Use reflection for Commons Compress codecs to avoid hard dep.

httpclient5/pom.xml

@@ -77,11 +77,6 @@
       <artifactId>log4j-core</artifactId>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>org.brotli</groupId>
-      <artifactId>dec</artifactId>
-      <optional>true</optional>
-    </dependency>
     <dependency>
       <groupId>com.kohlschutter.junixsocket</groupId>
       <artifactId>junixsocket-core</artifactId>
@@ -121,6 +116,7 @@
     <dependency>
       <groupId>com.aayushatharva.brotli4j</groupId>
       <artifactId>brotli4j</artifactId>
+      <optional>true</optional>
     </dependency>
   </dependencies>
 

httpclient5/src/main/java/org/apache/hc/client5/http/entity/BrotliInputStreamFactory.java

@@ -29,9 +29,10 @@
 import java.io.IOException;
 import java.io.InputStream;
 
+import com.aayushatharva.brotli4j.decoder.BrotliInputStream;
+
 import org.apache.hc.core5.annotation.Contract;
 import org.apache.hc.core5.annotation.ThreadingBehavior;
-import org.brotli.dec.BrotliInputStream;
 
 /**
  * {@link InputStreamFactory} for handling Brotli Content Coded responses.

httpclient5/src/main/java/org/apache/hc/client5/http/entity/compress/CommonsCompressCodecFactory.java

