markcapaldi
diff --git a/‎LibGit2Sharp.Tests/IndexFixture.cs
Lines changed: 19 additions & 0 deletions b/‎LibGit2Sharp.Tests/IndexFixture.cs
Lines changed: 19 additions & 0 deletions
diff --git a/‎LibGit2Sharp/Index.cs
Lines changed: 39 additions & 5 deletions b/‎LibGit2Sharp/Index.cs
Lines changed: 39 additions & 5 deletions
@@ -411,6 +411,25 @@ public void CanAddAnEntryToTheIndexFromAFileInTheWorkdir(string pathInTheWorkdir
             }
         }
 
+        [Fact]
+        public void CanAddAnEntryToTheIndexFromABlob()
+        {
+            var path = SandboxStandardTestRepoGitDir();
+            using (var repo = new Repository(path))
+            {
+                const string targetIndexEntryPath = "1.txt";
+                var before = repo.RetrieveStatus(targetIndexEntryPath);
+                Assert.Equal(FileStatus.Unaltered, before);
+
+                var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+
+                repo.Index.Add(blob, targetIndexEntryPath, Mode.NonExecutableFile);
+
+                var after = repo.RetrieveStatus(targetIndexEntryPath);
+                Assert.Equal(FileStatus.Staged | FileStatus.Modified, after);
+            }
+        }
+
         [Fact]
         public void AddingAnEntryToTheIndexFromAUnknwonFileInTheWorkdirThrows()
         {
 
@@ -198,6 +198,36 @@ public virtual void Add(string pathInTheWorkdir)
             UpdatePhysicalIndex();
         }
 
+        /// <summary>
+        /// Adds an entry in the <see cref="Index"/> from a <see cref="Blob"/>.
+        /// <para>
+        ///   If an entry with the same path already exists in the <see cref="Index"/>,
+        ///   the newly added one will overwrite it.
+        /// </para>
+        /// </summary>
+        /// <param name="blob">The <see cref="Blob"/> which content should be added to the <see cref="Index"/>.</param>
+        /// <param name="indexEntryPath">The path to be used in the <see cref="Index"/>.</param>
+        /// or <see cref="Mode.SymbolicLink"/>.</param>
+        public virtual void Add(Blob blob, string indexEntryPath, Mode indexEntryMode)
+        {
+            Ensure.ArgumentConformsTo(indexEntryMode, m => m.HasAny(TreeEntryDefinition.BlobModes), "indexEntryMode");
+
+            if (blob == null)
+            {
+                throw new ArgumentNullException("blob");
+            }
+
+            if (indexEntryPath == null)
+            {
+                throw new ArgumentNullException("indexEntryPath");
+            }
+
+            AddEntryToTheIndex(indexEntryPath, blob.Id, indexEntryMode);
+
+            UpdatePhysicalIndex();
+        }
+
         private void UpdatePhysicalIndex()
         {
             Proxy.git_index_write(handle);
@@ -219,7 +249,11 @@ internal void Replace(TreeChanges changes)
                     case ChangeKind.Deleted:
                         /* Fall through */
                     case ChangeKind.Modified:
-                        ReplaceIndexEntryWith(treeEntryChanges);
+                        AddEntryToTheIndex(
+                            treeEntryChanges.OldPath,
+                            treeEntryChanges.OldOid,
+                            treeEntryChanges.OldMode);
+
                         continue;
 
                     default:
@@ -241,13 +275,13 @@ public virtual ConflictCollection Conflicts
             }
         }
 
-        private void ReplaceIndexEntryWith(TreeEntryChanges treeEntryChanges)
+        private void AddEntryToTheIndex(string path, ObjectId id, Mode mode)
         {
             var indexEntry = new GitIndexEntry
             {
-                Mode = (uint)treeEntryChanges.OldMode,
-                Id = treeEntryChanges.OldOid.Oid,
-                Path = StrictFilePathMarshaler.FromManaged(treeEntryChanges.OldPath),
+                Mode = (uint)mode,
+                Id = id.Oid,
+                Path = StrictFilePathMarshaler.FromManaged(path),
             };
 
             Proxy.git_index_add(handle, indexEntry);