ruzstd/
streaming_decoder.rs

1use core::borrow::BorrowMut;
2
3use crate::frame_decoder::{BlockDecodingStrategy, FrameDecoder, FrameDecoderError};
4use crate::io::{Error, ErrorKind, Read};
5
6/// High level Zstandard frame decoder that can be used to decompress a given Zstandard frame.
7///
8/// This decoder implements `io::Read`, so you can interact with it by calling
9/// `io::Read::read_to_end` / `io::Read::read_exact` or passing this to another library / module as a source for the decoded content
10///
11/// If you need more control over how decompression takes place, you can use
12/// the lower level [FrameDecoder], which allows for greater control over how
13/// decompression takes place but the implementor must call
14/// [FrameDecoder::decode_blocks] repeatedly to decode the entire frame.
15///
16/// ## Caveat
17/// [StreamingDecoder] expects the underlying stream to only contain a single frame,
18/// yet the specification states that a single archive may contain multiple frames.
19///
20/// To decode all the frames in a finite stream, the calling code needs to recreate
21/// the instance of the decoder and handle
22/// [crate::frame::ReadFrameHeaderError::SkipFrame]
23/// errors by skipping forward the `length` amount of bytes, see <https://github.com/KillingSpark/zstd-rs/issues/57>
24///
25/// ```no_run
26/// // `read_to_end` is not implemented by the no_std implementation.
27/// #[cfg(feature = "std")]
28/// {
29///     use std::fs::File;
30///     use std::io::Read;
31///     use ruzstd::{StreamingDecoder};
32///
33///     // Read a Zstandard archive from the filesystem then decompress it into a vec.
34///     let mut f: File = todo!("Read a .zstd archive from somewhere");
35///     let mut decoder = StreamingDecoder::new(f).unwrap();
36///     let mut result = Vec::new();
37///     Read::read_to_end(&mut decoder, &mut result).unwrap();
38/// }
39/// ```
40pub struct StreamingDecoder<READ: Read, DEC: BorrowMut<FrameDecoder>> {
41    pub decoder: DEC,
42    source: READ,
43}
44
45impl<READ: Read, DEC: BorrowMut<FrameDecoder>> StreamingDecoder<READ, DEC> {
46    pub fn new_with_decoder(
47        mut source: READ,
48        mut decoder: DEC,
49    ) -> Result<StreamingDecoder<READ, DEC>, FrameDecoderError> {
50        decoder.borrow_mut().init(&mut source)?;
51        Ok(StreamingDecoder { decoder, source })
52    }
53}
54
55impl<READ: Read> StreamingDecoder<READ, FrameDecoder> {
56    pub fn new(
57        mut source: READ,
58    ) -> Result<StreamingDecoder<READ, FrameDecoder>, FrameDecoderError> {
59        let mut decoder = FrameDecoder::new();
60        decoder.init(&mut source)?;
61        Ok(StreamingDecoder { decoder, source })
62    }
63}
64
65impl<READ: Read, DEC: BorrowMut<FrameDecoder>> StreamingDecoder<READ, DEC> {
66    /// Gets a reference to the underlying reader.
67    pub fn get_ref(&self) -> &READ {
68        &self.source
69    }
70
71    /// Gets a mutable reference to the underlying reader.
72    ///
73    /// It is inadvisable to directly read from the underlying reader.
74    pub fn get_mut(&mut self) -> &mut READ {
75        &mut self.source
76    }
77
78    /// Destructures this object into the inner reader.
79    pub fn into_inner(self) -> READ
80    where
81        READ: Sized,
82    {
83        self.source
84    }
85
86    /// Destructures this object into both the inner reader and [FrameDecoder].
87    pub fn into_parts(self) -> (READ, DEC)
88    where
89        READ: Sized,
90    {
91        (self.source, self.decoder)
92    }
93
94    /// Destructures this object into the inner [FrameDecoder].
95    pub fn into_frame_decoder(self) -> DEC {
96        self.decoder
97    }
98}
99
100impl<READ: Read, DEC: BorrowMut<FrameDecoder>> Read for StreamingDecoder<READ, DEC> {
101    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
102        let decoder = self.decoder.borrow_mut();
103        if decoder.is_finished() && decoder.can_collect() == 0 {
104            //No more bytes can ever be decoded
105            return Ok(0);
106        }
107
108        // need to loop. The UpToBytes strategy doesn't take any effort to actually reach that limit.
109        // The first few calls can result in just filling the decode buffer but these bytes can not be collected.
110        // So we need to call this until we can actually collect enough bytes
111
112        // TODO add BlockDecodingStrategy::UntilCollectable(usize) that pushes this logic into the decode_blocks function
113        while decoder.can_collect() < buf.len() && !decoder.is_finished() {
114            //More bytes can be decoded
115            let additional_bytes_needed = buf.len() - decoder.can_collect();
116            match decoder.decode_blocks(
117                &mut self.source,
118                BlockDecodingStrategy::UptoBytes(additional_bytes_needed),
119            ) {
120                Ok(_) => { /*Nothing to do*/ }
121                Err(e) => {
122                    let err;
123                    #[cfg(feature = "std")]
124                    {
125                        err = Error::new(ErrorKind::Other, e);
126                    }
127                    #[cfg(not(feature = "std"))]
128                    {
129                        err = Error::new(ErrorKind::Other, alloc::boxed::Box::new(e));
130                    }
131                    return Err(err);
132                }
133            }
134        }
135
136        decoder.read(buf)
137    }
138}
ruzstd/streaming_decoder.rs

ruzstd/
streaming_decoder.rs
