Allow handling of odd-sized short Shas in OdbBackend

lofcz · Aug 15, 2013 · 7eb9ccf · 7eb9ccf
1 parent 3e29b4b
commit 7eb9ccf
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Showing 2 changed files with 60 additions and 5 deletions.
diff --git a/LibGit2Sharp.Tests/OdbBackendFixture.cs b/LibGit2Sharp.Tests/OdbBackendFixture.cs
@@ -3,6 +3,7 @@
 using System.IO;
 using System.Linq;
 using System.Security.Cryptography;
+using System.Text;
 using LibGit2Sharp.Tests.TestHelpers;
 using Xunit;
 
@@ -85,6 +86,43 @@ public void CanGeneratePredictableObjectShasWithAProvidedBackend()
             }
         }
 
+        [Fact]
+        public void CanRetrieveObjectsThroughOddSizedShortShas()
+        {
+            string repoPath = InitNewRepository();
+
+            using (var repo = new Repository(repoPath))
+            {
+                var backend = new MockOdbBackend();
+                repo.ObjectDatabase.AddBackend(backend, priority: 5);
+
+                AddCommitToRepo(repo);
+
+                var blob1 = repo.Lookup<Blob>("9daeaf");
+                Assert.NotNull(blob1);
+
+                const string dummy = "dummy\n";
+
+                // Inserts a fake blob with a similarly prefixed sha
+                var fakeId = new ObjectId("9daeaf0000000000000000000000000000000000");
+                using (var ms = new MemoryStream(Encoding.UTF8.GetBytes(dummy)))
+                {
+                    Assert.Equal(0, backend.Write(fakeId.RawId, ms, dummy.Length, ObjectType.Blob));
+                }
+
+                var blob2 = repo.Lookup<Blob>(fakeId);
+                Assert.NotNull(blob2);
+
+                Assert.Throws<AmbiguousSpecificationException>(() => repo.Lookup<Blob>("9daeaf"));
+
+                var newBlob1 = repo.Lookup("9daeafb");
+                var newBlob2 = repo.Lookup("9daeaf0");
+
+                Assert.Equal(blob1, newBlob1);
+                Assert.Equal(blob2, newBlob2);
+            }
+        }
+
         #region MockOdbBackend
 
         private class MockOdbBackend : OdbBackend
@@ -125,7 +163,7 @@ public override int Read(byte[] oid, out Stream data, out ObjectType objectType)
                 return GIT_ENOTFOUND;
             }
 
-            public override int ReadPrefix(byte[] shortOid, out byte[] oid, out Stream data, out ObjectType objectType)
+            public override int ReadPrefix(byte[] shortOid, int len, out byte[] oid, out Stream data, out ObjectType objectType)
             {
                 oid = null;
                 data = null;
@@ -137,7 +175,8 @@ public override int ReadPrefix(byte[] shortOid, out byte[] oid, out Stream data,
                 {
                     bool match = true;
 
-                    for (int i = 0; i < shortOid.Length; i++)
+                    int length = len >> 1;
+                    for (int i = 0; i < length; i++)
                     {
                         if (gitObject.ObjectId[i] != shortOid[i])
                         {
@@ -146,6 +185,17 @@ public override int ReadPrefix(byte[] shortOid, out byte[] oid, out Stream data,
                         }
                     }
 
+                    if (match && ((len & 1) == 1))
+                    {
+                        var a = gitObject.ObjectId[length] >> 4;
+                        var b = shortOid[length] >> 4;
+
+                        if (a != b)
+                        {
+                            match = false;
+                        }
+                    }
+
                     if (!match)
                     {
                         continue;

diff --git a/LibGit2Sharp/OdbBackend.cs b/LibGit2Sharp/OdbBackend.cs
@@ -61,6 +61,7 @@ public abstract int Read(byte[] oid,
         /// Requests that this backend read an object. The object ID may not be complete (may be a prefix).
         /// </summary>
         public abstract int ReadPrefix(byte[] shortOid,
+            int prefixLen,
             out byte[] oid,
             out Stream data,
             out ObjectType objectType);
@@ -275,10 +276,14 @@ private unsafe static int ReadPrefix(
                     {
                         // The length of short_oid is described in characters (40 per full ID) vs. bytes (20)
                         // which is what we care about.
-                        byte[] shortOidArray = new byte[(long)len >> 1];
-                        Array.Copy(short_oid.Id, shortOidArray, shortOidArray.Length);
+                        var oidLen = (int)len;
 
-                        int toReturn = odbBackend.ReadPrefix(shortOidArray, out oid, out dataStream, out objectType);
+                        // Ensure we allocate enough space to cope with odd-sized prefix
+                        int arraySize = (oidLen + 1) >> 1;
+                        var shortOidArray = new byte[arraySize];
+                        Array.Copy(short_oid.Id, shortOidArray, arraySize);
+
+                        int toReturn = odbBackend.ReadPrefix(shortOidArray, oidLen, out oid, out dataStream, out objectType);
 
                         if (0 == toReturn)
                         {