Allow getting a ParquetFileReader and the SchemaManifest from an Arrow.FileReader

cpp/CMakeLists.txt

@@ -67,6 +67,8 @@ add_library(ParquetSharpNative SHARED
 	arrow/ArrowWriterPropertiesBuilder.cpp
 	arrow/FileReader.cpp
 	arrow/FileWriter.cpp
+	arrow/SchemaField.cpp
+	arrow/SchemaManifest.cpp
 	encryption/CryptoFactory.cpp
 	encryption/DecryptionConfiguration.cpp
 	encryption/EncryptionConfiguration.cpp

cpp/arrow/FileReader.cpp

@@ -4,6 +4,7 @@
 #include <arrow/c/bridge.h>
 #include <arrow/record_batch.h>
 #include <parquet/arrow/reader.h>
+#include <parquet/file_reader.h>
 
 #include "cpp/ParquetSharpExport.h"
 #include "../ExceptionInfo.h"
@@ -104,6 +105,20 @@ extern "C"
     )
   }
 
+  PARQUETSHARP_EXPORT ExceptionInfo* FileReader_ParquetReader(
+      FileReader* reader,
+      parquet::ParquetFileReader** parquet_reader)
+  {
+    TRYCATCH(*parquet_reader = reader->parquet_reader();)
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* FileReader_Manifest(
+      FileReader* reader,
+      const SchemaManifest** manifest)
+  {
+    TRYCATCH(*manifest = &(reader->manifest());)
+  }
+
   PARQUETSHARP_EXPORT void FileReader_Free(FileReader* reader)
   {
     delete reader;

cpp/arrow/SchemaField.cpp

@@ -0,0 +1,42 @@
+#include <arrow/c/abi.h>
+#include <arrow/c/bridge.h>
+#include <parquet/arrow/schema.h>
+#include <parquet/exception.h>
+
+#include "cpp/ParquetSharpExport.h"
+#include "../ExceptionInfo.h"
+
+using namespace parquet::arrow;
+
+extern "C"
+{
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaField_ChildrenLength(const SchemaField* field, int32_t* length)
+  {
+    TRYCATCH(*length = static_cast<int32_t>(field->children.size());)
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaField_Child(const SchemaField* field, int32_t index, const SchemaField** child)
+  {
+    TRYCATCH(
+      if (index >= static_cast<int32_t>(field->children.size()))
+      {
+        throw std::out_of_range("Child field index out of range");
+      }
+      *child = &(field->children[index]);
+    )
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaField_ColumnIndex(const SchemaField* field, int32_t* column_index)
+  {
+    TRYCATCH(
+      *column_index = field->column_index;
+    )
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaField_Field(const SchemaField* field, struct ArrowSchema* arrow_field)
+  {
+    TRYCATCH(
+      PARQUET_THROW_NOT_OK(arrow::ExportField(*(field->field), arrow_field));
+    )
+  }
+}

cpp/arrow/SchemaManifest.cpp

@@ -0,0 +1,38 @@
+#include <parquet/arrow/schema.h>
+#include <parquet/exception.h>
+
+#include "cpp/ParquetSharpExport.h"
+#include "../ExceptionInfo.h"
+
+using namespace parquet::arrow;
+
+extern "C"
+{
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaManifest_SchemaFieldsLength(const SchemaManifest* manifest, int32_t* length)
+  {
+    TRYCATCH(*length = static_cast<int32_t>(manifest->schema_fields.size());)
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaManifest_SchemaField(const SchemaManifest* manifest, int32_t index, const SchemaField** field)
+  {
+    TRYCATCH(
+      if (index >= static_cast<int32_t>(manifest->schema_fields.size()))
+      {
+        throw std::out_of_range("Field index out of range");
+      }
+      *field = &(manifest->schema_fields[index]);
+    )
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaManifest_GetColumnField(const SchemaManifest* manifest, int32_t column_index, const SchemaField** field)
+  {
+    TRYCATCH(
+      PARQUET_THROW_NOT_OK(manifest->GetColumnField(column_index, field));
+    )
+  }
+
+  PARQUETSHARP_EXPORT ExceptionInfo* SchemaManifest_GetParent(const SchemaManifest* manifest, const SchemaField* field, const SchemaField** parent)
+  {
+    TRYCATCH(*parent = manifest->GetParent(field);)
+  }
+}

csharp.test/Arrow/TestFileReader.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Apache.Arrow;
@@ -195,6 +196,168 @@ public async Task TestReadSelectedColumns()
             Assert.That(rowsRead, Is.EqualTo(RowsPerRowGroup * NumRowGroups));
         }
 
