dcsctp: Add Data Generator

The Data Generator is a testonly library for generating
Data with correct sequence numbers.

Bug: webrtc:12614
Change-Id: Ifc04dfd14d858d905312ffed13e8905c23d59923
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/214041
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33667}

net/dcsctp/testing/data_generator.h

@@ -0,0 +1,59 @@
+/*
+ *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef NET_DCSCTP_TESTING_DATA_GENERATOR_H_
+#define NET_DCSCTP_TESTING_DATA_GENERATOR_H_
+
+#include <cstdint>
+#include <vector>
+
+#include "absl/strings/string_view.h"
+#include "absl/types/optional.h"
+#include "api/array_view.h"
+#include "net/dcsctp/common/internal_types.h"
+#include "net/dcsctp/packet/data.h"
+
+namespace dcsctp {
+
+struct DataGeneratorOptions {
+  StreamID stream_id = StreamID(1);
+  absl::optional<MID> message_id = absl::nullopt;
+  PPID ppid = PPID(53);
+};
+
+// Generates Data with correct sequence numbers, and used only in unit tests.
+class DataGenerator {
+ public:
+  explicit DataGenerator(MID start_message_id = MID(0))
+      : message_id_(start_message_id) {}
+
+  // Generates ordered "data" with the provided `payload` and flags, which can
+  // contain "B" for setting the "is_beginning" flag, and/or "E" for setting the
+  // "is_end" flag.
+  Data Ordered(std::vector<uint8_t> payload,
+               absl::string_view flags = "",
+               const DataGeneratorOptions opts = {});
+
+  // Generates unordered "data" with the provided `payload` and flags, which can
+  // contain "B" for setting the "is_beginning" flag, and/or "E" for setting the
+  // "is_end" flag.
+  Data Unordered(std::vector<uint8_t> payload,
+                 absl::string_view flags = "",
+                 const DataGeneratorOptions opts = {});
+
+  // Resets the Message ID identifier - simulating a "stream reset".
+  void ResetStream() { message_id_ = MID(0); }
+
+ private:
+  MID message_id_;
+  FSN fsn_ = FSN(0);
+};
+}  // namespace dcsctp
+
+#endif  // NET_DCSCTP_TESTING_DATA_GENERATOR_H_