DRAFT: Add DekuWriterMut

[wcampbell0x2a]

Example that this allows. Basically, when you write, you can read from a Reader!

pub enum Data {
    /// On read: Save current stream_position() as `Offset`, seek `header.filesize`
    /// This will be used to seek this this position if we want to extract *just* this file
    Offset(u64),
    /// On write: Write `Reader` to write buffer
    Reader(Box<dyn ReadSeek>),
}

impl DekuReader<'_, u32> for Data {
    fn from_reader_with_ctx<R: Read + Seek>(
        reader: &mut Reader<R>,
        filesize: u32,
    ) -> Result<Data, DekuError> {
        let reader = reader.as_mut();

        // Save the current offset, this is where the file exists for reading later
        let current_pos = reader.stream_position().unwrap();

        // Seek past that file
        let position = filesize as i64 + pad_to_4(filesize as usize) as i64;
        let _ = reader.seek(SeekFrom::Current(position));

        Ok(Self::Offset(current_pos))
    }
}

impl DekuWriterMut for Data {
    fn to_writer_mut<W: Write + Seek>(
        &mut self,
        writer: &mut Writer<W>,
        _: (),
    ) -> Result<(), DekuError> {
        if let Self::Reader(reader) = self {
            // read from reader
            let mut data = vec![];
            reader.read_to_end(&mut data).unwrap();

            // write to deku
            data.to_writer(writer, ())?;

            // add padding
            for _ in 0..pad_to_4(data.len()) {
                0_u8.to_writer(writer, ())?;
            }
        } else {
            panic!("ah");
        }

        Ok(())
    }
}

#[derive(DekuWriteMut)]
pub struct Object {
    // other fields
    data: Data,
}

• Add DekuWriterMut, to include parsers that mutate from &mut self during parsing.
• Impls:
  • bool
  • Box
  • IpAddr,
  • NonZero
  • Primitive
  • Slice
  • Vec
  • ()
• Add small example for a Writer that needs Mut

TODO

• Make sure the code coverage is good
• Support Cow?
• Support HashMap?
• Support HashSet?

[github-actions]

Benchmark for e52c5f4

Click to view benchmark

Test	Base	PR	%
deku_read_bits	1261.4±13.10ns	1295.9±19.04ns	+2.74%
deku_read_byte	3.4±0.09ns	3.4±0.08ns	0.00%
deku_read_enum	2.6±0.18ns	2.6±0.17ns	0.00%
deku_read_vec	33.2±0.44ns	33.1±0.54ns	-0.30%
deku_write_bits	153.9±2.69ns	164.7±4.54ns	+7.02%
deku_write_byte	24.5±0.41ns	24.6±0.51ns	+0.41%
deku_write_enum	22.7±0.38ns	22.7±0.42ns	0.00%
deku_write_vec	444.0±16.35ns	443.0±7.05ns	-0.23%