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//! Provides the [Engine] abstraction and out of the box implementations.
#[cfg(any(feature = "alloc", feature = "std", test))]
use crate::chunked_encoder;
use crate::{
encode::{encode_with_padding, EncodeSliceError},
encoded_len, DecodeError, DecodeSliceError,
};
#[cfg(any(feature = "alloc", feature = "std", test))]
use alloc::vec::Vec;
#[cfg(any(feature = "alloc", feature = "std", test))]
use alloc::{string::String, vec};
pub mod general_purpose;
#[cfg(test)]
mod naive;
#[cfg(test)]
mod tests;
pub use general_purpose::{GeneralPurpose, GeneralPurposeConfig};
/// An `Engine` provides low-level encoding and decoding operations that all other higher-level parts of the API use. Users of the library will generally not need to implement this.
///
/// Different implementations offer different characteristics. The library currently ships with
/// [GeneralPurpose] that offers good speed and works on any CPU, with more choices
/// coming later, like a constant-time one when side channel resistance is called for, and vendor-specific vectorized ones for more speed.
///
/// See [general_purpose::STANDARD_NO_PAD] if you just want standard base64. Otherwise, when possible, it's
/// recommended to store the engine in a `const` so that references to it won't pose any lifetime
/// issues, and to avoid repeating the cost of engine setup.
///
/// Since almost nobody will need to implement `Engine`, docs for internal methods are hidden.
// When adding an implementation of Engine, include them in the engine test suite:
// - add an implementation of [engine::tests::EngineWrapper]
// - add the implementation to the `all_engines` macro
// All tests run on all engines listed in the macro.
pub trait Engine: Send + Sync {
/// The config type used by this engine
type Config: Config;
/// The decode estimate used by this engine
type DecodeEstimate: DecodeEstimate;
/// This is not meant to be called directly; it is only for `Engine` implementors.
/// See the other `encode*` functions on this trait.
///
/// Encode the `input` bytes into the `output` buffer based on the mapping in `encode_table`.
///
/// `output` will be long enough to hold the encoded data.
///
/// Returns the number of bytes written.
///
/// No padding should be written; that is handled separately.
///
/// Must not write any bytes into the output slice other than the encoded data.
#[doc(hidden)]
fn internal_encode(&self, input: &[u8], output: &mut [u8]) -> usize;
/// This is not meant to be called directly; it is only for `Engine` implementors.
///
/// As an optimization to prevent the decoded length from being calculated twice, it is
/// sometimes helpful to have a conservative estimate of the decoded size before doing the
/// decoding, so this calculation is done separately and passed to [Engine::decode()] as needed.
#[doc(hidden)]
fn internal_decoded_len_estimate(&self, input_len: usize) -> Self::DecodeEstimate;
/// This is not meant to be called directly; it is only for `Engine` implementors.
/// See the other `decode*` functions on this trait.
///
/// Decode `input` base64 bytes into the `output` buffer.
///
/// `decode_estimate` is the result of [Engine::internal_decoded_len_estimate()], which is passed in to avoid
/// calculating it again (expensive on short inputs).`
///
/// Each complete 4-byte chunk of encoded data decodes to 3 bytes of decoded data, but this
/// function must also handle the final possibly partial chunk.
/// If the input length is not a multiple of 4, or uses padding bytes to reach a multiple of 4,
/// the trailing 2 or 3 bytes must decode to 1 or 2 bytes, respectively, as per the
///
/// Decoding must not write any bytes into the output slice other than the decoded data.
///
/// Non-canonical trailing bits in the final tokens or non-canonical padding must be reported as
/// errors unless the engine is configured otherwise.
///
/// # Panics
///
/// Panics if `output` is too small.
#[doc(hidden)]
fn internal_decode(
&self,
input: &[u8],
output: &mut [u8],
decode_estimate: Self::DecodeEstimate,
) -> Result<DecodeMetadata, DecodeError>;
/// Returns the config for this engine.
fn config(&self) -> &Self::Config;
/// Encode arbitrary octets as base64 using the provided `Engine`.
