rclone: add timeout option and documentation

changelog/unreleased/pull-3514

@@ -0,0 +1,7 @@
+Enhancement: Support timeout configurable for rclone backend
+
+A slow rclone backend could cause restic to time out while waiting for the repository to open.
+Restic now offers an `-o rclone.timeout` option to make this timeout configurable.
+
+https://github.com/restic/restic/issues/3511
+https://github.com/restic/restic/pull/3514

doc/030_preparing_a_new_repo.rst

@@ -607,10 +607,11 @@ configuring a bandwidth limit for rclone can be achieved by setting the
 
 For debugging rclone, you can set the environment variable ``RCLONE_VERBOSE=2``.
 
-The rclone backend has two additional options:
+The rclone backend has three additional options:
 
  * ``-o rclone.program`` specifies the path to rclone, the default value is just ``rclone``
  * ``-o rclone.args`` allows setting the arguments passed to rclone, by default this is ``serve restic --stdio --b2-hard-delete``
+*  ``-o rclone.timeout`` specifies timeout for waiting on repository opening, the default value is ``1m``
 
 The reason for the ``--b2-hard-delete`` parameters can be found in the corresponding GitHub `issue #1657`_.
 

internal/backend/rclone/backend.go

@@ -222,7 +222,7 @@ func newBackend(cfg Config, lim limiter.Limiter) (*Backend, error) {
 	// send an HTTP request to the base URL, see if the server is there
 	client := &http.Client{
 		Transport: debug.RoundTripper(tr),
-		Timeout:   60 * time.Second,
+		Timeout:   cfg.Timeout * 60 * time.Second,
 	}
 
 	// request a random file which does not exist. we just want to test when

internal/backend/rclone/config.go

@@ -2,6 +2,7 @@ package rclone
 
 import (
 	"strings"
+	"time"
 
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/options"
@@ -12,13 +13,15 @@ type Config struct {
 	Program     string `option:"program" help:"path to rclone (default: rclone)"`
 	Args        string `option:"args"    help:"arguments for running rclone (default: serve restic --stdio --b2-hard-delete)"`
 	Remote      string
-	Connections uint `option:"connections" help:"set a limit for the number of concurrent connections (default: 5)"`
+	Connections uint          `option:"connections" help:"set a limit for the number of concurrent connections (default: 5)"`
+	Timeout     time.Duration `option:"timeout"     help:"set a timeout limit to wait for rclone to establish a connection (default: 1m)"`
 }
 
 var defaultConfig = Config{
 	Program:     "rclone",
 	Args:        "serve restic --stdio --b2-hard-delete",
 	Connections: 5,
+	Timeout:     "1m",
 }
 
 func init() {

internal/backend/rclone/config_test.go

@@ -17,6 +17,7 @@ func TestParseConfig(t *testing.T) {
 				Program:     defaultConfig.Program,
 				Args:        defaultConfig.Args,
 				Connections: defaultConfig.Connections,
+				Timeout:     defaultConfig.Timeout,
 			},
 		},
 	}