implement readPauseKey function for Unix and default platforms

Author: OutOfBedlam

jsh/lib/pretty/pretty.go

@@ -128,19 +128,18 @@ func PauseTerminal() bool {
 	fmt.Fprintf(os.Stdout, ":")
 	// switch stdin into 'raw' mode
 	if oldState, err := term.MakeRaw(int(os.Stdin.Fd())); err == nil {
-		var b []byte = make([]byte, 3)
-		if _, err := os.Stdin.Read(b); err == nil {
-			term.Restore(int(os.Stdin.Fd()), oldState)
+		if key, err := readPauseKey(os.Stdin); err == nil {
+			_ = term.Restore(int(os.Stdin.Fd()), oldState)
 			// remove prompt, erase the current line
 			fmt.Fprintf(os.Stdout, "\x1b[2K")
 			// cursor backward
 			fmt.Fprintf(os.Stdout, "\x1b[1D")
-			if b[0] == 'q' || b[0] == 'Q' {
+			if key == 'q' || key == 'Q' {
 				return false
 			}
 			return true
 		}
-		term.Restore(int(os.Stdin.Fd()), oldState)
+		_ = term.Restore(int(os.Stdin.Fd()), oldState)
 	}
 	return true
 }

jsh/lib/pretty/pretty_internal_test.go

@@ -6,6 +6,7 @@ import (
 	"math"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -105,6 +106,41 @@ func TestTerminalHelpersCoverage(t *testing.T) {
 	}
 }
 
+func TestReadPauseKeyDrainsBufferedInput(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("buffered terminal input draining is Unix-specific")
+	}
+
+	rIn, wIn, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("os.Pipe() failed: %v", err)
+	}
+	defer rIn.Close()
+
+	if _, err := wIn.Write([]byte("\x1b[A")); err != nil {
+		t.Fatalf("pipe write failed: %v", err)
+	}
+
+	key, err := readPauseKey(rIn)
+	if err != nil {
+		t.Fatalf("readPauseKey() error = %v", err)
+	}
+	if key != '\x1b' {
+		t.Fatalf("readPauseKey() = %q, want ESC", key)
+	}
+
+	if err := wIn.Close(); err != nil {
+		t.Fatalf("pipe close failed: %v", err)
+	}
+	remaining, err := io.ReadAll(rIn)
+	if err != nil {
+		t.Fatalf("pipe read failed: %v", err)
+	}
+	if len(remaining) != 0 {
+		t.Fatalf("readPauseKey() left buffered input %q", string(remaining))
+	}
+}
+
 func TestFormattingHelpersCoverage(t *testing.T) {
 	if got := Bytes(int64(2048)); got != "2.0KB" {
 		t.Fatalf("Bytes() = %q", got)

jsh/lib/pretty/terminal_default.go

@@ -0,0 +1,18 @@
+//go:build !darwin && !linux && !freebsd && !openbsd && !netbsd
+
+package pretty
+
+import "os"
+
+func readPauseKey(input *os.File) (byte, error) {
+	buf := []byte{0}
+	for {
+		n, err := input.Read(buf)
+		if err != nil {
+			return 0, err
+		}
+		if n > 0 {
+			return buf[0], nil
+		}
+	}
+}

jsh/lib/pretty/terminal_unix.go

@@ -0,0 +1,41 @@
+//go:build darwin || linux || freebsd || openbsd || netbsd
+
+package pretty
+
+import (
+	"errors"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func readPauseKey(input *os.File) (byte, error) {
+	fd := int(input.Fd())
+	buf := []byte{0}
+	for {
+		n, err := input.Read(buf)
+		if err != nil {
+			return 0, err
+		}
+		if n > 0 {
+			break
+		}
+	}
+
+	drain := make([]byte, 32)
+	for {
+		pollFds := []unix.PollFd{{Fd: int32(fd), Events: unix.POLLIN}}
+		ready, err := unix.Poll(pollFds, 10)
+		if errors.Is(err, unix.EINTR) {
+			continue
+		}
+		if err != nil || ready <= 0 || pollFds[0].Revents&unix.POLLIN == 0 {
+			break
+		}
+		if n, err := input.Read(drain); err != nil || n == 0 {
+			break
+		}
+	}
+
+	return buf[0], nil
+}