feat: «Здесь» from a machine's file pane opens the terminal in that pane's folder (the agent starts the shell there; an older agent, or a folder gone, at home)

internal/agent/client.go

@@ -330,7 +330,7 @@ func (a *Agent) pollOnce(ctx, reqCtx context.Context) error {
 func (a *Agent) dispatch(ctx context.Context, msg proto.ControlMessage) {
 	switch msg.Type {
 	case proto.CtrlOpenTerminal:
-		go a.runTerminal(ctx, msg.SessionID, msg.User)
+		go a.runTerminal(ctx, msg.SessionID, msg.User, msg.Dir)
 	case proto.CtrlOpenForward:
 		go a.runForward(ctx, msg.SessionID, msg.Port)
 	case proto.CtrlTask:

internal/agent/session.go

@@ -16,8 +16,8 @@ import (
 
 // runTerminal spawns a PTY and bridges it to the session.
 // user is the OS user to run the shell as ("" = the agent's own user).
-func (a *Agent) runTerminal(parent context.Context, sid, user string) {
-	term, err := StartPTY(user)
+func (a *Agent) runTerminal(parent context.Context, sid, user, dir string) {
+	term, err := StartPTY(user, dir)
 	if err != nil {
 		log.Printf("term %s: start pty: %v", sid, err)
 		// Show the reason in the browser terminal before closing it.

internal/agent/terminal.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -41,8 +43,12 @@ func CloseTerminals() {
 // StartPTY launches a login shell attached to a new PTY. With user empty (or
 // equal to the agent's own user) it is the agent's shell - root by default,
 // since the agent runs as a root systemd service. Any other user is entered via
-// `su -l`, which only a root agent can do without a password.
-func StartPTY(user string) (*PTY, error) {
+// `su -l`, which only a root agent can do without a password. dir, when it
+// is a folder, is where the shell starts instead of home.
+func StartPTY(user, dir string) (*PTY, error) {
+	if dir != "" && (!filepath.IsAbs(dir) || strings.ContainsAny(dir, "\x00\r\n") || !isDir(dir)) {
+		dir = ""
+	}
 	var cmd *exec.Cmd
 	env := append(os.Environ(), "TERM=xterm-256color")
 	if user == "" || user == currentUser() {
@@ -54,6 +60,9 @@ func StartPTY(user string) (*PTY, error) {
 			cmd.Dir = home
 			env = append(env, "HOME="+home)
 		}
+		if dir != "" {
+			cmd.Dir = dir
+		}
 	} else {
 		if !validUserName(user) {
 			return nil, fmt.Errorf("недопустимое имя пользователя %q", user)
@@ -69,6 +78,11 @@ func StartPTY(user string) (*PTY, error) {
 			return nil, fmt.Errorf("su не найден: %w", err)
 		}
 		cmd = exec.Command(su, "-l", user)
+		// su -l always goes home; to start elsewhere, its shell changes
+		// directory first and becomes the login shell (sh and csh alike).
+		if dir != "" {
+			cmd = exec.Command(su, "-l", user, "-c", "cd "+shQuote(dir)+"; exec \"$SHELL\" -l")
+		}
 		// su -l goes to the user's home; starting there too keeps the shell
 		// out of "/" should it not.
 		if home := homeDir(user); isDir(home) {
@@ -126,3 +140,9 @@ func (p *PTY) Close() error {
 	})
 	return err
 }
+
+// shQuote puts s in single quotes for sh and csh alike, closing and
+// reopening them around each quote inside.
+func shQuote(s string) string {
+	return "'" + strings.ReplaceAll(s, "'", `'\''`) + "'"
+}

internal/agent/terminal_test.go

@@ -0,0 +1,62 @@
+package agent
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// A terminal opened with a folder starts its shell there; a folder that is
+// not there leaves it at home.
+func TestStartPTYDir(t *testing.T) {
+	dir, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	sub := filepath.Join(dir, "sub dir")
+	if err := os.Mkdir(sub, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if got := ptyPwd(t, sub); got != sub {
+		t.Fatalf("pwd = %q, want %q", got, sub)
+	}
+	home, _ := filepath.EvalSymlinks(homeDir(""))
+	if got := ptyPwd(t, filepath.Join(dir, "missing")); got != home {
+		t.Fatalf("pwd for a missing folder = %q, want home %q", got, home)
+	}
+}
+
+// ptyPwd opens a terminal at dir and returns where its shell is.
+func ptyPwd(t *testing.T, dir string) string {
+	t.Helper()
+	t.Setenv("SHELL", "/bin/sh")
+	p, err := StartPTY("", dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer p.Close()
+	if _, err := p.Write([]byte("echo \"@@$(pwd -P)@@\"\n")); err != nil {
+		t.Fatal(err)
+	}
+	var out strings.Builder
+	buf := make([]byte, 4096)
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		n, err := p.Read(buf)
+		out.Write(buf[:n])
+		s := out.String()
+		// The echoed command line has "@@$(pwd" in it; the answer does not.
+		for _, part := range strings.Split(s, "@@") {
+			if strings.HasPrefix(part, "/") && strings.Contains(s, part+"@@") {
+				return part
+			}
+		}
+		if err != nil {
+			break
+		}
+	}
+	t.Fatalf("no pwd in %q", out.String())
+	return ""
+}