Support IPv6 in SFTP backend

The previous code was doing its own hostname:port splitting, which
caused IPv6 addresses to be misinterpreted.

doc/030_preparing_a_new_repo.rst

@@ -86,10 +86,21 @@ specify the user this way: ``user@domain@host``.
           want to specify a path relative to the user's home directory, pass a
           relative path to the sftp backend.
 
-The backend config string does not allow specifying a port. If you need
-to contact an sftp server on a different port, you can create an entry
-in the ``ssh`` file, usually located in your user's home directory at
-``~/.ssh/config`` or in ``/etc/ssh/ssh_config``:
+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)
+at port 2222 with username ``user`` can be specified as
+
+::
+
+    sftp://user@[::1]:2222//srv/restic-repo
+
+Note the double slash: the first slash separates the connection settings from
+the path, while the second is the start of the path. To specify a relative
+path, use one slash.
+
+Alternatively, you can create an entry in the ``ssh`` configuration file,
+usually located in your home directory at ``~/.ssh/config`` or in
+``/etc/ssh/ssh_config``:
 
 ::
 

internal/backend/sftp/config.go

@@ -11,9 +11,10 @@ import (
 
 // Config collects all information required to connect to an sftp server.
 type Config struct {
-	User, Host, Path string
-	Layout           string `option:"layout" help:"use this backend directory layout (default: auto-detect)"`
-	Command          string `option:"command" help:"specify command to create sftp connection"`
+	User, Host, Port, Path string
+
+	Layout  string `option:"layout" help:"use this backend directory layout (default: auto-detect)"`
+	Command string `option:"command" help:"specify command to create sftp connection"`
 }
 
 func init() {
@@ -21,12 +22,12 @@ func init() {
 }
 
 // ParseConfig parses the string s and extracts the sftp config. The
-// supported configuration formats are sftp://user@host/directory
+// supported configuration formats are sftp://user@host[:port]/directory
 //  and sftp:user@host:directory.  The directory will be path Cleaned and can
 //  be an absolute path if it starts with a '/' (e.g.
 //  sftp://user@host//absolute and sftp:user@host:/absolute).
 func ParseConfig(s string) (interface{}, error) {
-	var user, host, dir string
+	var user, host, port, dir string
 	switch {
 	case strings.HasPrefix(s, "sftp://"):
 		// parse the "sftp://user@host/path" url format
@@ -37,7 +38,8 @@ func ParseConfig(s string) (interface{}, error) {
 		if url.User != nil {
 			user = url.User.Username()
 		}
-		host = url.Host
+		host = url.Hostname()
+		port = url.Port()
 		dir = url.Path
 		if dir == "" {
 			return nil, errors.Errorf("invalid backend %q, no directory specified", s)
@@ -76,6 +78,7 @@ func ParseConfig(s string) (interface{}, error) {
 	return Config{
 		User: user,
 		Host: host,
+		Port: port,
 		Path: p,
 	}, nil
 }

internal/backend/sftp/config_test.go

@@ -23,11 +23,11 @@ var configTests = []struct {
 	},
 	{
 		"sftp://host:10022//dir/subdir",
-		Config{Host: "host:10022", Path: "/dir/subdir"},
+		Config{Host: "host", Port: "10022", Path: "/dir/subdir"},
 	},
 	{
 		"sftp://user@host:10022//dir/subdir",
-		Config{User: "user", Host: "host:10022", Path: "/dir/subdir"},
+		Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir"},
 	},
 	{
 		"sftp://user@host/dir/subdir/../other",
@@ -38,6 +38,17 @@ var configTests = []struct {
 		Config{User: "user", Host: "host", Path: "dir/subdir"},
 	},
 
+	// IPv6 address.
+	{
+		"sftp://user@[::1]/dir",
+		Config{User: "user", Host: "::1", Path: "dir"},
+	},
+	// IPv6 address with port.
+	{
+		"sftp://user@[::1]:22/dir",
+		Config{User: "user", Host: "::1", Port: "22", Path: "dir"},
+	},
+
 	// second form, user specified sftp:user@host:/dir
 	{
 		"sftp:user@host:/dir/subdir",

internal/backend/sftp/sftp.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"os/exec"
 	"path"
-	"strings"
 	"time"
 
 	"github.com/restic/restic/internal/errors"
@@ -190,10 +189,11 @@ func buildSSHCommand(cfg Config) (cmd string, args []string, err error) {
 
 	cmd = "ssh"
 
-	hostport := strings.Split(cfg.Host, ":")
-	args = []string{hostport[0]}
-	if len(hostport) > 1 {
-		args = append(args, "-p", hostport[1])
+	host, port := cfg.Host, cfg.Port
+
+	args = []string{host}
+	if port != "" {
+		args = append(args, "-p", port)
 	}
 	if cfg.User != "" {
 		args = append(args, "-l")

internal/backend/sftp/sshcmd_test.go

@@ -21,23 +21,35 @@ var sshcmdTests = []struct {
 		[]string{"host", "-s", "sftp"},
 	},
 	{
-		Config{Host: "host:10022", Path: "/dir/subdir"},
+		Config{Host: "host", Port: "10022", Path: "/dir/subdir"},
 		"ssh",
 		[]string{"host", "-p", "10022", "-s", "sftp"},
 	},
 	{
-		Config{User: "user", Host: "host:10022", Path: "/dir/subdir"},
+		Config{User: "user", Host: "host", Port: "10022", Path: "/dir/subdir"},
 		"ssh",
 		[]string{"host", "-p", "10022", "-l", "user", "-s", "sftp"},
 	},
+	{
+		// 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"},
+	},
 }
 
 func TestBuildSSHCommand(t *testing.T) {
-	for _, test := range sshcmdTests {
+	for i, test := range sshcmdTests {
 		t.Run("", func(t *testing.T) {
 			cmd, args, err := buildSSHCommand(test.cfg)
 			if err != nil {
-				t.Fatal(err)
+				t.Fatalf("%v in test %d", err, i)
 			}
 
 			if cmd != test.cmd {
@@ -45,7 +57,8 @@ func TestBuildSSHCommand(t *testing.T) {
 			}
 
 			if !reflect.DeepEqual(test.args, args) {
-				t.Fatalf("wrong args, want:\n  %v\ngot:\n  %v", test.args, args)
+				t.Fatalf("wrong args in test %d, want:\n  %v\ngot:\n  %v",
+					i, test.args, args)
 			}
 		})
 	}