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use {
alloc::vec::Vec,
crate::Result,
super::{Debt64, LastChars},
};
struct Decoder<'a> {
bytes: &'a [u8],
index: usize,
len: usize,
allows_line_separators: bool,
must_or_can_use_pad: bool,
allows_invalid_chars: bool,
last_chars: &'a LastChars,
}
impl<'a> Decoder<'a> {
fn new(bytes: &'a [u8], allows_line_separators: bool, must_or_can_use_pad: bool, allows_invalid_chars: bool, last_chars: &'a LastChars)
-> Self {
Self {
bytes,
index: 0,
len: bytes.len(),
allows_line_separators,
must_or_can_use_pad,
allows_invalid_chars,
last_chars,
}
}
fn decode_bits(&mut self) -> Result<Option<(u8, bool)>> {
loop {
if self.index >= self.len {
return Ok(None);
}
let byte = self.bytes[self.index];
self.index += 1;
match byte {
b'A'..=b'Z' => return Ok(Some((byte - b'A', false))),
b'a'..=b'z' => return Ok(Some((byte - b'a' + 26, false))),
b'0'..=b'9' => return Ok(Some((byte - b'0' + 52, false))),
b'=' => return if self.index > 1 && self.must_or_can_use_pad {
Ok(Some((0, true)))
} else {
Err(err!("Invalid pad char: '='"))
},
b'\r' | b'\n' | b' ' => if self.allows_line_separators {
match byte {
b' ' => (),
b'\r' => {
if self.index >= self.len || self.bytes[self.index] != b'\n' {
return Err(err!("Invalid line separator: {:?}", &byte));
}
self.index += 1;
},
_ => (),
};
if self.index < self.len {
if matches!(self.bytes[self.index], b'\r' | b'\n') {
return Err(err!("Duplicate line separators"));
}
} else {
return Ok(None);
};
} else {
return Err(err!("Invalid line separator: {:02x}", byte));
},
_ => {
if self.last_chars.first == byte as char {
return Ok(Some((62, false)));
} else if self.last_chars.last == byte as char {
return Ok(Some((63, false)));
} else {
if self.allows_invalid_chars == false {
return Err(err!("Invalid byte: {:?}", byte));
}
}
},
};
}
}
fn has_more_bytes(&self) -> bool {
self.index < self.len
}
}
pub (super) fn decode<B>(bytes: B, debt64: &Debt64) -> Result<Vec<u8>> where B: AsRef<[u8]> {
let bytes = bytes.as_ref();
let mut result = Vec::with_capacity(debt64.estimate_decoding_capacity(bytes));
let must_use_pad = debt64.must_use_pad();
let mut decoder = Decoder::new(
bytes, debt64.line_separators().is_some(), must_use_pad || debt64.can_use_pad(), debt64.allows_invalid_chars(), debt64.last_chars()
);
loop {
let first_bits = match decoder.decode_bits()? {
Some((first_bits, is_pad_char)) => if is_pad_char {
return Err(err!("Invalid pad character at first byte"));
} else {
first_bits
},
None => break,
};
let second_bits = match decoder.decode_bits()? {
Some((second_bits, is_pad_char)) => if is_pad_char {
return Err(err!("Invalid pad character at second byte"));
} else {
result.push((first_bits << 2) | (second_bits >> 4));
second_bits
},
None => return Err(err!("Missing second byte")),
};
let (third_bits, third_byte_is_pad_char) = match decoder.decode_bits()? {
Some((third_bits, is_pad_char)) => {
if is_pad_char == false {
result.push((second_bits << 4) | (third_bits >> 2));
}
(third_bits, is_pad_char)
},
None => if must_use_pad {
return Err(err!("Missing pad char '=' for third byte"));
} else {
break;
},
};
match decoder.decode_bits()? {
Some((fourth_bits, is_pad_char)) => {
if third_byte_is_pad_char {
if is_pad_char == false {
return Err(err!("Invalid character after first pad character"));
}
} else if is_pad_char == false {
result.push((third_bits << 6) | fourth_bits);
}
if is_pad_char {
if decoder.has_more_bytes() {
return Err(err!("Invalid character after ending"));
} else {
break;
}
}
},
None => if must_use_pad {
return Err(err!("Missing pad char '=' for fourth byte"));
} else {
break;
},
};
}
Ok(result)
}