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//! Buffered Base64 encoder.
use crate::{
Encoding,
Error::{self, InvalidLength},
LineEnding, MIN_LINE_WIDTH,
};
use core::{cmp, marker::PhantomData, str};
#[cfg(feature = "std")]
use std::io;
#[cfg(doc)]
use crate::{Base64, Base64Unpadded};
/// Stateful Base64 encoder with support for buffered, incremental encoding.
///
/// The `E` type parameter can be any type which impls [`Encoding`] such as
/// [`Base64`] or [`Base64Unpadded`].
pub struct Encoder<'o, E: Encoding> {
/// Output buffer.
output: &'o mut [u8],
/// Cursor within the output buffer.
position: usize,
/// Block buffer used for non-block-aligned data.
block_buffer: BlockBuffer,
/// Configuration and state for line-wrapping the output at a specified
/// column.
line_wrapper: Option<LineWrapper>,
/// Phantom parameter for the Base64 encoding in use.
encoding: PhantomData<E>,
}
impl<'o, E: Encoding> Encoder<'o, E> {
/// Create a new encoder which writes output to the given byte slice.
///
/// Output constructed using this method is not line-wrapped.
pub fn new(output: &'o mut [u8]) -> Result<Self, Error> {
if output.is_empty() {
return Err(InvalidLength);
}
Ok(Self {
output,
position: 0,
block_buffer: BlockBuffer::default(),
line_wrapper: None,
encoding: PhantomData,
})
}
/// Create a new encoder which writes line-wrapped output to the given byte
/// slice.
///
/// Output will be wrapped at the specified interval, using the provided
/// line ending. Use [`LineEnding::default()`] to use the conventional line
/// ending for the target OS.
///
/// Minimum allowed line width is 4.
pub fn new_wrapped(
output: &'o mut [u8],
width: usize,
ending: LineEnding,
) -> Result<Self, Error> {
let mut encoder = Self::new(output)?;
encoder.line_wrapper = Some(LineWrapper::new(width, ending)?);
Ok(encoder)
}
/// Encode the provided buffer as Base64, writing it to the output buffer.
///
/// # Returns
/// - `Ok(bytes)` if the expected amount of data was read
/// - `Err(Error::InvalidLength)` if there is insufficient space in the output buffer
pub fn encode(&mut self, mut input: &[u8]) -> Result<(), Error> {
// If there's data in the block buffer, fill it
if !self.block_buffer.is_empty() {
self.process_buffer(&mut input)?;
}
while !input.is_empty() {
// Attempt to encode a stride of block-aligned data
let in_blocks = input.len() / 3;
let out_blocks = self.remaining().len() / 4;
let mut blocks = cmp::min(in_blocks, out_blocks);
// When line wrapping, cap the block-aligned stride at near/at line length
if let Some(line_wrapper) = &self.line_wrapper {
line_wrapper.wrap_blocks(&mut blocks)?;
}
if blocks > 0 {
let len = blocks.checked_mul(3).ok_or(InvalidLength)?;
let (in_aligned, in_rem) = input.split_at(len);
input = in_rem;
self.perform_encode(in_aligned)?;
}
// If there's remaining non-aligned data, fill the block buffer
if !input.is_empty() {
self.process_buffer(&mut input)?;
}
}
Ok(())
}
/// Get the position inside of the output buffer where the write cursor
/// is currently located.
pub fn position(&self) -> usize {
self.position
}
/// Finish encoding data, returning the resulting Base64 as a `str`.
pub fn finish(self) -> Result<&'o str, Error> {
self.finish_with_remaining().map(|(base64, _)| base64)
}
/// Finish encoding data, returning the resulting Base64 as a `str`
/// along with the remaining space in the output buffer.
pub fn finish_with_remaining(mut self) -> Result<(&'o str, &'o mut [u8]), Error> {
if !self.block_buffer.is_empty() {
let buffer_len = self.block_buffer.position;
let block = self.block_buffer.bytes;
self.perform_encode(&block[..buffer_len])?;
}
let (base64, remaining) = self.output.split_at_mut(self.position);
Ok((str::from_utf8(base64)?, remaining))
}
/// Borrow the remaining data in the buffer.
fn remaining(&mut self) -> &mut [u8] {
&mut self.output[self.position..]
}
/// Fill the block buffer with data, consuming and encoding it when the
/// buffer is full.
fn process_buffer(&mut self, input: &mut &[u8]) -> Result<(), Error> {
self.block_buffer.fill(input)?;
if self.block_buffer.is_full() {
let block = self.block_buffer.take();
self.perform_encode(&block)?;
}
Ok(())
}
/// Perform Base64 encoding operation.
fn perform_encode(&mut self, input: &[u8]) -> Result<usize, Error> {
let mut len = E::encode(input, self.remaining())?.as_bytes().len();
// Insert newline characters into the output as needed
if let Some(line_wrapper) = &mut self.line_wrapper {
line_wrapper.insert_newlines(&mut self.output[self.position..], &mut len)?;
}
self.position = self.position.checked_add(len).ok_or(InvalidLength)?;
Ok(len)
}
}
#[cfg(feature = "std")]
impl<'o, E: Encoding> io::Write for Encoder<'o, E> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
self.encode(buf)?;
Ok(buf.len())
}
fn flush(&mut self) -> io::Result<()> {
// TODO(tarcieri): return an error if there's still data remaining in the buffer?
Ok(())
}
}
/// Base64 encode buffer for a 1-block output.
