[libc-commits] [libc] [libc][NFC] Add FieldTokenizer and FlatFileDatabase (PR #214720)

[Alexey Samsonov via libc-commits]

================
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// In-place field tokenizer for colon-separated flat database files.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PWD_FIELD_TOKENIZER_H
+#define LLVM_LIBC_SRC_PWD_FIELD_TOKENIZER_H
+
+#include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/span.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace pwd {
+
+// In-place field tokenizer for delimited database records.
+template <char Separator> class FieldTokenizer {
+  char *data_ptr;
+  size_t data_len;
+
+public:
+  LIBC_INLINE constexpr explicit FieldTokenizer(cpp::span<char> buf)
+      : data_ptr(buf.data()), data_len(buf.size()) {}
+
+  // Extracts the next null-terminated field.
+  LIBC_INLINE cpp::optional<cpp::span<char>> next_field() {
+    if (data_len == 0)
+      return cpp::nullopt;
+
+    cpp::string_view sv(data_ptr, data_len);
+    size_t pos = sv.find_first_of(Separator);
+
+    // If a delimiter was found, replace it with a null terminator and return
+    // the field.
+    if (pos != cpp::string_view::npos) {
+      data_ptr[pos] = '\0';
+      auto field = cpp::span<char>(data_ptr, pos + 1);
----------------
vonosmas wrote:

This can be
```
auto field = data.first(pos + 1);
data = data.subspan(pos + 1);
return field;
```


https://github.com/llvm/llvm-project/pull/214720