preserves/implementations/rust/src/value/codec.rs

use std::io::Read;
use std::convert::TryInto;
use crate::value::value::{Value, AValue, Set, Dictionary};
use num::bigint::BigInt;

pub type Result<V> = std::result::Result<V, Error>;

#[derive(Debug)]
pub enum Error {
    Io(std::io::Error),
    Syntax(&'static str),
    Eof,
}

impl From<std::io::Error> for Error {
    fn from(v: std::io::Error) -> Self {
        Error::Io(v)
    }
}

impl From<std::str::Utf8Error> for Error {
    fn from(_v: std::str::Utf8Error) -> Self {
        Error::Syntax("Invalid UTF-8")
    }
}

impl Error {
    pub fn is_io(&self) -> bool { if let Error::Io(_) = *self { true } else { false } }
    pub fn is_syntax(&self) -> bool { if let Error::Syntax(_) = *self { true } else { false } }
    pub fn is_eof(&self) -> bool { if let Error::Eof = *self { true } else { false } }
}

pub type PlaceholderMap = std::collections::BTreeMap<usize, Value>;

pub struct Decoder<R: Read> {
    read: R,
    index: usize,
    buf: Box<Option<Option<u8>>>,
    placeholders: PlaceholderMap,
}

impl<R: Read> Decoder<R> {
    pub fn new(read: R, placeholders: Option<PlaceholderMap>) -> Self {
        Decoder{
            read,
            index: 0,
            buf: Box::new(None),
            placeholders: placeholders.unwrap_or(PlaceholderMap::new())
        }
    }

    fn prime_if_possible(&mut self) -> Result<()> {
        match *self.buf {
            None => {
                let bs = &mut [0];
                *self.buf = Some(match self.read.read(bs)? {
                    0 => None,
                    1 => {
                        self.index = self.index + 1;
                        Some(bs[0])
                    },
                    _ => panic!("buffer overrun")
                })
            }
            Some(_) => ()
        }
        Ok(())
    }

    pub fn skip(&mut self) -> Result<()> {
        self.prime_if_possible()?;
        *self.buf = None;
        Ok(())
    }

    pub fn peek(&mut self) -> Result<u8> {
        self.prime_if_possible()?;
        match *self.buf {
            Some(Some(v)) => Ok(v),
            Some(None) => Err(Error::Eof),
            None => panic!()
        }
    }

    pub fn read(&mut self) -> Result<u8> {
        let v = self.peek()?;
        self.skip()?;
        Ok(v)
    }

    pub fn readbytes(&mut self, n: usize) -> Result<Vec<u8>> {
        if (*self.buf).is_some() {
            panic!();
        }
        let mut bs = vec![0; n];
        match self.read.read_exact(&mut bs) {
            Ok(()) => Ok(bs),
            Err(e) =>
                if e.kind() == std::io::ErrorKind::UnexpectedEof {
                    Err(Error::Eof)
                } else {
                    Err(Error::from(e))
                }
        }
    }

    pub fn readvalues(&mut self, mut count: usize) -> Result<Vec<AValue>> {
        let mut pieces: Vec<AValue> = Vec::new();
        while count > 0 {
            pieces.push(self.next()?);
            count = count - 1;
        }
        Ok(pieces)
    }

    pub fn nextop(&mut self) -> Result<(u8, u8, u8)> {
        let b = self.read()?;
        let major = b >> 6;
        let minor = (b >> 4) & 3;
        let arg = b & 15;
        Ok((major, minor, arg))
    }

    pub fn varint(&mut self) -> Result<usize> {
        let v = self.read()?;
        if v < 128 {
            Ok(usize::from(v))
        } else {
            Ok(self.varint()? * 128 + usize::from(v - 128))
        }
    }

    pub fn wirelength(&mut self, arg: u8) -> Result<usize> {
        if arg < 15 {
            Ok(usize::from(arg))
        } else {
            self.varint()
        }
    }

    pub fn peekend(&mut self) -> Result<bool> {
        if self.peek()? == 4 {
            self.skip()?;
            Ok(true)
        } else {
            Ok(false)
        }
    }

    pub fn decodeint(bs: &[u8]) -> BigInt {
        BigInt::from_signed_bytes_be(bs)
    }

