140 lines
3.9 KiB
Rust
140 lines
3.9 KiB
Rust
use crate::error::{Error, Result};
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use crate::wstr::WStr;
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/// A cursor over an in-memory byte buffer that decodes the Wolf wire primitives.
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///
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/// `Int` = u32 little-endian, `Byte` = u8, `String` = u32 length prefix plus that many
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/// raw bytes (kept undecoded, see [`WStr`]).
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pub struct Reader<'a> {
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data: &'a [u8],
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pos: usize,
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}
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impl<'a> Reader<'a> {
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pub fn new(data: &'a [u8]) -> Self {
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Reader { data, pos: 0 }
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}
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pub fn pos(&self) -> usize {
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self.pos
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}
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pub fn len(&self) -> usize {
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self.data.len()
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}
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pub fn is_empty(&self) -> bool {
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self.data.is_empty()
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}
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pub fn remaining(&self) -> usize {
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self.data.len().saturating_sub(self.pos)
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}
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pub fn is_eof(&self) -> bool {
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self.pos >= self.data.len()
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}
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pub fn seek(&mut self, pos: usize) {
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self.pos = pos;
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}
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/// Absolute byte at `idx` without moving the cursor.
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pub fn at(&self, idx: usize) -> Option<u8> {
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self.data.get(idx).copied()
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}
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pub fn skip(&mut self, n: usize, context: &'static str) -> Result<()> {
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self.ensure(n, context)?;
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self.pos += n;
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Ok(())
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}
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fn ensure(&self, n: usize, context: &'static str) -> Result<()> {
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if self.pos + n > self.data.len() {
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return Err(Error::UnexpectedEof {
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context,
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needed: n,
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pos: self.pos,
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len: self.data.len(),
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});
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}
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Ok(())
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}
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pub fn read_u8(&mut self) -> Result<u8> {
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self.ensure(1, "u8")?;
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let v = self.data[self.pos];
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self.pos += 1;
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Ok(v)
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}
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pub fn read_u32(&mut self) -> Result<u32> {
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self.ensure(4, "u32")?;
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let b = &self.data[self.pos..self.pos + 4];
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self.pos += 4;
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Ok(u32::from_le_bytes([b[0], b[1], b[2], b[3]]))
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}
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/// Peek the next u32 without advancing the cursor.
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pub fn peek_u32(&self) -> Result<u32> {
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self.ensure(4, "peek u32")?;
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let b = &self.data[self.pos..self.pos + 4];
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Ok(u32::from_le_bytes([b[0], b[1], b[2], b[3]]))
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}
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pub fn read_bytes(&mut self, n: usize) -> Result<Vec<u8>> {
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self.ensure(n, "fixed bytes")?;
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let v = self.data[self.pos..self.pos + n].to_vec();
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self.pos += n;
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Ok(v)
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}
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/// `String`: u32 byte-length prefix + that many raw bytes.
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pub fn read_string(&mut self) -> Result<WStr> {
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let size = self.read_u32()? as usize;
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let bytes = self.read_bytes(size)?;
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Ok(WStr(bytes))
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}
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/// `ByteArray`: u32 count + that many bytes.
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pub fn read_byte_array(&mut self) -> Result<Vec<u8>> {
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let size = self.read_u32()? as usize;
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self.read_bytes(size)
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}
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/// `IntArray`: u32 count + that many u32s.
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pub fn read_int_array(&mut self) -> Result<Vec<u32>> {
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let size = self.read_u32()? as usize;
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let mut out = Vec::with_capacity(size.min(1 << 16));
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for _ in 0..size {
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out.push(self.read_u32()?);
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}
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Ok(out)
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}
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/// `StringArray`: u32 count + that many `String`s.
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pub fn read_string_array(&mut self) -> Result<Vec<WStr>> {
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let size = self.read_u32()? as usize;
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let mut out = Vec::with_capacity(size.min(1 << 16));
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for _ in 0..size {
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out.push(self.read_string()?);
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}
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Ok(out)
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}
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/// Verify a fixed marker/magic byte sequence and advance past it.
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pub fn verify(&mut self, expected: &[u8], context: &'static str) -> Result<()> {
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self.ensure(expected.len(), context)?;
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let found = &self.data[self.pos..self.pos + expected.len()];
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if found != expected {
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return Err(Error::BadMagic {
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context,
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expected: expected.to_vec(),
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found: found.to_vec(),
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});
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}
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self.pos += expected.len();
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Ok(())
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}
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}
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