/// Hand-rolled percent decoder -- handles `%XX` and `+` for spaces.

/// I didn't want to pull in a dep just for this.

pub fn percent_decode(s: &str) -> String {

let mut result = Vec::with_capacity(s.len());

let bytes = s.as_bytes();

let mut i = 0;

while i < bytes.len() {

if bytes[i] == b'%' && i + 2 < bytes.len() {

if let (Some(hi), Some(lo)) = (hex_val(bytes[i + 1]), hex_val(bytes[i + 2])) {

result.push(hi << 4 | lo);

i += 3;

continue;

}

} else if bytes[i] == b'+' {

result.push(b' ');

i += 1;

continue;

}

result.push(bytes[i]);

i += 1;

}

String::from_utf8(result).unwrap_or_else(|_| s.to_string())

}

fn hex_val(b: u8) -> Option<u8> {

match b {

b'0'..=b'9' => Some(b - b'0'),

b'a'..=b'f' => Some(b - b'a' + 10),

b'A'..=b'F' => Some(b - b'A' + 10),

_ => None,

}

}

#[cfg(test)]

mod tests {

use super::*;

#[test]

fn decode_basic() {

assert_eq!(percent_decode("hello%20world"), "hello world");

assert_eq!(percent_decode("hello+world"), "hello world");

}

#[test]

fn decode_hex_cases() {

assert_eq!(percent_decode("abc%3D123%26key"), "abc=123&key");

}

#[test]

fn decode_passthrough() {

assert_eq!(percent_decode("plain"), "plain");

}

}