Introduce ObjectDatabase.ShortenObjectId()

Fix #677

Author: nulltoken

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/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();