Provide correct pty/tty file paths on OpenBSD

While here, add test coverage for opening the TTY from the given filename.

doc_test.go

@@ -3,6 +3,7 @@ package pty
 import (
 	"bytes"
 	"io"
+	"os"
 	"testing"
 )
 
@@ -65,6 +66,41 @@ func TestName(t *testing.T) {
 	}
 }
 
+func TestOpenByName(t *testing.T) {
+        t.Parallel()
+
+        pty, tty, err := Open()
+        if err != nil {
+                t.Fatal(err)
+        }
+        defer pty.Close()
+        defer tty.Close()
+
+        ttyFile, err := os.OpenFile(tty.Name(), os.O_RDWR, 0600)
+        if err != nil {
+                t.Fatalf("Failed to open tty file: %v", err)
+        }
+        defer ttyFile.Close()
+
+        // Ensure we can write to the newly opened tty file and read on the pty.
+        text := []byte("ping")
+        n, err := ttyFile.Write(text)
+        if err != nil {
+                t.Errorf("Unexpected error from Write: %s", err)
+        }
+        if n != len(text) {
+                t.Errorf("Unexpected count returned from Write, got %d expected %d", n, len(text))
+        }
+
+        buffer := make([]byte, len(text))
+        if err := readBytes(pty, buffer); err != nil {
+                t.Errorf("Unexpected error from readBytes: %s", err)
+        }
+        if !bytes.Equal(text, buffer) {
+                t.Errorf("Unexpected result returned from Read, got %v expected %v", buffer, text)
+        }
+}
+
 func TestGetsize(t *testing.T) {
 	t.Parallel()
 

pty_openbsd.go

@@ -9,6 +9,17 @@ import (
 	"unsafe"
 )
 
+func cInt8ToString(in []int8) string {
+	var s []byte
+	for _, v := range in {
+		if v == 0 {
+			break
+		}
+		s = append(s, byte(v))
+	}
+	return string(s)
+}
+
 func open() (pty, tty *os.File, err error) {
 	/*
 	 * from ptm(4):
@@ -29,8 +40,8 @@ func open() (pty, tty *os.File, err error) {
 		return nil, nil, err
 	}
 
-	pty = os.NewFile(uintptr(ptm.Cfd), "/dev/ptm")
-	tty = os.NewFile(uintptr(ptm.Sfd), "/dev/ptm")
+	pty = os.NewFile(uintptr(ptm.Cfd), cInt8ToString(ptm.Cn[:]))
+	tty = os.NewFile(uintptr(ptm.Sfd), cInt8ToString(ptm.Sn[:]))
 
 	return pty, tty, nil
 }