[cdc_rsync] Move sockets to common (#95)

There are no real changes, just moving files around. Sockets will be
used in the future to find available ports in cdc_stream. Therefore,
they need to be in common.

common/fake_socket.cc

@@ -0,0 +1,71 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "common/fake_socket.h"
+
+namespace cdc_ft {
+
+FakeSocket::FakeSocket() = default;
+
+FakeSocket::~FakeSocket() = default;
+
+absl::Status FakeSocket::Send(const void* buffer, size_t size) {
+  // Wait until we can send again.
+  std::unique_lock<std::mutex> suspend_lock(suspend_mutex_);
+  suspend_cv_.wait(suspend_lock, [this]() { return !sending_suspended_; });
+  suspend_lock.unlock();
+
+  std::unique_lock<std::mutex> lock(data_mutex_);
+  data_.append(static_cast<const char*>(buffer), size);
+  lock.unlock();
+  data_cv_.notify_all();
+  return absl::OkStatus();
+}
+
+absl::Status FakeSocket::Receive(void* buffer, size_t size,
+                                 bool allow_partial_read,
+                                 size_t* bytes_received) {
+  *bytes_received = 0;
+  std::unique_lock<std::mutex> lock(data_mutex_);
+  data_cv_.wait(lock, [this, size, allow_partial_read]() {
+    size_t min_size = allow_partial_read ? 1 : size;
+    return data_.size() >= min_size || shutdown_;
+  });
+  if (shutdown_) {
+    return absl::UnavailableError("Pipe is shut down");
+  }
+  size_t to_copy = std::min(size, data_.size());
+  memcpy(buffer, data_.data(), to_copy);
+  *bytes_received = to_copy;
+
+  // This is horribly inefficent, but should be OK in a fake.
+  data_.erase(0, to_copy);
+  return absl::OkStatus();
+}
+
+void FakeSocket::ShutdownSendingEnd() {
+  std::unique_lock<std::mutex> lock(data_mutex_);
+  shutdown_ = true;
+  lock.unlock();
+  data_cv_.notify_all();
+}
+
+void FakeSocket::SuspendSending(bool suspended) {
+  std::unique_lock<std::mutex> lock(suspend_mutex_);
+  sending_suspended_ = suspended;
+  lock.unlock();
+  suspend_cv_.notify_all();
+}
+
+}  // namespace cdc_ft