[cdc_stream] Automatically start service (#28)

Starts the streaming service if it's not up and running. This required
adding the ability to run a detached process. By default, all child
processes are killed when the parent process exits. Since detached
child processes don't run with a console, they need to create sub-
processes with CREATE_NO_WINDOW since otherwise a new console pops up,
e.g. for every ssh command.

Polls for 20 seconds while the service starts up. For this purpose,
a BackgroundServiceClient is added. This will be reused in a future CL
by a new stop-service command to exit the service.

Also adds --service-port as additional argument to start-service.

README.md

@@ -211,20 +211,12 @@ cdc_rsync C:\path\to\assets\* user@linux.device.com:~/assets -vr
 
 ### CDC Stream
 
-`cdc_stream` consists of a background service, which has to be started in
-advance with
-```
-cdc_stream start-service
-```
-The service logs to `%APPDATA%\cdc-file-transfer\logs` by default. Try
-`cdc_stream --help` to get a list of available flags.
-
 To stream the Windows directory `C:\path\to\assets` to `~/assets` on the Linux
 device, run
 ```
 cdc_stream start C:\path\to\assets user@linux.device.com:~/assets
 ```
-This makes all files and directories of `C:\path\to\assets` available on
+This makes all files and directories in `C:\path\to\assets` available on
 `~/assets` immediately, as if it were a local copy. However, data is streamed
 from Windows to Linux as files are accessed.
 
@@ -235,14 +227,31 @@ cdc_stream stop user@linux.device.com:~/assets
 
 ## Troubleshooting
 
-`cdc_rsync` always logs to the console. By default, the `cdc_stream` service
-logs to a timestamped file in `%APPDATA%\cdc-file-transfer\logs`. It can be
-switched to log to console by starting it with `--log-to-stdout`:
-```
-cdc_stream start-service --log_to_stdout
-```
+On first run, `cdc_stream` starts a background service, which does all the work.
+The `cdc_stream start` and `cdc_stream stop` commands are just RPC clients that
+talk to the service.
 
-Both `cdc_rsync` and `cdc_stream` support command line flags to control log
-verbosity. Passing `-vvv` prints debug logs, `-vvvv` prints verbose logs. The
-debug logs contain all SSH and SCP commands that are attempted to run, which is
-very useful for troubleshooting.
+The service logs to `%APPDATA%\cdc-file-transfer\logs` by default. The logs are
+useful to investigate issues with asset streaming. To pass custom arguments, or
+to debug the service, create a JSON config file at
+`%APPDATA%\cdc-file-transfer\cdc_stream.json` with command line flags.
+For instance,
+```
+{ "verbosity":3 }
+```
+instructs the service to log debug messages. Try `cdc_stream start-service -h`
+for a list of available flags. Alternatively, run the service manually with
+```
+cdc_stream start-service
+```
+and pass the flags as command line arguments. When you run the service manually,
+the flag `--log-to-stdout` is particularly useful as it logs to the console
+instead of to the file.
+
+`cdc_rsync` always logs to the console. To increase log verbosity, pass `-vvv`
+for debug logs or `-vvvv` for verbose logs.
+
+For both sync and stream, the debug logs contain all SSH and SCP commands that
+are attempted to run, which is very useful for troubleshooting. If a command
+fails unexpectedly, copy it and run it in isolation. Pass `-vv` or `-vvv` for
+additional debug output.

cdc_stream/BUILD

@@ -45,6 +45,7 @@ cc_library(
     srcs = ["start_command.cc"],
     hdrs = ["start_command.h"],
     deps = [
+        ":background_service_client",
         ":base_command",
         ":local_assets_stream_manager_client",
         ":session_management_server",
@@ -78,6 +79,18 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "background_service_client",
+    srcs = ["background_service_client.cc"],
+    hdrs = ["background_service_client.h"],
+    deps = [
+        "//common:grpc_status",
+        "//common:status_macros",
+        "//proto:background_service_grpc_proto",
+        "@com_google_absl//absl/status",
+    ],
+)
+
 cc_library(
     name = "asset_stream_server",
     srcs = [
@@ -112,6 +125,8 @@ cc_library(
     deps = [
         ":base_command",
         ":multi_session",
+        ":session_management_server",
+        "//absl_helper:jedec_size_flag",
         "//common:log",
         "//common:path",
         "//common:status_macros",

