fix(pty): resize via raw master fd — keep poller registration

commit: ffe9b7ef9dcd00a1d042c0bf2b60e75e7567da50
author: brice · 3mo ago · 2026-07-02 11:06 UTC
parent: 7ac6830
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

2 files · +22 -27

M internal/adapters/pty/pty_linux.go +20 -11


@@ -108,9 +108,6 @@ type linuxPTY struct {
108	108		master *os.File
109	109		cmd *exec.Cmd
110	110
111		-	waitOnce sync.Once
112		-	waitErr error
113		-
114	111		closeOnce sync.Once
115	112		closeErr error
116	113		}

@@ -137,8 +134,24 @@ func (p *linuxPTY) Write(b []byte) (int, error) {
137	134
138	135		// Resize updates the terminal window size, which also delivers SIGWINCH to the
139	136		// child's foreground process group.
	137	+	//
	138	+	// The ioctl goes through SyscallConn rather than os.File.Fd(): Fd() would flip
	139	+	// the master to blocking mode and detach it from the runtime poller, turning
	140	+	// every subsequent Read into a thread-parking syscall and breaking the
	141	+	// Close-unblocks-Read behavior. Control also pins the fd for the duration and
	142	+	// fails cleanly (os.ErrClosed) after Close.
140	143		func (p *linuxPTY) Resize(sz domain.Size) error {
141		-	return setWinsize(int(p.master.Fd()), sz)
	144	+	rc, err := p.master.SyscallConn()
	145	+	if err != nil {
	146	+	return fmt.Errorf("pty: resize: %w", err)
	147	+	}
	148	+	var ioctlErr error
	149	+	if err := rc.Control(func(fd uintptr) {
	150	+	ioctlErr = setWinsize(int(fd), sz)
	151	+	}); err != nil {
	152	+	return fmt.Errorf("pty: resize: %w", err)
	153	+	}
	154	+	return ioctlErr
142	155		}
143	156
144	157		// Pid reports the child process id.

@@ -159,9 +172,11 @@ func (p *linuxPTY) Close() error {
159	172		// leader thanks to Setsid). Ignore errors: the child may already be gone.
160	173		_ = unix.Kill(-pid, unix.SIGHUP)
161	174
	175	+	// Reap the child (exit status is intentionally discarded; the port has no
	176	+	// Wait — "child gone" surfaces to callers as io.EOF on Read).
162	177		reaped := make(chan struct{})
163	178		go func() {
164		-	p.wait()
	179	+	_ = p.cmd.Wait()
165	180		close(reaped)
166	181		}()
167	182

@@ -177,12 +192,6 @@ func (p *linuxPTY) Close() error {
177	192		return p.closeErr
178	193		}
179	194
180		-	// wait reaps the child exactly once, memoizing the exit error.
181		-	func (p *linuxPTY) wait() error {
182		-	p.waitOnce.Do(func() { p.waitErr = p.cmd.Wait() })
183		-	return p.waitErr
184		-	}
185		-
186	195		// setWinsize applies sz to the terminal referenced by fd via TIOCSWINSZ.
187	196		func setWinsize(fd int, sz domain.Size) error {
188	197		return unix.IoctlSetWinsize(fd, unix.TIOCSWINSZ, &unix.Winsize{

