[GitHub] [beam] sjvanrossum commented on a diff in pull request #24093: Add ZstdCoder to wrap coders with Zstandard compression

[GitBox <gi...@apache.org>]

sjvanrossum commented on code in PR #24093:
URL: https://github.com/apache/beam/pull/24093#discussion_r1020423196


##########
sdks/java/core/src/main/java/org/apache/beam/sdk/coders/ZstdCoder.java:
##########
@@ -0,0 +1,110 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.beam.sdk.coders;
+
+import com.github.luben.zstd.Zstd;
+import com.github.luben.zstd.ZstdCompressCtx;
+import com.github.luben.zstd.ZstdDecompressCtx;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.List;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.util.CoderUtils;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.ImmutableList;
+
+/**
+ * Wraps an existing coder with Zstandard compression. It makes sense to use this coder when it's
+ * likely that the encoded value is quite large and compressible or when a dictionary is available
+ * to improve compression performance.
+ */
+public class ZstdCoder<T> extends StructuredCoder<T> {
+  private final Coder<T> innerCoder;
+  private final @Nullable byte[] dict;
+  private final int level;
+
+  /** Wraps the given coder into a {@link ZstdCoder}. */
+  public static <T> ZstdCoder<T> of(Coder<T> innerCoder, byte[] dict, int level) {
+    return new ZstdCoder<>(innerCoder, dict, level);
+  }
+
+  /** Wraps the given coder into a {@link ZstdCoder}. */
+  public static <T> ZstdCoder<T> of(Coder<T> innerCoder, byte[] dict) {
+    return new ZstdCoder<>(innerCoder, dict, Zstd.defaultCompressionLevel());
+  }
+
+  /** Wraps the given coder into a {@link ZstdCoder}. */
+  public static <T> ZstdCoder<T> of(Coder<T> innerCoder, int level) {
+    return new ZstdCoder<>(innerCoder, null, level);
+  }
+
+  /** Wraps the given coder into a {@link ZstdCoder}. */
+  public static <T> ZstdCoder<T> of(Coder<T> innerCoder) {
+    return new ZstdCoder<>(innerCoder, null, Zstd.defaultCompressionLevel());
+  }
+
+  private ZstdCoder(Coder<T> innerCoder, @Nullable byte[] dict, int level) {
+    this.innerCoder = innerCoder;
+    this.dict = dict;
+    this.level = level;
+  }
+
+  @Override
+  public void encode(T value, OutputStream os) throws IOException {
+    ZstdCompressCtx ctx = new ZstdCompressCtx();
+    try {
+      ctx.setLevel(level);
+      ctx.setMagicless(true); // No magic since we know this will be compressed data on decode.
+      ctx.setDictID(false); // No dict ID since we initialize the coder with the expected dict.
+      ctx.loadDict(dict);
+
+      byte[] encoded = CoderUtils.encodeToByteArray(innerCoder, value);

Review Comment:
   That has my preference as well and should work fine if we can consume the whole stream.
   I tried this out on a ByteArrayInputStream and found that ZstdInputStream consumes beyond the encoded frame's end, so this doesn't seem to work in nested contexts.



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