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diff --git a/third_party/libwebrtc/net/dcsctp/fuzzers/dcsctp_fuzzers.h b/third_party/libwebrtc/net/dcsctp/fuzzers/dcsctp_fuzzers.h
new file mode 100644
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+++ b/third_party/libwebrtc/net/dcsctp/fuzzers/dcsctp_fuzzers.h
@@ -0,0 +1,119 @@
+/*
+ *  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_FUZZERS_DCSCTP_FUZZERS_H_
+#define NET_DCSCTP_FUZZERS_DCSCTP_FUZZERS_H_
+
+#include <deque>
+#include <memory>
+#include <set>
+#include <vector>
+
+#include "api/array_view.h"
+#include "api/task_queue/task_queue_base.h"
+#include "net/dcsctp/public/dcsctp_socket.h"
+
+namespace dcsctp {
+namespace dcsctp_fuzzers {
+
+// A fake timeout used during fuzzing.
+class FuzzerTimeout : public Timeout {
+ public:
+  explicit FuzzerTimeout(std::set<TimeoutID>& active_timeouts)
+      : active_timeouts_(active_timeouts) {}
+
+  void Start(DurationMs duration_ms, TimeoutID timeout_id) override {
+    // Start is only allowed to be called on stopped or expired timeouts.
+    if (timeout_id_.has_value()) {
+      // It has been started before, but maybe it expired. Ensure that it's not
+      // running at least.
+      RTC_DCHECK(active_timeouts_.find(*timeout_id_) == active_timeouts_.end());
+    }
+    timeout_id_ = timeout_id;
+    RTC_DCHECK(active_timeouts_.insert(timeout_id).second);
+  }
+
+  void Stop() override {
+    // Stop is only allowed to be called on active timeouts. Not stopped or
+    // expired.
+    RTC_DCHECK(timeout_id_.has_value());
+    RTC_DCHECK(active_timeouts_.erase(*timeout_id_) == 1);
+    timeout_id_ = absl::nullopt;
+  }
+
+  // A set of all active timeouts, managed by `FuzzerCallbacks`.
+  std::set<TimeoutID>& active_timeouts_;
+  // If present, the timout is active and will expire reported as `timeout_id`.
+  absl::optional<TimeoutID> timeout_id_;
+};
+
+class FuzzerCallbacks : public DcSctpSocketCallbacks {
+ public:
+  static constexpr int kRandomValue = 42;
+  void SendPacket(rtc::ArrayView<const uint8_t> data) override {
+    sent_packets_.emplace_back(std::vector<uint8_t>(data.begin(), data.end()));
+  }
+  std::unique_ptr<Timeout> CreateTimeout(
+      webrtc::TaskQueueBase::DelayPrecision precision) override {
+    // The fuzzer timeouts don't implement |precision|.
+    return std::make_unique<FuzzerTimeout>(active_timeouts_);
+  }
+  TimeMs TimeMillis() override { return TimeMs(42); }
+  uint32_t GetRandomInt(uint32_t low, uint32_t high) override {
+    return kRandomValue;
+  }
+  void OnMessageReceived(DcSctpMessage message) override {}
+  void OnError(ErrorKind error, absl::string_view message) override {}
+  void OnAborted(ErrorKind error, absl::string_view message) override {}
+  void OnConnected() override {}
+  void OnClosed() override {}
+  void OnConnectionRestarted() override {}
+  void OnStreamsResetFailed(rtc::ArrayView<const StreamID> outgoing_streams,
+                            absl::string_view reason) override {}
+  void OnStreamsResetPerformed(
+      rtc::ArrayView<const StreamID> outgoing_streams) override {}
+  void OnIncomingStreamsReset(
+      rtc::ArrayView<const StreamID> incoming_streams) override {}
+
+  std::vector<uint8_t> ConsumeSentPacket() {
+    if (sent_packets_.empty()) {
+      return {};
+    }
+    std::vector<uint8_t> ret = sent_packets_.front();
+    sent_packets_.pop_front();
+    return ret;
+  }
+
+  // Given an index among the active timeouts, will expire that one.
+  absl::optional<TimeoutID> ExpireTimeout(size_t index) {
+    if (index < active_timeouts_.size()) {
+      auto it = active_timeouts_.begin();
+      std::advance(it, index);
+      TimeoutID timeout_id = *it;
+      active_timeouts_.erase(it);
+      return timeout_id;
+    }
+    return absl::nullopt;
+  }
+
+ private:
+  // Needs to be ordered, to allow fuzzers to expire timers.
+  std::set<TimeoutID> active_timeouts_;
+  std::deque<std::vector<uint8_t>> sent_packets_;
+};
+
+// Given some fuzzing `data` will send packets to the socket as well as calling
+// API methods.
+void FuzzSocket(DcSctpSocketInterface& socket,
+                FuzzerCallbacks& cb,
+                rtc::ArrayView<const uint8_t> data);
+
+}  // namespace dcsctp_fuzzers
+}  // namespace dcsctp
+#endif  // NET_DCSCTP_FUZZERS_DCSCTP_FUZZERS_H_