///
/// This handles a partial block of data, i.e. data which hasn't been
#[derive(Clone, Default, Debug)]
struct BlockBuffer {
/// 3 decoded bytes to be encoded to a 4-byte Base64-encoded input.
bytes: [u8; Self::SIZE],
/// Position within the buffer.
position: usize,
}
impl BlockBuffer {
/// Size of the buffer in bytes: 3-bytes of unencoded input which
/// Base64 encode to 4-bytes of output.
const SIZE: usize = 3;
/// Fill the remaining space in the buffer with the input data.
fn fill(&mut self, input: &mut &[u8]) -> Result<(), Error> {
let remaining = Self::SIZE.checked_sub(self.position).ok_or(InvalidLength)?;
let len = cmp::min(input.len(), remaining);
self.bytes[self.position..][..len].copy_from_slice(&input[..len]);
self.position = self.position.checked_add(len).ok_or(InvalidLength)?;
*input = &input[len..];
Ok(())
}
/// Take the output buffer, resetting the position to 0.
fn take(&mut self) -> [u8; Self::SIZE] {
debug_assert!(self.is_full());
let result = self.bytes;
*self = Default::default();
result
}
/// Is the buffer empty?
fn is_empty(&self) -> bool {
self.position == 0
}
/// Is the buffer full?
fn is_full(&self) -> bool {
self.position == Self::SIZE
}
}
/// Helper for wrapping Base64 at a given line width.
#[derive(Debug)]
struct LineWrapper {
/// Number of bytes remaining in the current line.
remaining: usize,
/// Column at which Base64 should be wrapped.
width: usize,
/// Newline characters to use at the end of each line.
ending: LineEnding,
}
impl LineWrapper {
/// Create a new linewrapper.
fn new(width: usize, ending: LineEnding) -> Result<Self, Error> {
if width < MIN_LINE_WIDTH {
return Err(InvalidLength);
}
Ok(Self {
remaining: width,
width,
ending,
})
}
/// Wrap the number of blocks to encode near/at EOL.
fn wrap_blocks(&self, blocks: &mut usize) -> Result<(), Error> {
if blocks.checked_mul(4).ok_or(InvalidLength)? >= self.remaining {
*blocks = self.remaining / 4;
}
Ok(())
}
/// Insert newlines into the output buffer as needed.
fn insert_newlines(&mut self, mut buffer: &mut [u8], len: &mut usize) -> Result<(), Error> {
let mut buffer_len = *len;
if buffer_len <= self.remaining {
self.remaining = self
.remaining
.checked_sub(buffer_len)
.ok_or(InvalidLength)?;
return Ok(());
}
buffer = &mut buffer[self.remaining..];
buffer_len = buffer_len
.checked_sub(self.remaining)
.ok_or(InvalidLength)?;
// The `wrap_blocks` function should ensure the buffer is no larger than a Base64 block
debug_assert!(buffer_len <= 4, "buffer too long: {}", buffer_len);
// Ensure space in buffer to add newlines
let buffer_end = buffer_len
.checked_add(self.ending.len())
.ok_or(InvalidLength)?;
if buffer_end >= buffer.len() {
return Err(InvalidLength);
}
// Shift the buffer contents to make space for the line ending
for i in (0..buffer_len).rev() {
buffer[i.checked_add(self.ending.len()).ok_or(InvalidLength)?] = buffer[i];
}
buffer[..self.ending.len()].copy_from_slice(self.ending.as_bytes());
*len = (*len).checked_add(self.ending.len()).ok_or(InvalidLength)?;
self.remaining = self.width.checked_sub(buffer_len).ok_or(InvalidLength)?;
Ok(())
}
}
#[cfg(test)]
mod tests {
use crate::{alphabet::Alphabet, test_vectors::*, Base64, Base64Unpadded, Encoder, LineEnding};
#[test]
fn encode_padded() {
encode_test::<Base64>(PADDED_BIN, PADDED_BASE64, None);
}
#[test]
fn encode_unpadded() {
encode_test::<Base64Unpadded>(UNPADDED_BIN, UNPADDED_BASE64, None);
}
#[test]
fn encode_multiline_padded() {
encode_test::<Base64>(MULTILINE_PADDED_BIN, MULTILINE_PADDED_BASE64, Some(70));
}
#[test]
fn encode_multiline_unpadded() {
encode_test::<Base64Unpadded>(MULTILINE_UNPADDED_BIN, MULTILINE_UNPADDED_BASE64, Some(70));
}
#[test]
fn no_trailing_newline_when_aligned() {
let mut buffer = [0u8; 64];
let mut encoder = Encoder::<Base64>::new_wrapped(&mut buffer, 64, LineEnding::LF).unwrap();
encoder.encode(&[0u8; 48]).unwrap();
// Ensure no newline character is present in this case
assert_eq!(
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
encoder.finish().unwrap()
);
}
/// Core functionality of an encoding test.
fn encode_test<V: Alphabet>(input: &[u8], expected: &str, wrapped: Option<usize>) {
let mut buffer = [0u8; 1024];
for chunk_size in 1..input.len() {
let mut encoder = match wrapped {
Some(line_width) => {
Encoder::<V>::new_wrapped(&mut buffer, line_width, LineEnding::LF)
}
None => Encoder::<V>::new(&mut buffer),
}
.unwrap();
for chunk in input.chunks(chunk_size) {
encoder.encode(chunk).unwrap();
}
assert_eq!(expected, encoder.finish().unwrap());
}
}
}