cdc_stream/asset_stream_config.cc

@@ -20,6 +20,7 @@
 #include "absl/strings/str_join.h"
 #include "absl_helper/jedec_size_flag.h"
 #include "cdc_stream/base_command.h"
+#include "cdc_stream/session_management_server.h"
 #include "common/buffer.h"
 #include "common/path.h"
 #include "common/status_macros.h"
@@ -41,6 +42,13 @@ AssetStreamConfig::~AssetStreamConfig() = default;
 
 void AssetStreamConfig::RegisterCommandLineFlags(lyra::command& cmd,
                                                  BaseCommand& base_command) {
+  service_port_ = SessionManagementServer::kDefaultServicePort;
+  cmd.add_argument(lyra::opt(service_port_, "port")
+                       .name("--service-port")
+                       .help("Local port to use while connecting to the local "
+                             "asset stream service, default: " +
+                             std::to_string(service_port_)));
+
   session_cfg_.verbosity = kDefaultVerbosity;
   cmd.add_argument(lyra::opt(session_cfg_.verbosity, "num")
                        .name("--verbosity")
@@ -174,6 +182,7 @@ absl::Status AssetStreamConfig::LoadFromFile(const std::string& path) {
     }                                     \
   } while (0)
 
+  ASSIGN_VAR(service_port_, "service-port", Int);
   ASSIGN_VAR(session_cfg_.verbosity, "verbosity", Int);
   ASSIGN_VAR(session_cfg_.fuse_debug, "debug", Bool);
   ASSIGN_VAR(session_cfg_.fuse_singlethreaded, "singlethreaded", Bool);
@@ -212,6 +221,7 @@ absl::Status AssetStreamConfig::LoadFromFile(const std::string& path) {
 
 std::string AssetStreamConfig::ToString() {
   std::ostringstream ss;
+  ss << "service-port                 = " << service_port_ << std::endl;
   ss << "verbosity                    = " << session_cfg_.verbosity
      << std::endl;
   ss << "debug                        = " << session_cfg_.fuse_debug

cdc_stream/asset_stream_config.h

@@ -76,6 +76,9 @@ class AssetStreamConfig {
   // read from the JSON file.
   std::string GetFlagReadErrors();
 
+  // Gets the port to use for the asset streaming service.
+  uint16_t service_port() const { return service_port_; }
+
   // Session configuration.
   const SessionConfig& session_cfg() const { return session_cfg_; }
 
@@ -91,6 +94,13 @@ class AssetStreamConfig {
   bool log_to_stdout() const { return log_to_stdout_; }
 
  private:
+  // Jedec parser for Lyra options. Usage:
+  //   lyra::opt(JedecParser("size-flag", &size_bytes), "bytes"))
+  // Sets jedec_parse_error_ on error, Lyra doesn't support errors from lambdas.
+  std::function<void(const std::string&)> JedecParser(const char* flag_name,
+                                                      uint64_t* bytes);
+
+  uint16_t service_port_ = 0;
   SessionConfig session_cfg_;
   bool log_to_stdout_ = false;
 

cdc_stream/background_service_client.cc

@@ -0,0 +1,56 @@
+// 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 "cdc_stream/background_service_client.h"
+
+#include "absl/status/status.h"
+#include "common/grpc_status.h"
+#include "common/status_macros.h"
+#include "grpcpp/channel.h"
+
+namespace cdc_ft {
+
+using GetPidResponse = backgroundservice::GetPidResponse;
+using EmptyProto = google::protobuf::Empty;
+
+BackgroundServiceClient::BackgroundServiceClient(
+    std::shared_ptr<grpc::Channel> channel) {
+  stub_ = BackgroundService::NewStub(std::move(channel));
+}
+
+BackgroundServiceClient::~BackgroundServiceClient() = default;
+
+absl::Status BackgroundServiceClient::Exit() {
+  EmptyProto request;
+  EmptyProto response;
+  grpc::ClientContext context;
+  return ToAbslStatus(stub_->Exit(&context, request, &response));
+}
+
+absl::StatusOr<int> BackgroundServiceClient::GetPid() {
+  EmptyProto request;
+  GetPidResponse response;
+  grpc::ClientContext context;
+  RETURN_IF_ERROR(ToAbslStatus(stub_->GetPid(&context, request, &response)));
+  return response.pid();
+}
+
+absl::Status BackgroundServiceClient::IsHealthy() {
+  EmptyProto request;
+  EmptyProto response;
+  grpc::ClientContext context;
+  return ToAbslStatus(stub_->HealthCheck(&context, request, &response));
+}
+
+}  // namespace cdc_ft