@@ -0,0 +1,177 @@
+/*
+ * ====================================================================
+ * 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+
+package org.apache.hc.client5.http.entity.compress;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.lang.reflect.Method;
+import java.util.Locale;
+
+import org.apache.hc.core5.annotation.Contract;
+import org.apache.hc.core5.annotation.Internal;
+import org.apache.hc.core5.annotation.ThreadingBehavior;
+import org.apache.hc.core5.io.IOFunction;
+
+/**
+ * Reflection-based codecs factory for Apache Commons Compress.
+ * <p>
+ * This class never links Commons Compress at compile time. At runtime, it
+ * reflectively locates {@code CompressorStreamFactory} and creates encoder /
+ * decoder streams for IANA tokens (e.g. {@code "zstd"}, {@code "xz"}) only
+ * when the relevant classes (and any helper JARs) are present.
+ * </p>
+ * <p>
+ * Use {@link #runtimeAvailable(ContentCoding)} to probe whether a given coding
+ * can be provided by the current classpath configuration. Callers can then
+ * register codecs conditionally without hard dependencies.
+ * </p>
+ *
+ * @since 5.6
+ */
+@Internal
+@Contract(threading = ThreadingBehavior.STATELESS)
+final class CommonsCompressCodecFactory {
+
+    private static final String FACTORY_CLASS =
+            "org.apache.commons.compress.compressors.CompressorStreamFactory";
+
+    // CC stream classes
+    private static final String CC_BROTLI = "org.apache.commons.compress.compressors.brotli.BrotliCompressorInputStream";
+    private static final String CC_ZSTD = "org.apache.commons.compress.compressors.zstandard.ZstdCompressorInputStream";
+    private static final String CC_XZ = "org.apache.commons.compress.compressors.xz.XZCompressorInputStream";
+    private static final String CC_LZMA = "org.apache.commons.compress.compressors.lzma.LZMACompressorInputStream";
+    private static final String CC_LZ4_F = "org.apache.commons.compress.compressors.lz4.FramedLZ4CompressorInputStream";
+    private static final String CC_LZ4_B = "org.apache.commons.compress.compressors.lz4.BlockLZ4CompressorInputStream";
+    private static final String CC_BZIP2 = "org.apache.commons.compress.compressors.bzip2.BZip2CompressorInputStream";
+    private static final String CC_PACK200 = "org.apache.commons.compress.compressors.pack200.Pack200CompressorInputStream";
+    private static final String CC_DEFLATE64 = "org.apache.commons.compress.compressors.deflate64.Deflate64CompressorInputStream";
+
+    // Helper libs
+    private static final String H_BROTLI = "org.brotli.dec.BrotliInputStream";
+    private static final String H_ZSTD = "com.github.luben.zstd.ZstdInputStream";
+    private static final String H_XZ = "org.tukaani.xz.XZInputStream";
+
+    private CommonsCompressCodecFactory() {
+    }
+
+    private static boolean isPresent(final String className) {
+        try {
+            Class.forName(className, false, CommonsCompressCodecFactory.class.getClassLoader());
+            return true;
+        } catch (final ClassNotFoundException | LinkageError ex) {
+            return false;
+        }
+    }
+
+    /**
+     * Creates a lazy decoder that instantiates the Commons Compress stream
+     * reflectively on first use. Throws {@link IOException} if Commons Compress
+     * is not available or the codec cannot be created.
+     */
+    static IOFunction<InputStream, InputStream> decoder(final String token) {
+        final String enc = token.toLowerCase(Locale.ROOT);
+        return in -> {
+            try {
+                final ClassLoader cl = CommonsCompressCodecFactory.class.getClassLoader();
+                final Class<?> factoryCls = Class.forName(FACTORY_CLASS, false, cl);
+                final Object factory = factoryCls.getConstructor().newInstance();
+                final Method m = factoryCls.getMethod("createCompressorInputStream", String.class, InputStream.class);
+                final Object stream = m.invoke(factory, enc, in);
+                return (InputStream) stream;
+            } catch (final ClassNotFoundException e) {
+                throw new IOException("Apache Commons Compress is not on the classpath", e);
+            } catch (final ReflectiveOperationException | IllegalArgumentException | LinkageError e) {
+                throw new IOException("Unable to decode Content-Encoding '" + enc + '\'', e);
+            }
+        };
+    }
+
+    /**
+     * Creates a lazy encoder that instantiates the Commons Compress stream
+     * reflectively on first use. Throws {@link IOException} if Commons Compress
+     * is not available or the codec cannot be created.
+     */
+    static IOFunction<OutputStream, OutputStream> encoder(final String token) {
+        final String enc = token.toLowerCase(Locale.ROOT);
+        return out -> {
+            try {
+                final ClassLoader cl = CommonsCompressCodecFactory.class.getClassLoader();
+                final Class<?> factoryCls = Class.forName(FACTORY_CLASS, false, cl);
+                final Object factory = factoryCls.getConstructor().newInstance();
+                final Method m = factoryCls.getMethod("createCompressorOutputStream", String.class, OutputStream.class);
+                final Object cos = m.invoke(factory, enc, out);
+                return (OutputStream) cos;
+            } catch (final ClassNotFoundException e) {
+                throw new IOException("Apache Commons Compress is not on the classpath", e);
+            } catch (final ReflectiveOperationException | IllegalArgumentException | LinkageError e) {
+                throw new IOException("Unable to encode using Content-Encoding '" + enc + '\'', e);
+            }
+        };
+    }
+
+    /**
+     * Best-effort availability probe for optional Commons-Compress codecs.
+     * <p>
+     * Returns {@code true} only if the CC factory and the codec-specific
+     * implementation (and helper classes if required) are present on the
+     * classpath. Built-in gzip/deflate are handled elsewhere and are not
+     * probed here.
+     * </p>
+     */
+    static boolean runtimeAvailable(final ContentCoding coding) {
+        if (coding == null) {
+            return false;
+        }
+        if (!isPresent(FACTORY_CLASS)) {
+            return false;
+        }
+        switch (coding) {
+            case BROTLI:
+                return isPresent(CC_BROTLI) && isPresent(H_BROTLI);
+            case ZSTD:
+                return isPresent(CC_ZSTD) && isPresent(H_ZSTD);
+            case XZ:
+                return isPresent(CC_XZ) && isPresent(H_XZ);
+            case LZMA:
+                return isPresent(CC_LZMA) && isPresent(H_XZ);
+            case LZ4_FRAMED:
+                return isPresent(CC_LZ4_F);
+            case LZ4_BLOCK:
+                return isPresent(CC_LZ4_B);
+            case BZIP2:
+                return isPresent(CC_BZIP2);
+            case PACK200:
+                return isPresent(CC_PACK200) || isPresent("java.util.jar.Pack200");
+            case DEFLATE64:
+                return isPresent(CC_DEFLATE64);
+            default:
+                return false;
+        }
+    }
+}

httpclient5/src/main/java/org/apache/hc/client5/http/entity/compress/CommonsCompressSupport.java

@@ -33,9 +33,12 @@
 import org.apache.hc.core5.annotation.ThreadingBehavior;
 
 /**
- * Utility that answers the question “Is Apache Commons Compress
- * on the class-path and in a usable state?”  Both the encoder and
- * decoder registries rely on this information.
+ * Lightweight guard that checks whether the Commons Compress factory
+ * class is loadable with the current class loader.
+ * <p>
+ * Used by the codec registry to decide if reflective wiring of optional
+ * codecs should even be attempted.
+ * </p>
  *
  * @since 5.6
  */
@@ -46,8 +49,11 @@ final class CommonsCompressSupport {
     private static final String CCSF =
             "org.apache.commons.compress.compressors.CompressorStreamFactory";
 
-    /** Non-instantiable. */
-    private CommonsCompressSupport() { }
+    /**
+     * Non-instantiable.
+     */
+    private CommonsCompressSupport() {
+    }
 
     /**
      * Returns {@code true} if the core Commons Compress class can be loaded