Simplify dealing with missing git objects

LibGit2Sharp.Tests/BlobFixture.cs

@@ -15,6 +15,7 @@ public void CanGetBlobAsText()
             using (var repo = new Repository(path))
             {
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
 
                 var text = blob.GetContentText();
 
@@ -36,6 +37,7 @@ public void CanGetBlobAsFilteredText(string autocrlf, string expectedText)
                 repo.Config.Set("core.autocrlf", autocrlf);
 
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
 
                 var text = blob.GetContentText(new FilteringOptions("foo.txt"));
 
@@ -67,6 +69,7 @@ public void CanGetBlobAsTextWithVariousEncodings(string encodingName, int expect
                 var commit = repo.Commit("bom", Constants.Signature, Constants.Signature);
 
                 var blob = (Blob)commit.Tree[bomFile].Target;
+                Assert.False(blob.IsMissing);
                 Assert.Equal(expectedContentBytes, blob.Size);
                 using (var stream = blob.GetContentStream())
                 {
@@ -92,6 +95,7 @@ public void CanGetBlobSize()
             using (var repo = new Repository(path))
             {
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
                 Assert.Equal(10, blob.Size);
             }
         }
@@ -104,6 +108,7 @@ public void CanLookUpBlob()
             {
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
                 Assert.NotNull(blob);
+                Assert.False(blob.IsMissing);
             }
         }
 
@@ -114,6 +119,7 @@ public void CanReadBlobStream()
             using (var repo = new Repository(path))
             {
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
 
                 var contentStream = blob.GetContentStream();
                 Assert.Equal(blob.Size, contentStream.Length);
@@ -140,6 +146,7 @@ public void CanReadBlobFilteredStream(string autocrlf, string expectedContent)
                 repo.Config.Set("core.autocrlf", autocrlf);
 
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
 
                 var contentStream = blob.GetContentStream(new FilteringOptions("foo.txt"));
                 Assert.Equal(expectedContent.Length, contentStream.Length);
@@ -164,6 +171,7 @@ public void CanReadBlobFilteredStreamOfUnmodifiedBinary()
                 using (var stream = new MemoryStream(binaryContent))
                 {
                     Blob blob = repo.ObjectDatabase.CreateBlob(stream);
+                    Assert.False(blob.IsMissing);
 
                     using (var filtered = blob.GetContentStream(new FilteringOptions("foo.txt")))
                     {
@@ -196,6 +204,7 @@ public void CanStageAFileGeneratedFromABlobContentStream()
                 Assert.Equal("baae1fb3760a73481ced1fa03dc15614142c19ef", entry.Id.Sha);
 
                 var blob = repo.Lookup<Blob>(entry.Id.Sha);
+                Assert.False(blob.IsMissing);
 
                 using (Stream stream = blob.GetContentStream())
                 using (Stream file = File.OpenWrite(Path.Combine(repo.Info.WorkingDirectory, "small.fromblob.txt")))
@@ -217,10 +226,35 @@ public void CanTellIfTheBlobContentLooksLikeBinary()
             using (var repo = new Repository(path))
             {
                 var blob = repo.Lookup<Blob>("a8233120f6ad708f843d861ce2b7228ec4e3dec6");
+                Assert.False(blob.IsMissing);
                 Assert.False(blob.IsBinary);
             }
         }
 
+        [Fact]
+        public void CanTellIsABlobIsMissing()
+        {
+            string repoPath = SandboxBareTestRepo();
+
+            // Manually delete the objects directory to simulate a partial clone
+            Directory.Delete(Path.Combine(repoPath, "objects", "a8"), true);
+
+            using (var repo = new Repository(repoPath)) 
+            {
+                // Look for the commit that reference the blob which is now missing
+                var commit = repo.Lookup<Commit>("4a202b346bb0fb0db7eff3cffeb3c70babbd2045");
+                var blob = (Blob) commit.Tree["README"].Target;
+
+                Assert.Equal("a8233120f6ad708f843d861ce2b7228ec4e3dec6", blob.Sha);
+                Assert.NotNull(blob);
+                Assert.True(blob.IsMissing);
+                Assert.Throws<NotFoundException>(() => blob.Size);
+                Assert.Throws<NotFoundException>(() => blob.IsBinary);
+                Assert.Throws<NotFoundException>(() => blob.GetContentText());
+                Assert.Throws<NotFoundException>(() => blob.GetContentText(new FilteringOptions("foo.txt")));
+            }
+        }
+
         private static void SkipIfNotSupported(string autocrlf)
         {
             InconclusiveIf(() => autocrlf == "true" && Constants.IsRunningOnUnix, "Non-Windows does not support core.autocrlf = true");