cdc_stream/background_service_client.h

@@ -0,0 +1,56 @@
+/*
+ * 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_STREAM_BACKGROUND_SERVICE_CLIENT_H_
+#define CDC_STREAM_BACKGROUND_SERVICE_CLIENT_H_
+
+#include <memory>
+
+#include "absl/status/status.h"
+#include "absl/status/statusor.h"
+#include "proto/background_service.grpc.pb.h"
+
+namespace grpc_impl {
+class Channel;
+}
+
+namespace cdc_ft {
+
+// gRpc client for managing the asset streaming service.
+class BackgroundServiceClient {
+ public:
+  // |channel| is a grpc channel to use.
+  explicit BackgroundServiceClient(std::shared_ptr<grpc::Channel> channel);
+
+  ~BackgroundServiceClient();
+
+  // Initialize service shutdown.
+  absl::Status Exit();
+
+  // Returns the PID of the service process.
+  absl::StatusOr<int> GetPid();
+
+  // Verifies that the service is running and able to take requests.
+  absl::Status IsHealthy();
+
+ private:
+  using BackgroundService = backgroundservice::BackgroundService;
+  std::unique_ptr<BackgroundService::Stub> stub_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // CDC_STREAM_BACKGROUND_SERVICE_CLIENT_H_

cdc_stream/background_service_impl.cc

@@ -30,8 +30,8 @@ void BackgroundServiceImpl::SetExitCallback(ExitCallback exit_callback) {
 }
 
 grpc::Status BackgroundServiceImpl::Exit(grpc::ServerContext* context,
-                                         const ExitRequest* request,
-                                         ExitResponse* response) {
+                                         const EmptyProto* request,
+                                         EmptyProto* response) {
   LOG_INFO("RPC:Exit");
   if (exit_callback_) {
     return ToGrpcStatus(exit_callback_());
@@ -40,7 +40,7 @@ grpc::Status BackgroundServiceImpl::Exit(grpc::ServerContext* context,
 }
 
 grpc::Status BackgroundServiceImpl::GetPid(grpc::ServerContext* context,
-                                           const GetPidRequest* request,
+                                           const EmptyProto* request,
                                            GetPidResponse* response) {
   LOG_INFO("RPC:GetPid");
   response->set_pid(static_cast<int32_t>(Util::GetPid()));

cdc_stream/background_service_impl.h

@@ -30,9 +30,6 @@ namespace cdc_ft {
 class BackgroundServiceImpl final
     : public backgroundservice::BackgroundService::Service {
  public:
-  using ExitRequest = backgroundservice::ExitRequest;
-  using ExitResponse = backgroundservice::ExitResponse;
-  using GetPidRequest = backgroundservice::GetPidRequest;
   using GetPidResponse = backgroundservice::GetPidResponse;
   using EmptyProto = google::protobuf::Empty;
 
@@ -43,11 +40,10 @@ class BackgroundServiceImpl final
   using ExitCallback = std::function<absl::Status()>;
   void SetExitCallback(ExitCallback exit_callback);
 
-  grpc::Status Exit(grpc::ServerContext* context, const ExitRequest* request,
-                    ExitResponse* response) override;
+  grpc::Status Exit(grpc::ServerContext* context, const EmptyProto* request,
+                    EmptyProto* response) override;
 
