Add a streaming writer

Fixes #75

src/encoder.rs

@@ -3,7 +3,7 @@ extern crate deflate;
 use std::borrow::Cow;
 use std::error;
 use std::fmt;
-use std::io::{self, Write};
+use std::io::{self, Read, Write};
 use std::mem;
 use std::result;
 
@@ -153,6 +153,23 @@ impl<W: Write> Writer<W> {
         }
         self.write_chunk(chunk::IDAT, &zlib.finish()?)
     }
+
+    /// Create an stream writer.
+    ///
+    /// This allows you create images that do not fit
+    /// in memory. The default chunk size is 4K, use
+    /// `stream_writer_with_size` to set another chuck
+    /// size.
+    pub fn stream_writer(&mut self) -> StreamWriter<W> {
+        self.stream_writer_with_size(4 * 1024)
+    }
+
+    /// Create a stream writer with custom buffer size.
+    ///
+    /// See `stream_writer`
+    pub fn stream_writer_with_size(&mut self, size: usize) -> StreamWriter<W> {
+        StreamWriter::new(self, size)
+    }
 }
 
 impl<W: Write> Drop for Writer<W> {
@@ -161,6 +178,126 @@ impl<W: Write> Drop for Writer<W> {
     }
 }
 
+struct ChunkWriter<'a, W: Write> {
+    writer: &'a mut Writer<W>,
+    buffer: Vec<u8>,
+    index: usize,
+}
+
+impl<'a, W: Write> ChunkWriter<'a, W> {
+    fn new(writer: &'a mut Writer<W>, buf_len: usize) -> ChunkWriter<'a, W> {
+        ChunkWriter {
+            writer,
+            buffer: vec![0; buf_len],
+            index: 0,
+        }
+    }
+}
+
+impl<'a, W: Write> Write for ChunkWriter<'a, W> {
+    fn write(&mut self, mut buf: &[u8]) -> io::Result<usize> {
+        let written = buf.read(&mut self.buffer[self.index..])?;
+        self.index += written;
+
+        if self.index + 1 >= self.buffer.len() {
+            self.writer.write_chunk(chunk::IDAT, &self.buffer)?;
+            self.index = 0;
+        }
+
+        Ok(written)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        if self.index > 0 {
+            self.writer.write_chunk(chunk::IDAT, &self.buffer[..self.index+1])?;
+        }
+        self.index = 0;
+        Ok(())
+    }
+}
+
+impl<'a, W: Write> Drop for ChunkWriter<'a, W> {
+    fn drop(&mut self) {
+        let _ = self.flush();
+    }
+}
+
+
+/// Streaming png writer
+///
+/// This may may silently fail in the destructor so it is a good idea to call
+/// `finish` or `flush` before droping. 
+pub struct StreamWriter<'a, W: Write> {
+    writer: deflate::write::ZlibEncoder<ChunkWriter<'a, W>>,
+    prev_buf: Vec<u8>,
+    curr_buf: Vec<u8>,
+    index: usize,
+    bpp: usize,
+    filter: FilterType,
+}
+
+impl<'a, W: Write> StreamWriter<'a, W> {
+    fn new(writer: &'a mut Writer<W>, buf_len: usize) -> StreamWriter<'a, W> {
+        let bpp      = writer.info.bytes_per_pixel();
+        let in_len   = writer.info.raw_row_length() - 1;
+        let filter   = writer.info.filter;
+        let prev_buf = vec![0; in_len];
+        let curr_buf = vec![0; in_len];
+
+        let compression = writer.info.compression.clone();
+        let chunk_writer = ChunkWriter::new(writer, buf_len);
+        let zlib = deflate::write::ZlibEncoder::new(chunk_writer, compression);
+
+        StreamWriter {
+            writer: zlib,
+            index: 0,
+            prev_buf,
+            curr_buf,
+            bpp,
+            filter,
+        }
+    }
+
+    pub fn finish(mut self) -> Result<()> {
+        // TODO: call `writer.finish` somehow?
+        self.flush()?;
+        Ok(())
+    }
+}
+
+impl<'a, W: Write> Write for StreamWriter<'a, W> {
+    fn write(&mut self, mut buf: &[u8]) -> io::Result<usize> {
+        let written = buf.read(&mut self.curr_buf[self.index..])?;
+        self.index += written;
+
+        if self.index >= self.curr_buf.len() {
+            self.writer.write_all(&[self.filter as u8])?;
+            filter(self.filter, self.bpp, &self.prev_buf, &mut self.curr_buf);
+            self.writer.write_all(&self.curr_buf)?;
+            mem::swap(&mut self.prev_buf, &mut self.curr_buf);
+            self.index = 0;
+        }
+
+        Ok(written)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.writer.flush()?;
+        if self.index > 0 {
+            dbg!(self.index);
+            let message = format!("wrong data size, got {} bytes too many", self.index);
+            return Err(EncodingError::Format(message.into()).into());
+        }
+        Ok(())
+    }
+}
+
+impl<'a, W: Write> Drop for StreamWriter<'a, W> {
+    fn drop(&mut self) {
+        let _ = self.flush();
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -213,6 +350,53 @@ mod tests {
         }
     }
 
