Implement ObjectDatabase.ShortenObjectId()

LibGit2Sharp.Tests/ObjectDatabaseFixture.cs

@@ -556,5 +556,47 @@ public void CalculatingHistoryDivergenceWithBadParamsThrows()
                     () => repo.ObjectDatabase.CalculateHistoryDivergence(null, repo.Head.Tip));
             }
         }
+
+        [Fact]
+        public void CanShortenObjectIdentifier()
+        {
+            /*
+             * $ echo "aabqhq" | git hash-object -t blob --stdin
+             * dea509d0b3cb8ee0650f6ca210bc83f4678851ba
+             * 
+             * $ echo "aaazvc" | git hash-object -t blob --stdin
+             * dea509d097ce692e167dfc6a48a7a280cc5e877e
+             */
+
+            string path = CloneBareTestRepo();
+            using (var repo = new Repository(path))
+            {
+                repo.Config.Set("core.abbrev", 4);
+
+                Blob blob1 = CreateBlob(repo, "aabqhq\n");
+                Assert.Equal("dea509d0b3cb8ee0650f6ca210bc83f4678851ba", blob1.Sha);
+
+                Assert.Equal("dea5", repo.ObjectDatabase.ShortenObjectId(blob1));
+                Assert.Equal("dea509d0b3cb", repo.ObjectDatabase.ShortenObjectId(blob1, 12));
+                Assert.Equal("dea509d0b3cb8ee0650f6ca210bc83f4678851b", repo.ObjectDatabase.ShortenObjectId(blob1, 39));
+
+                Blob blob2 = CreateBlob(repo, "aaazvc\n");
+                Assert.Equal("dea509d09", repo.ObjectDatabase.ShortenObjectId(blob2));
+                Assert.Equal("dea509d09", repo.ObjectDatabase.ShortenObjectId(blob2, 4));
+                Assert.Equal("dea509d0b", repo.ObjectDatabase.ShortenObjectId(blob1));
+                Assert.Equal("dea509d0b", repo.ObjectDatabase.ShortenObjectId(blob1, 7));
+
+                Assert.Equal("dea509d0b3cb", repo.ObjectDatabase.ShortenObjectId(blob1, 12));
+                Assert.Equal("dea509d097ce", repo.ObjectDatabase.ShortenObjectId(blob2, 12));
+            }
+        }
+
+        private static Blob CreateBlob(Repository repo, string content)
+        {
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(content)))
+            {
+                return repo.ObjectDatabase.CreateBlob(stream);
+            }
+        }
     }
 }

LibGit2Sharp.Tests/OdbBackendFixture.cs

@@ -177,6 +177,50 @@ public void CanPushWithACustomBackend()
             }
         }
 
+        [Fact]
+        public void CanShortenObjectIdentifier()
+        {
+            /*
+             * $ echo "aabqhq" | git hash-object -t blob --stdin
+             * dea509d0b3cb8ee0650f6ca210bc83f4678851ba
+             * 
+             * $ echo "aaazvc" | git hash-object -t blob --stdin
+             * dea509d097ce692e167dfc6a48a7a280cc5e877e
+             */
+
+            string path = CloneBareTestRepo();
+            using (var repo = new Repository(path))
+            {
+                repo.ObjectDatabase.AddBackend(new MockOdbBackend(), 5);
+
+                repo.Config.Set("core.abbrev", 4);
+
+                Blob blob1 = CreateBlob(repo, "aabqhq\n");
+                Assert.Equal("dea509d0b3cb8ee0650f6ca210bc83f4678851ba", blob1.Sha);
+
+                Assert.Equal("dea5", repo.ObjectDatabase.ShortenObjectId(blob1));
+                Assert.Equal("dea509d0b3cb", repo.ObjectDatabase.ShortenObjectId(blob1, 12));
+                Assert.Equal("dea509d0b3cb8ee0650f6ca210bc83f4678851b", repo.ObjectDatabase.ShortenObjectId(blob1, 39));
+
+                Blob blob2 = CreateBlob(repo, "aaazvc\n");
+                Assert.Equal("dea509d09", repo.ObjectDatabase.ShortenObjectId(blob2));
+                Assert.Equal("dea509d09", repo.ObjectDatabase.ShortenObjectId(blob2, 4));
+                Assert.Equal("dea509d0b", repo.ObjectDatabase.ShortenObjectId(blob1));
+                Assert.Equal("dea509d0b", repo.ObjectDatabase.ShortenObjectId(blob1, 7));
+
+                Assert.Equal("dea509d0b3cb", repo.ObjectDatabase.ShortenObjectId(blob1, 12));
+                Assert.Equal("dea509d097ce", repo.ObjectDatabase.ShortenObjectId(blob2, 12));
+            }
+        }
+
+        private static Blob CreateBlob(Repository repo, string content)
+        {
+            using (var stream = new MemoryStream(Encoding.UTF8.GetBytes(content)))
+            {
+                return repo.ObjectDatabase.CreateBlob(stream);
+            }
+        }
+
         #region MockOdbBackend
 
         private class MockOdbBackend : OdbBackend
@@ -190,6 +234,7 @@ protected override OdbBackendOperations SupportedOperations
                         OdbBackendOperations.Write |
                         OdbBackendOperations.WriteStream |
                         OdbBackendOperations.Exists |
+                        OdbBackendOperations.ExistsPrefix |
                         OdbBackendOperations.ForEach |
                         OdbBackendOperations.ReadHeader;
                 }
@@ -301,6 +346,37 @@ public override bool Exists(ObjectId oid)
                 return m_objectIdToContent.ContainsKey(oid);
             }
 
