Support decoding WebP compressed TIFFs (#336)

Co-authored-by: A. Molzer <5550310+197g@users.noreply.github.com>

src/decoder/image.rs

@@ -526,13 +526,14 @@ impl Image {
         }
     }
 
-    fn create_reader<'r, R: 'r + Read>(
+    fn create_reader<'r, R: 'r + Read + Seek>(
         reader: R,
         compression_method: CompressionMethod,
         compressed_length: u64,
         // FIXME: these should be `expect` attributes or we choose another way of passing them.
         #[cfg_attr(not(feature = "jpeg"), allow(unused_variables))] jpeg_tables: Option<&[u8]>,
         #[cfg_attr(not(feature = "fax"), allow(unused_variables))] dimensions: (u32, u32),
+        #[cfg_attr(not(feature = "webp"), allow(unused_variables))] samples: u16,
     ) -> TiffResult<Box<dyn Read + 'r>> {
         Ok(match compression_method {
             CompressionMethod::None => Box::new(reader),
@@ -607,6 +608,13 @@ impl Image {
                 reader,
                 compressed_length,
             )?),
+            #[cfg(feature = "webp")]
+            CompressionMethod::WebP => Box::new(super::stream::WebPReader::new(
+                reader,
+                compressed_length,
+                samples,
+            )?),
+
             method => {
                 return Err(TiffError::UnsupportedError(
                     TiffUnsupportedError::UnsupportedCompressionMethod(method),
@@ -805,7 +813,7 @@ impl Image {
 
     pub(crate) fn expand_chunk(
         &self,
-        reader: &mut ValueReader<impl Read>,
+        reader: &mut ValueReader<impl Read + Seek>,
         buf: &mut [u8],
         layout: &ReadoutLayout,
         chunk_index: u32,
@@ -919,6 +927,7 @@ impl Image {
             *compressed_bytes,
             self.jpeg_tables.as_deref().map(|a| &**a),
             chunk_dims,
+            self.samples,
         )?;
 
         if is_output_chunk_rows && is_all_bits {

src/decoder/stream.rs

@@ -1,4 +1,6 @@
 //! All IO functionality needed for TIFF decoding
+#[cfg(feature = "webp")]
+use std::io::Cursor;
 use std::io::{self, BufRead, BufReader, Read, Seek, Take};
 
 pub use crate::tags::ByteOrder;
@@ -354,6 +356,61 @@ impl<R: Read> Read for Group4Reader<R> {
     }
 }
 
+#[cfg(feature = "webp")]
+pub struct WebPReader {
+    inner: Cursor<Vec<u8>>,
+}
+
+#[cfg(feature = "webp")]
+impl WebPReader {
+    pub fn new<R: Read + Seek>(
+        reader: R,
+        compressed_length: u64,
+        samples: u16,
+    ) -> crate::TiffResult<Self> {
+        let mut decoder =
+            image_webp::WebPDecoder::new(io::BufReader::new(reader.take(compressed_length)))
+                .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
+
+        if !(samples == 4 || (samples == 3 && !decoder.has_alpha())) {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "bad sample count for WebP compressed data",
+            )
+            .into());
+        }
+
+        let total_bytes =
+            samples as usize * decoder.dimensions().0 as usize * decoder.dimensions().1 as usize;
+        let mut data = vec![0; total_bytes];
+
+        decoder
+            .read_image(&mut data)
+            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
+
+        // Add a fully opaque alpha channel if needed
+        if samples == 4 && !decoder.has_alpha() {
+            for i in (0..(total_bytes / 4)).rev() {
+                data[i * 4 + 3] = 255;
+                data[i * 4 + 2] = data[i * 3 + 2];
+                data[i * 4 + 1] = data[i * 3 + 1];
+                data[i * 4] = data[i * 3];
+            }
+        }
+
+        Ok(Self {
+            inner: Cursor::new(data),
+        })
+    }
+}
+
+#[cfg(feature = "webp")]
+impl Read for WebPReader {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.read(buf)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

src/tags.rs

@@ -267,6 +267,9 @@ pub enum CompressionMethod(u16) unknown(
 
     // Self-assigned by libtiff
     ZSTD = 0xC350,
+
+    // Self-assigned by libtiff
+    WebP = 0xC351,
 }
 }