prefix_uvarint 0.4.1

//! Extensions to `std::io` traits to support reading/writing prefix varints.
use std::io::{BufRead, Error, ErrorKind, Read, Result, Write};

use crate::{DecodeError, PrefixVarInt, MAX_1BYTE_TAG, MAX_LEN};

impl From<DecodeError> for Error {
    fn from(value: DecodeError) -> Self {
        let kind = match value {
            DecodeError::UnexpectedEob => ErrorKind::UnexpectedEof,
            DecodeError::Overflow => ErrorKind::InvalidData,
        };
        Error::new(kind, value)
    }
}

/// Prefix varint code a value and write it to `w`.
#[inline]
pub fn write_prefix_varint<PV: PrefixVarInt, W: Write>(v: PV, w: &mut W) -> Result<()> {
    w.write_all(v.to_prefix_varint_bytes().as_slice())
}

/// Read and decode a prefix varint value from `r`.
/// Prefer `read_prefix_varint_buf()` wherever possible as it should be more efficient.
#[inline]
pub fn read_prefix_varint<PV: PrefixVarInt, R: Read>(r: &mut R) -> Result<PV> {
    let mut buf = [0u8; MAX_LEN];
    r.read_exact(&mut buf[..1])?;
    let tag = buf[0];
    if tag <= MAX_1BYTE_TAG {
        return PV::from_prefix_varint_raw(tag.into()).ok_or_else(|| DecodeError::Overflow.into());
    }
    let rem = tag.leading_ones() as usize;
    r.read_exact(&mut buf[1..(1 + rem)])?;
    PV::decode_prefix_varint(buf.as_slice())
        .map(|(v, _)| v)
        .map_err(|e| e.into())
}

/// Read and decode a prefix varint value from `r`.
#[inline]
pub fn read_prefix_varint_buf<PV: PrefixVarInt, R: BufRead>(r: &mut R) -> Result<PV> {
    let buf = r.fill_buf()?;
    if buf.len() >= MAX_LEN {
        let (v, len) = PV::decode_prefix_varint(buf).map_err(Error::from)?;
        r.consume(len);
        Ok(v)
    } else {
        read_prefix_varint(r)
    }
}