[JGIT PATCH 00/14] TreeWalk D/F conflict detection

This series is about fixing the "mistake" in Git trees where
subtrees sort as through their name is "path/" and not "path".

Within a TreeWalk this is a problem because the tree contents:

    Tree 1     Tree 2
  ------------------------
    100644 a
               100644 a.c
               040000 a
    100644 b

needs to merge together both "a" paths from tree 1 and tree 2, but
these appear at different points in time when we merge-sort the two
trees together.

We use an infinite look-ahead and look-behind to identify these cases
and make the iteration look like this instead:

    Tree 1     Tree 2
  ------------------------
    100644 a   040000 a
               100644 a.c
    100644 b

which allows the application to handle the D/F conflict in a single
step, even though the contents of "a" may now be out-of-order within
the DirCache.  Fortunately DirCacheBuilder can automatically fix this
sort of ordering problem.


Shawn O. Pearce (14):
  Detect path names which overflow the name length field in the index
  Fix NB.decodeUInt16 to correctly handle the high byte
  Add test cases for NB.encode and NB.decode family of routines
  Fix DirCache's skip over null byte padding when reading a DIRC file
  Fix usage of assertEquals in DirCacheIteratorTest
  Refactor AbstractTreeIterator.pathCompare to force another mode
  Micro-optimize AbstractTreeIterator.pathCompare
  Optimize path comparsion within subtrees during TreeWalk
  Refactor AbstractTreeIterator semantics to start on first entry
  Make all AbstractTreeIterator implementations bi-directional
  Expose beginning of iterator indication from AbstractTreeIterator
  Allow application code to set ObjectIds in DirCacheEntry
  Create NameConflictTreeWalk to transparently detect D/F conflicts
  Add test case for NameConflictTreeWalk

 .../spearce/egit/core/ContainerTreeIterator.java   |    9 +-
 .../jgit/dircache/DirCacheBuilderIteratorTest.java |    2 +-
 .../jgit/dircache/DirCacheIteratorTest.java        |   28 +-
 .../jgit/treewalk/CanonicalTreeParserTest.java     |  261 ++++++++++++++++
 .../jgit/treewalk/NameConflictTreeWalkTest.java    |  205 ++++++++++++
 .../tst/org/spearce/jgit/util/NBTest.java          |  328 ++++++++++++++++++++
 .../src/org/spearce/jgit/dircache/DirCache.java    |    2 +-
 .../jgit/dircache/DirCacheBuildIterator.java       |    9 +-
 .../org/spearce/jgit/dircache/DirCacheEntry.java   |   41 +++-
 .../spearce/jgit/dircache/DirCacheIterator.java    |   84 +++--
 .../jgit/treewalk/AbstractTreeIterator.java        |  129 +++++---
 .../spearce/jgit/treewalk/CanonicalTreeParser.java |   94 +++++-
 .../spearce/jgit/treewalk/EmptyTreeIterator.java   |   12 +-
 .../spearce/jgit/treewalk/FileTreeIterator.java    |    5 +-
 .../jgit/treewalk/NameConflictTreeWalk.java        |  237 ++++++++++++++
 .../src/org/spearce/jgit/treewalk/TreeWalk.java    |   18 +-
 .../spearce/jgit/treewalk/WorkingTreeIterator.java |  132 ++++-----
 org.spearce.jgit/src/org/spearce/jgit/util/NB.java |   29 ++-
 18 files changed, 1418 insertions(+), 207 deletions(-)
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/treewalk/CanonicalTreeParserTest.java
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/treewalk/NameConflictTreeWalkTest.java
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/util/NBTest.java
 create mode 100644 org.spearce.jgit/src/org/spearce/jgit/treewalk/NameConflictTreeWalk.java

C Git supports long paths within the index file by setting the
length portion of the flags field to 4095 (0xfff) and then it
does a simple C strlen() on the remaining part of the string
to locate the first null byte.

The trick works because every index record must have between
1 and 8 null bytes trailing the entry as padding.  C Git had
this rule to make it easy to pass the mmap'd name portion of
an entry directly to system calls, and it helped to ensure
all members were aligned properly in memory.

We now support infinite length paths (well, up to 2GB) by
using the same encoding strategy, however paths under the
4095 limit still perform better as they do not require a
single byte read loop and a growing/shrinking byte buffer.

Signed-off-by: Shawn O. Pearce <redacted>
---
 .../jgit/dircache/DirCacheLargePathTest.java       |  106 ++++++++++++++++++++
 .../org/spearce/jgit/dircache/DirCacheEntry.java   |   39 ++++++--
 2 files changed, 136 insertions(+), 9 deletions(-)
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/dircache/DirCacheLargePathTest.java

