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use std::fmt;
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Encoding {
Ignore,
Ascii,
Utf8,
}
impl From<Encoding> for Box<dyn EncodingChecker> {
fn from(val: Encoding) -> Self {
match val {
Encoding::Ignore => Box::new(Ignore::new()),
Encoding::Ascii => Box::new(Ascii::new()),
Encoding::Utf8 => Box::new(Utf8::new()),
}
}
}
impl fmt::Display for Encoding {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let name = match self {
Encoding::Utf8 => "UTF-8",
Encoding::Ascii => "Ascii",
Encoding::Ignore => "<none>",
};
write!(f, "{}", name)
}
}
pub trait EncodingChecker {
fn feed(&mut self, byte: u8) -> bool;
}
struct Ignore;
impl Ignore {
fn new() -> Self {
Ignore
}
}
impl EncodingChecker for Ignore {
fn feed(&mut self, _byte: u8) -> bool {
true
}
}
struct Ascii;
impl Ascii {
fn new() -> Self {
Ascii
}
}
impl EncodingChecker for Ascii {
fn feed(&mut self, byte: u8) -> bool {
byte < 128
}
}
struct Utf8 {
counter: Option<u8>,
}
impl Utf8 {
fn new() -> Self {
Utf8 { counter: None }
}
}
impl EncodingChecker for Utf8 {
fn feed(&mut self, byte: u8) -> bool {
let counter = match self.counter {
Some(counter) => {
if byte & 0xc0 == 0x80 {
if counter == 0 {
None
} else {
Some(counter - 1)
}
} else {
return false;
}
}
None => {
if byte & 0x80 == 0 {
None
} else if byte & 0xe0 == 0xc0 {
Some(0)
} else if byte & 0xf0 == 0xe0 {
Some(1)
} else if byte & 0xf8 == 0xf0 {
Some(2)
} else {
return false;
}
}
};
self.counter = counter;
true
}
}
#[cfg(test)]
mod tests {
use super::*;
fn feed_valid(encoding: &mut dyn EncodingChecker, bytes: &[u8]) {
for byte in bytes {
assert!(encoding.feed(*byte));
}
}
fn feed_invalid(encoding: &mut dyn EncodingChecker, bytes: &[u8]) {
let mut flag = true;
for byte in bytes {
flag &= encoding.feed(*byte);
}
assert!(!flag);
}
#[test]
fn ascii() {
feed_valid(&mut Ascii::new(), b"Hello world!");
feed_valid(&mut Ascii::new(), &[0, 0x7f]);
feed_invalid(&mut Ascii::new(), "Ahoj světe!".as_bytes());
}
#[test]
fn utf8() {
feed_valid(&mut Utf8::new(), b"Hello world!");
feed_valid(&mut Utf8::new(), &[0, 0x7f]);
feed_valid(&mut Utf8::new(), "Ahoj světe!".as_bytes());
feed_valid(
&mut Utf8::new(),
&[0xc0, 0x80, 0xe0, 0x80, 0x80, 0xf0, 0x80, 0x80, 0x80],
);
feed_valid(
&mut Utf8::new(),
&[0xc0, 0xbf, 0xe0, 0xbf, 0xbf, 0xf0, 0xbf, 0xbf, 0xbf],
);
feed_invalid(&mut Utf8::new(), &[0x80]);
feed_invalid(&mut Utf8::new(), &[0xc0, 0x7f]);
feed_invalid(&mut Utf8::new(), &[0xc0, 0x80, 0x80]);
}
}