feat: add table metadata reader and writer

src/iceberg/json_internal.cc

@@ -1209,4 +1209,20 @@ Result<std::unique_ptr<TableMetadata>> TableMetadataFromJson(const nlohmann::jso
   return table_metadata;
 }
 
+Result<nlohmann::json> FromJsonString(const std::string& json_string) {
+  try {
+    return nlohmann::json::parse(json_string);
+  } catch (const std::exception& e) {
+    return JsonParseError("Failed to parse JSON string: {}", e.what());
+  }
+}
+
+Result<std::string> ToJsonString(const nlohmann::json& json) {
+  try {
+    return json.dump();
+  } catch (const std::exception& e) {
+    return JsonParseError("Failed to serialize to JSON string: {}", e.what());
+  }
+}
+
 }  // namespace iceberg

src/iceberg/json_internal.h

@@ -244,4 +244,16 @@ nlohmann::json ToJson(const TableMetadata& table_metadata);
 /// \return A `TableMetadata` object or an error if the conversion fails.
 Result<std::unique_ptr<TableMetadata>> TableMetadataFromJson(const nlohmann::json& json);
 
+/// \brief Deserialize a JSON string into a `nlohmann::json` object.
+///
+/// \param json_string The JSON string to deserialize.
+/// \return A `nlohmann::json` object or an error if the deserialization fails.
+Result<nlohmann::json> FromJsonString(const std::string& json_string);
+
+/// \brief Serialize a `nlohmann::json` object into a JSON string.
+///
+/// \param json The `nlohmann::json` object to serialize.
+/// \return A JSON string or an error if the serialization fails.
+Result<std::string> ToJsonString(const nlohmann::json& json);
+
 }  // namespace iceberg

src/iceberg/table_metadata.cc

@@ -23,10 +23,17 @@
 #include <ranges>
 #include <string>
 
+#include <nlohmann/json.hpp>
+
+#include "iceberg/file_io.h"
+#include "iceberg/json_internal.h"
 #include "iceberg/partition_spec.h"
 #include "iceberg/result.h"
 #include "iceberg/schema.h"
+#include "iceberg/snapshot.h"
 #include "iceberg/sort_order.h"
+#include "iceberg/util/macros.h"
+
 namespace iceberg {
 
 std::string ToString(const SnapshotLogEntry& entry) {
@@ -69,4 +76,100 @@ Result<std::shared_ptr<SortOrder>> TableMetadata::SortOrder() const {
   return *iter;
 }
 
