fix(output): report terminal status when writer is not a file

The underlying writer doesn't have to be a *os.File for it to be a TTY.
For example, a PTY ssh session is a TTY. However, the std library
returns a io.ReadWriter for the ssh session.

Combined with the WithUnsafe() option, we can query the terminal of an
ssh session using Termenv.

termenv_unix.go

@@ -6,6 +6,7 @@ package termenv
 import (
 	"fmt"
 	"io"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -113,8 +114,8 @@ func (o Output) backgroundColor() Color {
 	return ANSIColor(0)
 }
 
-func (o *Output) waitForData(timeout time.Duration) error {
-	fd := o.TTY().Fd()
+func (o *Output) waitForData(f *os.File, timeout time.Duration) error {
+	fd := f.Fd()
 	tv := unix.NsecToTimeval(int64(timeout))
 	var readfds unix.FdSet
 	readfds.Set(int(fd))
@@ -137,15 +138,15 @@ func (o *Output) waitForData(timeout time.Duration) error {
 	return nil
 }
 
-func (o *Output) readNextByte() (byte, error) {
-	if !o.unsafe {
-		if err := o.waitForData(OSCTimeout); err != nil {
+func (o *Output) readNextByte(rw io.ReadWriter) (byte, error) {
+	if f, ok := rw.(*os.File); ok && !o.unsafe {
+		if err := o.waitForData(f, OSCTimeout); err != nil {
 			return 0, err
 		}
 	}
 
 	var b [1]byte
-	n, err := o.TTY().Read(b[:])
+	n, err := rw.Read(b[:])
 	if err != nil {
 		return 0, err
 	}
@@ -160,15 +161,15 @@ func (o *Output) readNextByte() (byte, error) {
 // readNextResponse reads either an OSC response or a cursor position response:
 //   - OSC response: "\x1b]11;rgb:1111/1111/1111\x1b\\"
 //   - cursor position response: "\x1b[42;1R"
-func (o *Output) readNextResponse() (response string, isOSC bool, err error) {
-	start, err := o.readNextByte()
+func (o *Output) readNextResponse(rw io.ReadWriter) (response string, isOSC bool, err error) {
+	start, err := o.readNextByte(rw)
 	if err != nil {
 		return "", false, err
 	}
 
 	// first byte must be ESC
 	for start != ESC {
-		start, err = o.readNextByte()
+		start, err = o.readNextByte(rw)
 		if err != nil {
 			return "", false, err
 		}
@@ -177,7 +178,7 @@ func (o *Output) readNextResponse() (response string, isOSC bool, err error) {
 	response += string(start)
 
 	// next byte is either '[' (cursor position response) or ']' (OSC response)
-	tpe, err := o.readNextByte()
+	tpe, err := o.readNextByte(rw)
 	if err != nil {
 		return "", false, err
 	}
@@ -195,7 +196,7 @@ func (o *Output) readNextResponse() (response string, isOSC bool, err error) {
 	}
 
 	for {
-		b, err := o.readNextByte()
+		b, err := o.readNextByte(rw)
 		if err != nil {
 			return "", false, err
 		}
@@ -231,13 +232,17 @@ func (o Output) termStatusReport(sequence int) (string, error) {
 		return "", ErrStatusReport
 	}
 
-	tty := o.TTY()
-	if tty == nil {
+	tty, ok := o.Writer().(io.ReadWriter)
+	if tty == nil || !ok {
 		return "", ErrStatusReport
 	}
 
 	if !o.unsafe {
-		fd := int(tty.Fd())
+		f, ok := tty.(*os.File)
+		if !ok {
+			return "", ErrStatusReport
+		}
+		fd := int(f.Fd())
 		// if in background, we can't control the terminal
 		if !isForeground(fd) {
 			return "", ErrStatusReport
@@ -264,7 +269,7 @@ func (o Output) termStatusReport(sequence int) (string, error) {
 	fmt.Fprintf(tty, CSI+"6n")
 
 	// read the next response
-	res, isOSC, err := o.readNextResponse()
+	res, isOSC, err := o.readNextResponse(tty)
 	if err != nil {
 		return "", fmt.Errorf("%s: %s", ErrStatusReport, err)
 	}
@@ -275,7 +280,7 @@ func (o Output) termStatusReport(sequence int) (string, error) {
 	}
 
 	// read the cursor query response next and discard the result
-	_, _, err = o.readNextResponse()
+	_, _, err = o.readNextResponse(tty)
 	if err != nil {
 		return "", err
 	}