Releasing the former Stadia file transfer tools

The tools allow efficient and fast synchronization of large directory
trees from a Windows workstation to a Linux target machine.

cdc_rsync* support efficient copy of files by using content-defined
chunking (CDC) to identify chunks within files that can be reused.

asset_stream_manager + cdc_fuse_fs support efficient streaming of a
local directory to a remote virtual file system based on FUSE. It also
employs CDC to identify and reuse unchanged data chunks.

cdc_rsync/base/server_exit_code.h

@@ -0,0 +1,63 @@
+/*
+ * 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 CDC_RSYNC_BASE_SERVER_EXIT_CODE_H_
+#define CDC_RSYNC_BASE_SERVER_EXIT_CODE_H_
+
+namespace cdc_ft {
+
+// Since the client cannot distinguish between stderr and stdout (ssh.exe sends
+// both to stdout), the server marks the beginning and ending of error messages
+// with this marker char. The client interprets everything in between as an
+// error message.
+constexpr char kServerErrorMarker = 0x1e;
+
+enum ServerExitCode {
+  // Pick a range of exit codes that does not overlap with unrelated exit codes
+  // like bash exit codes.
+  // - 126: error from bash when binary can't be started (permission denied).
+  // - 127: error from bash when binary isn't found
+  // - 255: ssh.exe error code.
+  // Note that codes must be <= 255.
+
+  // KEEP UPDATED!
+  kServerExitCodeMin = 50,
+
+  // Generic error on startup, before out-of-date check, e.g. bad args.
+  kServerExitCodeGenericStartup = 50,
+
+  // A gamelet component is outdated and needs to be re-uploaded.
+  kServerExitCodeOutOfDate = 51,
+
+  //
+  // All other exit codes must be strictly bigger than kServerErrorOutOfDate.
+  // They are guaranteed to be past the out-of-date check.
+  //
+
+  // Unspecified error.
+  kServerExitCodeGeneric = 52,
+
+  // Binding to the forward port failed, probably because there's another
+  // instance of cdc_rsync running.
+  kServerExitCodeAddressInUse = 53,
+
+  // KEEP UPDATED!
+  kServerExitCodeMax = 53,
+};
+
+}  // namespace cdc_ft
+
+#endif  // CDC_RSYNC_BASE_SERVER_EXIT_CODE_H_