From 3187f6f0b694633ac1b2b2720df3ca2f823fc4e2 Mon Sep 17 00:00:00 2001
From: philjdf <git@pfelton.co.uk>
Date: Tue, 11 Jan 2022 18:17:02 +0000
Subject: [PATCH 1/2] Fix GetEnumerator

---
 csharp.test/TestLogicalTypeRoundtrip.cs | 43 +++++++++++++++++++++++++
 csharp/LogicalColumnReader.cs           |  4 ++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/csharp.test/TestLogicalTypeRoundtrip.cs b/csharp.test/TestLogicalTypeRoundtrip.cs
index 12026627..b198e1f7 100644
--- a/csharp.test/TestLogicalTypeRoundtrip.cs
+++ b/csharp.test/TestLogicalTypeRoundtrip.cs
@@ -288,6 +288,49 @@ public static void TestNestedStructArray([Values(Repetition.Required, Repetition
             fileReader.Close();
         }
 
+        [Test]
+        public static void TestLargeArraysEnumerator()
+        {
+            CheckEnumerator(Enumerable.Range(0, 4100).ToArray());
+            CheckEnumerator(Enumerable.Range(0, 4100).Select(i => new[] {$"row {i}"}).ToArray());
+        }
+
+        private static void CheckEnumerator<T>(T[] values)
+        {
+            using var buffer = new ResizableBuffer();
+
+            using (var output = new BufferOutputStream(buffer))
+            {
+                var columns = new Column[] {new Column<T>("col0")};
+
+                using var fileWriter = new ParquetFileWriter(output, columns);
+                using var rowGroupWriter = fileWriter.AppendBufferedRowGroup();
+
+                using var col = rowGroupWriter.Column(0).LogicalWriter<T>();
+                col.WriteBatch(values);
+
+                fileWriter.Close();
+            }
+
+            using (var input = new BufferReader(buffer))
+            {
+                using var fileReader = new ParquetFileReader(input);
+                using var rowGroupReader = fileReader.RowGroup(0);
+
+                using var col = rowGroupReader.Column(0).LogicalReader<T>();
+
+                var enumerator = col.GetEnumerator();
+                for (var i = 0; i < values.Length; i++)
+                {
+                    Assert.IsTrue(enumerator.MoveNext());
+                    Assert.AreEqual(values[i], enumerator.Current);
+                }
+                Assert.IsFalse(enumerator.MoveNext());
+
+                fileReader.Close();
+            }
+        }
+
         [Test]
         public static void TestBigArrayRoundtrip()
         {
diff --git a/csharp/LogicalColumnReader.cs b/csharp/LogicalColumnReader.cs
index 906939ea..b7d38d02 100644
--- a/csharp/LogicalColumnReader.cs
+++ b/csharp/LogicalColumnReader.cs
@@ -44,7 +44,7 @@ internal static LogicalColumnReader<TElement> Create<TElement>(ColumnReader colu
             }
         }
 
-        public bool HasNext => Source.HasNext;
+        public abstract bool HasNext { get; }
 
         public abstract TReturn Apply<TReturn>(ILogicalColumnReaderVisitor<TReturn> visitor);
 
@@ -153,6 +153,8 @@ private static (short definitionLevelDelta, int schemaSlice) StructSkip(ReadOnly
             return (definitionLevel, schemaSlice);
         }
 
+        public override bool HasNext => !_bufferedReader.IsEofDefinition;
+
         public override int ReadBatch(Span<TElement> destination)
         {
             short definitionLevel = 0;

From b211af36a1f39e986a38c074c718466975a14c25 Mon Sep 17 00:00:00 2001
From: philjdf <git@pfelton.co.uk>
Date: Wed, 12 Jan 2022 00:13:52 +0000
Subject: [PATCH 2/2] Make the test clearer

---
 csharp.test/TestLogicalTypeRoundtrip.cs | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/csharp.test/TestLogicalTypeRoundtrip.cs b/csharp.test/TestLogicalTypeRoundtrip.cs
index b198e1f7..9d9ffd38 100644
--- a/csharp.test/TestLogicalTypeRoundtrip.cs
+++ b/csharp.test/TestLogicalTypeRoundtrip.cs
@@ -288,14 +288,19 @@ public static void TestNestedStructArray([Values(Repetition.Required, Repetition
             fileReader.Close();
         }
 
+        /// <summary>
+        /// This checks that LogicalColumnReader's GetEnumerator() works correctly
+        /// when the column is longer than the buffer length but not an exact multiple
+        /// (see https://github.com/G-Research/ParquetSharp/issues/242).
+        /// </summary>
         [Test]
         public static void TestLargeArraysEnumerator()
         {
-            CheckEnumerator(Enumerable.Range(0, 4100).ToArray());
-            CheckEnumerator(Enumerable.Range(0, 4100).Select(i => new[] {$"row {i}"}).ToArray());
+            CheckEnumerator(4096, Enumerable.Range(0, 4100).ToArray());
+            CheckEnumerator(4096, Enumerable.Range(0, 4100).Select(i => new[] {$"row {i}"}).ToArray());
         }
 
-        private static void CheckEnumerator<T>(T[] values)
+        private static void CheckEnumerator<T>(int bufferLength, T[] values)
         {
             using var buffer = new ResizableBuffer();
 
@@ -306,7 +311,7 @@ private static void CheckEnumerator<T>(T[] values)
                 using var fileWriter = new ParquetFileWriter(output, columns);
                 using var rowGroupWriter = fileWriter.AppendBufferedRowGroup();
 
-                using var col = rowGroupWriter.Column(0).LogicalWriter<T>();
+                using var col = rowGroupWriter.Column(0).LogicalWriter<T>(bufferLength);
                 col.WriteBatch(values);
 
                 fileWriter.Close();
@@ -317,7 +322,7 @@ private static void CheckEnumerator<T>(T[] values)
                 using var fileReader = new ParquetFileReader(input);
                 using var rowGroupReader = fileReader.RowGroup(0);
 
-                using var col = rowGroupReader.Column(0).LogicalReader<T>();
+                using var col = rowGroupReader.Column(0).LogicalReader<T>(bufferLength);
 
                 var enumerator = col.GetEnumerator();
                 for (var i = 0; i < values.Length; i++)