-  grpc::Status GetPid(grpc::ServerContext* context,
-                      const GetPidRequest* request,
+  grpc::Status GetPid(grpc::ServerContext* context, const EmptyProto* request,
                       GetPidResponse* response) override;
 
   grpc::Status HealthCheck(grpc::ServerContext* context,

cdc_stream/local_assets_stream_manager_client.cc

@@ -28,15 +28,6 @@ using StartSessionResponse = localassetsstreammanager::StartSessionResponse;
 using StopSessionRequest = localassetsstreammanager::StopSessionRequest;
 using StopSessionResponse = localassetsstreammanager::StopSessionResponse;
 
-LocalAssetsStreamManagerClient::LocalAssetsStreamManagerClient(
-    uint16_t service_port) {
-  std::string client_address = absl::StrFormat("localhost:%u", service_port);
-  std::shared_ptr<grpc::Channel> channel = grpc::CreateCustomChannel(
-      client_address, grpc::InsecureChannelCredentials(),
-      grpc::ChannelArguments());
-  stub_ = LocalAssetsStreamManager::NewStub(std::move(channel));
-}
-
 LocalAssetsStreamManagerClient::LocalAssetsStreamManagerClient(
     std::shared_ptr<grpc::Channel> channel) {
   stub_ = LocalAssetsStreamManager::NewStub(std::move(channel));

cdc_stream/local_assets_stream_manager_client.h

@@ -20,7 +20,6 @@
 #include <memory>
 
 #include "absl/status/status.h"
-#include "grpcpp/channel.h"
 #include "proto/local_assets_stream_manager.grpc.pb.h"
 
 namespace grpc_impl {
@@ -32,8 +31,6 @@ namespace cdc_ft {
 // gRpc client for starting/stopping asset streaming sessions.
 class LocalAssetsStreamManagerClient {
  public:
-  explicit LocalAssetsStreamManagerClient(uint16_t service_port);
-
   // |channel| is a grpc channel to use.
   explicit LocalAssetsStreamManagerClient(
       std::shared_ptr<grpc::Channel> channel);

cdc_stream/local_assets_stream_manager_service_impl.cc

@@ -277,6 +277,7 @@ absl::Status LocalAssetsStreamManagerServiceImpl::InitSsh(
         absl::StrFormat(" --organization %s", Quoted(organization_id));
   }
   start_info.name = "ggp ssh init";
+  start_info.flags = ProcessFlags::kNoWindow;
 
   std::string output;
   start_info.stdout_handler = [&output, this](const char* data,

cdc_stream/session_management_server.h

@@ -36,7 +36,7 @@ class ProcessFactory;
 // - Background
 class SessionManagementServer {
  public:
-  static constexpr int kDefaultServicePort = 44432;
+  static constexpr uint16_t kDefaultServicePort = 44432;
 
   SessionManagementServer(grpc::Service* session_service,
                           grpc::Service* background_service,

cdc_stream/start_command.cc

@@ -16,12 +16,19 @@
 
 #include <memory>
 
+#include "cdc_stream/background_service_client.h"
 #include "cdc_stream/local_assets_stream_manager_client.h"
 #include "cdc_stream/session_management_server.h"
 #include "common/log.h"
 #include "common/path.h"
+#include "common/process.h"
 #include "common/remote_util.h"
 #include "common/status_macros.h"
+#include "common/stopwatch.h"
+#include "common/util.h"
+#include "grpcpp/channel.h"
+#include "grpcpp/create_channel.h"
+#include "grpcpp/support/channel_arguments.h"
 #include "lyra/lyra.hpp"
 
 namespace cdc_ft {
@@ -29,6 +36,19 @@ namespace {
 constexpr int kDefaultVerbosity = 2;
 }  // namespace
 
+namespace {
+// Time to poll until the streaming service becomes healthy.
+constexpr double kServiceStartupTimeoutSec = 20.0;
+
+std::shared_ptr<grpc::Channel> CreateChannel(uint16_t service_port) {
+  std::string client_address = absl::StrFormat("localhost:%u", service_port);
+  return grpc::CreateCustomChannel(client_address,
+                                   grpc::InsecureChannelCredentials(),
+                                   grpc::ChannelArguments());
+}
+
+}  // namespace
+
 StartCommand::StartCommand(int* exit_code)
     : BaseCommand("start",
                   "Start streaming files from a Windows to a Linux device",
@@ -89,16 +109,33 @@ void StartCommand::RegisterCommandLineFlags(lyra::command& cmd) {
 absl::Status StartCommand::Run() {
   LogLevel level = Log::VerbosityToLogLevel(verbosity_);
   ScopedLog scoped_log(std::make_unique<ConsoleLog>(level));
-  LocalAssetsStreamManagerClient client(service_port_);
 
   std::string full_src_dir = path::GetFullPath(src_dir_);
   std::string user_host, mount_dir;
   RETURN_IF_ERROR(LocalAssetsStreamManagerClient::ParseUserHostDir(
       user_host_dir_, &user_host, &mount_dir));
 