/// Returns a `String`.
///
/// # Example
///
/// ```rust
/// use base64::{Engine as _, engine::{self, general_purpose}, alphabet};
///
/// let b64 = general_purpose::STANDARD.encode(b"hello world~");
/// println!("{}", b64);
///
/// const CUSTOM_ENGINE: engine::GeneralPurpose =
/// engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::NO_PAD);
///
/// let b64_url = CUSTOM_ENGINE.encode(b"hello internet~");
#[cfg(any(feature = "alloc", feature = "std", test))]
#[inline]
fn encode<T: AsRef<[u8]>>(&self, input: T) -> String {
fn inner<E>(engine: &E, input_bytes: &[u8]) -> String
where
E: Engine + ?Sized,
{
let encoded_size = encoded_len(input_bytes.len(), engine.config().encode_padding())
.expect("integer overflow when calculating buffer size");
let mut buf = vec![0; encoded_size];
encode_with_padding(input_bytes, &mut buf[..], engine, encoded_size);
String::from_utf8(buf).expect("Invalid UTF8")
}
inner(self, input.as_ref())
}
/// Encode arbitrary octets as base64 into a supplied `String`.
/// Writes into the supplied `String`, which may allocate if its internal buffer isn't big enough.
///
/// # Example
///
/// ```rust
/// use base64::{Engine as _, engine::{self, general_purpose}, alphabet};
/// const CUSTOM_ENGINE: engine::GeneralPurpose =
/// engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::NO_PAD);
///
/// fn main() {
/// let mut buf = String::new();
/// general_purpose::STANDARD.encode_string(b"hello world~", &mut buf);
/// println!("{}", buf);
///
/// buf.clear();
/// CUSTOM_ENGINE.encode_string(b"hello internet~", &mut buf);
/// println!("{}", buf);
/// }
/// ```
#[cfg(any(feature = "alloc", feature = "std", test))]
#[inline]
fn encode_string<T: AsRef<[u8]>>(&self, input: T, output_buf: &mut String) {
fn inner<E>(engine: &E, input_bytes: &[u8], output_buf: &mut String)
where
E: Engine + ?Sized,
{
let mut sink = chunked_encoder::StringSink::new(output_buf);
chunked_encoder::ChunkedEncoder::new(engine)
.encode(input_bytes, &mut sink)
.expect("Writing to a String shouldn't fail");
}
inner(self, input.as_ref(), output_buf)
}
/// Encode arbitrary octets as base64 into a supplied slice.
/// Writes into the supplied output buffer.
///
/// This is useful if you wish to avoid allocation entirely (e.g. encoding into a stack-resident
/// or statically-allocated buffer).
///
/// # Example
///
/// ```rust
/// use base64::{Engine as _, engine::general_purpose};
/// let s = b"hello internet!";
/// let mut buf = Vec::new();
/// // make sure we'll have a slice big enough for base64 + padding
/// buf.resize(s.len() * 4 / 3 + 4, 0);
///
/// let bytes_written = general_purpose::STANDARD.encode_slice(s, &mut buf).unwrap();
///
/// // shorten our vec down to just what was written
/// buf.truncate(bytes_written);
///
/// assert_eq!(s, general_purpose::STANDARD.decode(&buf).unwrap().as_slice());
/// ```
#[inline]
fn encode_slice<T: AsRef<[u8]>>(
&self,
input: T,
output_buf: &mut [u8],
) -> Result<usize, EncodeSliceError> {
fn inner<E>(
engine: &E,
input_bytes: &[u8],
output_buf: &mut [u8],
) -> Result<usize, EncodeSliceError>
where
E: Engine + ?Sized,
{
let encoded_size = encoded_len(input_bytes.len(), engine.config().encode_padding())
.expect("usize overflow when calculating buffer size");
if output_buf.len() < encoded_size {
return Err(EncodeSliceError::OutputSliceTooSmall);
}
let b64_output = &mut output_buf[0..encoded_size];
encode_with_padding(input_bytes, b64_output, engine, encoded_size);
Ok(encoded_size)
}
inner(self, input.as_ref(), output_buf)
}
/// Decode the input into a new `Vec`.
