Merge pull request #4945 from dotCooCoo/fix/ai-zstd-trailing-zero

.ai import: a Zstandard frame that ends in a zero byte keeps it

crates/eps/src/import/ai.rs

@@ -158,11 +158,11 @@ impl Codec {
                 flate2::read::ZlibDecoder::new(data).take(max + 1).read_to_end(&mut out).map_err(|_| damaged("its zlib compression"))?;
             }
             Codec::Zstd => {
-                // The data may be several frames one after the other, padded with zeros.
-                let end = data.iter().rposition(|b| *b != 0).map_or(0, |i| i + 1);
-                let mut src = data.get(..end).unwrap_or_default();
+                // The data may be several frames one after the other, padded with zeros. A frame
+                // can itself end in a zero byte, so the padding is what is left after the last frame.
+                let mut src = data;
                 let mut frames = 0usize;
-                while !src.is_empty() {
+                while src.iter().any(|b| *b != 0) {
                     frames += 1;
                     if frames > MAX_FRAMES {
                         return Err(damaged("its Zstandard compression"));

crates/eps/src/import/ai/tests.rs

@@ -1472,6 +1472,19 @@ fn many_zstandard_frames_are_read_in_one_pass_and_capped() {
     assert!(started.elapsed() < std::time::Duration::from_secs(20), "{:?}", started.elapsed());
 }
 
+/// A Zstandard frame that ends in a zero byte keeps it: only the zeros after the last frame are
+/// padding.
+#[test]
+fn a_zstandard_frame_ending_in_a_zero_byte_is_read_whole() {
+    // Magic number, a single-segment header with a 1-byte content size of 3, and one raw block
+    // (last, 3 bytes) holding `ab` and a zero byte.
+    let frame = [0x28, 0xB5, 0x2F, 0xFD, 0x20, 3, 0x19, 0, 0, b'a', b'b', 0];
+    for padding in [0, 64] {
+        let raw = [&b"%AI24_ZStandard_Data"[..], &frame, &frame, &vec![0; padding]].concat();
+        assert_eq!(decode_private(&raw).unwrap(), b"ab\0ab\0");
+    }
+}
+
 #[test]
 fn closing_brackets_without_their_opening_dont_rescan_the_stack() {
     let n = 200_000;