+  LocalAssetsStreamManagerClient client(CreateChannel(service_port_));
   absl::Status status =
       client.StartSession(full_src_dir, user_host, ssh_port_, mount_dir,
                           ssh_command_, scp_command_);
+
+  if (absl::IsUnavailable(status)) {
+    LOG_DEBUG("StartSession status: %s", status.ToString());
+    LOG_INFO("Streaming service is unavailable. Starting it...");
+    status = StartStreamingService();
+
+    if (status.ok()) {
+      LOG_INFO("Streaming service successfully started");
+
+      // Recreate client. The old channel might still be in a transient failure
+      // state.
+      LocalAssetsStreamManagerClient new_client(CreateChannel(service_port_));
+      status = new_client.StartSession(full_src_dir, user_host, ssh_port_,
+                                       mount_dir, ssh_command_, scp_command_);
+    }
+  }
+
   if (status.ok()) {
     LOG_INFO("Started streaming directory '%s' to '%s:%s'", src_dir_, user_host,
              mount_dir);
@@ -107,4 +144,44 @@ absl::Status StartCommand::Run() {
   return status;
 }
 
+absl::Status StartCommand::StartStreamingService() {
+  std::string exe_dir;
+  RETURN_IF_ERROR(path::GetExeDir(&exe_dir),
+                  "Failed to get executable directory");
+  std::string exe_path = path::Join(exe_dir, "cdc_stream");
+
+  // Try starting the service first.
+  WinProcessFactory process_factory;
+  ProcessStartInfo start_info;
+  start_info.command =
+      absl::StrFormat("%s start-service --verbosity=%i --service-port=%i",
+                      exe_path, verbosity_, service_port_);
+  start_info.flags = ProcessFlags::kDetached;
+  std::unique_ptr<Process> service_process = process_factory.Create(start_info);
+  RETURN_IF_ERROR(service_process->Start(),
+                  "Failed to start asset streaming service");
+
+  // Poll until the service becomes healthy.
+  LOG_INFO("Streaming service initializing...");
+  Stopwatch sw;
+  while (sw.ElapsedSeconds() < kServiceStartupTimeoutSec) {
+    // The channel is in some transient failure state, and it's faster to
+    // reconnect instead of waiting for it to return.
+    BackgroundServiceClient bg_client(CreateChannel(service_port_));
+    absl::Status status = bg_client.IsHealthy();
+    if (status.ok()) {
+      return absl::OkStatus();
+    }
+    LOG_DEBUG("Health check result: %s", status.ToString());
+    Util::Sleep(100);
+  }
+
+  // Kill the process.
+  service_process->Terminate();
+  return absl::DeadlineExceededError(
+      absl::StrFormat("Timed out after %0.0f seconds waiting for the asset "
+                      "streaming service to become healthy",
+                      kServiceStartupTimeoutSec));
+}
+
 }  // namespace cdc_ft

cdc_stream/start_command.h

@@ -20,6 +20,10 @@
 #include "absl/status/status.h"
 #include "cdc_stream/base_command.h"
 
