '&mut Vec<u8>: Truncate' is not satisfied

#[wasm_bindgen]
pub fn save(&mut self) -> () {
    set_panic_hook();
    let mut buf = Cursor::new(&mut self.buffer);
    self.tag.save_to(&mut buf, WriteOptions::default());
}

What is the correct way to implement it?

[Serial-ATA]

0.19.1 is out now, you should be able to write to a Cursor<&mut Vec<u8>> now.

[jerry7536]

another error 😂 any suggestion?

error[E0277]: the trait bound `&mut Vec<u8>: lofty::io::Length` is not satisfied
  --> src\tag.rs:50:18
   |
50 |         self.tag.save_to(&mut buf, WriteOptions::default());
   |                  ^^^^^^^ the trait `lofty::io::Length` is not implemented for `&mut Vec<u8>`, which is required by `std::io::Cursor<&mut Vec<u8>>: lofty::io::Length`
   |
   = help: the trait `lofty::io::Length` is implemented for `Vec<u8>`
   = note: `lofty::io::Length` is implemented for `&Vec<u8>`, but not for `&mut Vec<u8>`
   = note: required for `std::io::Cursor<&mut Vec<u8>>` to implement `lofty::io::Length`

[Serial-ATA]

That's my fault again. I thought impl<T: Length> Truncate for &T would've applied for &mut T as well. I'll have to release 0.19.2 soon. This time I'll make a test.

[Serial-ATA]

Should be good now, try with 0.19.2

[jerry7536]

Yeah, that works!
Thanks for your great work!

[jerry7536]

Finally open source it: https://github.com/subframe7536/music-metadata-wasm