feat: agent keeps SSH file sessions and runs file operations on the host by commands

internal/agent/sshfs.go

@@ -0,0 +1,525 @@
+package agent
+
+// Files on an SSH host, for the panel's file panes: the agent keeps one SSH
+// connection per pane and runs plain commands there - stat, cat, mv, rm - as
+// the tar transfer does. No SFTP is needed on the host. A connection that
+// dropped is opened again once with what it was opened with; one left alone
+// for sshfsIdle is closed.
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"path"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+	"unicode/utf8"
+
+	"golang.org/x/crypto/ssh"
+
+	"github.com/x-grk/longpolling-remote-access/internal/proto"
+)
+
+const sshfsIdle = 10 * time.Minute
+
+type sshfsConn struct {
+	mu      sync.Mutex
+	client  *ssh.Client
+	target  proto.SSHTarget // kept in the agent's memory to reconnect once after a drop
+	statFmt string          // "gnu", "bsd" or "ls"
+	home    string
+	last    time.Time
+}
+
+var (
+	sshfsConns   sync.Map // id -> *sshfsConn
+	sshfsJanitor sync.Once
+)
+
+// statCommand lists dir's entries as "type|size|mtime|mode|name" lines.
+func statCommand(flavour, dir string) string {
+	d := shq(strings.TrimSuffix(dir, "/") + "/")
+	loop := "cd " + d + " && for f in .[!.]* ..?* *; do [ -e \"$f\" ] || [ -L \"$f\" ] || continue; "
+	switch flavour {
+	case "bsd":
+		return loop + "stat -f '%HT|%z|%m|%Sp|%N' -- \"$f\"; done"
+	case "ls":
+		return "cd " + d + " && LC_ALL=C ls -la"
+	}
+	return loop + "stat -c '%F|%s|%Y|%A|%n' -- \"$f\"; done"
+}
+
+// parseStatLine reads one line of statCommand's output.
+func parseStatLine(line string) (proto.FSEntry, bool) {
+	p := strings.SplitN(line, "|", 5)
+	if len(p) != 5 {
+		return proto.FSEntry{}, false
+	}
+	size, err1 := strconv.ParseInt(p[1], 10, 64)
+	mt, err2 := strconv.ParseInt(p[2], 10, 64)
+	if err1 != nil || err2 != nil {
+		return proto.FSEntry{}, false
+	}
+	t := strings.ToLower(p[0])
+	return proto.FSEntry{Name: p[4], IsDir: strings.Contains(t, "directory"), Size: size, MTime: mt, Mode: p[3]}, true
+}
+
+// parseLsLine reads a line of "ls -la" for a host with no stat: no times.
+func parseLsLine(line string) (proto.FSEntry, bool) {
+	f := strings.Fields(line)
+	if len(f) < 9 || len(f[0]) < 10 {
+		return proto.FSEntry{}, false
+	}
+	size, err := strconv.ParseInt(f[4], 10, 64)
+	if err != nil {
+		return proto.FSEntry{}, false
+	}
+	// The name is what follows the eighth field, spaces and all.
+	rest := line
+	for i := 0; i < 8; i++ {
+		rest = strings.TrimLeft(rest, " ")
+		rest = rest[strings.IndexByte(rest, ' ')+1:]
+	}
+	name := strings.TrimLeft(rest, " ")
+	if f[0][0] == 'l' {
+		if i := strings.Index(name, " -> "); i >= 0 {
+			name = name[:i]
+		}
+	}
+	if name == "." || name == ".." {
+		return proto.FSEntry{}, false
+	}
+	return proto.FSEntry{Name: name, IsDir: f[0][0] == 'd', Size: size, Mode: f[0]}, true
+}
+
+func randHex(n int) string {
+	b := make([]byte, n)
+	_, _ = rand.Read(b)
+	return hex.EncodeToString(b)
+}
+
+// sshfsOpen connects for a file pane and tells the host's home.