+    #[test]
+    fn roundtrip_stream() {
+        // More loops = more random testing, but also more test wait time
+        for _ in 0..10 {
+            for path in glob::glob("tests/pngsuite/*.png").unwrap().map(|r| r.unwrap()) {
+                if path.file_name().unwrap().to_str().unwrap().starts_with("x") {
+                    // x* files are expected to fail to decode
+                    continue;
+                }
+                // Decode image
+                let decoder = ::Decoder::new(File::open(path).unwrap());
+                let (info, mut reader) = decoder.read_info().unwrap();
+                if info.line_size != 32 {
+                    // TODO encoding only works with line size 32?
+                    continue;
+                }
+                let mut buf = vec![0; info.buffer_size()];
+                reader.next_frame(&mut buf).unwrap();
+                // Encode decoded image
+                let mut out = Vec::new();
+                {
+                    let mut wrapper = RandomChunkWriter {
+                        rng: self::rand::thread_rng(),
+                        w: &mut out
+                    };
+
+                    let mut encoder = Encoder::new(&mut wrapper, info.width, info.height).write_header().unwrap();
+                    let mut stream_writer = encoder.stream_writer();
+
+                    let mut outer_wrapper = RandomChunkWriter {
+                        rng: self::rand::thread_rng(),
+                        w: &mut stream_writer
+                    };
+
+                    outer_wrapper.write_all(&buf).unwrap();
+                }
+                // Decode encoded decoded image
+                let decoder = ::Decoder::new(&*out);
+                let (info, mut reader) = decoder.read_info().unwrap();
+                let mut buf2 = vec![0; info.buffer_size()];
+                reader.next_frame(&mut buf2).unwrap();
+                // check if the encoded image is ok:
+                assert_eq!(buf, buf2);
+            }
+        }
+    }
+
     #[test]
     fn expect_error_on_wrong_image_len() -> Result<()> {
         use std::io::Cursor;
@@ -254,4 +438,4 @@ mod tests {
         }
     }
 
-}
+}

src/lib.rs

@@ -59,7 +59,7 @@ mod utils;
 pub use crate::common::*;
 pub use crate::decoder::{Decoder, Reader, OutputInfo, StreamingDecoder, Decoded, DecodingError, Limits};
 #[cfg(feature = "png-encoding")]
-pub use crate::encoder::{Encoder, Writer, EncodingError};
+pub use crate::encoder::{Encoder, Writer, StreamWriter, EncodingError};
 pub use crate::filter::FilterType;
 
 pub use crate::traits::{Parameter, HasParameters};