ApplyCommand: add a stream to apply a delta patch

Add a new BinaryDeltaInputStream that applies a delta provided by
another InputStream to a given base. Because delta application needs
random access to the base, the base itself cannot be yet another
InputStream. But at least this enables streaming of the result.

Add a simple test using delta hunks generated by C git.

Bug: 371725
Change-Id: Ibd26fa2f49860737ad5c5387f7f4870d3e85e628
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

3 files changed, 105 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.forward b/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.forward
new file mode 100644
index 0000000000..878b167ae9
--- /dev/null
+++ b/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.forward
@@ -0,0 +1 @@
+ScmZp0Xmwa1z*+$U3j_csN(Dmz
diff --git a/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.reverse b/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.reverse
new file mode 100644
index 0000000000..7ff7a08ad0
--- /dev/null
+++ b/org.eclipse.jgit.test/tst-rsrc/org/eclipse/jgit/util/io/delta1.reverse
@@ -0,0 +1 @@
+TcmZp5XmD5{u!xa=5hEi28?FP4
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/BinaryDeltaInputStreamTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/BinaryDeltaInputStreamTest.java
new file mode 100644
index 0000000000..d9297fcd9c
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/io/BinaryDeltaInputStreamTest.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2021 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.util.io;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.util.zip.InflaterInputStream;
+
+import org.junit.Test;
+
+/**
+ * Crude tests for the {@link BinaryDeltaInputStream} using delta diffs
+ * generated by C git.
+ */
+public class BinaryDeltaInputStreamTest {
+
+	private InputStream getBinaryHunk(String name) {
+		return this.getClass().getResourceAsStream(name);
+	}
+
+	@Test
+	public void testBinaryDelta() throws Exception {
+		// Prepare our test data
+		byte[] data = new byte[8192];
+		for (int i = 0; i < data.length; i++) {
+			data[i] = (byte) (255 - (i % 256));
+		}
+		// Same, but with five 'x' inserted in the middle.
+		int middle = data.length / 2;
+		byte[] newData = new byte[data.length + 5];
+		System.arraycopy(data, 0, newData, 0, middle);
+		for (int i = 0; i < 5; i++) {
+			newData[middle + i] = 'x';
+		}
+		System.arraycopy(data, middle, newData, middle + 5, middle);
+		// delta1.forward has the instructions
+		// @formatter:off
+		// COPY 0 4096
+		// INSERT 5 xxxxx
+		// COPY 0 4096
+		// @formatter:on
+		// Note that the way we built newData could be expressed as
+		// @formatter:off
+		// COPY 0 4096
+		// INSERT 5 xxxxx
+		// COPY 4096 4096
+		// @formatter:on
+		try (ByteArrayOutputStream out = new ByteArrayOutputStream();
+				BinaryDeltaInputStream input = new BinaryDeltaInputStream(data,
+						new InflaterInputStream(new BinaryHunkInputStream(
+								getBinaryHunk("delta1.forward"))))) {
+			byte[] buf = new byte[1024];
+			int n;
+			while ((n = input.read(buf)) >= 0) {
+				out.write(buf, 0, n);
+			}
+			assertArrayEquals(newData, out.toByteArray());
+			assertTrue(input.isFullyConsumed());
+		}
+		// delta1.reverse has the instructions
+		// @formatter:off
+		// COPY 0 4096
+		// COPY 256 3840
+		// COPY 256 256
+		// @formatter:on
+		// Note that there are alternatives, for instance
+		// @formatter:off
+		// COPY 0 4096
+		// COPY 4101 4096
+		// @formatter:on
+		// or
+		// @formatter:off
+		// COPY 0 4096
+		// COPY 0 4096
+		// @formatter:on
+		try (ByteArrayOutputStream out = new ByteArrayOutputStream();
+				BinaryDeltaInputStream input = new BinaryDeltaInputStream(
+						newData,
+						new InflaterInputStream(new BinaryHunkInputStream(
+								getBinaryHunk("delta1.reverse"))))) {
+			long expectedSize = input.getExpectedResultSize();
+			assertEquals(data.length, expectedSize);
+			byte[] buf = new byte[1024];
+			int n;
+			while ((n = input.read(buf)) >= 0) {
+				out.write(buf, 0, n);
+			}
+			assertArrayEquals(data, out.toByteArray());
+			assertTrue(input.isFullyConsumed());
+		}
+	}
+}