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use std::io::{self, Read};
use std::str;
use std::fmt;
#[derive(Debug)]
pub enum CharReadError {
UnexpectedEof,
Utf8(str::Utf8Error),
Io(io::Error)
}
impl From<str::Utf8Error> for CharReadError {
fn from(e: str::Utf8Error) -> CharReadError {
CharReadError::Utf8(e)
}
}
impl From<io::Error> for CharReadError {
fn from(e: io::Error) -> CharReadError {
CharReadError::Io(e)
}
}
impl fmt::Display for CharReadError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
use self::CharReadError::*;
match *self {
UnexpectedEof => write!(f, "unexpected end of stream"),
Utf8(ref e) => write!(f, "UTF-8 decoding error: {}", e),
Io(ref e) => write!(f, "I/O error: {}", e)
}
}
}
pub fn next_char_from<R: Read>(source: &mut R) -> Result<Option<char>, CharReadError> {
const MAX_CODEPOINT_LEN: usize = 4;
let mut bytes = source.bytes();
let mut buf = [0u8; MAX_CODEPOINT_LEN];
let mut pos = 0;
loop {
let next = match bytes.next() {
Some(Ok(b)) => b,
Some(Err(e)) => return Err(e.into()),
None if pos == 0 => return Ok(None),
None => return Err(CharReadError::UnexpectedEof)
};
buf[pos] = next;
pos += 1;
match str::from_utf8(&buf[..pos]) {
Ok(s) => return Ok(s.chars().next()), // always Some(..)
Err(_) if pos < MAX_CODEPOINT_LEN => {},
Err(e) => return Err(e.into())
}
}
}
#[cfg(test)]
mod tests {
#[test]
fn test_next_char_from() {
use std::io;
use std::error::Error;
let mut bytes: &[u8] = "correct".as_bytes(); // correct ASCII
assert_eq!(super::next_char_from(&mut bytes).unwrap(), Some('c'));
let mut bytes: &[u8] = "правильно".as_bytes(); // correct BMP
assert_eq!(super::next_char_from(&mut bytes).unwrap(), Some('п'));
let mut bytes: &[u8] = "😊".as_bytes(); // correct non-BMP
assert_eq!(super::next_char_from(&mut bytes).unwrap(), Some('😊'));
let mut bytes: &[u8] = b""; // empty
assert_eq!(super::next_char_from(&mut bytes).unwrap(), None);
let mut bytes: &[u8] = b"\xf0\x9f\x98"; // incomplete code point
match super::next_char_from(&mut bytes).unwrap_err() {
super::CharReadError::UnexpectedEof => {},
e => panic!("Unexpected result: {:?}", e)
};
let mut bytes: &[u8] = b"\xff\x9f\x98\x32"; // invalid code point
match super::next_char_from(&mut bytes).unwrap_err() {
super::CharReadError::Utf8(_) => {},
e => panic!("Unexpected result: {:?}", e)
};
// error during read
struct ErrorReader;
impl io::Read for ErrorReader {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
Err(io::Error::new(io::ErrorKind::Other, "test error"))
}
}
let mut r = ErrorReader;
match super::next_char_from(&mut r).unwrap_err() {
super::CharReadError::Io(ref e) if e.kind() == io::ErrorKind::Other &&
e.description() == "test error" => {},
e => panic!("Unexpected result: {:?}", e)
}
}
}