+func (a *Agent) sshfsOpen(ctx context.Context, t proto.SSHTarget) (any, error) {
+	client, _, err := a.sshConnect(ctx, t, func(string, string) {})
+	if err != nil {
+		return nil, err
+	}
+	c := &sshfsConn{client: client, target: t, last: time.Now()}
+	out, _ := sshRun(client, "stat -c %F / >/dev/null 2>&1 && echo GNU; stat -f %HT / >/dev/null 2>&1 && echo BSD; echo \"$HOME\"")
+	lines := strings.Split(strings.TrimSpace(out), "\n")
+	switch {
+	case strings.Contains(out, "GNU"):
+		c.statFmt = "gnu"
+	case strings.Contains(out, "BSD"):
+		c.statFmt = "bsd"
+	default:
+		c.statFmt = "ls"
+	}
+	c.home = strings.TrimSpace(lines[len(lines)-1])
+	if !strings.HasPrefix(c.home, "/") {
+		c.home = "/"
+	}
+	id := randHex(12)
+	sshfsConns.Store(id, c)
+	sshfsJanitor.Do(func() { go sshfsSweep() })
+	return map[string]string{"id": id, "home": c.home}, nil
+}
+
+// sshfsSweep closes connections nobody used for sshfsIdle.
+func sshfsSweep() {
+	for range time.Tick(time.Minute) {
+		sshfsConns.Range(func(k, v any) bool {
+			c := v.(*sshfsConn)
+			c.mu.Lock()
+			idle := time.Since(c.last) > sshfsIdle
+			c.mu.Unlock()
+			if idle {
+				sshfsClose(k.(string))
+			}
+			return true
+		})
+	}
+}
+
+func sshfsClose(id string) {
+	if v, ok := sshfsConns.LoadAndDelete(id); ok {
+		_ = v.(*sshfsConn).client.Close()
+	}
+}
+
+func sshfsGet(id string) (*sshfsConn, error) {
+	v, ok := sshfsConns.Load(id)
+	if !ok {
+		return nil, errors.New("подключение закрыто - откройте файлы по SSH снова")
+	}
+	c := v.(*sshfsConn)
+	c.mu.Lock()
+	c.last = time.Now()
+	c.mu.Unlock()
+	return c, nil
+}
+
+// session opens an SSH session on the connection; a connection that dropped
+// is opened again once.
+func (a *Agent) sshfsSession(c *sshfsConn) (*ssh.Session, error) {
+	c.mu.Lock()
+	client := c.client
+	c.mu.Unlock()
+	s, err := client.NewSession()
+	if err == nil {
+		return s, nil
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 40*time.Second)
+	defer cancel()
+	nc, _, cerr := a.sshConnect(ctx, c.target, func(string, string) {})
+	if cerr != nil {
+		return nil, fmt.Errorf("подключение к хосту потеряно: %v", cerr)
+	}
+	c.mu.Lock()
+	_ = c.client.Close()
+	c.client = nc
+	c.mu.Unlock()
+	return nc.NewSession()
+}
+
+// run runs cmd on the host with stdin, returning its output; a failure
+// carries what the command said on stderr.
+func (a *Agent) sshfsRun(c *sshfsConn, cmd string, stdin io.Reader) ([]byte, error) {
+	s, err := a.sshfsSession(c)
+	if err != nil {
+		return nil, err
+	}
+	defer s.Close()
+	var out, errb bytes.Buffer
+	s.Stdout = &out
+	s.Stderr = &limitBuf{b: &errb, max: 4096}
+	if stdin != nil {
+		s.Stdin = stdin
+	}
+	if err := s.Run(cmd); err != nil {
+		msg := strings.TrimSpace(errb.String())
+		if msg == "" {
+			msg = err.Error()
+		}
+		if len(msg) > 300 {
+			msg = msg[:300]
+		}
+		return out.Bytes(), errors.New(msg)
+	}
+	return out.Bytes(), nil
+}
+
+// sshfsTask runs one sshfs.* task.
