1 files changed, 79 insertions, 0 deletions
diff --git a/lib/libc/include/string-file.h b/lib/libc/include/string-file.h
new file mode 100644
index 0000000..1632933
--- /dev/null
+++ b/lib/libc/include/string-file.h
@@ -0,0 +1,79 @@
+// Copyright 2021 The Fuchsia Authors
+// Copyright (c) 2008 Travis Geiselbrecht
+//
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT
+
+#ifndef ZIRCON_KERNEL_LIB_LIBC_INCLUDE_STRING_FILE_H_
+#define ZIRCON_KERNEL_LIB_LIBC_INCLUDE_STRING_FILE_H_
+
+#ifdef __cplusplus
+#include <stdio.h>
+
+#include <ktl/algorithm.h>
+#include <ktl/span.h>
+#include <ktl/string_view.h>
+
+// FILE* wrapper over a string.
+class StringFile : public FILE {
+ public:
+  StringFile() = delete;
+  StringFile(const StringFile &) = delete;
+  StringFile operator=(const StringFile &) = delete;
+
+  explicit StringFile(ktl::span<char> s) : FILE(this), buffer_(s) {}
+
+  ~StringFile() = default;
+
+  // Adds a null character at the end of the current buffer and returns a view
+  // into the written section.
+  ktl::span<char> take() &&;
+
+  // Returns |str.size()| and writes as much of |str| as it would fit in the
+  // buffer [offest_, size - 1) while reserving the last byte for null
+  // character.
+  int Write(ktl::string_view str);
+
+  // Returns a region representing the currently used portion of the buffer.
+  ktl::span<char> used_region() const {
+    return (offset_ > 0) ? ktl::span<char>{buffer_.data(), offset_} : ktl::span<char>{};
+  }
+
+  // Returns a region representing the remaining unused space in the buffer,
+  // _not_ including the space reserved for the final null character.
+  ktl::span<char> available_region() const {
+    const size_t available = ktl::max<size_t>(buffer_.size() - offset_, 1) - 1;
+    return (available > 0) ? ktl::span<char>{buffer_.data() + offset_, available}
+                            : ktl::span<char>{};
+  }
+
+  // Skip up to |amt| bytes in the buffer, advancing the write pointer as if we
+  // had written data, but without actually changing the buffer.
+  void Skip(size_t amt) {
+    amt = ktl::min(amt, available_region().size());
+    offset_ += amt;
+  }
+
+  // Provide two ways for users to convert the currently used buffer into a
+  // string_view.  Given a string file |S|, users may say either:
+  //
+  // 1) S.as_string_view();   // or
+  // 2) static_cast<ktl::string_view>(S);
+  //
+  // to perform the conversion.
+  //
+  ktl::string_view as_string_view() const {
+    return (offset_ > 0) ? ktl::string_view{buffer_.data(), offset_} : ktl::string_view{};
+  }
+
+  explicit operator ktl::string_view() const { return this->as_string_view(); }
+
+ private:
+  ktl::span<char> buffer_;
+  size_t offset_ = 0;
+};
+
+#endif  // __cplusplus
+
+#endif  // ZIRCON_KERNEL_LIB_LIBC_INCLUDE_STRING_FILE_H_