Bypass extra array-copy in deflate decompression

Author: Col-E

src/main/java/software/coley/llzip/format/compression/DeflateDecompressor.java

@@ -1,10 +1,9 @@
 package software.coley.llzip.format.compression;
 
 import software.coley.llzip.format.model.LocalFileHeader;
-import software.coley.llzip.util.BufferData;
 import software.coley.llzip.util.ByteData;
+import software.coley.llzip.util.FastWrapOutputStream;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
@@ -21,7 +20,7 @@ public ByteData decompress(LocalFileHeader header, ByteData data) throws IOExcep
 		if (header.getCompressionMethod() != ZipCompressions.DEFLATED)
 			throw new IOException("LocalFileHeader contents not using 'Deflated'!");
 		Inflater inflater = new Inflater(true);
-		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		FastWrapOutputStream out = new FastWrapOutputStream();
 		try {
 			byte[] output = new byte[1024];
 			byte[] buffer = new byte[1024];
@@ -43,12 +42,12 @@ public ByteData decompress(LocalFileHeader header, ByteData data) throws IOExcep
 					out.write(output, 0, count);
 				}
 			} while (!inflater.finished() && !inflater.needsDictionary());
-		}catch (DataFormatException e) {
+		} catch (DataFormatException e) {
 			String s = e.getMessage();
 			throw (ZipException) new ZipException(s != null ? null : "Invalid ZLIB data format").initCause(e);
 		} finally {
 			inflater.end();
 		}
-		return BufferData.wrap(out.toByteArray());
+		return out.wrap();
 	}
 }

src/main/java/software/coley/llzip/format/compression/UnsafeDeflateDecompressor.java

@@ -1,11 +1,10 @@
 package software.coley.llzip.format.compression;
 
 import software.coley.llzip.format.model.LocalFileHeader;
-import software.coley.llzip.util.BufferData;
 import software.coley.llzip.util.ByteData;
+import software.coley.llzip.util.FastWrapOutputStream;
 import software.coley.llzip.util.UnsafeInflater;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.util.ArrayDeque;
 import java.util.Deque;
@@ -24,7 +23,7 @@ public class UnsafeDeflateDecompressor implements Decompressor {
 	public ByteData decompress(LocalFileHeader header, ByteData data) throws IOException {
 		if (header.getCompressionMethod() != ZipCompressions.DEFLATED)
 			throw new IOException("LocalFileHeader contents not using 'Deflated'!");
-		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		FastWrapOutputStream out = new FastWrapOutputStream();
 		UnsafeInflater inflater;
 		Deque<UnsafeInflater> inflaters = INFLATERS;
 		synchronized (inflaters) {
@@ -72,6 +71,6 @@ public ByteData decompress(LocalFileHeader header, ByteData data) throws IOExcep
 				inflater.end();
 			}
 		}
-		return BufferData.wrap(out.toByteArray());
+		return out.wrap();
 	}
 }

src/main/java/software/coley/llzip/util/BufferData.java

@@ -153,4 +153,18 @@ public static BufferData wrap(ByteBuffer buffer) {
 	public static BufferData wrap(byte[] array) {
 		return new BufferData(ByteBuffer.wrap(array).order(ByteOrder.LITTLE_ENDIAN), new AtomicBoolean());
 	}
+
+	/**
+	 * @param array
+	 * 		Byte array to wrap.
+	 * @param offset
+	 * 		Offset into the array to start at.
+	 * @param length
+	 * 		Length of content.
+	 *
+	 * @return Buffer data.
+	 */
+	public static BufferData wrap(byte[] array, int offset, int length) {
+		return new BufferData(ByteBuffer.wrap(array, offset, length).order(ByteOrder.LITTLE_ENDIAN), new AtomicBoolean());
+	}
 }

src/main/java/software/coley/llzip/util/FastWrapOutputStream.java

@@ -0,0 +1,9 @@
+package software.coley.llzip.util;
+
+import java.io.ByteArrayOutputStream;
+
+public final class FastWrapOutputStream extends ByteArrayOutputStream {
+	public BufferData wrap() {
+		return BufferData.wrap(buf, 0, count);
+	}
+}