+namespace {
+
+template <typename T>
+bool SharedPtrVectorEquals(const std::vector<std::shared_ptr<T>>& lhs,
+                           const std::vector<std::shared_ptr<T>>& rhs) {
+  if (lhs.size() != rhs.size()) {
+    return false;
+  }
+  for (size_t i = 0; i < lhs.size(); ++i) {
+    if (*lhs[i] != *rhs[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool SnapshotRefEquals(
+    const std::unordered_map<std::string, std::shared_ptr<SnapshotRef>>& lhs,
+    const std::unordered_map<std::string, std::shared_ptr<SnapshotRef>>& rhs) {
+  if (lhs.size() != rhs.size()) {
+    return false;
+  }
+  for (const auto& [key, value] : lhs) {
+    auto iter = rhs.find(key);
+    if (iter == rhs.end()) {
+      return false;
+    }
+    if (*iter->second != *value) {
+      return false;
+    }
+  }
+  return true;
+}
+
+}  // namespace
+
+bool operator==(const TableMetadata& lhs, const TableMetadata& rhs) {
+  return lhs.format_version == rhs.format_version && lhs.table_uuid == rhs.table_uuid &&
+         lhs.location == rhs.location &&
+         lhs.last_sequence_number == rhs.last_sequence_number &&
+         lhs.last_updated_ms == rhs.last_updated_ms &&
+         lhs.last_column_id == rhs.last_column_id &&
+         lhs.current_schema_id == rhs.current_schema_id &&
+         SharedPtrVectorEquals(lhs.schemas, rhs.schemas) &&
+         lhs.default_spec_id == rhs.default_spec_id &&
+         lhs.last_partition_id == rhs.last_partition_id &&
+         lhs.properties == rhs.properties &&
+         lhs.current_snapshot_id == rhs.current_snapshot_id &&
+         SharedPtrVectorEquals(lhs.snapshots, rhs.snapshots) &&
+         lhs.snapshot_log == rhs.snapshot_log && lhs.metadata_log == rhs.metadata_log &&
+         SharedPtrVectorEquals(lhs.sort_orders, rhs.sort_orders) &&
+         lhs.default_sort_order_id == rhs.default_sort_order_id &&
+         SnapshotRefEquals(lhs.refs, rhs.refs) &&
+         SharedPtrVectorEquals(lhs.statistics, rhs.statistics) &&
+         SharedPtrVectorEquals(lhs.partition_statistics, rhs.partition_statistics) &&
+         lhs.next_row_id == rhs.next_row_id;
+}
+
+Result<MetadataFileCodecType> TableMetadataUtil::CodecFromFileName(
+    std::string_view file_name) {
+  if (file_name.find(".metadata.json") == std::string::npos) {
+    return InvalidArgument("{} is not a valid metadata file", file_name);
+  }
+
+  // We have to be backward-compatible with .metadata.json.gz files
+  if (file_name.ends_with(".metadata.json.gz")) {
+    return MetadataFileCodecType::kGzip;
+  }
+
+  std::string_view file_name_without_suffix =
+      file_name.substr(0, file_name.find_last_of(".metadata.json"));
+  if (file_name_without_suffix.ends_with(".gz")) {
+    return MetadataFileCodecType::kGzip;
+  }
+  return MetadataFileCodecType::kNone;
+}
+
+Result<std::unique_ptr<TableMetadata>> TableMetadataUtil::Read(
+    FileIO& io, const std::string& location, std::optional<size_t> length) {
+  ICEBERG_ASSIGN_OR_RAISE(auto codec_type, CodecFromFileName(location));
+  if (codec_type == MetadataFileCodecType::kGzip) {
+    return NotImplemented("Reading gzip-compressed metadata files is not supported yet");
+  }
+
+  ICEBERG_ASSIGN_OR_RAISE(auto content, io.ReadFile(location, length));
+  ICEBERG_ASSIGN_OR_RAISE(auto json, FromJsonString(content));
+  return TableMetadataFromJson(json);
+}
+
+Status TableMetadataUtil::Write(FileIO& io, const std::string& location,
+                                const TableMetadata& metadata) {
+  auto json = ToJson(metadata);
+  ICEBERG_ASSIGN_OR_RAISE(auto json_string, ToJsonString(json));
+  return io.WriteFile(location, json_string);
+}
+
 }  // namespace iceberg

src/iceberg/table_metadata.h

@@ -24,6 +24,7 @@
 
 #include <memory>
 #include <string>
+#include <string_view>
 #include <unordered_map>
 #include <vector>
 
@@ -132,6 +133,12 @@ struct ICEBERG_EXPORT TableMetadata {
   Result<std::shared_ptr<PartitionSpec>> PartitionSpec() const;
   /// \brief Get the current sort order, return NotFoundError if not found
   Result<std::shared_ptr<SortOrder>> SortOrder() const;
+
+  friend bool operator==(const TableMetadata& lhs, const TableMetadata& rhs);
+
+  friend bool operator!=(const TableMetadata& lhs, const TableMetadata& rhs) {
+    return !(lhs == rhs);
+  }
 };
 
 /// \brief Returns a string representation of a SnapshotLogEntry
@@ -140,4 +147,37 @@ ICEBERG_EXPORT std::string ToString(const SnapshotLogEntry& entry);
 /// \brief Returns a string representation of a MetadataLogEntry
 ICEBERG_EXPORT std::string ToString(const MetadataLogEntry& entry);
 
