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use crate::error::{Error, Result};
use crate::jpeg::byteorder::ReadBytesExt;
use crate::jpeg::marker::Marker;
use crate::jpeg::parser::{parse_sof, parse_sos, skip_marker, CodingProcess, FrameInfo, ScanInfo};
use std::io;
use std::io::Read;
pub struct PositionTrackingReader<R> {
reader: R,
position: usize,
}
impl<R> PositionTrackingReader<R> {
pub fn position(&self) -> usize {
self.position
}
}
impl<R: Read> Read for PositionTrackingReader<R> {
#[inline]
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let n = self.reader.read(buf)?;
self.position += n;
Ok(n)
}
#[inline]
fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
self.reader.read_exact(buf)?;
self.position += buf.len();
Ok(())
}
}
/// JPEG decoder
pub struct Decoder<R> {
reader: PositionTrackingReader<R>,
frame: Option<FrameInfo>,
}
#[derive(Debug)]
pub enum MarkerData {
Frame(FrameInfo),
Scan(ScanInfo),
Other(Marker),
}
#[derive(Debug)]
pub struct MarkerPosition {
pub position: usize,
pub marker: MarkerData,
}
impl<R: Read> Decoder<R> {
/// Creates a new `Decoder` using the reader `reader`.
pub fn new(reader: R) -> Self {
Self {
reader: PositionTrackingReader {
reader,
position: 0,
},
frame: None,
}
}
pub fn decode(&mut self) -> Result<Vec<MarkerPosition>> {
let mut positions = Vec::new();
if self.frame.is_none() && (self.reader.read_u8()? != 0xFF || Marker::from_u8(self.reader.read_u8()?) != Some(Marker::SOI)) {
return Err(Error::Format("first two bytes is not a SOI marker"));
}
let mut pending_marker = None;
loop {
let (position, marker) = match pending_marker.take() {
Some(m) => m,
None => match self.read_marker() {
Ok(m) => m,
Err(_) => break,
},
};
match marker {
// Frame header
Marker::SOF(..) => {
// Section 4.10
// "An image contains only one frame in the cases of sequential and
// progressive coding processes; an image contains multiple frames for the
// hierarchical mode."
if self.frame.is_some() {
return Err(Error::Unsupported);
}
let frame = parse_sof(&mut self.reader, marker)?;
let component_count = frame.components.len();
if frame.is_differential {
return Err(Error::Unsupported);
}
if frame.coding_process == CodingProcess::Lossless {
return Err(Error::Unsupported);
}
if frame.precision != 8 {
return Err(Error::Unsupported);
}
if frame.image_size.height == 0 {
return Err(Error::Unsupported);
}
if component_count != 1 && component_count != 3 && component_count != 4 {
return Err(Error::Unsupported);
}
self.frame = Some(frame.clone());
positions.push(MarkerPosition {
position,
marker: MarkerData::Frame(frame),
});
},
// Scan header
Marker::SOS => {
if self.frame.is_none() {
return Err(Error::Format("scan encountered before frame"));
}
let frame = self.frame.clone().ok_or(Error::Unsupported)?;
let scan = parse_sos(&mut self.reader, &frame)?;
pending_marker = Some(self.skip_scan()?);
positions.push(MarkerPosition {
position,
marker: MarkerData::Scan(scan),
});
},
// Restart
Marker::RST(..) => {
},
// End of image
Marker::EOI => {
positions.push(MarkerPosition {
position,
marker: MarkerData::Other(marker),
});
break;
},
marker => {
skip_marker(&mut self.reader, marker)?;
positions.push(MarkerPosition {
position,
marker: MarkerData::Other(marker),
});
},
}
}
Ok(positions)
}
fn read_marker(&mut self) -> Result<(usize, Marker)> {
// This should be an error as the JPEG spec doesn't allow extraneous data between marker segments.
// libjpeg allows this though and there are images in the wild utilising it, so we are
// forced to support this behavior.
// Sony Ericsson P990i is an example of a device which produce this sort of JPEGs.
while self.reader.read_u8()? != 0xFF {}
let mut byte = self.reader.read_u8()?;
// Section B.1.1.2
// "Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’."
while byte == 0xFF {
byte = self.reader.read_u8()?;
}
let position = self.reader.position() - 2;
match byte {
0x00 => Err(Error::Format("FF 00 found where marker was expected")),
_ => Ok((position, Marker::from_u8(byte).ok_or(Error::Unsupported)?)),
}
}
fn skip_scan(&mut self) -> Result<(usize, Marker)> {
loop {
let byte = self.reader.read_u8()?;
if byte == 0xFF {
let mut next_byte = self.reader.read_u8()?;
// Check for byte stuffing.
if next_byte != 0x00 {
// We seem to have reached the end of entropy-coded data and encountered a
// marker. Since we can't put data back into the reader, we have to continue
// reading to identify the marker so we can pass it on.
// Section B.1.1.2
// "Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’."
while next_byte == 0xFF {
next_byte = self.reader.read_u8()?;
}
let position = self.reader.position() - 2;
return match next_byte {
0x00 => Err(Error::Format("FF 00 found where marker was expected")),
_ => Ok((position, Marker::from_u8(next_byte).ok_or(Error::Unsupported)?)),
};
}
}
}
}
}