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use std::io::{self, Write};
use crate::stream::raw::{InBuffer, Operation, OutBuffer};
// input -> [ zstd -> buffer -> writer ]
/// Implements the [`Write`] API around an [`Operation`].
///
/// This can be used to wrap a raw in-memory operation in a write-focused API.
///
/// It can be used with either compression or decompression, and forwards the
/// output to a wrapped `Write`.
pub struct Writer<W, D> {
writer: W,
operation: D,
offset: usize,
buffer: Vec<u8>,
// When `true`, indicates that nothing should be added to the buffer.
// All that's left if to empty the buffer.
finished: bool,
finished_frame: bool,
}
impl<W, D> Writer<W, D>
where
W: Write,
D: Operation,
{
/// Creates a new `Writer`.
///
/// All output from the given operation will be forwarded to `writer`.
pub fn new(writer: W, operation: D) -> Self {
Writer {
writer,
operation,
offset: 0,
// 32KB buffer? That's what flate2 uses
buffer: Vec::with_capacity(32 * 1024),
finished: false,
finished_frame: false,
}
}
/// Ends the stream.
///
/// This *must* be called after all data has been written to finish the
/// stream.
///
/// If you forget to call this and just drop the `Writer`, you *will* have
/// an incomplete output.
///
/// Keep calling it until it returns `Ok(())`, then don't call it again.
pub fn finish(&mut self) -> io::Result<()> {
loop {
// Keep trying until we're really done.
self.write_from_offset()?;
// At this point the buffer has been fully written out.
if self.finished {
return Ok(());
}
// Let's fill this buffer again!
let finished_frame = self.finished_frame;
let hint =
self.with_buffer(|dst, op| op.finish(dst, finished_frame));
self.offset = 0;
// println!("Hint: {:?}\nOut:{:?}", hint, &self.buffer);
// We return here if zstd had a problem.
// Could happen with invalid data, ...
let hint = hint?;
if hint != 0 && self.buffer.is_empty() {
// This happens if we are decoding an incomplete frame.
return Err(io::Error::new(
io::ErrorKind::UnexpectedEof,
"incomplete frame",
));
}
// println!("Finishing {}, {}", bytes_written, hint);
self.finished = hint == 0;
}
}
/// Run the given closure on `self.buffer`.
///
/// The buffer will be cleared, and made available wrapped in an `OutBuffer`.
fn with_buffer<F, T>(&mut self, f: F) -> T
where
F: FnOnce(&mut OutBuffer<'_, Vec<u8>>, &mut D) -> T,
{
self.buffer.clear();
let mut output = OutBuffer::around(&mut self.buffer);
// eprintln!("Output: {:?}", output);
f(&mut output, &mut self.operation)
}
/// Attempt to write `self.buffer` to the wrapped writer.
///
/// Returns `Ok(())` once all the buffer has been written.
fn write_from_offset(&mut self) -> io::Result<()> {
// The code looks a lot like `write_all`, but keeps track of what has
// been written in case we're interrupted.
while self.offset < self.buffer.len() {
match self.writer.write(&self.buffer[self.offset..]) {
Ok(0) => {
return Err(io::Error::new(
io::ErrorKind::WriteZero,
"writer will not accept any more data",
))
}
Ok(n) => self.offset += n,
Err(ref e) if e.kind() == io::ErrorKind::Interrupted => (),
Err(e) => return Err(e),
}
}
Ok(())
}
/// Return the wrapped `Writer` and `Operation`.
///
/// Careful: if you call this before calling [`Writer::finish()`], the
/// output may be incomplete.
pub fn into_inner(self) -> (W, D) {
(self.writer, self.operation)
}
/// Gives a reference to the inner writer.
pub fn writer(&self) -> &W {
&self.writer
}
/// Gives a mutable reference to the inner writer.
pub fn writer_mut(&mut self) -> &mut W {
&mut self.writer
}
/// Gives a reference to the inner operation.
pub fn operation(&self) -> &D {
&self.operation
}
/// Gives a mutable reference to the inner operation.
pub fn operation_mut(&mut self) -> &mut D {
&mut self.operation
}
/// Returns the offset in the current buffer. Only useful for debugging.
#[cfg(test)]
pub fn offset(&self) -> usize {
self.offset
}
/// Returns the current buffer. Only useful for debugging.
#[cfg(test)]
pub fn buffer(&self) -> &[u8] {
&self.buffer
}
}
impl<W, D> Write for Writer<W, D>
where
W: Write,
D: Operation,
{
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
// Keep trying until _something_ has been consumed.
// As soon as some input has been taken, we cannot afford
// to take any chance: if an error occurs, the user couldn't know
// that some data _was_ successfully written.
loop {
// First, write any pending data from `self.buffer`.
self.write_from_offset()?;
// At this point `self.buffer` can safely be discarded.
// Support writing concatenated frames by re-initializing the
// context.
if self.finished_frame {
self.operation.reinit()?;
self.finished_frame = false;
}
let mut src = InBuffer::around(buf);
let hint = self.with_buffer(|dst, op| op.run(&mut src, dst));
let bytes_read = src.pos;
// eprintln!(
// "Write Hint: {:?}\n src: {:?}\n dst: {:?}",
// hint, src, self.buffer
// );
self.offset = 0;
let hint = hint?;
if hint == 0 {
self.finished_frame = true;
}
// As we said, as soon as we've consumed something, return.
if bytes_read > 0 || buf.is_empty() {
// println!("Returning {}", bytes_read);
return Ok(bytes_read);
}
}
}
fn flush(&mut self) -> io::Result<()> {
let mut finished = self.finished;
loop {
// If the output is blocked or has an error, return now.
self.write_from_offset()?;
if finished {
break;
}
let hint = self.with_buffer(|dst, op| op.flush(dst));
self.offset = 0;
let hint = hint?;
finished = hint == 0;
}
self.writer.flush()
}
}
#[cfg(test)]
mod tests {
use super::Writer;
use std::io::Write;
#[test]
fn test_noop() {
use crate::stream::raw::NoOp;
let input = b"AbcdefghAbcdefgh.";
// Test writer
let mut output = Vec::new();
{
let mut writer = Writer::new(&mut output, NoOp);
writer.write_all(input).unwrap();
writer.finish().unwrap();
}
assert_eq!(&output, input);
}
#[test]
fn test_compress() {
use crate::stream::raw::Encoder;
let input = b"AbcdefghAbcdefgh.";
// Test writer
let mut output = Vec::new();
{
let mut writer =
Writer::new(&mut output, Encoder::new(1).unwrap());
writer.write_all(input).unwrap();
writer.finish().unwrap();
}
// println!("Output: {:?}", output);
let decoded = crate::decode_all(&output[..]).unwrap();
assert_eq!(&decoded, input);
}
#[test]
fn test_decompress() {
use crate::stream::raw::Decoder;
let input = b"AbcdefghAbcdefgh.";
let compressed = crate::encode_all(&input[..], 1).unwrap();
// Test writer
let mut output = Vec::new();
{
let mut writer = Writer::new(&mut output, Decoder::new().unwrap());
writer.write_all(&compressed).unwrap();
writer.finish().unwrap();
}
// println!("Output: {:?}", output);
assert_eq!(&output, input);
}
}