1 files changed, 55 insertions, 0 deletions
diff --git a/third_party/libwebrtc/net/dcsctp/rx/reassembly_streams.cc b/third_party/libwebrtc/net/dcsctp/rx/reassembly_streams.cc
new file mode 100644
index 0000000000..9fd52fb15d
--- /dev/null
+++ b/third_party/libwebrtc/net/dcsctp/rx/reassembly_streams.cc
@@ -0,0 +1,55 @@
+/*
+ *  Copyright (c) 2022 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.
+ */
+#include "net/dcsctp/rx/reassembly_streams.h"
+
+#include <cstddef>
+#include <map>
+#include <utility>
+
+namespace dcsctp {
+
+ReassembledMessage AssembleMessage(std::map<UnwrappedTSN, Data>::iterator start,
+                                   std::map<UnwrappedTSN, Data>::iterator end) {
+  size_t count = std::distance(start, end);
+
+  if (count == 1) {
+    // Fast path - zero-copy
+    Data& data = start->second;
+
+    return ReassembledMessage{
+        .tsns = {start->first},
+        .message = DcSctpMessage(data.stream_id, data.ppid,
+                                 std::move(start->second.payload)),
+    };
+  }
+
+  // Slow path - will need to concatenate the payload.
+  std::vector<UnwrappedTSN> tsns;
+  std::vector<uint8_t> payload;
+
+  size_t payload_size = std::accumulate(
+      start, end, 0,
+      [](size_t v, const auto& p) { return v + p.second.size(); });
+
+  tsns.reserve(count);
+  payload.reserve(payload_size);
+  for (auto it = start; it != end; ++it) {
+    Data& data = it->second;
+    tsns.push_back(it->first);
+    payload.insert(payload.end(), data.payload.begin(), data.payload.end());
+  }
+
+  return ReassembledMessage{
+      .tsns = std::move(tsns),
+      .message = DcSctpMessage(start->second.stream_id, start->second.ppid,
+                               std::move(payload)),
+  };
+}
+}  // namespace dcsctp