dekaf: Swap to lz4_flex from lz4

Cargo.toml

@@ -59,7 +59,7 @@ flate2 = "1.0"
 futures = "0.3"
 futures-core = "0.3"
 futures-util = "0.3"
-fxhash = "0.2" # Used in `json` crate. Replace with xxhash.
+fxhash = "0.2"                                               # Used in `json` crate. Replace with xxhash.
 hex = "0.4.3"
 hexdump = "0.1"
 humantime = "2.1"
@@ -72,14 +72,17 @@ jemalloc-ctl = "0.3"
 json-patch = "0.3"
 jsonwebtoken = { version = "9", default-features = false }
 js-sys = "0.3.60"
-kafka-protocol = "0.11.0"
+# TODO(jshearer): Swap back after 0.13.0 is released, which includes
+# https://github.com/tychedelia/kafka-protocol-rs/pull/81
+kafka-protocol = { git = "https://github.com/tychedelia/kafka-protocol-rs.git", rev = "cabe835" }
 lazy_static = "1.4"
 libc = "0.2"
 librocksdb-sys = { version = "0.16.0", default-features = false, features = [
     "snappy",
     "rtti",
 ] }
 lz4 = "1.24.0"
+lz4_flex = "0.11.0"
 mime = "0.3"
 memchr = "2.5"
 metrics = "0.23.0"

crates/dekaf/Cargo.toml

@@ -37,6 +37,7 @@ hex = { workspace = true }
 hexdump = { workspace = true }
 itertools = { workspace = true }
 kafka-protocol = { workspace = true }
+lz4_flex = { workspace = true }
 md5 = { workspace = true }
 metrics = { workspace = true }
 metrics-prometheus = { workspace = true }

crates/dekaf/src/read.rs

@@ -1,10 +1,12 @@
 use super::{Collection, Partition};
 use anyhow::bail;
-use bytes::BufMut;
+use bytes::{Buf, BufMut, BytesMut};
 use doc::AsNode;
 use futures::StreamExt;
 use gazette::journal::{ReadJsonLine, ReadJsonLines};
 use gazette::{broker, journal, uuid};
+use kafka_protocol::records::Compression;
+use lz4_flex::frame::BlockMode;
 use std::time::Duration;
 
 pub struct Read {
@@ -255,7 +257,7 @@ impl Read {
             compression: Compression::None,
             version: 2,
         };
-        RecordBatchEncoder::encode(&mut buf, records.iter(), &opts)
+        RecordBatchEncoder::encode(&mut buf, records.iter(), &opts, Some(compressor))
             .expect("record encoding cannot fail");
 
         tracing::debug!(
@@ -276,3 +278,28 @@ impl Read {
         Ok((self, buf.freeze()))
     }
 }
+
+fn compressor<Output: BufMut>(
+    input: &mut BytesMut,
+    output: &mut Output,
+    c: Compression,
+) -> anyhow::Result<()> {
+    match c {
+        Compression::None => output.put(input),
+        Compression::Lz4 => {
+            let mut frame_info = lz4_flex::frame::FrameInfo::default();
+            // This breaks Go lz4 decoding
+            // frame_info.block_checksums = true;
+            frame_info.block_mode = BlockMode::Independent;
+
+            let mut encoder =
+                lz4_flex::frame::FrameEncoder::with_frame_info(frame_info, output.writer());
+
+            std::io::copy(&mut input.reader(), &mut encoder)?;
+
+            encoder.finish()?;
+        }
+        unsupported @ _ => bail!("Unsupported compression type {unsupported:?}"),
+    };
+    Ok(())
+}