+        [Test]
+        public void TestAccessUnderlyingReader()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            using var fileReader = new FileReader(inStream);
+            using var parquetReader = fileReader.ParquetReader;
+
+            // Verify we can access column statistics
+            for (var rowGroupIdx = 0; rowGroupIdx < NumRowGroups; ++rowGroupIdx)
+            {
+                using var rowGroup = parquetReader.RowGroup(rowGroupIdx);
+                using var colMetadata = rowGroup.MetaData.GetColumnChunkMetaData(1);
+                using var stats = colMetadata.Statistics as Statistics<int>;
+                Assert.That(stats, Is.Not.Null);
+                Assert.That(stats!.HasMinMax);
+                Assert.That(stats.Min, Is.EqualTo(rowGroupIdx * RowsPerRowGroup));
+                Assert.That(stats.Max, Is.EqualTo((rowGroupIdx + 1) * RowsPerRowGroup - 1));
+            }
+        }
+
+        [Test]
+        public void TestAccessUnderlyingReaderAfterDisposed()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            ParquetFileReader parquetReader;
+            using (var fileReader = new FileReader(inStream))
+            {
+                parquetReader = fileReader.ParquetReader;
+            }
+
+            using (parquetReader)
+            {
+                var exception = Assert.Throws<NullReferenceException>(() => { _ = parquetReader.FileMetaData; });
+                Assert.That(exception!.Message, Does.Contain("owning parent has been disposed"));
+            }
+        }
+
+        [Test]
+        public void TestSchemaManifest()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteNestedTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            using var fileReader = new FileReader(inStream);
+
+            var manifest = fileReader.SchemaManifest;
+            var fields = manifest.SchemaFields;
+
+            Assert.That(fields.Count, Is.EqualTo(2));
+
+            var structField = fields[0];
+            var structArrowField = structField.Field;
+
+            Assert.That(structArrowField.Name, Is.EqualTo("test_struct"));
+            Assert.That(structArrowField.DataType.TypeId, Is.EqualTo(ArrowTypeId.Struct));
+
+            Assert.That(structField.ColumnIndex, Is.EqualTo(-1));
+            var structFields = structField.Children;
+            Assert.That(structFields.Count, Is.EqualTo(2));
+            Assert.That(structFields[0].ColumnIndex, Is.EqualTo(0));
+            Assert.That(structFields[1].ColumnIndex, Is.EqualTo(1));
+            var structArrowFieldA = structFields[0].Field;
+            var structArrowFieldB = structFields[1].Field;
+            Assert.That(structArrowFieldA.Name, Is.EqualTo("a"));
+            Assert.That(structArrowFieldA.DataType.TypeId, Is.EqualTo(ArrowTypeId.Int32));
+            Assert.That(structArrowFieldB.Name, Is.EqualTo("b"));
+            Assert.That(structArrowFieldB.DataType.TypeId, Is.EqualTo(ArrowTypeId.Float));
+
+            Assert.That(fields[1].Children.Count, Is.EqualTo(0));
+            Assert.That(fields[1].ColumnIndex, Is.EqualTo(2));
+            var xArrowField = fields[1].Field;
+            Assert.That(xArrowField.Name, Is.EqualTo("x"));
+            Assert.That(xArrowField.DataType.TypeId, Is.EqualTo(ArrowTypeId.Int32));
+        }
+
+        [Test]
+        public void TestSchemaManifestGetSingleField()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteNestedTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            using var fileReader = new FileReader(inStream);
+
+            var manifest = fileReader.SchemaManifest;
+            var field = manifest.SchemaField(1);
+            Assert.That(field, Is.Not.Null);
+            var arrowField = field.Field;
+            Assert.That(arrowField.Name, Is.EqualTo("x"));
+            Assert.That(arrowField.DataType.TypeId, Is.EqualTo(ArrowTypeId.Int32));
+
+            var exception = Assert.Throws<ParquetException>(() => manifest.SchemaField(2));
+            Assert.That(exception!.Message, Does.Contain("out of range"));
+        }
+
+        [Test]
+        public void TestSchemaManifestGetColumnField()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteNestedTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            using var fileReader = new FileReader(inStream);
+
+            var manifest = fileReader.SchemaManifest;
+            var field = manifest.GetColumnField(2);
+            Assert.That(field, Is.Not.Null);
+            var arrowField = field.Field;
+            Assert.That(arrowField.Name, Is.EqualTo("x"));
+            Assert.That(arrowField.DataType.TypeId, Is.EqualTo(ArrowTypeId.Int32));
+
+            var exception = Assert.Throws<ParquetException>(() => manifest.GetColumnField(3));
+            Assert.That(exception!.Message, Does.Contain("Column index 3"));
+        }
+
+        [Test]
+        public void TestSchemaManifestGetFieldParent()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteNestedTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            using var fileReader = new FileReader(inStream);
+
+            var manifest = fileReader.SchemaManifest;
+            var field = manifest.GetColumnField(1);
+            var parent = manifest.GetParent(field);
+
+            Assert.That(parent, Is.Not.Null);
+            var arrowField = parent!.Field;
+            Assert.That(arrowField.Name, Is.EqualTo("test_struct"));
+            Assert.That(arrowField.DataType.TypeId, Is.EqualTo(ArrowTypeId.Struct));
+
+            var grandparent = manifest.GetParent(parent);
+            Assert.That(grandparent, Is.Null);
+        }
+
+        [Test]
+        public void TestAccessSchemaManifestFieldAfterDisposed()
+        {
+            using var buffer = new ResizableBuffer();
+            WriteTestFile(buffer);
+
+            using var inStream = new BufferReader(buffer);
+            SchemaField field;
+            using (var fileReader = new FileReader(inStream))
+            {
+                var manifest = fileReader.SchemaManifest;
+                field = manifest.SchemaFields[0];
+            }
+
+            var exception = Assert.Throws<NullReferenceException>(() => { _ = field.Field; });
+            Assert.That(exception!.Message, Does.Contain("owning parent has been disposed"));
+        }
+
         private static void WriteTestFile(ResizableBuffer buffer)
         {
             var columns = new Column[]
@@ -226,6 +389,44 @@ private static void WriteTestFile(ResizableBuffer buffer)
             fileWriter.Close();
         }
 