+/// \brief The codec type of the table metadata file.
+ICEBERG_EXPORT enum class MetadataFileCodecType {
+  kNone,
+  kGzip,
+};
+
+/// \brief Utility class for table metadata
+struct ICEBERG_EXPORT TableMetadataUtil {
+  /// \brief Get the codec type from the table metadata file name.
+  ///
+  /// \param file_name The name of the table metadata file.
+  /// \return The codec type of the table metadata file.
+  static Result<MetadataFileCodecType> CodecFromFileName(std::string_view file_name);
+
+  /// \brief Read the table metadata file.
+  ///
+  /// \param io The file IO to use to read the table metadata.
+  /// \param location The location of the table metadata file.
+  /// \param length The optional length of the table metadata file.
+  /// \return The table metadata.
+  static Result<std::unique_ptr<TableMetadata>> Read(
+      class FileIO& io, const std::string& location,
+      std::optional<size_t> length = std::nullopt);
+
+  /// \brief Write the table metadata to a file.
+  ///
+  /// \param io The file IO to use to write the table metadata.
+  /// \param location The location of the table metadata file.
+  /// \param metadata The table metadata to write.
+  static Status Write(FileIO& io, const std::string& location,
+                      const TableMetadata& metadata);
+};
+
 }  // namespace iceberg

test/CMakeLists.txt

@@ -69,7 +69,8 @@ if(ICEBERG_BUILD_BUNDLE)
   add_test(NAME avro_test COMMAND avro_test)
 
   add_executable(arrow_test)
-  target_sources(arrow_test PRIVATE arrow_test.cc arrow_fs_file_io_test.cc)
+  target_sources(arrow_test PRIVATE arrow_test.cc arrow_fs_file_io_test.cc
+                                    metadata_io_test.cc)
   target_link_libraries(arrow_test PRIVATE iceberg_bundle_static GTest::gtest_main
                                            GTest::gmock)
   add_test(NAME arrow_test COMMAND arrow_test)

test/arrow_fs_file_io_test.cc

@@ -19,45 +19,48 @@
 
 #include "iceberg/arrow/arrow_fs_file_io.h"
 
-#include <filesystem>
-
 #include <arrow/filesystem/localfs.h>
 #include <gtest/gtest.h>
 
 #include "matchers.h"
+#include "temp_file_test_base.h"
 
 namespace iceberg {
 
-class LocalFileIOTest : public testing::Test {
+class LocalFileIOTest : public TempFileTestBase {
  protected:
   void SetUp() override {
-    local_fs_ = std::make_shared<::arrow::fs::LocalFileSystem>();
-    file_io_ = std::make_shared<iceberg::arrow::ArrowFileSystemFileIO>(local_fs_);
+    TempFileTestBase::SetUp();
+    file_io_ = std::make_shared<iceberg::arrow::ArrowFileSystemFileIO>(
+        std::make_shared<::arrow::fs::LocalFileSystem>());
+    temp_filepath_ = CreateNewTempFilePath();
   }
 
-  std::shared_ptr<::arrow::fs::LocalFileSystem> local_fs_;
   std::shared_ptr<iceberg::FileIO> file_io_;
-  std::filesystem::path tmpfile = std::filesystem::temp_directory_path() / "123.txt";
+  std::string temp_filepath_;
 };
 
 TEST_F(LocalFileIOTest, ReadWriteFile) {
-  auto read_res = file_io_->ReadFile(tmpfile.string(), std::nullopt);
+  auto read_res = file_io_->ReadFile(temp_filepath_, std::nullopt);
   EXPECT_THAT(read_res, IsError(ErrorKind::kIOError));
   EXPECT_THAT(read_res, HasErrorMessage("Failed to open local file"));
 
