Custom error messages for IO with nonexistent files

cpp/src/io/utilities/data_sink.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2023, NVIDIA CORPORATION.
+ * Copyright (c) 2020-2024, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@
 
 namespace cudf {
 namespace io {
+
 /**
  * @brief Implementation class for storing data into a local file.
  */
@@ -34,7 +35,7 @@ class file_sink : public data_sink {
   explicit file_sink(std::string const& filepath)
   {
     _output_stream.open(filepath, std::ios::out | std::ios::binary | std::ios::trunc);
-    CUDF_EXPECTS(_output_stream.is_open(), "Cannot open output file");
+    if (!_output_stream.is_open()) { detail::throw_on_file_open_failure(filepath, true); }
 
     if (detail::cufile_integration::is_kvikio_enabled()) {
       _kvikio_file = kvikio::FileHandle(filepath, "w");

cpp/src/io/utilities/file_io_utilities.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2023, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2024, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,38 +13,61 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 #include "file_io_utilities.hpp"
 #include <cudf/detail/utilities/integer_utils.hpp>
 #include <io/utilities/config_utils.hpp>
 
 #include <rmm/device_buffer.hpp>
 
 #include <dlfcn.h>
+#include <errno.h>
+#include <string.h>
 
+#include <filesystem>
 #include <fstream>
 #include <numeric>
 
 namespace cudf {
 namespace io {
 namespace detail {
 
-size_t get_file_size(int file_descriptor)
+[[noreturn]] void throw_on_file_open_failure(std::string const& filepath, bool is_create)
 {
-  struct stat st;
-  CUDF_EXPECTS(fstat(file_descriptor, &st) != -1, "Cannot query file size");
-  return static_cast<size_t>(st.st_size);
+  // save errno because it may be overwritten by subsequent calls
+  auto const err = errno;
+
+  if (auto const path = std::filesystem::path(filepath); is_create) {
+    CUDF_EXPECTS(std::filesystem::exists(path.parent_path()),
+                 "Cannot create output file; directory does not exist");
+
+  } else {
+    CUDF_EXPECTS(std::filesystem::exists(path), "Cannot open file; it does not exist");
+  }
+
+  std::array<char, 1024> error_msg_buffer;
+  auto const error_msg = strerror_r(err, error_msg_buffer.data(), 1024);
+  CUDF_FAIL("Cannot open file; failed with errno: " + std::string{error_msg});
 }
 
-file_wrapper::file_wrapper(std::string const& filepath, int flags)
-  : fd(open(filepath.c_str(), flags)), _size{get_file_size(fd)}
+[[nodiscard]] int open_file_checked(std::string const& filepath, int flags, mode_t mode)
 {
-  CUDF_EXPECTS(fd != -1, "Cannot open file " + filepath);
+  auto const fd = open(filepath.c_str(), flags, mode);
+  if (fd == -1) { throw_on_file_open_failure(filepath, flags & O_CREAT); }
+
+  return fd;
+}
+
+[[nodiscard]] size_t get_file_size(int file_descriptor)
+{
+  struct stat st;
+  CUDF_EXPECTS(fstat(file_descriptor, &st) != -1, "Cannot query file size");
+  return static_cast<size_t>(st.st_size);
 }
 
 file_wrapper::file_wrapper(std::string const& filepath, int flags, mode_t mode)
-  : fd(open(filepath.c_str(), flags, mode)), _size{get_file_size(fd)}
+  : fd(open_file_checked(filepath.c_str(), flags, mode)), _size{get_file_size(fd)}
 {
-  CUDF_EXPECTS(fd != -1, "Cannot open file " + filepath);
 }
 
 file_wrapper::~file_wrapper() { close(fd); }

cpp/src/io/utilities/file_io_utilities.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2023, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2024, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,16 +34,17 @@ namespace cudf {
 namespace io {
 namespace detail {
 
+[[noreturn]] void throw_on_file_open_failure(std::string const& filepath, bool is_create);
+
 /**
  * @brief Class that provides RAII for file handling.
  */
 class file_wrapper {
-  int fd = -1;
-  size_t _size;
+  int fd       = -1;
+  size_t _size = 0;
 
  public:
-  explicit file_wrapper(std::string const& filepath, int flags);
-  explicit file_wrapper(std::string const& filepath, int flags, mode_t mode);
+  explicit file_wrapper(std::string const& filepath, int flags, mode_t mode = 0);
   ~file_wrapper();
   [[nodiscard]] auto size() const { return _size; }
   [[nodiscard]] auto desc() const { return fd; }