[cdc_stream] Use ephemeral ports (#100)

Instead of running netstat/ss on local and remote systems, just bind
with port 0 to find an ephemeral port. This is much more robust,
simpler and a bit faster. Since the remote port is only known after
running cdc_fuse_fs, port forwarding has to be set up after running
cdc_fuse_fs.

cdc_fuse_fs/BUILD

@@ -9,8 +9,10 @@ cc_binary(
         ":cdc_fuse_fs_lib",
         ":constants",
         "//absl_helper:jedec_size_flag",
+        "//common:client_socket",
         "//common:gamelet_component",
         "//common:log",
+        "//common:server_socket",
         "//data_store:data_provider",
         "//data_store:disk_data_store",
         "//data_store:grpc_reader",

cdc_fuse_fs/constants.h

@@ -19,15 +19,22 @@
 
 namespace cdc_ft {
 
-// FUSE prints this to stdout when the binary timestamp and file size match the
-// file on the workstation.
-static constexpr char kFuseUpToDate[] = "cdc_fuse_fs is up-to-date";
+// FUSE prints
+//   Port 12345 cdc_fuse_fs is up-to-date
+// to stdout when its version matches the version (=build version or
+// size/timestamp for DEV builds) on the local device. The port is the gRPC port
+// that FUSE will try to connect to.
+static constexpr char kFusePortPrefix[] = "Port ";
+static constexpr char kFuseUpToDate[] = " cdc_fuse_fs is up-to-date";
 
-// FUSE prints this to stdout when the binary timestamp or file size does not
-// match the file on the workstation. It indicates that the binary has to be
-// redeployed.
+// FUSE prints this to stdout when its version does not match the version on the
+// local device. It indicates that the binary has to be redeployed.
 static constexpr char kFuseNotUpToDate[] = "cdc_fuse_fs is not up-to-date";
 
+// FUSE prints this to stdout when it can connect to its port. This means that
+// port forwarding has finished setting up, and startup is finished.
+static constexpr char kFuseConnected[] = "cdc_fuse_fs is connected";
+
 }  // namespace cdc_ft
 
 #endif  // CDC_FUSE_FS_CONSTANTS_H_

cdc_fuse_fs/main.cc

@@ -21,9 +21,11 @@
 #include "cdc_fuse_fs/cdc_fuse_fs.h"
 #include "cdc_fuse_fs/config_stream_client.h"
 #include "cdc_fuse_fs/constants.h"
+#include "common/client_socket.h"
 #include "common/gamelet_component.h"
 #include "common/log.h"
 #include "common/path.h"
+#include "common/server_socket.h"
 #include "data_store/data_provider.h"
 #include "data_store/disk_data_store.h"
 #include "data_store/grpc_reader.h"
@@ -37,6 +39,8 @@ namespace {
 constexpr char kFuseFilename[] = "cdc_fuse_fs";
 constexpr char kLibFuseFilename[] = "libfuse.so";
 
+constexpr absl::Duration kConnectionTimeout = absl::Seconds(60);
+
 bool IsUpToDate(const std::string& components_arg) {
   // Components are expected to reside in the same dir as the executable.
   std::string component_dir;
@@ -107,7 +111,6 @@ ABSL_FLAG(
     "Whitespace-separated triples filename, size and timestamp of the "
     "workstation version of this binary and dependencies. Used for a fast "
     "up-to-date check.");
-ABSL_FLAG(uint16_t, port, 0, "Port to connect to on localhost");
 ABSL_FLAG(cdc_ft::JedecSize, prefetch_size, cdc_ft::JedecSize(512 << 10),
           "Additional data to request from the server when a FUSE read of "
           "maximum size is detected. This amount is added to the original "
@@ -138,7 +141,6 @@ int main(int argc, char* argv[]) {
   std::vector<char*> mount_args = absl::ParseCommandLine(argc, argv);
   std::string instance = absl::GetFlag(FLAGS_instance);
   std::string components = absl::GetFlag(FLAGS_components);
-  uint16_t port = absl::GetFlag(FLAGS_port);
   std::string cache_dir = absl::GetFlag(FLAGS_cache_dir);
   int cache_dir_levels = absl::GetFlag(FLAGS_cache_dir_levels);
   int verbosity = absl::GetFlag(FLAGS_verbosity);
@@ -159,7 +161,18 @@ int main(int argc, char* argv[]) {
     printf("%s\n", cdc_ft::kFuseNotUpToDate);
     return 0;
   }
-  printf("%s\n", cdc_ft::kFuseUpToDate);
+
+  // Find an available port.
+  absl::StatusOr<int> port_or = cdc_ft::ServerSocket::FindAvailablePort();
+  if (!port_or.ok()) {
+    LOG_ERROR("Failed to find available port: %s\n",
+              port_or.status().ToString());
+    return 1;
+  }
+  int port = *port_or;
+
+  // Write marker for the server.
+  printf("%s%i%s\n", cdc_ft::kFusePortPrefix, port, cdc_ft::kFuseUpToDate);
   fflush(stdout);
 
   // Create mount dir if it doesn't exist yet.
@@ -189,6 +202,18 @@ int main(int argc, char* argv[]) {
   store.value()->SetCapacity(cache_capacity);
   LOG_INFO("Caching chunks in '%s'", store.value()->RootDir());
 
+  // Wait for port forwarding to listen to |port|.
+  status =
+      cdc_ft::ClientSocket::WaitForConnection(port, cdc_ft::kConnectionTimeout);
+  if (!status.ok()) {
+    LOG_ERROR("Failed to connect to port %i: %s", port, status.ToString());
+    return static_cast<int>(status.code());
+  }
+
+  // Write another marker for the server.
+  printf("%s\n", cdc_ft::kFuseConnected);
+  fflush(stdout);
+
   // Start a gRpc client.
   std::string client_address = absl::StrFormat("localhost:%u", port);
   grpc::ChannelArguments channel_args;