From 13c571dda34bd85e6f7aa2e642fc13b643576a62 Mon Sep 17 00:00:00 2001
From: Mac Malainey <mac.malainey@ibm.com>
Date: Mon, 28 Oct 2024 13:11:43 -0400
Subject: [PATCH] add z/OS support

---
 io_test.go         | 14 +++++++++-
 pty_unsupported.go |  4 +--
 pty_zos.go         | 68 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 3 deletions(-)
 create mode 100644 pty_zos.go

diff --git a/io_test.go b/io_test.go
index 2d88a50..e699ec1 100644
--- a/io_test.go
+++ b/io_test.go
@@ -12,6 +12,8 @@ import (
 	"syscall"
 	"testing"
 	"time"
+
+	"golang.org/x/sys/unix"
 )
 
 const (
@@ -106,9 +108,19 @@ func prepare(t *testing.T) (ptmx *os.File, done func()) {
 	if err != nil {
 		t.Fatalf("Error: open: %s.\n", err)
 	}
-	t.Cleanup(func() { _ = ptmx.Close() })
+	_ptmx := ptmx
+	t.Cleanup(func() { _ = _ptmx.Close() })
 	t.Cleanup(func() { _ = pts.Close() })
 
+	// z/OS doesn't open a pollable FD - fix that here
+	if runtime.GOOS == "zos" {
+		if _, err = unix.Fcntl(uintptr(ptmx.Fd()), unix.F_SETFL, unix.O_NONBLOCK); err != nil {
+			t.Fatalf("Error: zos-nonblock: %s.\n", err)
+		}
+		ptmx = os.NewFile(ptmx.Fd(), "/dev/ptmx")
+		t.Cleanup(func() { _ = ptmx.Close() })
+	}
+
 	ctx, done := context.WithCancel(context.Background())
 	t.Cleanup(done)
 	go func() {
diff --git a/pty_unsupported.go b/pty_unsupported.go
index c771020..0971dc7 100644
--- a/pty_unsupported.go
+++ b/pty_unsupported.go
@@ -1,5 +1,5 @@
-//go:build !linux && !darwin && !freebsd && !dragonfly && !netbsd && !openbsd && !solaris
-// +build !linux,!darwin,!freebsd,!dragonfly,!netbsd,!openbsd,!solaris
+//go:build !linux && !darwin && !freebsd && !dragonfly && !netbsd && !openbsd && !solaris && !zos
+// +build !linux,!darwin,!freebsd,!dragonfly,!netbsd,!openbsd,!solaris,!zos
 
 package pty
 
diff --git a/pty_zos.go b/pty_zos.go
new file mode 100644
index 0000000..7cf494a
--- /dev/null
+++ b/pty_zos.go
@@ -0,0 +1,68 @@
+//go:build zos
+// +build zos
+
+package pty
+
+import (
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func open() (pty, tty *os.File, err error) {
+	ptmxfd, err := unix.Posix_openpt(os.O_RDWR|syscall.O_NOCTTY)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Needed for z/OS so that the characters are not garbled if ptyp* is untagged
+	cvtreq := unix.F_cnvrt{Cvtcmd: unix.SETCVTON, Pccsid: 0, Fccsid: 1047}
+	if _, err = unix.Fcntl(uintptr(ptmxfd), unix.F_CONTROL_CVT, &cvtreq); err != nil {
+		return nil, nil, err
+	}
+
+
+	p := os.NewFile(uintptr(ptmxfd), "/dev/ptmx")
+	if p == nil {
+		return nil, nil, err
+	}
+
+	// In case of error after this point, make sure we close the ptmx fd.
+	defer func() {
+		if err != nil {
+			_ = p.Close() // Best effort.
+		}
+	}()
+
+	sname, err := unix.Ptsname(ptmxfd)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	_, err = unix.Grantpt(ptmxfd)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if _, err = unix.Unlockpt(ptmxfd); err != nil {
+		return nil, nil, err
+	}
+
+	ptsfd, err := syscall.Open(sname, os.O_RDWR|syscall.O_NOCTTY, 0)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if _, err = unix.Fcntl(uintptr(ptsfd), unix.F_CONTROL_CVT, &cvtreq); err != nil {
+		return nil, nil, err
+	}
+
+	t := os.NewFile(uintptr(ptsfd), sname)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return p, t, nil
+}
+