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optimize CharReader

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This commit is contained in:
Skgland
2026-04-30 19:44:31 +02:00
parent 327a677a7c
commit f8ddd78776
1 changed files with 93 additions and 77 deletions
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142
src/parser/char_reader.rs
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@@ -102,19 +102,27 @@ impl<R> CharReader<R> {
}
impl<R: Read> CharReader<R> {
pub fn read_chunck(&mut self) -> io::Result<usize> {
let mut chunk = [0u8; 8 * 1024];
let nread = self.inner.read(&mut chunk)?;
self.buf.extend_from_slice(&chunk[..nread]);
Ok(nread)
}
pub fn refresh_buffer(&mut self) -> io::Result<&[u8]> {
// If we've reached the end of our internal buffer then we need to fetch
// some more data from the underlying reader.
// Branch using `>=` instead of the more correct `==`
// to tell the compiler that the pos..cap slice is always valid.
if self.pos >= self.buf.len() {
self.buf.clear();
// make some space in buf
if self.buf.len() > 4 {
// keep 4 bytes so that put_back_char can put back at least one char
self.buf.drain(4..);
}
self.pos = self.buf.len();
let mut chunk = [0u8; 8 * 1024];
let nread = self.inner.read(&mut chunk)?;
self.buf.extend_from_slice(&chunk[..nread]);
self.pos = 0;
self.read_chunck()?;
}
Ok(&self.buf[self.pos..])
@@ -143,93 +151,83 @@ impl<R: Read> CharRead for CharReader<R> {
// leading bytes until either the buffer is
// empty, or we have a valid code point.
let mut split_point = 1;
let mut badbytes = vec![];
// note we might have a sequence of invalid bytes followed by valid bytes followed by invalid bytes
loop {
let (bad, rest) = buf.split_at(split_point);
let err = str::from_utf8(buf).expect_err("the start of buf should be invalid utf-8");
assert_eq!(err.valid_up_to(), 0, "the error should be a prefix");
if rest.is_empty() || str::from_utf8(rest).is_ok() {
badbytes.extend_from_slice(bad);
break;
}
let invalid_prefix = err.error_len().expect("we should have at least 4 bytes");
split_point += 1;
}
let bad_bytes = buf[..invalid_prefix].to_vec();
// Raise the error. If we still have data in
// the buffer, it will be returned on the next
// loop.
io::Error::new(io::ErrorKind::InvalidData, BadUtf8Error { bytes: badbytes })
};
io::Error::new(
io::ErrorKind::InvalidData,
BadUtf8Error { bytes: bad_bytes },
)
}
loop {
// while we haven't consumed all bytes from the buffer
while self.pos < self.buf.len() {
// buf must be non-empty
let buf = &self.buf[self.pos..];
if !buf.is_empty() {
let e = match str::from_utf8(buf) {
// we need at most 4 bytes for a char so don't decode the whole buffer
// as it can be quite large and we are going to discard the remaining chars anyway
// if there is a valid prefix
let prefix = if buf.len() > 4 { &buf[..4] } else { buf };
let e = match str::from_utf8(prefix) {
Ok(s) => {
let mut chars = s.chars();
let c = chars.next().unwrap();
let c = chars.next().expect(
"a non-empty buffer that is valid utf-8 contains at least one character",
);
return Some(Ok(c));
}
Err(e) => e,
};
if buf.len() - e.valid_up_to() >= 4 {
if e.valid_up_to() != 0 {
// the valid prefix is non-empty so it is guaranteed that we can decode at least one char
let c = str::from_utf8(&prefix[..e.valid_up_to()])
.expect("prefix is verified valid up to this point")
.chars()
.next()
.expect("the valid prefix was non-empty");
return Some(Ok(c));
}
if e.error_len().is_some() {
return Some(Err(bad_bytes_error(buf)));
} else if self.pos >= self.buf.len() {
return None;
} else if self.buf.len() - self.pos >= 4 && self.pos < e.valid_up_to() {
return match str::from_utf8(&self.buf[self.pos..self.pos + e.valid_up_to()]) {
Ok(s) => {
let mut chars = s.chars();
let c = chars.next().unwrap();
Some(Ok(c))
}
Err(e) => {
let badbytes = self.buf[self.pos..self.pos + e.valid_up_to()].to_vec();
Some(Err(io::Error::new(
io::ErrorKind::InvalidData,
BadUtf8Error { bytes: badbytes },
)))
}
};
} else {
let buf_len = self.buf.len();
for (c, idx) in (self.pos..buf_len).enumerate() {
self.buf[c] = self.buf[idx];
}
self.buf.truncate(buf_len - self.pos);
// buf is too short to deterin if the remaining bytes in buf are a valid char
// i.e. the content of bufg is a prefix of a valid utf-8 encoded char
//
// we need to read more data from the underlying stream
// so that we can determin its validity
let buf_len = self.buf.len();
self.pos = 0;
if buf_len >= 4 {
continue;
if self.buf.len() > 4 {
// keep a prefix of 4 bytes so that we put back at least one char
self.buf.drain(4..self.pos);
self.pos = 4;
}
let mut word = [0u8; 4];
let word_slice = &mut word[buf_len..4];
match self.inner.read(word_slice) {
match self.read_chunck() {
Err(e) => return Some(Err(e)),
Ok(0) => return Some(Err(bad_bytes_error(&self.buf))),
Ok(nread) => {
self.buf.extend_from_slice(&word_slice[0..nread]);
Ok(_) => {
// successfully filled the buffer with another chuck of data
}
}
}
} else {
return None;
}
}
None
}
#[inline(always)]
@@ -394,6 +392,15 @@ mod tests {
std::io::ErrorKind::InvalidData
);
let err = read_string
.read_char()
.unwrap()
.unwrap_err()
.downcast::<BadUtf8Error>()
.unwrap();
read_string.consume(err.bytes.len());
for c in "more_text".chars() {
assert_eq!(read_string.peek_char().unwrap().ok(), Some(c));
assert_eq!(read_string.read_char().unwrap().ok(), Some(c));
@@ -404,6 +411,15 @@ mod tests {
std::io::ErrorKind::InvalidData
);
let err = read_string
.read_char()
.unwrap()
.unwrap_err()
.downcast::<BadUtf8Error>()
.unwrap();
read_string.consume(err.bytes.len());
assert!(read_string.read_char().is_none());
}