[Open Screen] Add openscreen::ByteView.
This is a drop-in replacment for absl::span<uint8_t> so we can remove
absl::span from public APIs (e.g. openscreen::cast::EncodedFrame).
Background: https://chromium-review.googlesource.com/c/openscreen/+/3961928
Bug: b/239435405
Change-Id: I76f89d2ab912626b98cdbbc2732186d014e1937a
Reviewed-on: https://chromium-review.googlesource.com/c/openscreen/+/3967215
Commit-Queue: Mark Foltz <mfoltz@chromium.org>
Reviewed-by: Ryan Keane <rwkeane@google.com>
Reviewed-by: Jordan Bayles <jophba@chromium.org>
diff --git a/platform/base/byte_view.h b/platform/base/byte_view.h
new file mode 100644
index 0000000..d3aad0b
--- /dev/null
+++ b/platform/base/byte_view.h
@@ -0,0 +1,94 @@
+// Copyright 2023 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PLATFORM_BASE_BYTE_VIEW_H_
+#define PLATFORM_BASE_BYTE_VIEW_H_
+
+#include <stddef.h>
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+#include "platform/base/macros.h"
+
+namespace openscreen {
+
+// Contains a pointer and length to a span of continguous and unowned bytes.
+// The underlying data cannot be modified.
+//
+// The API is a slimmed-down version of a C++20 std::span<const uint8_t> and is
+// intended to be forwards-compatible. Support for iterators and front/back can
+// be added as needed; we don't intend to add support for static extents.
+//
+// NOTE: Although other span implementations allow passing zero to last(), we do
+// not, as the behavior is undefined. Callers should explicitly create an empty
+// ByteView instead.
+//
+// TODO(https://issuetracker.google.com/254502854): Replace assert() expressions
+// with OSP_CHECK* macros once those are available to files in platform/.
+class ByteView {
+ public:
+ constexpr ByteView() noexcept = default;
+ constexpr ByteView(const uint8_t* data, size_t count)
+ : data_(data), count_(count) {}
+ explicit ByteView(const std::vector<uint8_t>& v)
+ : data_(v.data()), count_(v.size()) {}
+
+ constexpr ByteView(const ByteView&) noexcept = default;
+ constexpr ByteView& operator=(const ByteView&) noexcept = default;
+ ByteView(ByteView&&) noexcept = default;
+ ByteView& operator=(ByteView&&) noexcept = default;
+ ~ByteView() = default;
+
+ constexpr const uint8_t* data() const noexcept { return data_; }
+
+ constexpr const uint8_t& operator[](size_t idx) const {
+ assert(idx < count_);
+ return *(data_ + idx);
+ }
+
+ constexpr size_t size() const { return count_; }
+
+ [[nodiscard]] constexpr bool empty() const { return count_ == 0; }
+
+ constexpr ByteView first(size_t count) const {
+ assert(count <= count_);
+ return ByteView(data_, count);
+ }
+
+ constexpr ByteView last(size_t count) const {
+ assert(count <= count_);
+ assert(count != 0);
+ return ByteView(data_ + (count_ - count), count);
+ }
+
+ constexpr const uint8_t* begin() const noexcept { return data_; }
+ constexpr const uint8_t* end() const noexcept { return data_ + count_; }
+
+ void remove_prefix(size_t count) noexcept {
+ assert(count_ >= count);
+ data_ += count;
+ count_ -= count;
+ }
+
+ void remove_suffix(size_t count) noexcept {
+ assert(count_ >= count);
+ count_ -= count;
+ }
+
+ constexpr ByteView subspan(size_t offset, size_t count) const {
+ assert(offset + count < count_);
+ return ByteView(data_ + offset, count);
+ }
+
+ private:
+ const uint8_t* data_{nullptr};
+ size_t count_{0};
+};
+
+} // namespace openscreen
+
+#endif // PLATFORM_BASE_BYTE_VIEW_H_