LibGit2Sharp/Blob.cs

@@ -8,6 +8,9 @@ namespace LibGit2Sharp
     /// <summary>
     /// Stores the binary content of a tracked file.
     /// </summary>
+    /// <remarks>
+    /// Since the introduction of partially cloned repositories, blobs might be missing on your local repository (see https://git-scm.com/docs/partial-clone)
+    /// </remarks>
     public class Blob : GitObject
     {
         private readonly ILazy<Int64> lazySize;
@@ -22,8 +25,8 @@ protected Blob()
         internal Blob(Repository repo, ObjectId id)
             : base(repo, id)
         {
-            lazySize = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_blob_rawsize);
-            lazyIsBinary = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_blob_is_binary);
+            lazySize = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_blob_rawsize, throwIfMissing: true);
+            lazyIsBinary = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_blob_is_binary, throwIfMissing: true);
         }
 
         /// <summary>
@@ -33,16 +36,19 @@ internal Blob(Repository repo, ObjectId id)
         /// can be used.
         /// </para>
         /// </summary>
-        public virtual long Size { get { return lazySize.Value; } }
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
+        public virtual long Size => lazySize.Value;
 
         /// <summary>
         ///  Determine if the blob content is most certainly binary or not.
         /// </summary>
-        public virtual bool IsBinary { get { return lazyIsBinary.Value; } }
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
+        public virtual bool IsBinary => lazyIsBinary.Value;
 
         /// <summary>
         /// Gets the blob content in a <see cref="Stream"/>.
         /// </summary>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual Stream GetContentStream()
         {
             return Proxy.git_blob_rawcontent_stream(repo.Handle, Id, Size);
@@ -53,6 +59,7 @@ public virtual Stream GetContentStream()
         /// checked out to the working directory.
         /// <param name="filteringOptions">Parameter controlling content filtering behavior</param>
         /// </summary>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual Stream GetContentStream(FilteringOptions filteringOptions)
         {
             Ensure.ArgumentNotNull(filteringOptions, "filteringOptions");
@@ -64,6 +71,7 @@ public virtual Stream GetContentStream(FilteringOptions filteringOptions)
         /// Gets the blob content, decoded with UTF8 encoding if the encoding cannot be detected from the byte order mark
         /// </summary>
         /// <returns>Blob content as text.</returns>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual string GetContentText()
         {
             return ReadToEnd(GetContentStream(), null);
@@ -75,6 +83,7 @@ public virtual string GetContentText()
         /// </summary>
         /// <param name="encoding">The encoding of the text to use, if it cannot be detected</param>
         /// <returns>Blob content as text.</returns>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual string GetContentText(Encoding encoding)
         {
             Ensure.ArgumentNotNull(encoding, "encoding");
@@ -87,6 +96,7 @@ public virtual string GetContentText(Encoding encoding)
         /// </summary>
         /// <param name="filteringOptions">Parameter controlling content filtering behavior</param>
         /// <returns>Blob content as text.</returns>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual string GetContentText(FilteringOptions filteringOptions)
         {
             return GetContentText(filteringOptions, null);
@@ -101,6 +111,7 @@ public virtual string GetContentText(FilteringOptions filteringOptions)
         /// <param name="filteringOptions">Parameter controlling content filtering behavior</param>
         /// <param name="encoding">The encoding of the text. (default: detected or UTF8)</param>
         /// <returns>Blob content as text.</returns>
+        /// <exception cref="NotFoundException">Throws if blob is missing</exception>
         public virtual string GetContentText(FilteringOptions filteringOptions, Encoding encoding)
         {
             Ensure.ArgumentNotNull(filteringOptions, "filteringOptions");

LibGit2Sharp/Core/GitObjectLazyGroup.cs

@@ -21,11 +21,11 @@ protected override void EvaluateInternal(Action<ObjectHandle> evaluator)
             }
         }
 
-        public static ILazy<TResult> Singleton<TResult>(Repository repo, ObjectId id, Func<ObjectHandle, TResult> resultSelector)
+        public static ILazy<TResult> Singleton<TResult>(Repository repo, ObjectId id, Func<ObjectHandle, TResult> resultSelector, bool throwIfMissing = false)
         {
             return Singleton(() =>
             {
-                using (var osw = new ObjectSafeWrapper(id, repo.Handle))
+                using (var osw = new ObjectSafeWrapper(id, repo.Handle, throwIfMissing: throwIfMissing))
                 {
                     return resultSelector(osw.ObjectPtr);
                 }

LibGit2Sharp/Core/ObjectSafeWrapper.cs

@@ -7,7 +7,7 @@ internal class ObjectSafeWrapper : IDisposable
     {
         private readonly ObjectHandle objectPtr;
 
