taba-client 0.1.0-rc.4

//! Standard Base64 (RFC 4648), our own: the connector depends on no library for this.

const ALPHABET: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

pub fn encode(data: &[u8]) -> String {
    let mut out = String::with_capacity(data.len().div_ceil(3) * 4);
    for chunk in data.chunks(3) {
        let b = [
            chunk[0],
            *chunk.get(1).unwrap_or(&0),
            *chunk.get(2).unwrap_or(&0),
        ];
        let n = (u32::from(b[0]) << 16) | (u32::from(b[1]) << 8) | u32::from(b[2]);
        out.push(ALPHABET[(n >> 18) as usize & 63] as char);
        out.push(ALPHABET[(n >> 12) as usize & 63] as char);
        out.push(if chunk.len() > 1 {
            ALPHABET[(n >> 6) as usize & 63] as char
        } else {
            '='
        });
        out.push(if chunk.len() > 2 {
            ALPHABET[n as usize & 63] as char
        } else {
            '='
        });
    }
    out
}

/// Decodes base64 with or without padding; returns `None` if there is a character outside the alphabet or
/// the length is impossible.
pub fn decode(text: &str) -> Option<Vec<u8>> {
    let trimmed = text.trim_end_matches('=');
    if text.len() - trimmed.len() > 2 || trimmed.len() % 4 == 1 {
        return None;
    }
    let mut out = Vec::with_capacity(trimmed.len() * 3 / 4);
    let mut acc: u32 = 0;
    let mut bits = 0;
    for c in trimmed.bytes() {
        let v = match c {
            b'A'..=b'Z' => c - b'A',
            b'a'..=b'z' => c - b'a' + 26,
            b'0'..=b'9' => c - b'0' + 52,
            b'+' => 62,
            b'/' => 63,
            _ => return None,
        };
        acc = (acc << 6) | u32::from(v);
        bits += 6;
        if bits >= 8 {
            bits -= 8;
            out.push((acc >> bits) as u8);
            acc &= (1 << bits) - 1;
        }
    }
    Some(out)
}

#[cfg(test)]
mod tests;