sftp: add About support - fixes #3107

This adds support for using About with SFTP remotes. This works by calling the df command remotely.

backend/sftp/sftp.go

@@ -14,6 +14,7 @@ import (
 	"os/user"
 	"path"
 	"regexp"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -813,6 +814,47 @@ func (f *Fs) Hashes() hash.Set {
 	return set
 }
 
+// About gets usage stats
+func (f *Fs) About() (*fs.Usage, error) {
+	c, err := f.getSftpConnection()
+	if err != nil {
+		return nil, errors.Wrap(err, "About get SFTP connection")
+	}
+	session, err := c.sshClient.NewSession()
+	f.putSftpConnection(&c, err)
+	if err != nil {
+		return nil, errors.Wrap(err, "About put SFTP connection")
+	}
+
+	var stdout, stderr bytes.Buffer
+	session.Stdout = &stdout
+	session.Stderr = &stderr
+	escapedPath := shellEscape(f.root)
+	if f.opt.PathOverride != "" {
+		escapedPath = shellEscape(path.Join(f.opt.PathOverride, f.root))
+	}
+	if len(escapedPath) == 0 {
+		escapedPath = "/"
+	}
+	err = session.Run("df -k " + escapedPath)
+	if err != nil {
+		_ = session.Close()
+		return nil, errors.Wrap(err, "About invocation of df failed. Your remote may not support about.")
+	}
+	_ = session.Close()
+
+	usageTotal, usageUsed, usageAvail := parseUsage(stdout.Bytes())
+	if usageTotal < 0 || usageUsed < 0 || usageAvail < 0 {
+		return nil, errors.Wrap(err, "About failed to parse information")
+	}
+	usage := &fs.Usage{
+		Total: fs.NewUsageValue(usageTotal),
+		Used:  fs.NewUsageValue(usageUsed),
+		Free:  fs.NewUsageValue(usageAvail),
+	}
+	return usage, nil
+}
+
 // Fs is the filesystem this remote sftp file object is located within
 func (o *Object) Fs() fs.Info {
 	return o.fs
@@ -903,6 +945,34 @@ func parseHash(bytes []byte) string {
 	return strings.Split(string(bytes), " ")[0] // Split at hash / filename separator
 }
 
+// Parses the byte array output from the SSH session
+// returned by an invocation of df into
+// the disk size, used space, and avaliable space on the disk, in that order.
+// Only works when `df` has output info on only one disk
+func parseUsage(bytes []byte) (int64, int64, int64) {
+	lines := strings.Split(string(bytes), "\n")
+	if len(lines) < 2 {
+		return -1, -1, -1
+	}
+	split := strings.Fields(lines[1])
+	if len(split) < 6 {
+		return -1, -1, -1
+	}
+	spaceTotal, err := strconv.ParseInt(split[1], 10, 64)
+	if err != nil {
+		return -1, -1, -1
+	}
+	spaceUsed, err := strconv.ParseInt(split[2], 10, 64)
+	if err != nil {
+		return -1, -1, -1
+	}
+	spaceAvail, err := strconv.ParseInt(split[3], 10, 64)
+	if err != nil {
+		return -1, -1, -1
+	}
+	return spaceTotal * 1024, spaceUsed * 1024, spaceAvail * 1024
+}
+
 // Size returns the size in bytes of the remote sftp file
 func (o *Object) Size() int64 {
 	return o.size

backend/sftp/sftp_internal_test.go

@@ -35,3 +35,17 @@ func TestParseHash(t *testing.T) {
 		assert.Equal(t, test.checksum, got, fmt.Sprintf("Test %d sshOutput = %q", i, test.sshOutput))
 	}
 }
+
+func TestParseUsage(t *testing.T) {
+	for i, test := range []struct {
+		sshOutput string
+		usage     [3]int64
+	}{
+		{"Filesystem     1K-blocks     Used Available Use% Mounted on\n/dev/root       91283092 81111888  10154820  89% /", [3]int64{93473886208, 83058573312, 10398535680}},
+		{"Filesystem     1K-blocks  Used Available Use% Mounted on\ntmpfs             818256  1636    816620   1% /run", [3]int64{837894144, 1675264, 836218880}},
+		{"Filesystem   1024-blocks     Used Available Capacity iused      ifree %iused  Mounted on\n/dev/disk0s2   244277768 94454848 149566920    39%  997820 4293969459    0%   /", [3]int64{250140434432, 96721764352, 153156526080}},
+	} {
+		gotSpaceTotal, gotSpaceUsed, gotSpaceAvail := parseUsage([]byte(test.sshOutput))
+		assert.Equal(t, test.usage, [3]int64{gotSpaceTotal, gotSpaceUsed, gotSpaceAvail}, fmt.Sprintf("Test %d sshOutput = %q", i, test.sshOutput))
+	}
+}

docs/content/overview.md

@@ -149,7 +149,7 @@ operations more efficient.
 | Openstack Swift              | Yes † | Yes  | No   | No      | No      | Yes   | Yes          | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes |
 | pCloud                       | Yes   | Yes  | Yes  | Yes     | Yes     | No    | No           | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes |
 | QingStor                     | No    | Yes  | No   | No      | No      | Yes   | No           | No [#2178](https://github.com/ncw/rclone/issues/2178) | No  |
-| SFTP                         | No    | No   | Yes  | Yes     | No      | No    | Yes          | No [#2178](https://github.com/ncw/rclone/issues/2178) | No  |
+| SFTP                         | No    | No   | Yes  | Yes     | No      | No    | Yes          | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes  |
 | WebDAV                       | Yes   | Yes  | Yes  | Yes     | No      | No    | Yes ‡        | No [#2178](https://github.com/ncw/rclone/issues/2178) | Yes  |
 | Yandex Disk                  | Yes   | Yes  | Yes  | Yes     | Yes     | No    | Yes          | Yes         | Yes |
 | The local filesystem         | Yes   | No   | Yes  | Yes     | No      | No    | Yes          | No          | Yes |