 	master *os.File
 	cmd    *exec.Cmd
-	waitOnce sync.Once
-	waitErr  error
 	closeOnce sync.Once
 	closeErr  error
 }
 // Resize updates the terminal window size, which also delivers SIGWINCH to the
 // child's foreground process group.
+//
+// The ioctl goes through SyscallConn rather than os.File.Fd(): Fd() would flip
+// the master to blocking mode and detach it from the runtime poller, turning
+// every subsequent Read into a thread-parking syscall and breaking the
+// Close-unblocks-Read behavior. Control also pins the fd for the duration and
+// fails cleanly (os.ErrClosed) after Close.
 func (p *linuxPTY) Resize(sz domain.Size) error {
-	return setWinsize(int(p.master.Fd()), sz)
+	rc, err := p.master.SyscallConn()
+	if err != nil {
+		return fmt.Errorf("pty: resize: %w", err)
+	}
+	var ioctlErr error
+	if err := rc.Control(func(fd uintptr) {
+		ioctlErr = setWinsize(int(fd), sz)
+	}); err != nil {
+		return fmt.Errorf("pty: resize: %w", err)
+	}
+	return ioctlErr
 }
 // Pid reports the child process id.
 		// leader thanks to Setsid). Ignore errors: the child may already be gone.
 		_ = unix.Kill(-pid, unix.SIGHUP)
+		// Reap the child (exit status is intentionally discarded; the port has no
+		// Wait — "child gone" surfaces to callers as io.EOF on Read).
 		reaped := make(chan struct{})
 		go func() {
-			p.wait()
+			_ = p.cmd.Wait()
 			close(reaped)
 		}()
 	return p.closeErr
 }
-// wait reaps the child exactly once, memoizing the exit error.
-func (p *linuxPTY) wait() error {
-	p.waitOnce.Do(func() { p.waitErr = p.cmd.Wait() })
-	return p.waitErr
-}
 // setWinsize applies sz to the terminal referenced by fd via TIOCSWINSZ.
 func setWinsize(fd int, sz domain.Size) error {
 	return unix.IoctlSetWinsize(fd, unix.TIOCSWINSZ, &unix.Winsize{

M internal/adapters/pty/pty_linux_test.go +2 -16


@@ -7,6 +7,7 @@ import (
7	7		"errors"
8	8		"io"
9	9		"os"
	10	+	"strconv"
10	11		"strings"
11	12		"syscall"
12	13		"testing"

@@ -159,7 +160,7 @@ func TestClose_ReapsChildNoZombie(t *testing.T) {
159	160		err = syscall.Kill(pid, 0)
160	161		if err == nil {
161	162		// Still visible: ensure it is a zombie's parent-less remnant is not our child.
162		-	data, rerr := os.ReadFile("/proc/" + itoa(pid) + "/status")
	163	+	data, rerr := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/status")
163	164		if rerr == nil {
164	165		require.Contains(t, string(data), "State:\tZ", "child still alive and not a zombie")
165	166		}

@@ -231,18 +232,3 @@ func TestResize_DeliversSIGWINCH(t *testing.T) {
231	232		}
232	233		require.Contains(t, acc, "GOTWINCH")
233	234		}
234		-
235		-	// itoa avoids importing strconv just for a couple call sites in this file.
236		-	func itoa(i int) string {
237		-	if i == 0 {
238		-	return "0"
239		-	}
240		-	var b [20]byte
241		-	pos := len(b)
242		-	for i > 0 {
243		-	pos--
244		-	b[pos] = byte('0' + i%10)
245		-	i /= 10
246		-	}
247		-	return string(b[pos:])
248		-	}

 	"errors"
 	"io"
 	"os"
+	"strconv"
 	"strings"
 	"syscall"
 	"testing"
 	err = syscall.Kill(pid, 0)
 	if err == nil {
 		// Still visible: ensure it is a zombie's parent-less remnant is not our child.
-		data, rerr := os.ReadFile("/proc/" + itoa(pid) + "/status")
+		data, rerr := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/status")
 		if rerr == nil {
 			require.Contains(t, string(data), "State:\tZ", "child still alive and not a zombie")
 		}
 	}
 	require.Contains(t, acc, "GOTWINCH")
 }
-// itoa avoids importing strconv just for a couple call sites in this file.
-func itoa(i int) string {
-	if i == 0 {
-		return "0"
-	}
-	var b [20]byte
-	pos := len(b)
-	for i > 0 {
-		pos--
-		b[pos] = byte('0' + i%10)
-		i /= 10
-	}
-	return string(b[pos:])
-}