+            public override int ExistsPrefix(string shortSha, out ObjectId found)
+            {
+                found = null; 
+                int numFound = 0;
+
+                foreach (ObjectId id in m_objectIdToContent.Keys)
+                {
+                    if (!id.Sha.StartsWith(shortSha))
+                    {
+                        continue;
+                    }
+
+                    found = id;
+                    numFound++;
+
+                    if (numFound > 1)
+                    {
+                        found = null;
+                        return (int) ReturnCode.GIT_EAMBIGUOUS;
+                    }
+                }
+
+                if (numFound == 0)
+                {
+                    found = null;
+                    return (int)ReturnCode.GIT_ENOTFOUND;
+                }
+
+                return (int)ReturnCode.GIT_OK;
+            }
+
             public override int ReadHeader(ObjectId oid, out int length, out ObjectType objectType)
             {
                 objectType = default(ObjectType);

LibGit2Sharp/Core/GitOdbBackend.cs

@@ -30,7 +30,7 @@ static GitOdbBackend()
         public writestream_callback WriteStream;
         public readstream_callback ReadStream;
         public exists_callback Exists;
-        public IntPtr ExistsPrefix;
+        public exists_prefix_callback ExistsPrefix;
         public IntPtr Refresh;
         public foreach_callback Foreach;
         public IntPtr Writepack;
@@ -157,6 +157,23 @@ public delegate bool exists_callback(
             IntPtr backend,
             ref GitOid oid);
 
+        /// <summary>
+        /// The backend is passed a short OID and the number of characters in that short OID.
+        /// The backend is asked to return a value that indicates whether or not
+        /// the object exists in the backing store. The short OID might not be long enough to resolve
+        /// to just one object. In that case the backend should return GIT_EAMBIGUOUS.
+        /// </summary>
+        /// <param name="found_oid">[out] If the call is successful, the backend will write the full OID if the object here.</param>
+        /// <param name="backend">[in] A pointer to the backend which is being asked to perform the task.</param>
+        /// <param name="short_oid">[in] The short-form OID which the backend is being asked to look up.</param>
+        /// <param name="len">[in] The length of the short-form OID (short_oid).</param>
+        /// <returns>1 if the object exists, 0 if the object doesn't; an error code otherwise.</returns>
+        public delegate int exists_prefix_callback(
+            ref GitOid found_oid,
+            IntPtr backend,
+            ref GitOid short_oid,
+            UIntPtr len);
+
         /// <summary>
         /// The backend is passed a callback function and a void* to pass through to the callback. The backend is
         /// asked to iterate through all objects in the backing store, invoking the callback for each item.

LibGit2Sharp/Core/NativeMethods.cs

@@ -753,6 +753,11 @@ internal static extern int git_object_peel(
             GitObjectSafeHandle obj,
             GitObjectType type);
 
+        [DllImport(libgit2)]
+        internal static extern int git_object_short_id(
+            GitBuf buf,
+            GitObjectSafeHandle obj);
+
         [DllImport(libgit2)]
         internal static extern GitObjectType git_object_type(GitObjectSafeHandle obj);
 

LibGit2Sharp/Core/Proxy.cs

@@ -1251,6 +1251,19 @@ public static GitObjectSafeHandle git_object_peel(RepositorySafeHandle repo, Obj
             }
         }
 
+        public static string git_object_short_id(RepositorySafeHandle repo, ObjectId id)
+        {
+            using (ThreadAffinity())
+            using (var obj = new ObjectSafeWrapper(id, repo))
+            using (var buf = new GitBuf())
+            {
+                int res = NativeMethods.git_object_short_id(buf, obj.ObjectPtr);
+                Ensure.Int32Result(res);
+
+                return LaxUtf8Marshaler.FromNative(buf.ptr);
+            }
+        }
+
         public static GitObjectType git_object_type(GitObjectSafeHandle obj)
         {
             return NativeMethods.git_object_type(obj);