-        public unsafe ObjectSafeWrapper(ObjectId id, RepositoryHandle handle, bool allowNullObjectId = false)
+        public unsafe ObjectSafeWrapper(ObjectId id, RepositoryHandle handle, bool allowNullObjectId = false, bool throwIfMissing = false)
         {
             Ensure.ArgumentNotNull(handle, "handle");
 
@@ -20,13 +20,15 @@ public unsafe ObjectSafeWrapper(ObjectId id, RepositoryHandle handle, bool allow
                 Ensure.ArgumentNotNull(id, "id");
                 objectPtr = Proxy.git_object_lookup(handle, id, GitObjectType.Any);
             }
-        }
 
-        public ObjectHandle ObjectPtr
-        {
-            get { return objectPtr; }
+            if (objectPtr == null && throwIfMissing)
+            {
+                throw new NotFoundException($"No valid git object identified by '{id}' exists in the repository.");
+            }
         }
 
+        public ObjectHandle ObjectPtr => objectPtr;
+
         public void Dispose()
         {
             Dispose(true);

LibGit2Sharp/Core/Proxy.cs

@@ -72,7 +72,7 @@ public static unsafe ObjectId git_blob_create_from_workdir(RepositoryHandle repo
         public static unsafe UnmanagedMemoryStream git_blob_filtered_content_stream(RepositoryHandle repo, ObjectId id, string path, bool check_for_binary_data)
         {
             var buf = new GitBuf();
-            var handle = new ObjectSafeWrapper(id, repo).ObjectPtr;
+            var handle = new ObjectSafeWrapper(id, repo, throwIfMissing: true).ObjectPtr;
 
             return new RawContentStream(handle, h =>
             {
@@ -85,7 +85,7 @@ public static unsafe UnmanagedMemoryStream git_blob_filtered_content_stream(Repo
 
         public static unsafe UnmanagedMemoryStream git_blob_rawcontent_stream(RepositoryHandle repo, ObjectId id, Int64 size)
         {
-            var handle = new ObjectSafeWrapper(id, repo).ObjectPtr;
+            var handle = new ObjectSafeWrapper(id, repo, throwIfMissing: true).ObjectPtr;
             return new RawContentStream(handle, h => NativeMethods.git_blob_rawcontent(h), h => size);
         }
 

LibGit2Sharp/GitObject.cs

@@ -1,9 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Globalization;
 using LibGit2Sharp.Core;
-using LibGit2Sharp.Core.Handles;
 
 namespace LibGit2Sharp
 {
@@ -33,6 +31,8 @@ public abstract class GitObject : IEquatable<GitObject>, IBelongToARepository
         private static readonly LambdaEqualityHelper<GitObject> equalityHelper =
             new LambdaEqualityHelper<GitObject>(x => x.Id);
 
+        private readonly ILazy<bool> lazyIsMissing;
+
         /// <summary>
         /// The <see cref="Repository"/> containing the object.
         /// </summary>
@@ -53,13 +53,22 @@ protected GitObject(Repository repo, ObjectId id)
         {
             this.repo = repo;
             Id = id;
+            lazyIsMissing = GitObjectLazyGroup.Singleton(repo, id, handle => handle == null, throwIfMissing: false);
         }
 
         /// <summary>
         /// Gets the id of this object
         /// </summary>
         public virtual ObjectId Id { get; private set; }
 
+        /// <summary>
+        ///  Determine if the object is missing
+        /// </summary>
+        /// <remarks>
+        /// This is common when dealing with partially cloned repositories as blobs or trees could be missing
+        /// </remarks>
+        public virtual bool IsMissing => lazyIsMissing.Value;
+
         /// <summary>
         /// Gets the 40 character sha1 of this object.
         /// </summary>

LibGit2Sharp/Tree.cs

@@ -31,13 +31,13 @@ internal Tree(Repository repo, ObjectId id, string path)
         {
             this.path = path ?? "";
 
-            lazyCount = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_tree_entrycount);
+            lazyCount = GitObjectLazyGroup.Singleton(repo, id, Proxy.git_tree_entrycount, throwIfMissing: true);
         }
 
         /// <summary>
         /// Gets the number of <see cref="TreeEntry"/> immediately under this <see cref="Tree"/>.
         /// </summary>
-        public virtual int Count { get { return lazyCount.Value; } }
+        public virtual int Count => lazyCount.Value;
 
         /// <summary>
         /// Gets the <see cref="TreeEntry"/> pointed at by the <paramref name="relativePath"/> in this <see cref="Tree"/> instance.