+namespace grpc {
+class Channel;
+}
+
 namespace cdc_ft {
 
 // Handler for the start command. Sends an RPC call to the service to starts a
@@ -34,6 +38,9 @@ class StartCommand : public BaseCommand {
   absl::Status Run() override;
 
  private:
+  // Starts the asset streaming service.
+  absl::Status StartStreamingService();
+
   int verbosity_ = 0;
   uint16_t service_port_ = 0;
   uint16_t ssh_port_ = 0;

cdc_stream/start_service_command.cc

@@ -43,7 +43,7 @@ StartServiceCommand::StartServiceCommand(int* exit_code)
 StartServiceCommand::~StartServiceCommand() = default;
 
 void StartServiceCommand::RegisterCommandLineFlags(lyra::command& cmd) {
-  config_file_ = "%APPDATA%\\cdc-file-transfer\\assets_stream_manager.json";
+  config_file_ = "%APPDATA%\\cdc-file-transfer\\cdc_stream.json";
   cmd.add_argument(
       lyra::opt(config_file_, "path")
           .name("--config-file")
@@ -147,8 +147,7 @@ absl::Status StartServiceCommand::RunService() {
     RETURN_ABSL_IF_ERROR(
         session_service.StartSession(nullptr, &request, &response));
   }
-  RETURN_IF_ERROR(
-      sm_server.Start(SessionManagementServer::kDefaultServicePort));
+  RETURN_IF_ERROR(sm_server.Start(cfg_.service_port()));
   sm_server.RunUntilShutdown();
   return absl::OkStatus();
 }

cdc_stream/stop_command.cc

@@ -21,6 +21,9 @@
 #include "common/log.h"
 #include "common/path.h"
 #include "common/status_macros.h"
+#include "grpcpp/channel.h"
+#include "grpcpp/create_channel.h"
+#include "grpcpp/support/channel_arguments.h"
 #include "lyra/lyra.hpp"
 
 namespace cdc_ft {
@@ -58,7 +61,13 @@ void StopCommand::RegisterCommandLineFlags(lyra::command& cmd) {
 absl::Status StopCommand::Run() {
   LogLevel level = Log::VerbosityToLogLevel(verbosity_);
   ScopedLog scoped_log(std::make_unique<ConsoleLog>(level));
-  LocalAssetsStreamManagerClient client(service_port_);
+
+  std::string client_address = absl::StrFormat("localhost:%u", service_port_);
+  std::shared_ptr<grpc::Channel> channel = grpc::CreateCustomChannel(
+      client_address, grpc::InsecureChannelCredentials(),
+      grpc::ChannelArguments());
+
+  LocalAssetsStreamManagerClient client(channel);
 
   std::string user_host, mount_dir;
   RETURN_IF_ERROR(LocalAssetsStreamManagerClient::ParseUserHostDir(

common/port_manager_win.cc

@@ -213,6 +213,7 @@ absl::StatusOr<std::unordered_set<int>> PortManager::FindAvailableLocalPorts(
   ProcessStartInfo start_info;
   start_info.command = "netstat -a -n -p tcp";
   start_info.name = "netstat";
+  start_info.flags = ProcessFlags::kNoWindow;
 
   std::string output;
   start_info.stdout_handler = [&output](const char* data, size_t data_size) {
@@ -246,6 +247,7 @@ absl::StatusOr<std::unordered_set<int>> PortManager::FindAvailableRemotePorts(
   ProcessStartInfo start_info =
       remote_util->BuildProcessStartInfoForSsh(remote_command);
   start_info.name = "netstat";
+  start_info.flags = ProcessFlags::kNoWindow;
 
   std::string output;
   start_info.stdout_handler = [&output](const char* data, size_t data_size) {

common/process.h

@@ -33,6 +33,12 @@ namespace cdc_ft {
 absl::Status LogOutput(const char* name, const char* data, size_t data_size,
                        absl::optional<LogLevel> log_level = {});
 
+enum class ProcessFlags {
+  kNone = 0,
+  kDetached = 1 << 0,
+  kNoWindow = 1 << 1,
+};
+
 struct ProcessStartInfo {
   // Handler for stdout/stderr. |data| is guaranteed to be NULL terminated, so
   // it may be used like a C-string if it's known to be text, e.g. for printf().
@@ -63,8 +69,14 @@ struct ProcessStartInfo {
   OutputHandler stdout_handler;
   OutputHandler stderr_handler;
 
+  // Flags that define additional properties of the process.
+  ProcessFlags flags = ProcessFlags::kNone;
+
   // Returns |name| if set, otherwise |command|.
   const std::string& Name() const;
+
+  // Tests ALL flags (flags & flag) == flag.
+  bool HasFlag(ProcessFlags flag) const;
 };
 
