Merge pull request #4519 from adamantike/backend/sftp/add-args-option

backend/sftp: Add sftp.args option

changelog/unreleased/pull-4519

@@ -0,0 +1,16 @@
+Enhancement: Add config option to set SFTP command arguments
+
+The `sftp.args` option can be passed to restic (using `-o`) to specify
+custom arguments to be used by the SSH command executed by the SFTP
+backend.
+
+Before this change, a common scenario where a custom identity file was
+needed for the SSH connection, required the full command to be
+specified:
+`-o sftp.command='ssh user@host:port -i /ssh/my_private_key -s sftp'`
+
+With this new configuration option:
+`-o sftp.args='-i /ssh/my_private_key'`
+
+https://github.com/restic/restic/pull/4519
+https://github.com/restic/restic/issues/4241

doc/030_preparing_a_new_repo.rst

@@ -119,10 +119,10 @@ user's home directory.
 Also, if the SFTP server is enforcing domain-confined users, you can
 specify the user this way: ``user@domain@host``.
 
-.. note:: Please be aware that sftp servers do not expand the tilde character
+.. note:: Please be aware that SFTP servers do not expand the tilde character
           (``~``) normally used as an alias for a user's home directory. If you
           want to specify a path relative to the user's home directory, pass a
-          relative path to the sftp backend.
+          relative path to the SFTP backend.
 
 If you need to specify a port number or IPv6 address, you'll need to use
 URL syntax. E.g., the repository ``/srv/restic-repo`` on ``[::1]`` (localhost)
@@ -172,9 +172,11 @@ Then use it in the backend specification:
 
 Last, if you'd like to use an entirely different program to create the
 SFTP connection, you can specify the command to be run with the option
-``-o sftp.command="foobar"``.
+``-o sftp.command="foobar"``. Alternatively, ``-o sftp.args`` allows
+setting the arguments passed to the default SSH command (ignored when
+``sftp.command`` is set)
 
-.. note:: Please be aware that sftp servers close connections when no data is
+.. note:: Please be aware that SFTP servers close connections when no data is
           received by the client. This can happen when restic is processing huge
           amounts of unchanged data. To avoid this issue add the following lines 
           to the client's .ssh/config file:

internal/backend/sftp/config.go

@@ -15,6 +15,7 @@ type Config struct {
 
 	Layout  string `option:"layout"  help:"use this backend directory layout (default: auto-detect)"`
 	Command string `option:"command" help:"specify command to create sftp connection"`
+	Args    string `option:"args"    help:"specify arguments for ssh"`
 
 	Connections uint `option:"connections" help:"set a limit for the number of concurrent connections (default: 5)"`
 }

internal/backend/sftp/sftp.go

@@ -213,6 +213,9 @@ func buildSSHCommand(cfg Config) (cmd string, args []string, err error) {
 		if err != nil {
 			return "", nil, err
 		}
+		if cfg.Args != "" {
+			return "", nil, errors.New("cannot specify both sftp.command and sftp.args options")
+		}
 
 		return args[0], args[1:], nil
 	}
@@ -226,11 +229,19 @@ func buildSSHCommand(cfg Config) (cmd string, args []string, err error) {
 		args = append(args, "-p", port)
 	}
 	if cfg.User != "" {
-		args = append(args, "-l")
-		args = append(args, cfg.User)
+		args = append(args, "-l", cfg.User)
 	}
-	args = append(args, "-s")
-	args = append(args, "sftp")
+
+	if cfg.Args != "" {
+		a, err := backend.SplitShellStrings(cfg.Args)
+		if err != nil {
+			return "", nil, err
+		}
+
+		args = append(args, a...)
+	}
+
+	args = append(args, "-s", "sftp")
 	return cmd, args, nil
 }
 

internal/backend/sftp/sshcmd_test.go

@@ -9,38 +9,57 @@ var sshcmdTests = []struct {
 	cfg  Config
 	cmd  string
 	args []string
+	err  string
 }{
 	{
 		Config{User: "user", Host: "host", Path: "dir/subdir"},
 		"ssh",
 		[]string{"host", "-l", "user", "-s", "sftp"},
+		"",
 	},
 	{
 		Config{Host: "host", Path: "dir/subdir"},
 		"ssh",
 		[]string{"host", "-s", "sftp"},
+		"",
 	},
 	{
 		Config{Host: "host", Port: "10022", Path: "/dir/subdir"},
 		"ssh",
 		[]string{"host", "-p", "10022", "-s", "sftp"},
+		"",
 	},
 	{
 		Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir"},
 		"ssh",
 		[]string{"host", "-p", "10022", "-l", "user", "-s", "sftp"},
+		"",
+	},
+	{
+		Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir", Args: "-i /path/to/id_rsa"},
+		"ssh",
+		[]string{"host", "-p", "10022", "-l", "user", "-i", "/path/to/id_rsa", "-s", "sftp"},
+		"",
+	},
+	{
+		Config{Command: "ssh something", Args: "-i /path/to/id_rsa"},
+		"",
+		nil,
+		"cannot specify both sftp.command and sftp.args options",
 	},
 	{
 		// IPv6 address.
 		Config{User: "user", Host: "::1", Path: "dir"},
 		"ssh",
 		[]string{"::1", "-l", "user", "-s", "sftp"},
+		"",
 	},
 	{
 		// IPv6 address with zone and port.
 		Config{User: "user", Host: "::1%lo0", Port: "22", Path: "dir"},
 		"ssh",
 		[]string{"::1%lo0", "-p", "22", "-l", "user", "-s", "sftp"},
+		"",
 	},
 }
 
@@ -48,9 +67,15 @@ func TestBuildSSHCommand(t *testing.T) {
 	for i, test := range sshcmdTests {
 		t.Run("", func(t *testing.T) {
 			cmd, args, err := buildSSHCommand(test.cfg)
+			if test.err != "" {
+				if err.Error() != test.err {
+					t.Fatalf("expected error %v got %v", test.err, err.Error())
+				}
+			} else {
 				if err != nil {
 					t.Fatalf("%v in test %d", err, i)
 				}
+			}
 
 			if cmd != test.cmd {
 				t.Fatalf("cmd: want %v, got %v", test.cmd, cmd)