+        private static void WriteNestedTestFile(ResizableBuffer buffer)
+        {
+            var fields = new[]
+            {
+                new Field("test_struct", new StructType(
+                    new[]
+                    {
+                        new Field("a", new Int32Type(), false),
+                        new Field("b", new FloatType(), false),
+                    }), true),
+                new Field("x", new Int32Type(), false),
+            };
+            var schema = new Apache.Arrow.Schema(fields, null);
+
+            using var outStream = new BufferOutputStream(buffer);
+            using var writer = new FileWriter(outStream, schema);
+            for (var rowGroup = 0; rowGroup < NumRowGroups; ++rowGroup)
+            {
+                var start = rowGroup * RowsPerRowGroup;
+                var arrays = new List<IArrowArray>
+                {
+                    new StructArray(fields[0].DataType, RowsPerRowGroup, new IArrowArray[]
+                    {
+                        new Int32Array.Builder().AppendRange(Enumerable.Range(start, RowsPerRowGroup).ToArray()).Build(),
+                        new FloatArray.Builder().AppendRange(Enumerable.Range(start, RowsPerRowGroup).Select(i => i * 0.1f).ToArray())
+                            .Build(),
+                    }, new ArrowBuffer.BitmapBuilder().AppendRange(true, RowsPerRowGroup).Build()),
+                    new Int32Array.Builder().AppendRange(Enumerable.Range(start, RowsPerRowGroup).ToArray()).Build()
+                };
+
+                var batch = new RecordBatch(schema, arrays, RowsPerRowGroup);
+
+                writer.WriteRecordBatch(batch);
+            }
+
+            writer.Close();
+        }
+
         private const int NumRowGroups = 4;
         private const int RowsPerRowGroup = 100;
     }

csharp/Arrow/FileReader.cs

@@ -138,6 +138,30 @@ public unsafe IArrowArrayStream GetRecordBatchReader(
             return CArrowArrayStreamImporter.ImportArrayStream(&cStream);
         }
 
+        /// <summary>
+        /// Get the underlying ParquetFileReader used by this Arrow FileReader
+        /// </summary>
+        public ParquetFileReader ParquetReader
+        {
+            get
+            {
+                var readerPtr = ExceptionInfo.Return<IntPtr>(_handle, FileReader_ParquetReader);
+                return new ParquetFileReader(new ChildParquetHandle(readerPtr, _handle));
+            }
+        }
+
+        /// <summary>
+        /// Get the schema manifest, which describes the relationship between the Arrow schema and Parquet schema
+        /// </summary>
+        public SchemaManifest SchemaManifest
+        {
+            get
+            {
+                var manifestPtr = ExceptionInfo.Return<IntPtr>(_handle, FileReader_Manifest);
+                return new SchemaManifest(new ChildParquetHandle(manifestPtr, _handle));
+            }
+        }
+
         public void Dispose()
         {
             _handle.Dispose();
@@ -165,6 +189,12 @@ private static extern IntPtr FileReader_OpenFile(
         private static extern unsafe IntPtr FileReader_GetRecordBatchReader(
             IntPtr reader, int* rowGroups, int rowGroupsCount, int* columns, int columnsCount, CArrowArrayStream* stream);
 
+        [DllImport(ParquetDll.Name)]
+        private static extern IntPtr FileReader_ParquetReader(IntPtr reader, out IntPtr parquetReader);
+
+        [DllImport(ParquetDll.Name)]
+        private static extern IntPtr FileReader_Manifest(IntPtr reader, out IntPtr manifest);
+
         [DllImport(ParquetDll.Name)]
         private static extern void FileReader_Free(IntPtr reader);