Fix skipping of extra LZW data

Author: kornelski

src/reader/decoder.rs

@@ -772,7 +772,7 @@ impl StreamingDecoder {
                 if left > 0 {
                     let n = cmp::min(left, buf.len());
                     if self.lzw_reader.has_ended() || matches!(write_into, OutputBuffer::None) {
-                        return goto!(n, DecodeSubBlock(0), emit Decoded::Nothing);
+                        return goto!(n, DecodeSubBlock(left - n), emit Decoded::Nothing);
                     }
 
                     let (mut consumed, bytes_len) = self.lzw_reader.decode_bytes(&buf[..n], write_into)?;

tests/stall.rs

@@ -1,6 +1,6 @@
 #![cfg(feature = "std")]
 
-use std::{fs, sync::mpsc, thread, time::Duration};
+use std::{fs, sync::mpsc, thread, time::Duration, io};
 
 #[test]
 fn try_decode_crash_regression() {
@@ -42,3 +42,38 @@ fn decode(data: &[u8]) -> Result<(), gif::DecodingError> {
 
     Ok(())
 }
+
+#[test]
+fn one_byte_at_a_time() {
+    let r = OneByte {
+        data: include_bytes!("../tests/samples/moon_impact.gif"),
+    };
+    let frames = gif::DecodeOptions::new().read_info(r).unwrap()
+        .into_iter().enumerate().map(|(n, f)| {
+            f.expect(&n.to_string())
+        }).count();
+    assert_eq!(frames, 14);
+}
+
+struct OneByte<'a> {
+    data: &'a [u8],
+}
+
+impl io::BufRead for OneByte<'_> {
+    fn fill_buf(&mut self) -> io::Result<&[u8]> {
+        Ok(&self.data[..self.data.len().min(1)])
+    }
+    fn consume(&mut self, n: usize) {
+        debug_assert!(n <= 1);
+        self.data = &self.data[n..];
+    }
+}
+
+impl io::Read for OneByte<'_> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let n = self.data.len().min(buf.len()).min(1);
+        buf[..n].copy_from_slice(&self.data[..n]);
+        self.data = &self.data[n..];
+        Ok(n)
+    }
+}