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//! Provides [Alphabet] and constants for alphabets commonly used in the wild.
use crate::PAD_BYTE;
use core::{convert, fmt};
#[cfg(any(feature = "std", test))]
use std::error;
const ALPHABET_SIZE: usize = 64;
/// An alphabet defines the 64 ASCII characters (symbols) used for base64.
///
/// Common alphabets are provided as constants, and custom alphabets
/// can be made via `from_str` or the `TryFrom<str>` implementation.
///
/// # Examples
///
/// Building and using a custom Alphabet:
///
/// ```
/// let custom = base64::alphabet::Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/").unwrap();
///
/// let engine = base64::engine::GeneralPurpose::new(
/// &custom,
/// base64::engine::general_purpose::PAD);
/// ```
///
/// Building a const:
///
/// ```
/// use base64::alphabet::Alphabet;
///
/// static CUSTOM: Alphabet = {
/// // Result::unwrap() isn't const yet, but panic!() is OK
/// match Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/") {
/// Ok(x) => x,
/// Err(_) => panic!("creation of alphabet failed"),
/// }
/// };
/// ```
///
/// Building a lazy_static:
///
/// ```
/// use base64::{
/// alphabet::Alphabet,
/// engine::{general_purpose::GeneralPurpose, GeneralPurposeConfig},
/// };
///
/// lazy_static::lazy_static! {
/// static ref CUSTOM: Alphabet = Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/").unwrap();
/// }
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Alphabet {
pub(crate) symbols: [u8; ALPHABET_SIZE],
}
impl Alphabet {
/// Performs no checks so that it can be const.
/// Used only for known-valid strings.
const fn from_str_unchecked(alphabet: &str) -> Self {
let mut symbols = [0_u8; ALPHABET_SIZE];
let source_bytes = alphabet.as_bytes();
// a way to copy that's allowed in const fn
let mut index = 0;
while index < ALPHABET_SIZE {
symbols[index] = source_bytes[index];
index += 1;
}
Self { symbols }
}
/// Create an `Alphabet` from a string of 64 unique printable ASCII bytes.
///
/// The `=` byte is not allowed as it is used for padding.
pub const fn new(alphabet: &str) -> Result<Self, ParseAlphabetError> {
let bytes = alphabet.as_bytes();
if bytes.len() != ALPHABET_SIZE {
return Err(ParseAlphabetError::InvalidLength);
}
{
let mut index = 0;
while index < ALPHABET_SIZE {
let byte = bytes[index];
// must be ascii printable. 127 (DEL) is commonly considered printable
// for some reason but clearly unsuitable for base64.
if !(byte >= 32_u8 && byte <= 126_u8) {
return Err(ParseAlphabetError::UnprintableByte(byte));
}
// = is assumed to be padding, so cannot be used as a symbol
if byte == PAD_BYTE {
return Err(ParseAlphabetError::ReservedByte(byte));
}
// Check for duplicates while staying within what const allows.
// It's n^2, but only over 64 hot bytes, and only once, so it's likely in the single digit
// microsecond range.
let mut probe_index = 0;
while probe_index < ALPHABET_SIZE {
if probe_index == index {
probe_index += 1;
continue;
}
let probe_byte = bytes[probe_index];
if byte == probe_byte {
return Err(ParseAlphabetError::DuplicatedByte(byte));
}
probe_index += 1;
}
index += 1;
}
}
Ok(Self::from_str_unchecked(alphabet))
}
}
impl convert::TryFrom<&str> for Alphabet {
type Error = ParseAlphabetError;
fn try_from(value: &str) -> Result<Self, Self::Error> {
Self::new(value)
}
}
/// Possible errors when constructing an [Alphabet] from a `str`.
#[derive(Debug, Eq, PartialEq)]
pub enum ParseAlphabetError {
/// Alphabets must be 64 ASCII bytes
InvalidLength,
/// All bytes must be unique
DuplicatedByte(u8),
/// All bytes must be printable (in the range `[32, 126]`).
UnprintableByte(u8),
/// `=` cannot be used
ReservedByte(u8),
}
impl fmt::Display for ParseAlphabetError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Self::InvalidLength => write!(f, "Invalid length - must be 64 bytes"),
Self::DuplicatedByte(b) => write!(f, "Duplicated byte: {:#04x}", b),
Self::UnprintableByte(b) => write!(f, "Unprintable byte: {:#04x}", b),
Self::ReservedByte(b) => write!(f, "Reserved byte: {:#04x}", b),
}
}
}
#[cfg(any(feature = "std", test))]
impl error::Error for ParseAlphabetError {}
/// The standard alphabet (uses `+` and `/`).
///
pub const STANDARD: Alphabet = Alphabet::from_str_unchecked(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
);
/// The URL safe alphabet (uses `-` and `_`).
///
pub const URL_SAFE: Alphabet = Alphabet::from_str_unchecked(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
);
/// The `crypt(3)` alphabet (uses `.` and `/` as the first two values).
///
/// Not standardized, but folk wisdom on the net asserts that this alphabet is what crypt uses.
pub const CRYPT: Alphabet = Alphabet::from_str_unchecked(
"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz",
);
/// The bcrypt alphabet.
pub const BCRYPT: Alphabet = Alphabet::from_str_unchecked(
"./ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",
);
/// The alphabet used in IMAP-modified UTF-7 (uses `+` and `,`).
///
pub const IMAP_MUTF7: Alphabet = Alphabet::from_str_unchecked(
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,",
);
/// The alphabet used in BinHex 4.0 files.
///
pub const BIN_HEX: Alphabet = Alphabet::from_str_unchecked(
"!\"#$%&'()*+,-0123456789@ABCDEFGHIJKLMNPQRSTUVXYZ[`abcdehijklmpqr",
);
#[cfg(test)]
mod tests {
use crate::alphabet::*;
use core::convert::TryFrom as _;
#[test]
fn detects_duplicate_start() {
assert_eq!(
ParseAlphabetError::DuplicatedByte(b'A'),
Alphabet::new("AACDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
.unwrap_err()
);
}
#[test]
fn detects_duplicate_end() {
assert_eq!(
ParseAlphabetError::DuplicatedByte(b'/'),
Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789//")
.unwrap_err()
);
}
#[test]
fn detects_duplicate_middle() {
assert_eq!(
ParseAlphabetError::DuplicatedByte(b'Z'),
Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZZbcdefghijklmnopqrstuvwxyz0123456789+/")
.unwrap_err()
);
}
#[test]
fn detects_length() {
assert_eq!(
ParseAlphabetError::InvalidLength,
Alphabet::new(
"xxxxxxxxxABCDEFGHIJKLMNOPQRSTUVWXYZZbcdefghijklmnopqrstuvwxyz0123456789+/",
)
.unwrap_err()
);
}
#[test]
fn detects_padding() {
assert_eq!(
ParseAlphabetError::ReservedByte(b'='),
Alphabet::new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+=")
.unwrap_err()
);
}
#[test]
fn detects_unprintable() {
// form feed
assert_eq!(
ParseAlphabetError::UnprintableByte(0xc),
Alphabet::new("\x0cBCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
.unwrap_err()
);
}
#[test]
fn same_as_unchecked() {
assert_eq!(
STANDARD,
Alphabet::try_from("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
.unwrap()
);
}
}