Makes Brotli more native compilation friendly (#12409)

Motivation:
CompressorHttp2ConnectionEncoder shouldn't load anything specific to Brotli if it isn't available

Modification:
Allows a null Brotli option to be passed to CompressorHttp2ConnectionEncoder

Result:
GraalVM Native compilation without Brotli doesn't requires Brotli classes

codec-http/src/main/java/io/netty/handler/codec/http/HttpContentCompressor.java

@@ -178,8 +178,13 @@ public HttpContentCompressor(int contentSizeThreshold, CompressionOptions... com
         } else {
             ObjectUtil.deepCheckNotNull("compressionOptions", compressionOptions);
             for (CompressionOptions compressionOption : compressionOptions) {
-                if (compressionOption instanceof BrotliOptions) {
-                    // if we have BrotliOptions, it means Brotli is available
+                // BrotliOptions' class initialization depends on Brotli classes being on the classpath.
+                // The Brotli.isAvailable check ensures that BrotliOptions will only get instantiated if Brotli is
+                // on the classpath.
+                // This results in the static analysis of native-image identifying the instanceof BrotliOptions check
+                // and thus BrotliOptions itself as unreachable, enabling native-image to link all classes
+                // at build time and not complain about the missing Brotli classes.
+                if (Brotli.isAvailable() && compressionOption instanceof BrotliOptions) {
                     brotliOptions = (BrotliOptions) compressionOption;
                 } else if (compressionOption instanceof GzipOptions) {
                     gzipOptions = (GzipOptions) compressionOption;
@@ -207,7 +212,7 @@ public HttpContentCompressor(int contentSizeThreshold, CompressionOptions... com
         if (this.deflateOptions != null) {
             this.factories.put("deflate", new DeflateEncoderFactory());
         }
-        if (this.brotliOptions != null) {
+        if (Brotli.isAvailable() && this.brotliOptions != null) {
             this.factories.put("br", new BrEncoderFactory());
         }
         if (this.zstdOptions != null) {

codec-http2/src/main/java/io/netty/handler/codec/http2/CompressorHttp2ConnectionEncoder.java

@@ -24,6 +24,7 @@
 import io.netty.handler.codec.compression.BrotliEncoder;
 import io.netty.handler.codec.compression.ZlibCodecFactory;
 import io.netty.handler.codec.compression.ZlibWrapper;
+import io.netty.handler.codec.compression.Brotli;
 import io.netty.handler.codec.compression.BrotliOptions;
 import io.netty.handler.codec.compression.CompressionOptions;
 import io.netty.handler.codec.compression.DeflateOptions;
@@ -73,8 +74,17 @@ public class CompressorHttp2ConnectionEncoder extends DecoratingHttp2ConnectionE
      * with default implementation of {@link StandardCompressionOptions}
      */
     public CompressorHttp2ConnectionEncoder(Http2ConnectionEncoder delegate) {
-        this(delegate, StandardCompressionOptions.brotli(), StandardCompressionOptions.gzip(),
-                StandardCompressionOptions.deflate());
+        this(delegate, defaultCompressionOptions());
+    }
+
+    private static CompressionOptions[] defaultCompressionOptions() {
+        if (Brotli.isAvailable()) {
+            return new CompressionOptions[] {
+                    StandardCompressionOptions.brotli(),
+                    StandardCompressionOptions.gzip(),
+                    StandardCompressionOptions.deflate() };
+        }
+        return new CompressionOptions[] { StandardCompressionOptions.gzip(), StandardCompressionOptions.deflate() };
     }
 
     /**
@@ -113,7 +123,13 @@ public CompressorHttp2ConnectionEncoder(Http2ConnectionEncoder delegate,
         ObjectUtil.deepCheckNotNull("CompressionOptions", compressionOptionsArgs);
 
         for (CompressionOptions compressionOptions : compressionOptionsArgs) {
-            if (compressionOptions instanceof BrotliOptions) {
+            // BrotliOptions' class initialization depends on Brotli classes being on the classpath.
+            // The Brotli.isAvailable check ensures that BrotliOptions will only get instantiated if Brotli is on
+            // the classpath.
+            // This results in the static analysis of native-image identifying the instanceof BrotliOptions check
+            // and thus BrotliOptions itself as unreachable, enabling native-image to link all classes at build time
+            // and not complain about the missing Brotli classes.
+            if (Brotli.isAvailable() && compressionOptions instanceof BrotliOptions) {
                 brotliOptions = (BrotliOptions) compressionOptions;
             } else if (compressionOptions instanceof GzipOptions) {
                 gzipCompressionOptions = (GzipOptions) compressionOptions;
@@ -258,7 +274,7 @@ protected EmbeddedChannel newContentCompressor(ChannelHandlerContext ctx, CharSe
         if (DEFLATE.contentEqualsIgnoreCase(contentEncoding) || X_DEFLATE.contentEqualsIgnoreCase(contentEncoding)) {
             return newCompressionChannel(ctx, ZlibWrapper.ZLIB);
         }
-        if (brotliOptions != null && BR.contentEqualsIgnoreCase(contentEncoding)) {
+        if (Brotli.isAvailable() && brotliOptions != null && BR.contentEqualsIgnoreCase(contentEncoding)) {
             return new EmbeddedChannel(ctx.channel().id(), ctx.channel().metadata().hasDisconnect(),
                     ctx.channel().config(), new BrotliEncoder(brotliOptions.parameters()));
         }