///
/// # Example
///
/// ```rust
/// use base64::{Engine as _, alphabet, engine::{self, general_purpose}};
///
/// let bytes = general_purpose::STANDARD
/// .decode("aGVsbG8gd29ybGR+Cg==").unwrap();
/// println!("{:?}", bytes);
///
/// // custom engine setup
/// let bytes_url = engine::GeneralPurpose::new(
/// &alphabet::URL_SAFE,
/// general_purpose::NO_PAD)
/// .decode("aGVsbG8gaW50ZXJuZXR-Cg").unwrap();
/// println!("{:?}", bytes_url);
/// ```
#[cfg(any(feature = "alloc", feature = "std", test))]
#[inline]
fn decode<T: AsRef<[u8]>>(&self, input: T) -> Result<Vec<u8>, DecodeError> {
fn inner<E>(engine: &E, input_bytes: &[u8]) -> Result<Vec<u8>, DecodeError>
where
E: Engine + ?Sized,
{
let estimate = engine.internal_decoded_len_estimate(input_bytes.len());
let mut buffer = vec![0; estimate.decoded_len_estimate()];
let bytes_written = engine
.internal_decode(input_bytes, &mut buffer, estimate)?
.decoded_len;
buffer.truncate(bytes_written);
Ok(buffer)
}
inner(self, input.as_ref())
}
/// Decode the `input` into the supplied `buffer`.
///
/// Writes into the supplied `Vec`, which may allocate if its internal buffer isn't big enough.
/// Returns a `Result` containing an empty tuple, aka `()`.
///
/// # Example
///
/// ```rust
/// use base64::{Engine as _, alphabet, engine::{self, general_purpose}};
/// const CUSTOM_ENGINE: engine::GeneralPurpose =
/// engine::GeneralPurpose::new(&alphabet::URL_SAFE, general_purpose::PAD);
///
/// fn main() {
/// use base64::Engine;
/// let mut buffer = Vec::<u8>::new();
/// // with the default engine
/// general_purpose::STANDARD
/// .decode_vec("aGVsbG8gd29ybGR+Cg==", &mut buffer,).unwrap();
/// println!("{:?}", buffer);
///
/// buffer.clear();
///
/// // with a custom engine
/// CUSTOM_ENGINE.decode_vec(
/// "aGVsbG8gaW50ZXJuZXR-Cg==",
/// &mut buffer,
/// ).unwrap();
/// println!("{:?}", buffer);
/// }
/// ```
#[cfg(any(feature = "alloc", feature = "std", test))]
#[inline]
fn decode_vec<T: AsRef<[u8]>>(
&self,
input: T,
buffer: &mut Vec<u8>,
) -> Result<(), DecodeError> {
fn inner<E>(engine: &E, input_bytes: &[u8], buffer: &mut Vec<u8>) -> Result<(), DecodeError>
where
E: Engine + ?Sized,
{
let starting_output_len = buffer.len();
let estimate = engine.internal_decoded_len_estimate(input_bytes.len());
let total_len_estimate = estimate
.decoded_len_estimate()
.checked_add(starting_output_len)
.expect("Overflow when calculating output buffer length");
buffer.resize(total_len_estimate, 0);
let buffer_slice = &mut buffer.as_mut_slice()[starting_output_len..];
let bytes_written = engine
.internal_decode(input_bytes, buffer_slice, estimate)?
.decoded_len;
buffer.truncate(starting_output_len + bytes_written);
Ok(())
}
inner(self, input.as_ref(), buffer)
}
/// Decode the input into the provided output slice.
///
/// Returns the number of bytes written to the slice, or an error if `output` is smaller than
/// the estimated decoded length.
///
/// This will not write any bytes past exactly what is decoded (no stray garbage bytes at the end).
///
/// See [crate::decoded_len_estimate] for calculating buffer sizes.