+func (a *Agent) sshfsTask(ctx context.Context, env proto.TaskEnvelope) (any, error) {
+	var args proto.SSHFSArgs
+	if err := json.Unmarshal(env.Args, &args); err != nil {
+		return nil, err
+	}
+	switch env.Type {
+	case proto.TaskSSHFSOpen:
+		if args.SSH == nil {
+			return nil, errors.New("не указан хост")
+		}
+		return a.sshfsOpen(ctx, *args.SSH)
+	case proto.TaskSSHFSClose:
+		sshfsClose(args.Conn)
+		return nil, nil
+	}
+	c, err := sshfsGet(args.Conn)
+	if err != nil {
+		return nil, err
+	}
+	return a.sshfsOp(c, args.Op, args.Args)
+}
+
+func (a *Agent) sshfsOp(c *sshfsConn, op string, raw json.RawMessage) (any, error) {
+	switch op {
+	case "list":
+		var p proto.FSPathArgs
+		_ = json.Unmarshal(raw, &p)
+		dir := p.Path
+		if dir == "" || strings.HasPrefix(dir, "~") {
+			dir = c.home
+		}
+		out, err := a.sshfsRun(c, statCommand(c.statFmt, dir), nil)
+		if err != nil && len(out) == 0 {
+			return nil, err
+		}
+		entries := []proto.FSEntry{}
+		for _, line := range strings.Split(string(out), "\n") {
+			var e proto.FSEntry
+			var ok bool
+			if c.statFmt == "ls" {
+				e, ok = parseLsLine(line)
+			} else {
+				e, ok = parseStatLine(line)
+			}
+			if ok {
+				entries = append(entries, e)
+			}
+		}
+		return proto.FSListResult{Path: path.Clean(dir), Entries: entries}, nil
+	case "read":
+		var p proto.FSPathArgs
+		_ = json.Unmarshal(raw, &p)
+		size, _ := a.sshfsSize(c, p.Path)
+		out, err := a.sshfsRun(c, "head -c "+strconv.Itoa(proto.FSReadCap+1)+" -- "+shq(p.Path), nil)
+		if err != nil {
+			return nil, err
+		}
+		truncated := len(out) > proto.FSReadCap
+		if truncated {
+			out = out[:proto.FSReadCap]
+		}
+		return proto.FSReadResult{Path: p.Path, Size: size, Content: base64.StdEncoding.EncodeToString(out),
+			Truncated: truncated, Binary: !utf8.Valid(out) || bytes.IndexByte(out, 0) >= 0}, nil
+	case "write":
+		var p proto.FSWriteArgs
+		_ = json.Unmarshal(raw, &p)
+		data, err := base64.StdEncoding.DecodeString(p.Data)
+		if err != nil {
+			return nil, err
+		}
+		_, err = a.sshfsRun(c, writeCommand(p.Path), bytes.NewReader(data))
+		return map[string]string{"path": p.Path}, err
+	case "mkdir":
+		var p proto.FSPathArgs
+		_ = json.Unmarshal(raw, &p)
+		_, err := a.sshfsRun(c, "mkdir -p -- "+shq(p.Path), nil)
+		return map[string]string{"path": p.Path}, err
+	case "delete", "deltree":
+		var p proto.FSPathArgs
+		_ = json.Unmarshal(raw, &p)
+		if p.Path == "" || path.Clean(p.Path) == "/" {
+			return nil, errors.New("отказ: удаление корня запрещено")
+		}
+		flag := "-f"
+		if op == "deltree" {
+			flag = "-rf"
+		}
+		_, err := a.sshfsRun(c, "rm "+flag+" -- "+shq(p.Path), nil)
+		return map[string]string{"path": p.Path}, err
+	case "move":
+		var p proto.FSMoveArgs
+		_ = json.Unmarshal(raw, &p)
+		_, err := a.sshfsRun(c, "mv -- "+shq(p.Src)+" "+shq(p.Dst), nil)
+		return map[string]string{"src": p.Src, "dst": p.Dst}, err
+	case "copy":
+		var p proto.FSCopyArgs
+		_ = json.Unmarshal(raw, &p)
+		return nil, a.sshfsCopy(c, p)
+	case "stat":
+		var p proto.FSPathArgs
+		_ = json.Unmarshal(raw, &p)
+		return a.sshfsStat(c, p.Path)
+	case "chmod":
+		var p proto.FSChmodArgs
+		_ = json.Unmarshal(raw, &p)
+		rec := ""
+		if p.Recursive {
+			rec = "-R "
+		}
+		var cmds []string
+		if p.Mode != nil {
+			cmds = append(cmds, "chmod "+rec+fmt.Sprintf("%o", *p.Mode)+" -- "+shq(p.Path))
+		}
+		if p.Owner != "" || p.Group != "" {
+			who := p.Owner
+			if p.Group != "" {
+				who += ":" + p.Group
+			}
+			cmds = append(cmds, "chown "+rec+shq(who)+" -- "+shq(p.Path))
+		}
+		if len(cmds) == 0 {
+			return nil, nil
+		}
+		_, err := a.sshfsRun(c, strings.Join(cmds, " && "), nil)
+		return map[string]string{"path": p.Path}, err
+	}
+	return nil, errors.New("неизвестная операция")
+}
+
+// writeCommand writes stdin to p through a file beside it, so a broken
+// transfer leaves the old file as it was.
