dcsctp: Add data container

Represents data that is either received and extracted from a
DATA/I-DATA chunk, or data that is supposed to be sent, and
wrapped in a DATA/I-DATA chunk (depending on peer capabilities).

Bug: webrtc:12614
Change-Id: Iea831fa7ca939783a438f178740508e484920312
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213346
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33608}

net/dcsctp/packet/BUILD.gn

@@ -40,6 +40,15 @@ rtc_library("tlv_trait") {
   ]
 }
 
+rtc_source_set("data") {
+  deps = [
+    "../../../rtc_base",
+    "../../../rtc_base:checks",
+    "../../../rtc_base:rtc_base_approved",
+  ]
+  sources = [ "data.h" ]
+}
+
 rtc_library("crc32c") {
   deps = [
     "../../../api:array_view",

net/dcsctp/packet/data.h

@@ -0,0 +1,92 @@
+/*
+ *  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_PACKET_DATA_H_
+#define NET_DCSCTP_PACKET_DATA_H_
+
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+namespace dcsctp {
+
+// Represents data that is either received and extracted from a DATA/I-DATA
+// chunk, or data that is supposed to be sent, and wrapped in a DATA/I-DATA
+// chunk (depending on peer capabilities).
+//
+// The data wrapped in this structure is actually the same as the DATA/I-DATA
+// chunk (actually the union of them), but to avoid having all components be
+// aware of the implementation details of the different chunks, this abstraction
+// is used instead. A notable difference is also that it doesn't carry a
+// Transmission Sequence Number (TSN), as that is not known when a chunk is
+// created (assigned late, just when sending), and that the TSNs in DATA/I-DATA
+// are wrapped numbers, and within the library, unwrapped sequence numbers are
+// preferably used.
+struct Data {
+  Data(uint16_t stream_id,
+       uint16_t ssn,
+       uint32_t message_id,
+       uint32_t fsn,
+       uint32_t ppid,
+       std::vector<uint8_t> payload,
+       bool is_beginning,
+       bool is_end,
+       bool is_unordered)
+      : stream_id(stream_id),
+        ssn(ssn),
+        message_id(message_id),
+        fsn(fsn),
+        ppid(ppid),
+        payload(std::move(payload)),
+        is_beginning(is_beginning),
+        is_end(is_end),
+        is_unordered(is_unordered) {}
+
+  // Move-only, to avoid accidental copies.
+  Data(Data&& other) = default;
+  Data& operator=(Data&& other) = default;
+
+  // Creates a copy of this `Data` object.
+  Data Clone() {
+    return Data(stream_id, ssn, message_id, fsn, ppid, payload, is_beginning,
+                is_end, is_unordered);
+  }
+
+  // The size of this data, which translates to the size of its payload.
+  size_t size() const { return payload.size(); }
+
+  // Stream Identifier.
+  uint16_t stream_id;
+
+  // Stream Sequence Number (SSN), per stream, for ordered chunks. Defined by
+  // RFC4960 and used only in DATA chunks (not I-DATA).
+  uint16_t ssn;
+
+  // Message Identifier (MID) per stream and ordered/unordered. Defined by
+  // RFC8260, and used together with options.is_unordered and stream_id to
+  // uniquely identify a message. Used only in I-DATA chunks (not DATA).
+  uint32_t message_id;
+  // Fragment Sequence Number (FSN) per stream and ordered/unordered, as above.
+  uint32_t fsn;
+
+  // Payload Protocol Identifier (PPID).
+  uint32_t ppid;
+
+  // The actual data payload.
+  std::vector<uint8_t> payload;
+
+  // If this data represents the first, last or a middle chunk.
+  bool is_beginning;
+  bool is_end;
+  // If this data is sent/received unordered.
+  bool is_unordered;
+};
+}  // namespace dcsctp
+
+#endif  // NET_DCSCTP_PACKET_DATA_H_