Enable more HTTP decompression methods for remote cache

Bazel has support for compressed transfers from/to gRPC remote caches (#14041). However, this is not fully supported for HTTP protocol. This feature would allow to significantly decrease the network traffic for remote cache. The related issue is #23463.

In general, the `HTTPCacheClient` class can decompress the incoming HTTP content because it uses internally the `HttpContentDecompressor` from Netty library. But current implementation allows only "gzip" as acceptable encoding.
The version of Netty library used in Bazel has been updated recently to 4.1.110. This version supports much more compression methods than before. The suggested change allows using the new compression options with HTTP remote cache. "Zstd" compression is of particular interest because it is used in popular `bazel-remote` software.

Note: The suggested change forces the `bazel-remote` to send HTTP content with "zstd" encoding. For compatibility we may consider applying the `--remote_cache_compression` option to enable this functionality. I leaved it as is for now because "gzip" was used unconditionally.

Closes #27271.

PiperOrigin-RevId: 823203959
Change-Id: I5d8bf11cf3cddad688084bf1e6f53b8782f92f12

Author: AlexanderGolovlev

src/main/java/com/google/devtools/build/lib/remote/http/HttpDownloadHandler.java

@@ -16,10 +16,13 @@
 import static com.google.common.base.Preconditions.checkState;
 
 import com.google.auth.Credentials;
+import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Lists;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
+import io.netty.handler.codec.compression.Zstd;
 import io.netty.handler.codec.http.DefaultFullHttpRequest;
 import io.netty.handler.codec.http.HttpContent;
 import io.netty.handler.codec.http.HttpHeaderNames;
@@ -33,15 +36,19 @@
 import io.netty.handler.codec.http.HttpVersion;
 import io.netty.handler.codec.http.LastHttpContent;
 import io.netty.handler.timeout.ReadTimeoutException;
+import io.netty.util.AsciiString;
 import io.netty.util.internal.StringUtil;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.util.ArrayList;
 import java.util.Map.Entry;
 
 /** ChannelHandler for downloads. */
 final class HttpDownloadHandler extends AbstractHttpHandler<HttpObject> {
 
+  private static final String ACCEPT_ENCODING = getAcceptEncoding();
+
   private OutputStream out;
   private boolean keepAlive = HttpVersion.HTTP_1_1.isKeepAliveDefault();
   private boolean downloadSucceeded;
@@ -180,7 +187,7 @@ private HttpRequest buildRequest(String path, String host) {
     httpRequest.headers().set(HttpHeaderNames.HOST, host);
     httpRequest.headers().set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
     httpRequest.headers().set(HttpHeaderNames.ACCEPT, "*/*");
-    httpRequest.headers().set(HttpHeaderNames.ACCEPT_ENCODING, HttpHeaderValues.GZIP);
+    httpRequest.headers().set(HttpHeaderNames.ACCEPT_ENCODING, ACCEPT_ENCODING);
     return httpRequest;
   }
 
@@ -232,4 +239,14 @@ private void reset(ChannelHandlerContext ctx) {
       response = null;
     }
   }
+
+  private static String getAcceptEncoding() {
+    ArrayList<AsciiString> acceptEncoding =
+        Lists.newArrayList(
+            HttpHeaderValues.GZIP, HttpHeaderValues.DEFLATE, HttpHeaderValues.SNAPPY);
+    if (Zstd.isAvailable()) {
+      acceptEncoding.add(HttpHeaderValues.ZSTD);
+    }
+    return Joiner.on(",").join(acceptEncoding);
+  }
 }