diff --git a/org.spearce.jgit.test/tst/org/spearce/jgit/dircache/DirCacheLargePathTest.java b/org.spearce.jgit.test/tst/org/spearce/jgit/dircache/DirCacheLargePathTest.java
new file mode 100644
index 0000000..4ea286c
--- /dev/null
+++ b/org.spearce.jgit.test/tst/org/spearce/jgit/dircache/DirCacheLargePathTest.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2008, Google Inc.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Git Development Community nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.spearce.jgit.dircache;
+
+import java.io.IOException;
+
+import org.spearce.jgit.errors.CorruptObjectException;
+import org.spearce.jgit.lib.RepositoryTestCase;
+
+public class DirCacheLargePathTest extends RepositoryTestCase {
+	public void testPath_4090() throws Exception {
+		testLongPath(4090);
+	}
+
+	public void testPath_4094() throws Exception {
+		testLongPath(4094);
+	}
+
+	public void testPath_4095() throws Exception {
+		testLongPath(4095);
+	}
+
+	public void testPath_4096() throws Exception {
+		testLongPath(4096);
+	}
+
+	public void testPath_16384() throws Exception {
+		testLongPath(16384);
+	}
+
+	private void testLongPath(final int len) throws CorruptObjectException,
+			IOException {
+		final String longPath = makeLongPath(len);
+		final String shortPath = "~~~ shorter-path";
+
+		final DirCacheEntry longEnt = new DirCacheEntry(longPath);
+		final DirCacheEntry shortEnt = new DirCacheEntry(shortPath);
+		assertEquals(longPath, longEnt.getPathString());
+		assertEquals(shortPath, shortEnt.getPathString());
+
+		{
+			final DirCache dc1 = DirCache.lock(db);
+			{
+				final DirCacheBuilder b = dc1.builder();
+				b.add(longEnt);
+				b.add(shortEnt);
+				assertTrue(b.commit());
+			}
+			assertEquals(2, dc1.getEntryCount());
+			assertSame(longEnt, dc1.getEntry(0));
+			assertSame(shortEnt, dc1.getEntry(1));
+		}
+		{
+			final DirCache dc2 = DirCache.read(db);
+			assertEquals(2, dc2.getEntryCount());
+
+			assertNotSame(longEnt, dc2.getEntry(0));
+			assertEquals(longPath, dc2.getEntry(0).getPathString());
+
+			assertNotSame(shortEnt, dc2.getEntry(1));
+			assertEquals(shortPath, dc2.getEntry(1).getPathString());
+		}
+	}
+
+	private static String makeLongPath(final int len) {
+		final StringBuilder r = new StringBuilder(len);
+		for (int i = 0; i < len; i++)
+			r.append('a' + (i % 26));
+		return r.toString();
+	}
+}

diff --git a/org.spearce.jgit/src/org/spearce/jgit/dircache/DirCacheEntry.java b/org.spearce.jgit/src/org/spearce/jgit/dircache/DirCacheEntry.java
index 011bc16..dbd74b5 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/dircache/DirCacheEntry.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/dircache/DirCacheEntry.java

@@ -37,6 +37,8 @@
 
 package org.spearce.jgit.dircache;
 
+import java.io.ByteArrayOutputStream;
+import java.io.EOFException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;

@@ -105,18 +107,36 @@ DirCacheEntry(final byte[] sharedInfo, final int infoAt,
 		NB.readFully(in, info, infoOffset, INFO_LEN);
 
 		int pathLen = NB.decodeUInt16(info, infoOffset + P_FLAGS) & NAME_MASK;
-		if (pathLen == NAME_MASK)
-			throw new IOException("Path name too long for jgit");
-		path = new byte[pathLen];
-		NB.readFully(in, path, 0, pathLen);
+		int skipped = 0;
+		if (pathLen < NAME_MASK) {
+			path = new byte[pathLen];
+			NB.readFully(in, path, 0, pathLen);
+		} else {
+			final ByteArrayOutputStream tmp = new ByteArrayOutputStream();
+			{
+				final byte[] buf = new byte[NAME_MASK];
+				NB.readFully(in, buf, 0, NAME_MASK);
+				tmp.write(buf);
+			}
+			for (;;) {
+				final int c = in.read();
+				if (c < 0)
+					throw new EOFException("Short read of block.");
+				if (c == 0)
+					break;
+				tmp.write(c);
+			}
+			path = tmp.toByteArray();
+			pathLen = path.length;
+			skipped = 1; // we already skipped 1 '\0' above to break the loop.
+		}
 
 		// Index records are padded out to the next 8 byte alignment
 		// for historical reasons related to how C Git read the files.
 		//
 		final int actLen = INFO_LEN + pathLen;
 		final int expLen = (actLen + 8) & ~7;
-		if (actLen != expLen)
-			NB.skipFully(in, expLen - actLen);
+		NB.skipFully(in, expLen - actLen - skipped);
 	}
 
 	/**

@@ -140,9 +160,10 @@ public DirCacheEntry(final byte[] newPath) {
 		infoOffset = 0;
 
 		path = newPath;
-		if (path.length >= NAME_MASK)
-			throw new IllegalArgumentException("Path name too long for jgit");
-		NB.encodeInt16(info, infoOffset + P_FLAGS, path.length);
+		if (path.length < NAME_MASK)
+			NB.encodeInt16(info, infoOffset + P_FLAGS, path.length);
+		else
+			NB.encodeInt16(info, infoOffset + P_FLAGS, NAME_MASK);
 	}
 
 	void write(final OutputStream os) throws IOException {

-- 
1.6.0.96.g2fad1.dirty

Sorry about that, my git-send-email directory had this cover letter
laying around in it from last time.  There is no series, I only meant
to post the single patch "Support path names longer than 4095...".

Shawn O. Pearce (14):
  Detect path names which overflow the name length field in the index
  Fix NB.decodeUInt16 to correctly handle the high byte
  Add test cases for NB.encode and NB.decode family of routines
  Fix DirCache's skip over null byte padding when reading a DIRC file
  Fix usage of assertEquals in DirCacheIteratorTest
  Refactor AbstractTreeIterator.pathCompare to force another mode
  Micro-optimize AbstractTreeIterator.pathCompare
  Optimize path comparsion within subtrees during TreeWalk
  Refactor AbstractTreeIterator semantics to start on first entry
  Make all AbstractTreeIterator implementations bi-directional
  Expose beginning of iterator indication from AbstractTreeIterator
  Allow application code to set ObjectIds in DirCacheEntry
  Create NameConflictTreeWalk to transparently detect D/F conflicts
  Add test case for NameConflictTreeWalk

...

 18 files changed, 1418 insertions(+), 207 deletions(-)

-- 
Shawn.