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|
use core::borrow::BorrowMut;
use crate::frame_decoder::{BlockDecodingStrategy, FrameDecoder, FrameDecoderError};
use crate::io::{Error, ErrorKind, Read};
/// High level decoder that implements a io::Read that can be used with
/// io::Read::read_to_end / io::Read::read_exact or passing this to another library / module as a source for the decoded content
///
/// The lower level FrameDecoder by comparison allows for finer grained control but need sto have it's decode_blocks method called continously
/// to decode the zstd-frame.
pub struct StreamingDecoder<READ: Read, DEC: BorrowMut<FrameDecoder>> {
pub decoder: DEC,
source: READ,
}
impl<READ: Read, DEC: BorrowMut<FrameDecoder>> StreamingDecoder<READ, DEC> {
pub fn new_with_decoder(
mut source: READ,
mut decoder: DEC,
) -> Result<StreamingDecoder<READ, DEC>, FrameDecoderError> {
decoder.borrow_mut().init(&mut source)?;
Ok(StreamingDecoder { decoder, source })
}
}
impl<READ: Read> StreamingDecoder<READ, FrameDecoder> {
pub fn new(
mut source: READ,
) -> Result<StreamingDecoder<READ, FrameDecoder>, FrameDecoderError> {
let mut decoder = FrameDecoder::new();
decoder.init(&mut source)?;
Ok(StreamingDecoder { decoder, source })
}
pub fn inner(self) -> FrameDecoder {
self.decoder
}
}
impl<READ: Read, DEC: BorrowMut<FrameDecoder>> Read for StreamingDecoder<READ, DEC> {
fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
let decoder = self.decoder.borrow_mut();
if decoder.is_finished() && decoder.can_collect() == 0 {
//No more bytes can ever be decoded
return Ok(0);
}
// need to loop. The UpToBytes strategy doesn't take any effort to actually reach that limit.
// The first few calls can result in just filling the decode buffer but these bytes can not be collected.
// So we need to call this until we can actually collect enough bytes
// TODO add BlockDecodingStrategy::UntilCollectable(usize) that pushes this logic into the decode_blocks function
while decoder.can_collect() < buf.len() && !decoder.is_finished() {
//More bytes can be decoded
let additional_bytes_needed = buf.len() - decoder.can_collect();
match decoder.decode_blocks(
&mut self.source,
BlockDecodingStrategy::UptoBytes(additional_bytes_needed),
) {
Ok(_) => { /*Nothing to do*/ }
Err(e) => {
let err = Error::new(
ErrorKind::Other,
alloc::format!("Error in the zstd decoder: {:?}", e),
);
return Err(err);
}
}
}
decoder.read(buf)
}
}
|