+func writeCommand(p string) string {
+	tmp := path.Join(path.Dir(p), "."+path.Base(p)+".lpra-"+randHex(4))
+	return "cat > " + shq(tmp) + " && mv -f -- " + shq(tmp) + " " + shq(p) + " || { rm -f -- " + shq(tmp) + "; exit 1; }"
+}
+
+func (a *Agent) sshfsSize(c *sshfsConn, p string) (int64, error) {
+	cmd := "stat -c %s -- " + shq(p)
+	if c.statFmt == "bsd" {
+		cmd = "stat -f %z -- " + shq(p)
+	} else if c.statFmt == "ls" {
+		cmd = "wc -c < " + shq(p)
+	}
+	out, err := a.sshfsRun(c, cmd, nil)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.ParseInt(strings.TrimSpace(string(out)), 10, 64)
+}
+
+func (a *Agent) sshfsStat(c *sshfsConn, p string) (any, error) {
+	cmd := "stat -c '%F|%s|%Y|%a|%u|%g|%U|%G' -- " + shq(p)
+	if c.statFmt == "bsd" {
+		cmd = "stat -f '%HT|%z|%m|%Lp|%u|%g|%Su|%Sg' -- " + shq(p)
+	}
+	out, err := a.sshfsRun(c, cmd, nil)
+	if err != nil {
+		return nil, err
+	}
+	f := strings.Split(strings.TrimSpace(string(out)), "|")
+	if len(f) != 8 {
+		return nil, errors.New("не удалось прочитать свойства")
+	}
+	size, _ := strconv.ParseInt(f[1], 10, 64)
+	mt, _ := strconv.ParseInt(f[2], 10, 64)
+	mode, _ := strconv.ParseUint(f[3], 8, 32)
+	uid, _ := strconv.Atoi(f[4])
+	gid, _ := strconv.Atoi(f[5])
+	return proto.FSStatResult{Path: p, IsDir: strings.Contains(strings.ToLower(f[0]), "directory"), Size: size, MTime: mt,
+		Mode: uint32(mode), UID: uid, GID: gid, Owner: f[6], Group: f[7], Users: []string{}, Groups: []string{}}, nil
+}
+
+// sshfsCopy copies or moves on the host, by the conflict rule for what is
+// there already.
+func (a *Agent) sshfsCopy(c *sshfsConn, p proto.FSCopyArgs) error {
+	src, dst := shq(p.Src), shq(p.Dst)
+	exists, _ := a.sshfsRun(c, "test -e "+dst+" -o -L "+dst+" && echo EXISTS", nil)
+	there := strings.Contains(string(exists), "EXISTS")
+	if there {
+		switch p.Conflict {
+		case "replace":
+			if _, err := a.sshfsRun(c, "rm -rf -- "+dst, nil); err != nil {
+				return err
+			}
+		case "skip":
+			return nil
+		default:
+			return fmt.Errorf("%s уже существует", p.Dst)
+		}
+	}
+	cmd := "cp -a -- " + src + " " + dst
+	if p.Move {
+		cmd = "mv -- " + src + " " + dst
+	}
+	_, err := a.sshfsRun(c, cmd, nil)
+	return err
+}
+
+// doSSHFSSend sends a file of the host to the browser in pieces, as
+// doFSSend does with a local one: cat's output, piece after piece.
