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|
use super::*;
use ciborium_io::Read;
/// An error that occurred while decoding
#[derive(Debug)]
pub enum Error<T> {
/// An error occurred while reading bytes
///
/// Contains the underlying error reaturned while reading.
Io(T),
/// An error occurred while parsing bytes
///
/// Contains the offset into the stream where the syntax error occurred.
Syntax(usize),
}
impl<T> From<T> for Error<T> {
#[inline]
fn from(value: T) -> Self {
Self::Io(value)
}
}
/// A decoder for deserializing CBOR items
///
/// This decoder manages the low-level decoding of CBOR items into `Header`
/// objects. It also contains utility functions for parsing segmented bytes
/// and text inputs.
pub struct Decoder<R: Read> {
reader: R,
offset: usize,
buffer: Option<Title>,
}
impl<R: Read> From<R> for Decoder<R> {
#[inline]
fn from(value: R) -> Self {
Self {
reader: value,
offset: 0,
buffer: None,
}
}
}
impl<R: Read> Read for Decoder<R> {
type Error = R::Error;
#[inline]
fn read_exact(&mut self, data: &mut [u8]) -> Result<(), Self::Error> {
assert!(self.buffer.is_none());
self.reader.read_exact(data)?;
self.offset += data.len();
Ok(())
}
}
impl<R: Read> Decoder<R> {
#[inline]
fn pull_title(&mut self) -> Result<Title, Error<R::Error>> {
if let Some(title) = self.buffer.take() {
self.offset += title.1.as_ref().len() + 1;
return Ok(title);
}
let mut prefix = [0u8; 1];
self.read_exact(&mut prefix[..])?;
let major = match prefix[0] >> 5 {
0 => Major::Positive,
1 => Major::Negative,
2 => Major::Bytes,
3 => Major::Text,
4 => Major::Array,
5 => Major::Map,
6 => Major::Tag,
7 => Major::Other,
_ => unreachable!(),
};
let mut minor = match prefix[0] & 0b00011111 {
x if x < 24 => Minor::This(x),
24 => Minor::Next1([0; 1]),
25 => Minor::Next2([0; 2]),
26 => Minor::Next4([0; 4]),
27 => Minor::Next8([0; 8]),
31 => Minor::More,
_ => return Err(Error::Syntax(self.offset - 1)),
};
self.read_exact(minor.as_mut())?;
Ok(Title(major, minor))
}
#[inline]
fn push_title(&mut self, item: Title) {
assert!(self.buffer.is_none());
self.buffer = Some(item);
self.offset -= item.1.as_ref().len() + 1;
}
/// Pulls the next header from the input
#[inline]
pub fn pull(&mut self) -> Result<Header, Error<R::Error>> {
let offset = self.offset;
self.pull_title()?
.try_into()
.map_err(|_| Error::Syntax(offset))
}
/// Push a single header into the input buffer
///
/// # Panics
///
/// This function panics if called while there is already a header in the
/// input buffer. You should take care to call this function only after
/// pulling a header to ensure there is nothing in the input buffer.
#[inline]
pub fn push(&mut self, item: Header) {
self.push_title(Title::from(item))
}
/// Gets the current byte offset into the stream
///
/// The offset starts at zero when the decoder is created. Therefore, if
/// bytes were already read from the reader before the decoder was created,
/// you must account for this.
#[inline]
pub fn offset(&mut self) -> usize {
self.offset
}
/// Process an incoming bytes item
///
/// In CBOR, bytes can be segmented. The logic for this can be a bit tricky,
/// so we encapsulate that logic using this function. This function **MUST**
/// be called immediately after first pulling a `Header::Bytes(len)` from
/// the wire and `len` must be provided to this function from that value.
///
/// The `buf` parameter provides a buffer used when reading in the segmented
/// bytes. A large buffer will result in fewer calls to read incoming bytes
/// at the cost of memory usage. You should consider this trade off when
/// deciding the size of your buffer.
#[inline]
pub fn bytes(&mut self, len: Option<usize>) -> Segments<R, crate::seg::Bytes> {
self.push(Header::Bytes(len));
Segments::new(self, |header| match header {
Header::Bytes(len) => Ok(len),
_ => Err(()),
})
}
/// Process an incoming text item
///
/// In CBOR, text can be segmented. The logic for this can be a bit tricky,
/// so we encapsulate that logic using this function. This function **MUST**
/// be called immediately after first pulling a `Header::Text(len)` from
/// the wire and `len` must be provided to this function from that value.
///
/// The `buf` parameter provides a buffer used when reading in the segmented
/// text. A large buffer will result in fewer calls to read incoming bytes
/// at the cost of memory usage. You should consider this trade off when
/// deciding the size of your buffer.
#[inline]
pub fn text(&mut self, len: Option<usize>) -> Segments<R, crate::seg::Text> {
self.push(Header::Text(len));
Segments::new(self, |header| match header {
Header::Text(len) => Ok(len),
_ => Err(()),
})
}
}
|