 // Runs a background process and pipes stdin/stdout/stderr.
@@ -75,6 +87,8 @@ class Process {
   static constexpr uint32_t kExitCodeFailedToGetExitCode = 4000000002;
 
   explicit Process(const ProcessStartInfo& start_info);
+
+  // Terminates the process unless it's running with ProcessFlags::kDetached.
   virtual ~Process();
 
   // Start the background process.
@@ -140,6 +154,16 @@ class WinProcessFactory : public ProcessFactory {
   std::unique_ptr<Process> Create(const ProcessStartInfo& start_info) override;
 };
 
+inline ProcessFlags operator|(ProcessFlags a, ProcessFlags b) {
+  using T = std::underlying_type_t<ProcessFlags>;
+  return static_cast<ProcessFlags>(static_cast<T>(a) | static_cast<T>(b));
+}
+
+inline ProcessFlags operator&(ProcessFlags a, ProcessFlags b) {
+  using T = std::underlying_type_t<ProcessFlags>;
+  return static_cast<ProcessFlags>(static_cast<T>(a) & static_cast<T>(b));
+}
+
 }  // namespace cdc_ft
 
 #endif  // COMMON_PROCESS_H_

common/process_win.cc

@@ -49,6 +49,24 @@ void SetThreadName(const std::string& name) {
   }
 }
 
+int ToCreationFlags(ProcessFlags pflags) {
+#define HANDLE_FLAG(pflag, cflag)  \
+  if ((pflags & pflag) == pflag) { \
+    cflags |= cflag;               \
+    pdone = pdone | pflag;         \
+  }
+
+  int cflags = 0;
+  ProcessFlags pdone = ProcessFlags::kNone;
+  HANDLE_FLAG(ProcessFlags::kDetached, DETACHED_PROCESS);
+  HANDLE_FLAG(ProcessFlags::kNoWindow, CREATE_NO_WINDOW);
+  assert(pflags == pdone);
+
+#undef HANDLE_FLAG
+
+  return cflags;
+}
+
 std::atomic_int g_pipe_serial_number{0};
 
 // Creates a pipe suitable for overlapped IO. Regular anonymous pipes in Windows
@@ -567,6 +585,10 @@ const std::string& ProcessStartInfo::Name() const {
   return !name.empty() ? name : command;
 }
 
+bool ProcessStartInfo::HasFlag(ProcessFlags flag) const {
+  return (flags & flag) == flag;
+}
+
 Process::Process(const ProcessStartInfo& start_info)
     : start_info_(start_info) {}
 
@@ -593,6 +615,8 @@ class WinProcess : public Process {
   absl::Status GetStatus() const override;
 
  private:
+  void Reset();
+
   std::unique_ptr<ProcessInfo> process_info_;
   std::unique_ptr<MessagePumpThread> message_pump_;
 };
@@ -600,7 +624,14 @@ class WinProcess : public Process {
 WinProcess::WinProcess(const ProcessStartInfo& start_info)
     : Process(start_info) {}
 
-WinProcess::~WinProcess() { Terminate().IgnoreError(); }
+WinProcess::~WinProcess() {
+  if (start_info_.HasFlag(ProcessFlags::kDetached)) {
+    // If the process runs detached, just reset handles, don't terminate it.
+    Reset();
+  } else {
+    Terminate().IgnoreError();
+  }
+}
 
 absl::Status WinProcess::Start() {
   LOG_INFO("Starting process %s", start_info_.command.c_str());
@@ -676,10 +707,13 @@ absl::Status WinProcess::Start() {
   }
 
   JOBOBJECT_EXTENDED_LIMIT_INFORMATION jeli = {0};
-  jeli.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
+  if (!start_info_.HasFlag(ProcessFlags::kDetached)) {
+    jeli.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
+  }
   bool success = SetInformationJobObject(process_info_->job.Get(),
                                          JobObjectExtendedLimitInformation,
                                          &jeli, sizeof(jeli));
+
   if (!success) {
     return MakeStatus("SetInformationJobObject() failed: %s",
                       Util::GetLastWin32Error());
@@ -691,7 +725,7 @@ absl::Status WinProcess::Start() {
                           NULL,  // Process handle not inheritable
                           NULL,  // Thread handle not inheritable
                           TRUE,  // Inherit handles
-                          0,     // No creation flags
+                          ToCreationFlags(start_info_.flags),
                           NULL,  // Use parent's environment block
                           NULL,  // Use parent's starting directory
                           &si, &process_info_->pi);
@@ -785,32 +819,39 @@ absl::Status WinProcess::Terminate() {
     message_pump_.reset();
   }
 
