Add optional support for brotli content encoding

pom.xml

@@ -68,6 +68,13 @@
             <version>4.13.2</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+          <groupId>org.brotli</groupId>
+          <artifactId>dec</artifactId>
+          <version>0.1.2</version>
+          <scope>compile</scope>
+          <optional>true</optional>
+        </dependency>
     </dependencies>
 
     <properties>

src/org/netpreserve/jwarc/BrotliUtils.java

@@ -0,0 +1,22 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (C) 2024 National Library of Australia and the jwarc contributors
+ */
+
+package org.netpreserve.jwarc;
+
+import java.io.IOException;
+import java.nio.channels.Channels;
+import java.nio.channels.ReadableByteChannel;
+
+import org.brotli.dec.BrotliInputStream;
+
+/**
+ * Utility class to read brotli-encoded data, based on org.brotli:dec.
+ */
+public final class BrotliUtils {
+
+    public static ReadableByteChannel brotliChannel(ReadableByteChannel brotli) throws IOException {
+        return Channels.newChannel(new BrotliInputStream(Channels.newInputStream(brotli)));
+    }
+}

src/org/netpreserve/jwarc/DecodedBody.java

@@ -35,7 +35,12 @@ private DecodedBody(ReadableByteChannel channel, Encoding encoding) throws IOExc
             this.channel = IOUtils.gunzipChannel(channel);
             break;
         case BROTLI:
-            throw new IOException("Brotli encoding not yet supported");
+            try {
+                this.channel = BrotliUtils.brotliChannel(channel);
+            } catch (NoClassDefFoundError e) {
+                throw new IOException("Brotli decoder not found, please install org.brotli:dec", e);
+            }
+            break;
         default:
             throw new IOException("Unsupported encoding");
         }

src/org/netpreserve/jwarc/HttpMessage.java

@@ -42,6 +42,8 @@ public MessageBody bodyDecoded() throws IOException {
         } else if (contentEncodings.get(0).equalsIgnoreCase("gzip")
                 || contentEncodings.get(0).equalsIgnoreCase("x-gzip")) {
             return DecodedBody.create(payload, DecodedBody.Encoding.GZIP);
+        } else if (contentEncodings.get(0).equalsIgnoreCase("br")) {
+            return DecodedBody.create(payload, DecodedBody.Encoding.BROTLI);
         } else if (contentEncodings.get(0).equalsIgnoreCase("deflate")) {
             return DecodedBody.create(payload, DecodedBody.Encoding.DEFLATE);
         } else {