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use crate::io::WireType;
use crate::io::WireType::*;
use enc::read_single_byte;
use enc::var_int::VarInt128;
use std::io::{Read, Write};
impl WireType {
//! Transfer
/// Transfers the encoded value for this wire type from `r` to `w`.
///
/// This reads the value bytes from `r` and writes them to `w`. The field header has already
/// been consumed — this transfers only the value payload.
pub fn transfer<R, W>(self, r: &mut R, w: &mut W) -> Result<(), enc::Error>
where
R: Read,
W: Write,
{
match self {
Fixed1Byte => Self::transfer_fixed(r, w, 1),
Fixed2Byte => Self::transfer_fixed(r, w, 2),
Fixed4Byte => Self::transfer_fixed(r, w, 4),
Fixed8Byte => Self::transfer_fixed(r, w, 8),
Fixed16Byte => Self::transfer_fixed(r, w, 16),
VarInt => Self::transfer_varint(r, w),
LengthPrefixed => Self::transfer_length_prefixed(r, w),
List => Self::transfer_length_prefixed(r, w),
}
}
/// Transfers `n` fixed bytes from `r` to `w`.
fn transfer_fixed<R, W>(r: &mut R, w: &mut W, n: usize) -> Result<(), enc::Error>
where
R: Read,
W: Write,
{
let mut buf: [u8; 16] = [0u8; 16];
r.read_exact(&mut buf[..n])?;
w.write_all(&buf[..n])?;
Ok(())
}
/// Transfers a varint from `r` to `w`.
fn transfer_varint<R, W>(r: &mut R, w: &mut W) -> Result<(), enc::Error>
where
R: Read,
W: Write,
{
let mut buf: [u8; VarInt128::MAX_ENCODED_LEN] = [0u8; VarInt128::MAX_ENCODED_LEN];
let mut len: usize = 0;
while len < VarInt128::MAX_ENCODED_LEN {
let b: u8 = read_single_byte(r)?;
buf[len] = b;
len += 1;
if b & 0x80 == 0 {
w.write_all(&buf[..len])?;
return Ok(());
}
}
Err(enc::Error::InvalidEncodedData { reason: None }) // todo -- better error here
}
/// Transfers a length-prefixed or list value from `r` to `w`.
///
/// The varint length prefix is read into a small stack buffer and forwarded directly (skipping
/// the decode+re-encode round trip), while still being validated by the canonical varint
/// decoder. The payload bytes are then forwarded blindly — they are not validated since they
/// may contain any nested packet structure.
fn transfer_length_prefixed<R, W>(r: &mut R, w: &mut W) -> Result<(), enc::Error>
where
R: Read,
W: Write,
{
use enc::DecodeFromReadPrefix;
use enc::var_int::VarIntSize;
// Read varint bytes into a stack buffer until the high-bit-clear terminator.
let mut prefix_buf: [u8; VarIntSize::MAX_ENCODED_LEN] = [0u8; VarIntSize::MAX_ENCODED_LEN];
let mut prefix_len: usize = 0;
loop {
if prefix_len >= VarIntSize::MAX_ENCODED_LEN {
return Err(enc::Error::InvalidEncodedData { reason: None });
}
let b: u8 = read_single_byte(r)?;
prefix_buf[prefix_len] = b;
prefix_len += 1;
if b & 0x80 == 0 {
break;
}
}
// Decode the buffered prefix to validate it and extract the payload length.
let mut prefix_rest: &[u8] = &prefix_buf[1..prefix_len];
let len: usize =
VarIntSize::decode_from_read_prefix_with_first_byte(&mut prefix_rest, prefix_buf[0])?