    pub fn decodebinary(minor: u8, bs: Vec<u8>) -> Result<AValue> {
        Ok(match minor {
            0 => Value::from(Self::decodeint(&bs)).wrap(),
            1 => Value::from(std::str::from_utf8(&bs)?).wrap(),
            2 => Value::from(bs).wrap(),
            3 => Value::symbol(std::str::from_utf8(&bs)?).wrap(),
            _ => panic!()
        })
    }

    pub fn decodecompound(minor: u8, mut pieces: Vec<AValue>) -> Result<AValue> {
        match minor {
            0 =>
                if pieces.len() == 0 {
                    Err(Error::Syntax("Too few elements in encoded record"))
                } else {
                    let label = pieces.remove(0).rc();
                    Ok(Value::record(&label, pieces).wrap())
                },
            1 => Ok(Value::from(pieces).wrap()),
            2 => {
                let mut s = Set::new();
                while let Some(v) = pieces.pop() {
                    s.insert(v);
                }
                Ok(Value::Set(s).wrap())
            }
            3 =>
                if pieces.len() % 2 != 0 {
                    Err(Error::Syntax("Missing dictionary value"))
                } else {
                    let mut d = Dictionary::new();
                    while let Some(v) = pieces.pop() {
                        let k = pieces.pop().unwrap();
                        d.insert(k, v);
                    }
                    Ok(Value::Dictionary(d).wrap())
                },
            _ => panic!()
        }
    }

    pub fn binarystream(&mut self, minor: u8) -> Result<AValue> {
        let mut bs: Vec<u8> = Vec::new();
        while !self.peekend()? {
            match self.next()?.1.as_bytestring() {
                Some(chunk) => bs.extend_from_slice(chunk),
                None => return Err(Error::Syntax("Unexpected non-binary chunk")),
            }
        }
        Self::decodebinary(minor, bs)
    }

    pub fn valuestream(&mut self, minor: u8) -> Result<AValue> {
        let mut pieces: Vec<AValue> = Vec::new();
        while !self.peekend()? {
            pieces.push(self.next()?);
        }
        Self::decodecompound(minor, pieces)
    }

    pub fn next(&mut self) -> Result<AValue> {
        match self.nextop()? {
            (0, 0, 0) => Ok(Value::from(false).wrap()),
            (0, 0, 1) => Ok(Value::from(true).wrap()),
            (0, 0, 2) => {
                let bs: &[u8] = &self.readbytes(4)?;
                Ok(Value::from(f32::from_bits(u32::from_be_bytes(bs.try_into().unwrap()))).wrap())
            }
            (0, 0, 3) => {
                let bs: &[u8] = &self.readbytes(8)?;
                Ok(Value::from(f64::from_bits(u64::from_be_bytes(bs.try_into().unwrap()))).wrap())
            }
            (0, 0, 5) => {
                let a = self.next()?;
                let mut v = self.next()?;
                v.annotations_mut().push(a);
                Ok(v)
            }
            (0, 0, _) => Err(Error::Syntax("Invalid format A encoding")),
            (0, 1, arg) => {
                let n = self.wirelength(arg)?;
                match self.placeholders.get(&n) {
                    Some(v) => Ok(v.clone().wrap()),
                    None => Err(Error::Syntax("Invalid Preserves placeholder")),
                }
            }
            (0, 2, arg) => {
                let t = arg >> 2;
                let n = arg & 3;
                match t {
                    1 => self.binarystream(n),
                    2 => self.valuestream(n),
                    _ => Err(Error::Syntax("Invalid format C start byte")),
                }
            }
            (0, 3, arg) => {
                let n = if arg > 12 { i32::from(arg) - 16 } else { i32::from(arg) };
                Ok(Value::from(n).wrap())
            }
            (0, _, _) => panic!(),
            (1, minor, arg) => {
                let n = self.wirelength(arg)?;
                Self::decodebinary(minor, self.readbytes(n)?)
            }
            (2, minor, arg) => {
                let n = self.wirelength(arg)?;
                Self::decodecompound(minor, self.readvalues(n)?)
            }
            (3, _, _) => Err(Error::Syntax("Invalid lead byte (major 3)")),
            (_, _, _) => panic!(),
        }
    }
}