LibGit2Sharp/ObjectDatabase.cs

@@ -368,5 +368,30 @@ public virtual HistoryDivergence CalculateHistoryDivergence(Commit one, Commit a
 
             return new HistoryDivergence(repo, one, another);
         }
+
+        /// <summary>
+        /// Calculates the current shortest abbreviated <see cref="ObjectId"/>
+        /// string representation for a <see cref="GitObject"/>.
+        /// </summary>
+        /// <param name="gitObject">The <see cref="GitObject"/> which identifier should be shortened.</param>
+        /// <param name="minLength">Minimum length of the shortened representation.</param>
+        /// <returns>A short string representation of the <see cref="ObjectId"/>.</returns>
+        public virtual string ShortenObjectId(GitObject gitObject, int? minLength = null)
+        {
+            if (minLength.HasValue && (minLength <= 0 || minLength > ObjectId.HexSize))
+            {
+                throw new ArgumentOutOfRangeException("minLength", minLength,
+                    string.Format("Expected value should be greater than zero and less than or equal to {0}.", ObjectId.HexSize));
+            }
+
+            string shortSha = Proxy.git_object_short_id(repo.Handle, gitObject.Id);
+
+            if (minLength == null || (minLength <= shortSha.Length))
+            {
+                return shortSha;
+            }
+
+            return gitObject.Sha.Substring(0, minLength.Value);
+        }
     }
 }

LibGit2Sharp/ObjectId.cs

@@ -11,13 +11,13 @@ namespace LibGit2Sharp
     public sealed class ObjectId : IEquatable<ObjectId>
     {
         private readonly GitOid oid;
-        private const int rawSize = 20;
+        private const int rawSize = GitOid.Size;
         private readonly string sha;
 
         /// <summary>
         /// Size of the string-based representation of a SHA-1.
         /// </summary>
-        private const int HexSize = rawSize * 2;
+        internal const int HexSize = rawSize * 2;
 
         private const string hexDigits = "0123456789abcdef";
         private static readonly byte[] reverseHexDigits = BuildReverseHexDigits();

LibGit2Sharp/OdbBackend.cs

@@ -106,6 +106,11 @@ public abstract int WriteStream(
         /// </summary>
         public abstract bool Exists(ObjectId id);
 
+        /// <summary>
+        /// Requests that this backend check if an object ID exists. The object ID may not be complete (may be a prefix).
+        /// </summary>
+        public abstract int ExistsPrefix(string shortSha, out ObjectId found);
+
         /// <summary>
         /// Requests that this backend enumerate all items in the backing store.
         /// </summary>
@@ -169,6 +174,11 @@ internal IntPtr GitOdbBackendPointer
                         nativeBackend.Exists = BackendEntryPoints.ExistsCallback;
                     }
 
+                    if ((supportedOperations & OdbBackendOperations.ExistsPrefix) != 0)
+                    {
+                        nativeBackend.ExistsPrefix = BackendEntryPoints.ExistsPrefixCallback;
+                    }
+
                     if ((supportedOperations & OdbBackendOperations.ForEach) != 0)
                     {
                         nativeBackend.Foreach = BackendEntryPoints.ForEachCallback;
@@ -196,6 +206,7 @@ private static class BackendEntryPoints
             public static readonly GitOdbBackend.write_callback WriteCallback = Write;
             public static readonly GitOdbBackend.writestream_callback WriteStreamCallback = WriteStream;
             public static readonly GitOdbBackend.exists_callback ExistsCallback = Exists;
+            public static readonly GitOdbBackend.exists_prefix_callback ExistsPrefixCallback = ExistsPrefix;
             public static readonly GitOdbBackend.foreach_callback ForEachCallback = Foreach;
             public static readonly GitOdbBackend.free_callback FreeCallback = Free;
 
@@ -498,6 +509,40 @@ private static bool Exists(
                 }
             }
 
+            private static int ExistsPrefix(
+                ref GitOid found_oid,
+                IntPtr backend,
+                ref GitOid short_oid,
+                UIntPtr len)
+            {
+                OdbBackend odbBackend = MarshalOdbBackend(backend);
+                if (odbBackend == null)
+                {
+                    return (int)GitErrorCode.Error;
+                }
+
+                try
+                {
+                    ObjectId found;
+                    var shortSha = ObjectId.ToString(short_oid.Id, (int)len);
+
+                    found_oid.Id = ObjectId.Zero.RawId;
+                    int result = odbBackend.ExistsPrefix(shortSha, out found);
+
+                    if (result == (int) GitErrorCode.Ok)
+                    {
+                        found_oid.Id = found.RawId;
+                    }
+
+                    return result;
+                }
+                catch (Exception ex)
+                {
+                    Proxy.giterr_set_str(GitErrorCategory.Odb, ex);
+                    return (int)GitErrorCode.Error;
+                }
+            }
+
             private static int Foreach(
                 IntPtr backend,
                 GitOdbBackend.foreach_callback_callback cb,
@@ -620,10 +665,15 @@ protected enum OdbBackendOperations
             /// </summary>
             Exists = 64,
 
+            /// <summary>
+            /// This OdbBackend declares that it supports the ExistsPrefix method.
+            /// </summary>
+            ExistsPrefix = 128,
+
             /// <summary>
             /// This OdbBackend declares that it supports the Foreach method.
             /// </summary>
-            ForEach = 128,
+            ForEach = 256,
         }
 
         /// <summary>