-  auto write_res = file_io_->WriteFile(tmpfile.string(), "hello world");
+  auto write_res = file_io_->WriteFile(temp_filepath_, "hello world");
   EXPECT_THAT(write_res, IsOk());
 
-  read_res = file_io_->ReadFile(tmpfile.string(), std::nullopt);
+  read_res = file_io_->ReadFile(temp_filepath_, std::nullopt);
   EXPECT_THAT(read_res, IsOk());
   EXPECT_THAT(read_res, HasValue(::testing::Eq("hello world")));
 }
 
 TEST_F(LocalFileIOTest, DeleteFile) {
-  auto del_res = file_io_->DeleteFile(tmpfile.string());
+  auto write_res = file_io_->WriteFile(temp_filepath_, "hello world");
+  EXPECT_THAT(write_res, IsOk());
+
+  auto del_res = file_io_->DeleteFile(temp_filepath_);
   EXPECT_THAT(del_res, IsOk());
 
-  del_res = file_io_->DeleteFile(tmpfile.string());
+  del_res = file_io_->DeleteFile(temp_filepath_);
   EXPECT_THAT(del_res, IsError(ErrorKind::kIOError));
   EXPECT_THAT(del_res, HasErrorMessage("Cannot delete file"));
 }

test/metadata_io_test.cc

@@ -0,0 +1,81 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#include <arrow/filesystem/localfs.h>
+#include <gtest/gtest.h>
+
+#include "iceberg/arrow/arrow_fs_file_io.h"
+#include "iceberg/file_io.h"
+#include "iceberg/schema.h"
+#include "iceberg/snapshot.h"
+#include "iceberg/table_metadata.h"
+#include "matchers.h"
+#include "temp_file_test_base.h"
+
+namespace iceberg {
+
+class MetadataIOTest : public TempFileTestBase {
+ protected:
+  void SetUp() override {
+    TempFileTestBase::SetUp();
+    io_ = std::make_shared<iceberg::arrow::ArrowFileSystemFileIO>(
+        std::make_shared<::arrow::fs::LocalFileSystem>());
+    temp_filepath_ = CreateNewTempFilePathWithSuffix(".metadata.json");
+  }
+
+  std::shared_ptr<iceberg::FileIO> io_;
+  std::string temp_filepath_;
+};
+
+TEST_F(MetadataIOTest, ReadWriteMetadata) {
+  std::vector<SchemaField> schema_fields;
+  schema_fields.emplace_back(/*field_id=*/1, "x", std::make_shared<LongType>(),
+                             /*optional=*/false);
+  auto schema = std::make_shared<Schema>(std::move(schema_fields), /*schema_id=*/1);
+
+  TableMetadata metadata{.format_version = 1,
+                         .table_uuid = "1234567890",
+                         .location = "s3://bucket/path",
+                         .last_sequence_number = 0,
+                         .schemas = {schema},
+                         .current_schema_id = 1,
+                         .default_spec_id = 0,
+                         .last_partition_id = 0,
+                         .properties = {{"key", "value"}},
+                         .current_snapshot_id = 3051729675574597004,
+                         .snapshots = {std::make_shared<Snapshot>(Snapshot{
+                             .snapshot_id = 3051729675574597004,
+                             .sequence_number = 0,
+                             .timestamp_ms = TimePointMsFromUnixMs(1515100955770).value(),
+                             .manifest_list = "s3://a/b/1.avro",
+                             .summary = {{"operation", "append"}},
+                         })},
+                         .default_sort_order_id = 0,
+                         .next_row_id = 0};
+
+  EXPECT_THAT(TableMetadataUtil::Write(*io_, temp_filepath_, metadata), IsOk());
+
+  auto result = TableMetadataUtil::Read(*io_, temp_filepath_);
+  EXPECT_THAT(result, IsOk());
+
+  auto metadata_read = std::move(result.value());
+  EXPECT_EQ(*metadata_read, metadata);
+}
+
+}  // namespace iceberg