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use std::io::{self, BufRead, BufReader, Read};
/// Takes an `R: BufRead` and:
///
/// - skips the leading UTF-8 BOM if there is one
/// - skips the unix shebang if there is one (if the first character is a '#', skips everything up
/// until but not including the first '\n')
///
/// This mimics the initial behavior of luaL_loadfile(x). In order to correctly detect and skip the
/// BOM and unix shebang, the internal buffer of the BufRead must be >= 3 bytes.
pub fn skip_prefix<R: BufRead>(r: &mut R) -> Result<(), io::Error> {
if {
let buf = r.fill_buf()?;
buf.len() >= 3 && buf[0] == 0xef && buf[1] == 0xbb && buf[2] == 0xbf
} {
r.consume(3);
}
let buf = r.fill_buf()?;
let has_shebang = buf.len() >= 1 && buf[0] == b'#';
if has_shebang {
r.consume(1);
loop {
let to_consume = {
let buf = r.fill_buf()?;
let mut i = 0;
loop {
if i >= buf.len() || buf[i] == b'\n' {
break i;
}
i += 1;
}
};
if to_consume == 0 {
break;
} else {
r.consume(to_consume);
}
}
}
Ok(())
}
/// Reads a Lua script from a `R: Read` and wraps it in a BufReader
///
/// Also calls `skip_prefix` to skip any leading UTF-8 BOM or unix shebang.
pub fn buffered_read<R: Read>(r: R) -> Result<BufReader<R>, io::Error> {
let mut r = BufReader::new(r);
skip_prefix(&mut r)?;
Ok(r)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_skip_prefix() {
let test_file = [
0xef, 0xbb, 0xbf, b'#', 0x00, 0x00, 0x00, 0xff, b'\n', 0x1, 0x2, 0x3,
];
let mut reader = BufReader::with_capacity(3, &test_file[..]);
skip_prefix(&mut reader).unwrap();
let mut v = Vec::new();
reader.read_to_end(&mut v).unwrap();
assert_eq!(v, vec![b'\n', 0x1, 0x2, 0x3]);
}
}