use num_bigint::{BigUint};
use num_traits::{Zero, One, ToPrimitive};
use num_integer::Integer;
use failure::Fail;
pub fn encode(bytes: &[u8]) -> String {
if bytes.is_empty() { return "".into() }
let mut input = vec![1u8];
input.extend_from_slice(bytes);
let mut result = String::new();
let mut val = BigUint::from_bytes_be(&input);
let base:BigUint = (BASE.to_owned() as u64).into();
while val > BigUint::zero() {
let remainder = val.mod_floor(&base).to_usize().unwrap_or(0);
result.push(ALPHABET[remainder]);
val /= &base;
}
result
}
pub fn decode(input: &str) -> Result<Vec<u8>, Error> {
let mut val:BigUint = BigUint::zero();
let mut base_mul = BigUint::one();
let base:BigUint = (BASE.to_owned() as u64).into();
for c in input.chars().into_iter() {
let remainder:BigUint = char_to_remainder(c)?.into();
val += remainder*&base_mul;
base_mul *= &base;
}
Ok(val.to_bytes_be()[1..].to_vec())
}
#[derive(Debug, Fail)]
pub enum Error {
#[fail(display = "Invalid character '{}'", character)]
BadCharacter { character: char}
}
const BASE: usize = 62;
const ALPHABET: [char; BASE] = [
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
'y', 'z',
];
fn char_to_remainder(c: char) -> Result<u64, Error> {
let i = match c {
'0'...'9' => ((c as u64) % ('0' as u64)),
'A'...'Z' => ((c as u64) % ('A' as u64)) + 10,
'a'...'z' => ((c as u64) % ('a' as u64)) + 36,
_ => return Err(Error::BadCharacter { character: c })
};
Ok(i)
}
#[test]
fn test_encode() {
let cases:Vec<Vec<u8>> = vec![
vec![],
vec![0u8],
vec![1u8],
vec![0u8,0u8],
vec![0u8,1u8],
vec![1u8,0u8],
vec![1u8,1u8],
vec![0, 0, 0, 1],
[62u8; 10].to_vec(),
[63u8; 10].to_vec(),
[1u8; 10].to_vec(),
[0u8; 10].to_vec(),
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt".as_bytes().to_vec(),
vec![0xDE, 0xAD, 0xBE, 0xEF],
];
cases.into_iter().enumerate().for_each(|(case, input)| {
let encoded = encode(&input);
let decoded = decode(&encoded).expect("error decoding base62 input");
assert_eq!(input, decoded, "\nCase {}:\nbase62({})\nmismatch: \nencoded({:?}) != \ndecoded({:?})", case, encoded, input, decoded);
})
}
#[test]
fn test_invalid() {
decode("abc-").expect_err("expected invalid '-'");
decode("wSBzv9UB5PeI/26").expect_err("expected invalid '/'");
decode("jSO+uL8").expect_err("expected invalid '+");
}