use crate::encode::encode_to_slice;
use crate::{encode_config_slice, Config};
use std::{
cmp, fmt,
io::{ErrorKind, Result, Write},
};
pub(crate) const BUF_SIZE: usize = 1024;
/// The most bytes whose encoding will fit in `BUF_SIZE`
const MAX_INPUT_LEN: usize = BUF_SIZE / 4 * 3;
// 3 bytes of input = 4 bytes of base64, always (because we don't allow line wrapping)
const MIN_ENCODE_CHUNK_SIZE: usize = 3;
/// A `Write` implementation that base64 encodes data before delegating to the wrapped writer.
///
/// Because base64 has special handling for the end of the input data (padding, etc), there's a
/// `finish()` method on this type that encodes any leftover input bytes and adds padding if
/// appropriate. It's called automatically when deallocated (see the `Drop` implementation), but
/// any error that occurs when invoking the underlying writer will be suppressed. If you want to
/// handle such errors, call `finish()` yourself.
///
/// # Examples
///
/// ```
/// use std::io::Write;
///
/// // use a vec as the simplest possible `Write` -- in real code this is probably a file, etc.
/// let mut enc = base64::write::EncoderWriter::new(Vec::new(), base64::STANDARD);
///
/// // handle errors as you normally would
/// enc.write_all(b"asdf").unwrap();
///
/// // could leave this out to be called by Drop, if you don't care
/// // about handling errors or getting the delegate writer back
/// let delegate = enc.finish().unwrap();
///
/// // base64 was written to the writer
/// assert_eq!(b"YXNkZg==", &delegate[..]);
///
/// ```
///
/// # Panics
///
/// Calling `write()` (or related methods) or `finish()` after `finish()` has completed without
/// error is invalid and will panic.
///
/// # Errors
///
/// Base64 encoding itself does not generate errors, but errors from the wrapped writer will be
/// returned as per the contract of `Write`.
///
/// # Performance
///
/// It has some minor performance loss compared to encoding slices (a couple percent).
/// It does not do any heap allocation.
pub struct EncoderWriter<W: Write> {
config: Config,
/// Where encoded data is written to. It's an Option as it's None immediately before Drop is
/// called so that finish() can return the underlying writer. None implies that finish() has
/// been called successfully.
delegate: Option<W>,
/// Holds a partial chunk, if any, after the last `write()`, so that we may then fill the chunk
/// with the next `write()`, encode it, then proceed with the rest of the input normally.
extra_input: [u8; MIN_ENCODE_CHUNK_SIZE],
/// How much of `extra` is occupied, in `[0, MIN_ENCODE_CHUNK_SIZE]`.
extra_input_occupied_len: usize,
/// Buffer to encode into. May hold leftover encoded bytes from a previous write call that the underlying writer
/// did not write last time.
output: [u8; BUF_SIZE],
/// How much of `output` is occupied with encoded data that couldn't be written last time
output_occupied_len: usize,
/// panic safety: don't write again in destructor if writer panicked while we were writing to it
panicked: bool,
}
impl<W: Write> fmt::Debug for EncoderWriter<W> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
"extra_input: {:?} extra_input_occupied_len:{:?} output[..5]: {:?} output_occupied_len: {:?}",
self.extra_input,
self.extra_input_occupied_len,
&self.output[0..5],
self.output_occupied_len
)
}
}
impl<W: Write> EncoderWriter<W> {
/// Create a new encoder that will write to the provided delegate writer `w`.
pub fn new(w: W, config: Config) -> EncoderWriter<W> {
EncoderWriter {
config,
delegate: Some(w),
extra_input: [0u8; MIN_ENCODE_CHUNK_SIZE],
extra_input_occupied_len: 0,
output: [0u8; BUF_SIZE],
output_occupied_len: 0,
panicked: false,
}
}
/// Encode all remaining buffered data and write it, including any trailing incomplete input
/// triples and associated padding.
///
/// Once this succeeds, no further writes or calls to this method are allowed.
///
/// This may write to the delegate writer multiple times if the delegate writer does not accept
/// all input provided to its `write` each invocation.
///
/// If you don't care about error handling, it is not necessary to call this function, as the
/// equivalent finalization is done by the Drop impl.
///
/// Returns the writer that this was constructed around.