.value();
// Forward the prefix bytes verbatim.
w.write_all(&prefix_buf[..prefix_len])?;
// Transfer the payload.
let mut remaining: usize = len;
let mut buf: [u8; 1024] = [0u8; 1024]; // todo -- why 1024?
while remaining > 0 {
let chunk: usize = remaining.min(buf.len());
r.read_exact(&mut buf[..chunk])?;
w.write_all(&buf[..chunk])?;
remaining -= chunk;
}
Ok(())
}
}
#[cfg(test)]
mod tests {
use crate::io::WireType;
use crate::io::WireType::*;
use std::io::Cursor;
#[test]
#[allow(clippy::type_complexity)]
fn transfer() {
// 1500 byte payload to exercise the multi-chunk path in `transfer_length_prefixed`
// (chunk size = 1024). varint(1500) = [0xDC, 0x0B].
let mut large_lp: Vec<u8> = vec![0xDC, 0x0B];
large_lp.extend(std::iter::repeat_n(0xAB, 1500));
// 20 bytes all with the continuation bit set — exceeds VarInt128::MAX_ENCODED_LEN (19).
let overlong_varint: [u8; 20] = [0xFF; 20];
// 16 bytes all with the continuation bit set — exceeds the usize varint max for any
// supported pointer width (max is 10 on 64-bit, 5 on 32-bit).
let overlong_lp_prefix: [u8; 16] = [0xFF; 16];
// Each case: (wire type, input bytes, Some(expected output) for Ok, None for Err).
let cases: &[(WireType, &[u8], Option<&[u8]>)] = &[
// Fixed widths — output equals input.
(Fixed1Byte, &[0x42], Some(&[0x42])),
(Fixed2Byte, &[1, 2], Some(&[1, 2])),
(Fixed4Byte, &[1, 2, 3, 4], Some(&[1, 2, 3, 4])),
(
Fixed8Byte,
&[1, 2, 3, 4, 5, 6, 7, 8],
Some(&[1, 2, 3, 4, 5, 6, 7, 8]),
),
(
Fixed16Byte,
&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
Some(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]),
),
// VarInt: 1, 2, 3, and 5 byte forms.
(VarInt, &[0x42], Some(&[0x42])),
(VarInt, &[0xAC, 0x02], Some(&[0xAC, 0x02])),
(VarInt, &[0xFF, 0xFF, 0x03], Some(&[0xFF, 0xFF, 0x03])),
(
VarInt,
&[0xFF, 0xFF, 0xFF, 0xFF, 0x0F],
Some(&[0xFF, 0xFF, 0xFF, 0xFF, 0x0F]),
),
// VarInt: overlong — should reject.
(VarInt, &overlong_varint, None),
// LengthPrefixed: empty body, small body, large body that crosses the chunk boundary.
(LengthPrefixed, &[0x00], Some(&[0x00])),
(
LengthPrefixed,
&[0x03, b'a', b'b', b'c'],
Some(&[0x03, b'a', b'b', b'c']),
),
(
LengthPrefixed,
large_lp.as_slice(),
Some(large_lp.as_slice()),
),
// LengthPrefixed: overlong prefix — should reject.
(LengthPrefixed, &overlong_lp_prefix, None),
// List uses the same path as LengthPrefixed.
(List, &[0x00], Some(&[0x00])),
(List, &[0x03, 1, 2, 3], Some(&[0x03, 1, 2, 3])),
];
for (wire, input, expected) in cases {
let mut r: Cursor<&[u8]> = Cursor::new(*input);
let mut w: Vec<u8> = Vec::new();
let result: Result<(), enc::Error> = wire.transfer(&mut r, &mut w);
match (result, expected) {
(Ok(()), Some(exp)) => {
assert_eq!(
w.as_slice(),
*exp,
"wire={wire:?} input_len={}",
input.len()
);
}
(Err(_), None) => {}
(Ok(()), None) => {
panic!(
"wire={wire:?} input_len={}: expected error, got Ok",
input.len()
)
}
(Err(e), Some(_)) => {
panic!(
"wire={wire:?} input_len={}: expected Ok, got error: {e:?}",
input.len()
)
}
}
}
}
}