rclone: Rework backend option parsing

This change allows passing no arguments to rclone, using `-o
rclone.args=""`. It is helpful when running rclone remotely via SSH
using a key with a forced command (via `command=` in `authorized_keys`).

internal/backend/rclone/backend.go

@@ -127,8 +127,6 @@ func New(cfg Config, lim limiter.Limiter) (*Backend, error) {
 			return nil, err
 		}
 		args = append(args, a...)
-	} else {
-		args = append(args, "rclone")
 	}
 
 	// then add the arguments
@@ -139,10 +137,6 @@ func New(cfg Config, lim limiter.Limiter) (*Backend, error) {
 		}
 
 		args = append(args, a...)
-	} else {
-		args = append(args,
-			"serve", "restic", "--stdio",
-			"--b2-hard-delete", "--drive-use-trash=false")
 	}
 
 	// finally, add the remote

internal/backend/rclone/config.go

@@ -15,15 +15,19 @@ type Config struct {
 	Connections uint `option:"connections" help:"set a limit for the number of concurrent connections (default: 5)"`
 }
 
+var defaultConfig = Config{
+	Program:     "rclone",
+	Args:        "serve restic --stdio --b2-hard-delete --drive-use-trash=false",
+	Connections: 5,
+}
+
 func init() {
 	options.Register("rclone", Config{})
 }
 
 // NewConfig returns a new Config with the default values filled in.
 func NewConfig() Config {
-	return Config{
+	return defaultConfig
-		Connections: 5,
-	}
 }
 
 // ParseConfig parses the string s and extracts the remote server URL.

internal/backend/rclone/config_test.go

@@ -14,7 +14,9 @@ func TestParseConfig(t *testing.T) {
 			"rclone:local:foo:/bar",
 			Config{
 				Remote:      "local:foo:/bar",
-				Connections: 5,
+				Program:     defaultConfig.Program,
+				Args:        defaultConfig.Args,
+				Connections: defaultConfig.Connections,
 			},
 		},
 	}