///
/// # Errors
///
/// The first error that is not of `ErrorKind::Interrupted` will be returned.
pub fn finish(&mut self) -> Result<W> {
// If we could consume self in finish(), we wouldn't have to worry about this case, but
// finish() is retryable in the face of I/O errors, so we can't consume here.
if self.delegate.is_none() {
panic!("Encoder has already had finish() called")
};
self.write_final_leftovers()?;
let writer = self.delegate.take().expect("Writer must be present");
Ok(writer)
}
/// Write any remaining buffered data to the delegate writer.
fn write_final_leftovers(&mut self) -> Result<()> {
if self.delegate.is_none() {
// finish() has already successfully called this, and we are now in drop() with a None
// writer, so just no-op
return Ok(());
}
self.write_all_encoded_output()?;
if self.extra_input_occupied_len > 0 {
let encoded_len = encode_config_slice(
&self.extra_input[..self.extra_input_occupied_len],
self.config,
&mut self.output[..],
);
self.output_occupied_len = encoded_len;
self.write_all_encoded_output()?;
// write succeeded, do not write the encoding of extra again if finish() is retried
self.extra_input_occupied_len = 0;
}
Ok(())
}
/// Write as much of the encoded output to the delegate writer as it will accept, and store the
/// leftovers to be attempted at the next write() call. Updates `self.output_occupied_len`.
///
/// # Errors
///
/// Errors from the delegate writer are returned. In the case of an error,
/// `self.output_occupied_len` will not be updated, as errors from `write` are specified to mean
/// that no write took place.
fn write_to_delegate(&mut self, current_output_len: usize) -> Result<()> {
self.panicked = true;
let res = self
.delegate
.as_mut()
.expect("Writer must be present")
.write(&self.output[..current_output_len]);
self.panicked = false;
res.map(|consumed| {
debug_assert!(consumed <= current_output_len);
if consumed < current_output_len {
self.output_occupied_len = current_output_len.checked_sub(consumed).unwrap();
// If we're blocking on I/O, the minor inefficiency of copying bytes to the
// start of the buffer is the least of our concerns...
// Rotate moves more than we need to, but copy_within isn't stabilized yet.
self.output.rotate_left(consumed);
} else {
self.output_occupied_len = 0;
}
})
}
/// Write all buffered encoded output. If this returns `Ok`, `self.output_occupied_len` is `0`.
///
/// This is basically write_all for the remaining buffered data but without the undesirable
/// abort-on-`Ok(0)` behavior.
///
/// # Errors
///
/// Any error emitted by the delegate writer abort the write loop and is returned, unless it's
/// `Interrupted`, in which case the error is ignored and writes will continue.
fn write_all_encoded_output(&mut self) -> Result<()> {
while self.output_occupied_len > 0 {
let remaining_len = self.output_occupied_len;
match self.write_to_delegate(remaining_len) {
// try again on interrupts ala write_all
Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
// other errors return
Err(e) => return Err(e),
// success no-ops because remaining length is already updated
Ok(_) => {}
};
}
debug_assert_eq!(0, self.output_occupied_len);
Ok(())
}
}
impl<W: Write> Write for EncoderWriter<W> {
/// Encode input and then write to the delegate writer.
///
/// Under non-error circumstances, this returns `Ok` with the value being the number of bytes
/// of `input` consumed. The value may be `0`, which interacts poorly with `write_all`, which
/// interprets `Ok(0)` as an error, despite it being allowed by the contract of `write`. See
/// <https://github.com/rust-lang/rust/issues/56889> for more on that.
///
/// If the previous call to `write` provided more (encoded) data than the delegate writer could
/// accept in a single call to its `write`, the remaining data is buffered. As long as buffered
/// data is present, subsequent calls to `write` will try to write the remaining buffered data
/// to the delegate and return either `Ok(0)` -- and therefore not consume any of `input` -- or
/// an error.
///
/// # Errors
///
/// Any errors emitted by the delegate writer are returned.
fn write(&mut self, input: &[u8]) -> Result<usize> {
if self.delegate.is_none() {
panic!("Cannot write more after calling finish()");
}
if input.is_empty() {
return Ok(0);
}
// The contract of `Write::write` places some constraints on this implementation:
// - a call to `write()` represents at most one call to a wrapped `Write`, so we can't
// iterate over the input and encode multiple chunks.