///
/// See [Engine::decode_slice_unchecked] for a version that panics instead of returning an error
/// if the output buffer is too small.
#[inline]
fn decode_slice<T: AsRef<[u8]>>(
&self,
input: T,
output: &mut [u8],
) -> Result<usize, DecodeSliceError> {
fn inner<E>(
engine: &E,
input_bytes: &[u8],
output: &mut [u8],
) -> Result<usize, DecodeSliceError>
where
E: Engine + ?Sized,
{
let estimate = engine.internal_decoded_len_estimate(input_bytes.len());
if output.len() < estimate.decoded_len_estimate() {
return Err(DecodeSliceError::OutputSliceTooSmall);
}
engine
.internal_decode(input_bytes, output, estimate)
.map_err(|e| e.into())
.map(|dm| dm.decoded_len)
}
inner(self, input.as_ref(), output)
}
/// Decode the input into the provided output slice.
///
/// Returns the number of bytes written to the slice.
///
/// This will not write any bytes past exactly what is decoded (no stray garbage bytes at the end).
///
/// See [crate::decoded_len_estimate] for calculating buffer sizes.
///
/// See [Engine::decode_slice] for a version that returns an error instead of panicking if the output
/// buffer is too small.
///
/// # Panics
///
/// Panics if the provided output buffer is too small for the decoded data.
#[inline]
fn decode_slice_unchecked<T: AsRef<[u8]>>(
&self,
input: T,
output: &mut [u8],
) -> Result<usize, DecodeError> {
fn inner<E>(engine: &E, input_bytes: &[u8], output: &mut [u8]) -> Result<usize, DecodeError>
where
E: Engine + ?Sized,
{
engine
.internal_decode(
input_bytes,
output,
engine.internal_decoded_len_estimate(input_bytes.len()),
)
.map(|dm| dm.decoded_len)
}
inner(self, input.as_ref(), output)
}
}
/// The minimal level of configuration that engines must support.
pub trait Config {
/// Returns `true` if padding should be added after the encoded output.
///
/// Padding is added outside the engine's encode() since the engine may be used
/// to encode only a chunk of the overall output, so it can't always know when
/// the output is "done" and would therefore need padding (if configured).
// It could be provided as a separate parameter when encoding, but that feels like
// leaking an implementation detail to the user, and it's hopefully more convenient
// to have to only pass one thing (the engine) to any part of the API.
fn encode_padding(&self) -> bool;
}
/// The decode estimate used by an engine implementation. Users do not need to interact with this;
/// it is only for engine implementors.
///
/// Implementors may store relevant data here when constructing this to avoid having to calculate
/// them again during actual decoding.
pub trait DecodeEstimate {
/// Returns a conservative (err on the side of too big) estimate of the decoded length to use
/// for pre-allocating buffers, etc.
///
/// The estimate must be no larger than the next largest complete triple of decoded bytes.
/// That is, the final quad of tokens to decode may be assumed to be complete with no padding.
fn decoded_len_estimate(&self) -> usize;
}
/// Controls how pad bytes are handled when decoding.
///
/// Each [Engine] must support at least the behavior indicated by
/// [DecodePaddingMode::RequireCanonical], and may support other modes.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum DecodePaddingMode {
/// Canonical padding is allowed, but any fewer padding bytes than that is also allowed.
Indifferent,
/// Padding must be canonical (0, 1, or 2 `=` as needed to produce a 4 byte suffix).
RequireCanonical,
/// Padding must be absent -- for when you want predictable padding, without any wasted bytes.
RequireNone,
}
/// Metadata about the result of a decode operation
#[derive(PartialEq, Eq, Debug)]
pub struct DecodeMetadata {
/// Number of decoded bytes output
pub(crate) decoded_len: usize,
/// Offset of the first padding byte in the input, if any
pub(crate) padding_offset: Option<usize>,
}
impl DecodeMetadata {
pub(crate) fn new(decoded_bytes: usize, padding_index: Option<usize>) -> Self {
Self {
decoded_len: decoded_bytes,
padding_offset: padding_index,
}
}
}