+func (a *Agent) doSSHFSSend(ctx context.Context, env proto.TaskEnvelope) proto.TaskResult {
+	var args proto.FSXferArgs
+	if err := json.Unmarshal(env.Args, &args); err != nil || args.Chunk <= 0 {
+		return proto.TaskResult{Error: "плохой запрос"}
+	}
+	c, err := sshfsGet(args.Conn)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	size, err := a.sshfsSize(c, args.Path)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	if size > proto.FSFileCap {
+		return proto.TaskResult{Error: "файл больше 512 МБ"}
+	}
+	s, err := a.sshfsSession(c)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	defer s.Close()
+	out, _ := s.StdoutPipe()
+	if err := s.Start("cat -- " + shq(args.Path)); err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	sizeHdr := strconv.FormatInt(size, 10)
+	n := pieceCount(size, args.Chunk)
+	for i := 0; i < n; i++ {
+		buf := make([]byte, min(int64(args.Chunk), size-int64(i)*int64(args.Chunk)))
+		if _, err := io.ReadFull(out, buf); err != nil {
+			return proto.TaskResult{Error: "файл изменился во время чтения: " + err.Error()}
+		}
+		err := a.xferRequest(ctx, func(ctx context.Context) (*http.Request, error) {
+			req, err := http.NewRequestWithContext(ctx, http.MethodPost, a.xferURL(args.Xfer, i), bytes.NewReader(buf))
+			if err == nil {
+				req.Header.Set("X-Size", sizeHdr)
+				req.Header.Set("Content-Type", "application/octet-stream")
+			}
+			return req, err
+		}, func(*http.Response) error { return nil })
+		if err != nil {
+			return proto.TaskResult{Error: "передача прервана: " + err.Error()}
+		}
+	}
+	_ = s.Wait()
+	data, _ := json.Marshal(map[string]any{"path": args.Path, "size": size})
+	return proto.TaskResult{OK: true, Data: data}
+}
+
+// doSSHFSPut writes a file the browser uploads onto the host, through a file
+// beside it.
+func (a *Agent) doSSHFSPut(ctx context.Context, env proto.TaskEnvelope) proto.TaskResult {
+	var args proto.FSXferArgs
+	if err := json.Unmarshal(env.Args, &args); err != nil || args.Chunk <= 0 || args.Size < 0 || args.Size > proto.FSFileCap {
+		return proto.TaskResult{Error: "плохой запрос"}
+	}
+	c, err := sshfsGet(args.Conn)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	s, err := a.sshfsSession(c)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	defer s.Close()
+	in, _ := s.StdinPipe()
+	var errb bytes.Buffer
+	s.Stderr = &limitBuf{b: &errb, max: 4096}
+	if err := s.Start(writeCommand(args.Path)); err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	n := pieceCount(args.Size, args.Chunk)
+	for i := 0; i < n; i++ {
+		want := min(int64(args.Chunk), args.Size-int64(i)*int64(args.Chunk))
+		var data []byte
+		err := a.xferRequest(ctx, func(ctx context.Context) (*http.Request, error) {
+			return http.NewRequestWithContext(ctx, http.MethodGet, a.xferURL(args.Xfer, i)+"?ack="+strconv.Itoa(i), nil)
+		}, func(resp *http.Response) error {
+			b, err := io.ReadAll(io.LimitReader(resp.Body, int64(args.Chunk)+1))
+			if err == nil && int64(len(b)) != want {
+				err = errors.New("кусок не той длины")
+			}
+			data = b
+			return err
+		})
+		if err == nil {
+			_, err = in.Write(data)
+		}
+		if err != nil {
+			_ = s.Close()
+			return proto.TaskResult{Error: "загрузка прервана: " + err.Error()}
+		}
+	}
+	_ = in.Close()
+	if err := s.Wait(); err != nil {
+		msg := strings.TrimSpace(errb.String())
+		if msg == "" {
+			msg = err.Error()
+		}
+		return proto.TaskResult{Error: msg}
+	}
+	data, _ := json.Marshal(map[string]any{"path": args.Path, "size": args.Size})
+	return proto.TaskResult{OK: true, Data: data}
+}

internal/agent/sshfs_test.go

@@ -0,0 +1,47 @@
+package agent
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestParseStatLine(t *testing.T) {
+	// statCommand prints: type|size|mtime|mode|name
