[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/socket.h

@@ -0,0 +1,59 @@
+/*
+ * 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.
+ */
+
+#ifndef COMMON_SOCKET_H_
+#define COMMON_SOCKET_H_
+
+#include "absl/status/status.h"
+
+namespace cdc_ft {
+
+class Socket {
+ public:
+  Socket() = default;
+  virtual ~Socket() = default;
+
+  // Calls WSAStartup() on Windows, no-op on Linux.
+  // Must be called before using sockets.
+  static absl::Status Initialize();
+
+  // Calls WSACleanup() on Windows, no-op on Linux.
+  // Must be called after using sockets.
+  static absl::Status Shutdown();
+
+  // Send data to the socket.
+  virtual absl::Status Send(const void* buffer, size_t size) = 0;
+
+  // Receives data from the socket. Blocks until data is available or the
+  // sending end of the socket gets shut down by the sender.
+  // If |allow_partial_read| is false, blocks until |size| bytes are available.
+  // If |allow_partial_read| is true, may return with success if less than
+  // |size| (but more than 0) bytes were received.
+  // The number of bytes written to |buffer| is returned in |bytes_received|.
+  virtual absl::Status Receive(void* buffer, size_t size,
+                               bool allow_partial_read,
+                               size_t* bytes_received) = 0;
+};
+
+// Convenience class that calls Shutdown() on destruction. Logs on errors.
+class SocketFinalizer {
+ public:
+  ~SocketFinalizer();
+};
+
+}  // namespace cdc_ft
+
+#endif  // COMMON_SOCKET_H_