Limit zstd window size to web-safe value

zstd's memory buffer is limited to 8MB by Chromium and Firefox (at least), but the encoder can exceed that at level 20 and above. Ensure it's limited to 8MB.

Author: AlyoshaVasilieva

tower-http/src/compression/body.rs

@@ -340,7 +340,29 @@ where
     type Output = ZstdEncoder<Self::Input>;
 
     fn apply(input: Self::Input, quality: CompressionLevel) -> Self::Output {
-        ZstdEncoder::with_quality(input, quality.into_async_compression())
+        // See https://issues.chromium.org/issues/41493659:
+        //  "For memory usage reasons, Chromium limits the window size to 8MB"
+        // See https://datatracker.ietf.org/doc/html/rfc8878#name-window-descriptor
+        //  "For improved interoperability, it's recommended for decoders to support values
+        //  of Window_Size up to 8 MB and for encoders not to generate frames requiring a
+        //  Window_Size larger than 8 MB."
+        // Level 17 in zstd (as of v1.5.6) is the first level with a window size of 8 MB (2^23):
+        // https://github.com/facebook/zstd/blob/v1.5.6/lib/compress/clevels.h#L25-L51
+        // Set the parameter for all levels >= 17. This will either have no effect (but reduce
+        // the risk of future changes in zstd) or limit the window log to 8MB.
+        let needs_window_limit = match quality {
+            CompressionLevel::Best => true, // level 20
+            CompressionLevel::Precise(level) => level >= 17,
+            _ => false,
+        };
+        // The parameter is not set for levels below 17 as it will increase the window size
+        // for those levels.
+        if needs_window_limit {
+            let params = [async_compression::zstd::CParameter::window_log(23)];
+            ZstdEncoder::with_quality_and_params(input, quality.into_async_compression(), &params)
+        } else {
+            ZstdEncoder::with_quality(input, quality.into_async_compression())
+        }
     }
 
     fn get_pin_mut(pinned: Pin<&mut Self::Output>) -> Pin<&mut Self::Input> {