+	e, ok := parseStatLine("directory|4096|1760000000|drwxr-xr-x|my dir")
+	if !ok || !e.IsDir || e.Name != "my dir" || e.MTime != 1760000000 || e.Mode != "drwxr-xr-x" {
+		t.Fatalf("dir: %+v %v", e, ok)
+	}
+	e, ok = parseStatLine("regular file|12|1760000001|-rw-r--r--|a|b.txt")
+	if !ok || e.IsDir || e.Size != 12 || e.Name != "a|b.txt" {
+		t.Fatalf("file with | in name: %+v %v", e, ok)
+	}
+	if _, ok := parseStatLine("garbage"); ok {
+		t.Fatal("garbage parsed")
+	}
+}
+
+func TestStatCommandQuotes(t *testing.T) {
+	for _, fl := range []string{"gnu", "bsd"} {
+		c := statCommand(fl, "/srv/it's here")
+		if !strings.Contains(c, `'/srv/it'\''s here/'`) {
+			t.Errorf("%s: dir not quoted: %s", fl, c)
+		}
+	}
+}
+
+func TestParseLsLine(t *testing.T) {
+	e, ok := parseLsLine("-rw-r--r--  1 root root  1234 Oct 15 10:00 my file.txt")
+	if !ok || e.Name != "my file.txt" || e.Size != 1234 || e.IsDir {
+		t.Fatalf("file: %+v %v", e, ok)
+	}
+	e, ok = parseLsLine("lrwxrwxrwx  1 root root     7 Oct 15 10:00 link -> target")
+	if !ok || e.Name != "link" {
+		t.Fatalf("link: %+v %v", e, ok)
+	}
+	if _, ok := parseLsLine("drwxr-xr-x  2 root root  4096 Oct 15 10:00 .."); ok {
+		t.Fatal(".. listed")
+	}
+	if _, ok := parseLsLine("total 8"); ok {
+		t.Fatal("total parsed")
+	}
+}

internal/agent/task.go

@@ -26,6 +26,12 @@ func (a *Agent) runTask(ctx context.Context, taskID string) {
 		res = a.doFSPut(ctx, env)
 	case proto.TaskFSSend:
 		res = a.doFSSend(ctx, env)
+	case proto.TaskSSHFSSend:
+		res = a.doSSHFSSend(ctx, env)
+	case proto.TaskSSHFSPut:
+		res = a.doSSHFSPut(ctx, env)
+	case proto.TaskSSHFSOpen, proto.TaskSSHFSClose, proto.TaskSSHFSOp:
+		res = resultOf(a.sshfsTask(ctx, env))
 	case proto.TaskFSShipOut:
 		res = a.doShipOut(ctx, env)
 	case proto.TaskFSShipIn:
@@ -107,3 +113,15 @@ func itoa64(n int64) string {
 	}
 	return string(b[i:])
 }
+
+// resultOf makes a task's result of what it returned.
+func resultOf(data any, err error) proto.TaskResult {
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	raw, err := json.Marshal(data)
+	if err != nil {
+		return proto.TaskResult{Error: err.Error()}
+	}
+	return proto.TaskResult{OK: true, Data: raw}
+}

internal/proto/proto.go

@@ -167,6 +167,11 @@ const (
 	TaskDBAdd      = "db.add"      // add a row
 	TaskDBDel      = "db.del"      // delete rows by their keys
 	TaskDBSQL      = "db.sql"      // run a statement typed in the panel
+	TaskSSHFSOpen  = "sshfs.open"  // connect to an SSH host for a file pane; result {id, home}
+	TaskSSHFSClose = "sshfs.close" // drop that connection
+	TaskSSHFSOp    = "sshfs.op"    // a file operation on the host: list, read, write, mkdir, delete, deltree, move, copy, stat, chmod
+	TaskSSHFSSend  = "sshfs.send"  // a file of the host to the browser in pieces (FSXferArgs with Conn)
+	TaskSSHFSPut   = "sshfs.put"   // a file from the browser to the host in pieces
 	TaskFSShipOut  = "fs.ship.out" // pack a file or folder and send it to another machine
 	TaskFSShipIn   = "fs.ship.in"  // unpack what another machine sends
 )
@@ -186,6 +191,18 @@ type FSXferArgs struct {
 	Xfer  string `json:"xfer"`
 	Size  int64  `json:"size"`
 	Chunk int    `json:"chunk"`
+	// Conn is the SSH file connection the file is on (sshfs.send, sshfs.put).
+	Conn string `json:"conn,omitempty"`
+}
+
+// SSHFSArgs are the arguments of the sshfs.* tasks: the connection (Conn), or
+// where to connect (SSH, for open); for an operation its name (Op) and its
+// arguments (Args) in the shapes of the fs.* tasks.
+type SSHFSArgs struct {
+	Conn string          `json:"conn,omitempty"`
+	SSH  *SSHTarget      `json:"ssh,omitempty"`
+	Op   string          `json:"op,omitempty"`
+	Args json.RawMessage `json:"args,omitempty"`
 }
 
 // TaskEnvelope is what the agent fetches for a task id.