Support UTF-8 BOM in CSV reader (#13516)

Adds support to the CSV reader to skip the UTF-8 BOM bytes at the beginning of a text source.

Some text files may contain a BOM (byte order marker) at the beginning of the file to identify its encoding.
https://en.wikipedia.org/wiki/Byte_order_mark

cuDF only support UTF-8 encoding so skipping these bytes allows us to support these types of files.

Closes #12516

Authors:
  - David Wendt (https://github.com/davidwendt)

Approvers:
  - Nghia Truong (https://github.com/ttnghia)
  - Vukasin Milovanovic (https://github.com/vuule)

URL: #13516

cpp/src/io/csv/reader_impl.cu

@@ -413,9 +413,16 @@ std::pair<rmm::device_uvector<char>, selected_rows_offsets> select_data_and_row_
     auto data_size = (range_size_padded != 0) ? range_size_padded : source->size();
     auto buffer    = source->host_read(range_offset, data_size);
 
-    auto h_data = host_span<char const>(  //
-      reinterpret_cast<const char*>(buffer->data()),
-      buffer->size());
+    // check for and skip UTF-8 BOM
+    auto buffer_data         = buffer->data();
+    auto buffer_size         = buffer->size();
+    uint8_t const UTF8_BOM[] = {0xEF, 0xBB, 0xBF};
+    if (buffer_size > sizeof(UTF8_BOM) && memcmp(buffer_data, UTF8_BOM, sizeof(UTF8_BOM)) == 0) {
+      buffer_data += sizeof(UTF8_BOM);
+      buffer_size -= sizeof(UTF8_BOM);
+    }
+
+    auto h_data = host_span<char const>(reinterpret_cast<char const*>(buffer_data), buffer_size);
 
     std::vector<uint8_t> h_uncomp_data_owner;
 

cpp/tests/io/csv_test.cpp

@@ -2480,4 +2480,22 @@ TEST_F(CsvReaderTest, NullCount)
   EXPECT_EQ(result_view.column(2).null_count(), 8);
 }
 
+TEST_F(CsvReaderTest, UTF8BOM)
+{
+  std::string buffer = "\xEF\xBB\xBFMonth,Day,Year\nJune,6,2023\nAugust,25,1990\nMay,1,2000\n";
+  cudf::io::csv_reader_options in_opts =
+    cudf::io::csv_reader_options::builder(cudf::io::source_info{buffer.c_str(), buffer.size()});
+  auto const result      = cudf::io::read_csv(in_opts);
+  auto const result_view = result.tbl->view();
+  EXPECT_EQ(result_view.num_rows(), 3);
+  EXPECT_EQ(result.metadata.schema_info.front().name, "Month");
+
+  auto col1     = cudf::test::strings_column_wrapper({"June", "August", "May"});
+  auto col2     = cudf::test::fixed_width_column_wrapper<int64_t>({6, 25, 1});
+  auto col3     = cudf::test::fixed_width_column_wrapper<int64_t>({2023, 1990, 2000});
+  auto expected = cudf::table_view({col1, col2, col3});
+
+  CUDF_TEST_EXPECT_TABLES_EQUIVALENT(result_view, expected);
+}
+
 CUDF_TEST_PROGRAM_MAIN()