-  if (process_info_) {
-    bool result = true;
-    if (should_terminate) {
-      result = TerminateProcess(process_info_->pi.hProcess, 0);
-      if (!result && GetLastError() == ERROR_ACCESS_DENIED) {
-        // This means that the process has already exited, but in a way that
-        // the exit wasn't properly reported to this code (e.g. the process got
-        // killed somewhere). Just handle this silently.
-        LOG_DEBUG("Process '%s' already exited", start_info_.Name());
-        result = true;
-      }
+  std::string error_msg;
+  if (process_info_ && should_terminate &&
+      !TerminateProcess(process_info_->pi.hProcess, 0)) {
+    if (GetLastError() == ERROR_ACCESS_DENIED) {
+      // This means that the process has already exited, but in a way that
+      // the exit wasn't properly reported to this code (e.g. the process got
+      // killed somewhere). Just handle this silently.
+      LOG_DEBUG("Process '%s' already exited", start_info_.Name());
+    } else {
+      error_msg = Util::GetLastWin32Error();
     }
+  }
 
+  // Reset handles.
+  Reset();
+
+  if (!error_msg.empty()) {
+    return MakeStatus("TerminateProcess() failed: %s", error_msg);
+  }
+  return absl::OkStatus();
+}
+
+void WinProcess::Reset() {
+  // Shut down message pump.
+  message_pump_.reset();
+
+  if (process_info_) {
     // Close the handles that are not scoped handles.
     ScopedHandle(process_info_->pi.hProcess).Close();
     ScopedHandle(process_info_->pi.hThread).Close();
 
     process_info_.reset();
-
-    if (!result) {
-      return MakeStatus("TerminateProcess() failed: %s",
-                        Util::GetLastWin32Error());
-    }
   }
-
-  return absl::OkStatus();
 }
 
 ProcessFactory::~ProcessFactory() = default;

common/remote_util.cc

@@ -75,6 +75,7 @@ absl::Status RemoteUtil::Scp(std::vector<std::string> source_filepaths,
 
   // -p preserves timestamps. This enables timestamp-based up-to-date checks.
   ProcessStartInfo start_info;
+  start_info.flags = ProcessFlags::kNoWindow;
   start_info.command = absl::StrFormat(
       "%s "
       "%s %s -p -T "
@@ -147,6 +148,7 @@ ProcessStartInfo RemoteUtil::BuildProcessStartInfoForSshInternal(
       QuoteForWindows(ssh_command_), quiet_ || verbosity_ < 2 ? "-q" : "",
       forward_arg, QuoteForWindows(user_host_), ssh_port_, remote_command_arg);
   start_info.forward_output_to_log = forward_output_to_log_;
+  start_info.flags = ProcessFlags::kNoWindow;
   return start_info;
 }
 

proto/background_service.proto

@@ -23,22 +23,16 @@ import "google/protobuf/empty.proto";
 service BackgroundService {
   // Exit is used to ask the service to exit. In the case of the process
   // manager, this cascades to all background processes.
-  rpc Exit(ExitRequest) returns (ExitResponse) {}
+  rpc Exit(google.protobuf.Empty) returns (google.protobuf.Empty) {}
 
   // GetPid is used to get the PID of the service process.
-  rpc GetPid(GetPidRequest) returns (GetPidResponse) {}
+  rpc GetPid(google.protobuf.Empty) returns (GetPidResponse) {}
 
   // HealthCheck is used to verify that the service is running. It returns an
   // empty protobuf if the service is ready to serve requests.
   rpc HealthCheck(google.protobuf.Empty) returns (google.protobuf.Empty) {}
 }
 
-message ExitRequest {}
-
-message ExitResponse {}
-
-message GetPidRequest {}
-
 message GetPidResponse {
   int32 pid = 1;
 }