Enable customizing Zstd decoding parameters.

src/codec/zstd/decoder.rs

@@ -16,6 +16,16 @@ impl ZstdDecoder {
         }
     }
 
+    pub(crate) fn new_with_params(params: &[crate::zstd::DParameter]) -> Self {
+        let mut decoder = Decoder::new().unwrap();
+        for param in params {
+            decoder.set_parameter(param.as_zstd()).unwrap();
+        }
+        Self {
+            decoder: Unshared::new(decoder),
+        }
+    }
+
     pub(crate) fn new_with_dict(dictionary: &[u8]) -> io::Result<Self> {
         let mut decoder = Decoder::with_dictionary(dictionary)?;
         Ok(Self {

src/macros.rs

@@ -198,6 +198,17 @@ macro_rules! algos {
             }
         }
         { @dec
+            /// Creates a new decoder, using the specified parameters, which will read compressed
+            /// data from the given stream and emit a decompressed stream.
+            pub fn with_params(inner: $inner, params: &[crate::zstd::DParameter]) -> Self {
+                Self {
+                    inner: crate::$($mod::)+generic::Decoder::new(
+                        inner,
+                        crate::codec::ZstdDecoder::new_with_params(params),
+                    ),
+                }
+            }
+
             /// Creates a new decoder, using the specified compression level and pre-trained
             /// dictionary, which will read compressed data from the given stream and emit an
             /// uncompressed stream.

src/zstd.rs

@@ -1,6 +1,7 @@
 //! This module contains zstd-specific types for async-compression.
 
 use libzstd::stream::raw::CParameter::*;
+use libzstd::stream::raw::DParameter::*;
 
 /// A compression parameter for zstd. This is a stable wrapper around zstd's own `CParameter`
 /// type, to abstract over different versions of the zstd library.
@@ -110,3 +111,22 @@ impl CParameter {
         self.0
     }
 }
+
+/// A decompression parameter for zstd. This is a stable wrapper around zstd's own `DParameter`
+/// type, to abstract over different versions of the zstd library.
+///
+/// See the [zstd documentation](https://facebook.github.io/zstd/zstd_manual.html) for more
+/// information on these parameters.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct DParameter(libzstd::stream::raw::DParameter);
+
+impl DParameter {
+    /// Maximum window size in bytes (as a power of two)
+    pub fn window_log_max(value: u32) -> Self {
+        Self(WindowLogMax(value))
+    }
+
+    pub(crate) fn as_zstd(&self) -> libzstd::stream::raw::DParameter {
+        self.0
+    }
+}

tests/zstd.rs

@@ -2,3 +2,47 @@
 mod utils;
 
 test_cases!(zstd);
+
+use async_compression::zstd::DParameter;
+use tokio::io::AsyncWriteExt as _;
+
+#[tokio::test]
+async fn zstd_decode_large_window_size_default() {
+    let compressed = include_bytes!("./artifacts/long-window-size-lib.rs.zst");
+
+    // Default decoder should throw with an error, window size maximum is too low.
+    let mut decoder = async_compression::tokio::write::ZstdDecoder::new(Vec::new());
+    decoder.write_all(compressed).await.unwrap_err();
+}
+
+#[tokio::test]
+async fn zstd_decode_large_window_size_explicit_small_window_size() {
+    let compressed = include_bytes!("./artifacts/long-window-size-lib.rs.zst");
+
+    // Short window decoder should throw with an error, window size maximum is too low.
+    let mut decoder = async_compression::tokio::write::ZstdDecoder::with_params(
+        Vec::new(),
+        &[DParameter::window_log_max(16)],
+    );
+    decoder.write_all(compressed).await.unwrap_err();
+}
+
+#[tokio::test]
+async fn zstd_decode_large_window_size_explicit_large_window_size() {
+    let compressed = include_bytes!("./artifacts/long-window-size-lib.rs.zst");
+    let source = include_bytes!("./artifacts/lib.rs");
+
+    // Long window decoder should succeed as the window size is large enough to decompress the given input.
+    let mut long_window_size_decoder = async_compression::tokio::write::ZstdDecoder::with_params(
+        Vec::new(),
+        &[DParameter::window_log_max(31)],
+    );
+    // Long window size decoder should successfully decode the given input data.
+    long_window_size_decoder
+        .write_all(compressed)
+        .await
+        .unwrap();
+    long_window_size_decoder.shutdown().await.unwrap();
+
+    assert_eq!(long_window_size_decoder.into_inner(), source);
+}