1 files changed, 77 insertions, 0 deletions
diff --git a/intl/components/src/FormatBuffer.h b/intl/components/src/FormatBuffer.h
new file mode 100644
index 0000000000..774e74d2ba
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+++ b/intl/components/src/FormatBuffer.h
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef intl_components_FormatBuffer_h
+#define intl_components_FormatBuffer_h
+
+/**
+ * This file contains public adaptors for the mozilla::intl Buffer template
+ * argument. Adaptors that can automatically be deduced are kept as private
+ * in ICU4CGlue.h. There is also the SpiderMonkey specific adaptor
+ * js::intl::FormatBuffer in js/src/builtin/intl/FormatBuffer.h.
+ */
+
+#include "nsTString.h"
+
+namespace mozilla::intl {
+
+/**
+ * mozilla::intl APIs require sizeable buffers. This class abstracts over
+ * the nsTSubstring.
+ */
+template <typename T>
+class nsTStringToBufferAdapter {
+ public:
+  using CharType = T;
+
+  // Do not allow copy or move. Move could be added in the future if needed.
+  nsTStringToBufferAdapter(const nsTStringToBufferAdapter&) = delete;
+  nsTStringToBufferAdapter& operator=(const nsTStringToBufferAdapter&) = delete;
+
+  explicit nsTStringToBufferAdapter(nsTSubstring<CharType>& aString)
+      : mString(aString) {}
+
+  /**
+   * Ensures the buffer has enough space to accommodate |size| elements.
+   */
+  [[nodiscard]] bool reserve(size_t size) {
+    return mString.SetLength(size, fallible);
+  }
+
+  /**
+   * Returns the raw data inside the buffer.
+   */
+  CharType* data() { return mString.BeginWriting(); }
+
+  /**
+   * Returns the count of elements written into the buffer.
+   */
+  size_t length() const { return mString.Length(); }
+
+  /**
+   * Returns the buffer's overall capacity.
+   */
+  size_t capacity() const {
+    // nsString's Capacity() method is protected, so just return the length.
+    return mString.Length();
+  }
+
+  /**
+   * Resizes the buffer to the given amount of written elements.
+   */
+  void written(size_t amount) {
+    MOZ_ASSERT(amount <= mString.Length());
+    // This sets |mString|'s internal size so that it matches how much was
+    // written. This is necessary because the write happens across FFI
+    // boundaries.
+    mString.SetLength(amount);
+  }
+
+ private:
+  nsTSubstring<CharType>& mString;
+};
+
+}  // namespace mozilla::intl
+
+#endif /* intl_components_FormatBuffer_h */