module hex import strings // decode converts a hex string into an array of bytes. The expected // input format is 2 ASCII characters for each output byte. If the provided // string length is not a multiple of 2, an implicit `0` is prepended to it. pub fn decode(s string) ?[]u8 { mut hex_str := s if hex_str.len >= 2 { if s[0] == `0` && (s[1] == `x` || s[1] == `X`) { hex_str = s[2..] } } if hex_str.len == 0 { return []u8{} } else if hex_str.len == 1 { return [char2nibble(hex_str[0]) ?] } else if hex_str.len == 2 { n1 := char2nibble(hex_str[0]) ? n0 := char2nibble(hex_str[1]) ? return [(n1 << 4) | n0] } // calculate the first byte depending on if hex_str.len is odd mut val := char2nibble(hex_str[0]) ? if hex_str.len & 1 == 0 { val = (val << 4) | char2nibble(hex_str[1]) ? } // set cap to hex_str.len/2 rounded up mut bytes := []u8{len: 1, cap: (hex_str.len + 1) >> 1, init: val} // iterate over every 2 bytes // the start index depends on if hex_str.len is odd for i := 2 - (hex_str.len & 1); i < hex_str.len; i += 2 { n1 := char2nibble(hex_str[i]) ? n0 := char2nibble(hex_str[i + 1]) ? bytes << (n1 << 4) | n0 } return bytes } // encode converts an array of bytes into a string of ASCII hex bytes. The // output will always be a string with length a multiple of 2. [manualfree] pub fn encode(bytes []u8) string { mut sb := strings.new_builder(bytes.len * 2) for b in bytes { sb.write_string(b.hex()) } res := sb.str() unsafe { sb.free() } return res } // char2nibble converts an ASCII hex character to it's hex value fn char2nibble(b u8) ?u8 { match b { `0`...`9` { return b - u8(`0`) } `A`...`F` { return b - u8(`A`) + 10 } `a`...`f` { return b - u8(`a`) + 10 } else { return error('invalid hex char $b.ascii_str()') } } }