1 files changed, 174 insertions, 0 deletions
diff --git a/src/dec.rs b/src/dec.rs
new file mode 100644
index 0000000..8329634
--- /dev/null
+++ b/src/dec.rs
@@ -0,0 +1,174 @@
+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(()),
+        })
+    }
+}