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use super::{stream::FormatErrorInner, DecodingError, CHUNCK_BUFFER_SIZE};
use miniz_oxide::inflate::core::{decompress, inflate_flags, DecompressorOxide};
use miniz_oxide::inflate::TINFLStatus;
/// Ergonomics wrapper around `miniz_oxide::inflate::stream` for zlib compressed data.
pub(super) struct ZlibStream {
/// Current decoding state.
state: Box<DecompressorOxide>,
/// If there has been a call to decompress already.
started: bool,
/// A buffer of compressed data.
/// We use this for a progress guarantee. The data in the input stream is chunked as given by
/// the underlying stream buffer. We will not read any more data until the current buffer has
/// been fully consumed. The zlib decompression can not fully consume all the data when it is
/// in the middle of the stream, it will treat full symbols and maybe the last bytes need to be
/// treated in a special way. The exact reason isn't as important but the interface does not
/// promise us this. Now, the complication is that the _current_ chunking information of PNG
/// alone is not enough to determine this as indeed the compressed stream is the concatenation
/// of all consecutive `IDAT`/`fdAT` chunks. We would need to inspect the next chunk header.
///
/// Thus, there needs to be a buffer that allows fully clearing a chunk so that the next chunk
/// type can be inspected.
in_buffer: Vec<u8>,
/// The logical start of the `in_buffer`.
in_pos: usize,
/// Remaining buffered decoded bytes.
/// The decoder sometimes wants inspect some already finished bytes for further decoding. So we
/// keep a total of 32KB of decoded data available as long as more data may be appended.
out_buffer: Vec<u8>,
/// The cursor position in the output stream as a buffer index.
out_pos: usize,
}
impl ZlibStream {
pub(crate) fn new() -> Self {
ZlibStream {
state: Box::default(),
started: false,
in_buffer: Vec::with_capacity(CHUNCK_BUFFER_SIZE),
in_pos: 0,
out_buffer: vec![0; 2 * CHUNCK_BUFFER_SIZE],
out_pos: 0,
}
}
pub(crate) fn reset(&mut self) {
self.started = false;
self.in_buffer.clear();
self.out_buffer.clear();
self.out_pos = 0;
*self.state = DecompressorOxide::default();
}
/// Fill the decoded buffer as far as possible from `data`.
/// On success returns the number of consumed input bytes.
pub(crate) fn decompress(
&mut self,
data: &[u8],
image_data: &mut Vec<u8>,
) -> Result<usize, DecodingError> {
const BASE_FLAGS: u32 = inflate_flags::TINFL_FLAG_PARSE_ZLIB_HEADER
| inflate_flags::TINFL_FLAG_USING_NON_WRAPPING_OUTPUT_BUF
| inflate_flags::TINFL_FLAG_HAS_MORE_INPUT;
self.prepare_vec_for_appending();
let (status, mut in_consumed, out_consumed) = {
let in_data = if self.in_buffer.is_empty() {
data
} else {
&self.in_buffer[self.in_pos..]
};
decompress(
&mut self.state,
in_data,
self.out_buffer.as_mut_slice(),
self.out_pos,
BASE_FLAGS,
)
};
if !self.in_buffer.is_empty() {
self.in_pos += in_consumed;
}
if self.in_buffer.len() == self.in_pos {
self.in_buffer.clear();
self.in_pos = 0;
}
if in_consumed == 0 {
self.in_buffer.extend_from_slice(data);
in_consumed = data.len();
}
self.started = true;
self.out_pos += out_consumed;
self.transfer_finished_data(image_data);
match status {
TINFLStatus::Done | TINFLStatus::HasMoreOutput | TINFLStatus::NeedsMoreInput => {
Ok(in_consumed)
}
err => Err(DecodingError::Format(
FormatErrorInner::CorruptFlateStream { err }.into(),
)),
}
}
/// Called after all consecutive IDAT chunks were handled.
///
/// The compressed stream can be split on arbitrary byte boundaries. This enables some cleanup
/// within the decompressor and flushing additional data which may have been kept back in case
/// more data were passed to it.
pub(crate) fn finish_compressed_chunks(
&mut self,
image_data: &mut Vec<u8>,
) -> Result<(), DecodingError> {
const BASE_FLAGS: u32 = inflate_flags::TINFL_FLAG_PARSE_ZLIB_HEADER
| inflate_flags::TINFL_FLAG_USING_NON_WRAPPING_OUTPUT_BUF;
if !self.started {
return Ok(());
}
let tail = self.in_buffer.split_off(0);
let tail = &tail[self.in_pos..];
let mut start = 0;
loop {
self.prepare_vec_for_appending();
let (status, in_consumed, out_consumed) = {
// TODO: we may be able to avoid the indirection through the buffer here.
// First append all buffered data and then create a cursor on the image_data
// instead.
decompress(
&mut self.state,
&tail[start..],
self.out_buffer.as_mut_slice(),
self.out_pos,
BASE_FLAGS,
)
};
start += in_consumed;
self.out_pos += out_consumed;
match status {
TINFLStatus::Done => {
self.out_buffer.truncate(self.out_pos as usize);
image_data.append(&mut self.out_buffer);
return Ok(());
}
TINFLStatus::HasMoreOutput => {
let transferred = self.transfer_finished_data(image_data);
assert!(
transferred > 0 || in_consumed > 0 || out_consumed > 0,
"No more forward progress made in stream decoding."
);
}
err => {
return Err(DecodingError::Format(
FormatErrorInner::CorruptFlateStream { err }.into(),
));
}
}
}
}
/// Resize the vector to allow allocation of more data.
fn prepare_vec_for_appending(&mut self) {
if self.out_buffer.len().saturating_sub(self.out_pos) >= CHUNCK_BUFFER_SIZE {
return;
}
let buffered_len = self.decoding_size(self.out_buffer.len());
debug_assert!(self.out_buffer.len() <= buffered_len);
self.out_buffer.resize(buffered_len, 0u8);
}
fn decoding_size(&self, len: usize) -> usize {
// Allocate one more chunk size than currently or double the length while ensuring that the
// allocation is valid and that any cursor within it will be valid.
len
// This keeps the buffer size a power-of-two, required by miniz_oxide.
.saturating_add(CHUNCK_BUFFER_SIZE.max(len))
// Ensure all buffer indices are valid cursor positions.
// Note: both cut off and zero extension give correct results.
.min(u64::max_value() as usize)
// Ensure the allocation request is valid.
// TODO: maximum allocation limits?
.min(isize::max_value() as usize)
}
fn transfer_finished_data(&mut self, image_data: &mut Vec<u8>) -> usize {
let safe = self.out_pos.saturating_sub(CHUNCK_BUFFER_SIZE);
// TODO: allocation limits.
image_data.extend(self.out_buffer.drain(..safe));
self.out_pos -= safe;
safe
}
}