// - Errors mean that "no bytes were written to this writer", so we need to reset the
// internal state to what it was before the error occurred
// before reading any input, write any leftover encoded output from last time
if self.output_occupied_len > 0 {
let current_len = self.output_occupied_len;
return self
.write_to_delegate(current_len)
// did not read any input
.map(|_| 0);
}
debug_assert_eq!(0, self.output_occupied_len);
// how many bytes, if any, were read into `extra` to create a triple to encode
let mut extra_input_read_len = 0;
let mut input = input;
let orig_extra_len = self.extra_input_occupied_len;
let mut encoded_size = 0;
// always a multiple of MIN_ENCODE_CHUNK_SIZE
let mut max_input_len = MAX_INPUT_LEN;
// process leftover un-encoded input from last write
if self.extra_input_occupied_len > 0 {
debug_assert!(self.extra_input_occupied_len < 3);
if input.len() + self.extra_input_occupied_len >= MIN_ENCODE_CHUNK_SIZE {
// Fill up `extra`, encode that into `output`, and consume as much of the rest of
// `input` as possible.
// We could write just the encoding of `extra` by itself but then we'd have to
// return after writing only 4 bytes, which is inefficient if the underlying writer
// would make a syscall.
extra_input_read_len = MIN_ENCODE_CHUNK_SIZE - self.extra_input_occupied_len;
debug_assert!(extra_input_read_len > 0);
// overwrite only bytes that weren't already used. If we need to rollback extra_len
// (when the subsequent write errors), the old leading bytes will still be there.
self.extra_input[self.extra_input_occupied_len..MIN_ENCODE_CHUNK_SIZE]
.copy_from_slice(&input[0..extra_input_read_len]);
let len = encode_to_slice(
&self.extra_input[0..MIN_ENCODE_CHUNK_SIZE],
&mut self.output[..],
self.config.char_set.encode_table(),
);
debug_assert_eq!(4, len);
input = &input[extra_input_read_len..];
// consider extra to be used up, since we encoded it
self.extra_input_occupied_len = 0;
// don't clobber where we just encoded to
encoded_size = 4;
// and don't read more than can be encoded
max_input_len = MAX_INPUT_LEN - MIN_ENCODE_CHUNK_SIZE;
// fall through to normal encoding
} else {
// `extra` and `input` are non empty, but `|extra| + |input| < 3`, so there must be
// 1 byte in each.
debug_assert_eq!(1, input.len());
debug_assert_eq!(1, self.extra_input_occupied_len);
self.extra_input[self.extra_input_occupied_len] = input[0];
self.extra_input_occupied_len += 1;
return Ok(1);
};
} else if input.len() < MIN_ENCODE_CHUNK_SIZE {
// `extra` is empty, and `input` fits inside it
self.extra_input[0..input.len()].copy_from_slice(input);
self.extra_input_occupied_len = input.len();
return Ok(input.len());
};
// either 0 or 1 complete chunks encoded from extra
debug_assert!(encoded_size == 0 || encoded_size == 4);
debug_assert!(
// didn't encode extra input
MAX_INPUT_LEN == max_input_len
// encoded one triple
|| MAX_INPUT_LEN == max_input_len + MIN_ENCODE_CHUNK_SIZE
);
// encode complete triples only
let input_complete_chunks_len = input.len() - (input.len() % MIN_ENCODE_CHUNK_SIZE);
let input_chunks_to_encode_len = cmp::min(input_complete_chunks_len, max_input_len);
debug_assert_eq!(0, max_input_len % MIN_ENCODE_CHUNK_SIZE);
debug_assert_eq!(0, input_chunks_to_encode_len % MIN_ENCODE_CHUNK_SIZE);
encoded_size += encode_to_slice(
&input[..(input_chunks_to_encode_len)],
&mut self.output[encoded_size..],
self.config.char_set.encode_table(),
);
// not updating `self.output_occupied_len` here because if the below write fails, it should
// "never take place" -- the buffer contents we encoded are ignored and perhaps retried
// later, if the consumer chooses.
self.write_to_delegate(encoded_size)
// no matter whether we wrote the full encoded buffer or not, we consumed the same
// input
.map(|_| extra_input_read_len + input_chunks_to_encode_len)
.map_err(|e| {
// in case we filled and encoded `extra`, reset extra_len
self.extra_input_occupied_len = orig_extra_len;
e
})
}
/// Because this is usually treated as OK to call multiple times, it will *not* flush any
/// incomplete chunks of input or write padding.
/// # Errors
///
/// The first error that is not of [`ErrorKind::Interrupted`] will be returned.
fn flush(&mut self) -> Result<()> {
self.write_all_encoded_output()?;
self.delegate
.as_mut()
.expect("Writer must be present")
.flush()
}
}
impl<W: Write> Drop for EncoderWriter<W> {
fn drop(&mut self) {
if !self.panicked {
// like `BufWriter`, ignore errors during drop
let _ = self.write_final_leftovers();
}
}
}
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