gui: a /dev/draw layer in go, with no cgo and no devdraw

9fans.net/go/draw builds for plan9 but shells out to plan9port's
devdraw, which 9front does not have. This talks to /dev/draw itself:
the protocol is file i/o, so a pure-go client is a few hundred lines
under an already-complete idea.

draw/keyboard.go opens /dev/cons and turns the console raw, as
libdraw's initkeyboard does. Without it rio keeps its line editor on
the window and paints what you type over the drawing.

draw/snarf.go writes /dev/snarf, which is what every other program on
the system means by copy.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/gui/draw/keyboard.go b/gui/draw/keyboard.go
new file mode 100644
index 0000000..3885364
--- /dev/null
+++ b/gui/draw/keyboard.go
@@ -0,0 +1,65 @@
+package draw
+
+import (
+	"bufio"
+	"os"
+	"unicode/utf8"
+)
+
+// Keyboardctl delivers runes typed at the window.
+//
+// Opening it also turns the console raw. Without that, rio keeps its own
+// line editor on the window and echoes what you type into the text layer,
+// painting over whatever the program has drawn. Holding consctl open is
+// what keeps raw mode; closing it puts the window back as it was.
+type Keyboardctl struct {
+	C    <-chan rune
+	ctl  *os.File
+	cons *os.File
+}
+
+func OpenKeyboard(dev string) (*Keyboardctl, error) {
+	ctl, err := os.OpenFile(dev+"/consctl", os.O_WRONLY, 0)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := ctl.WriteString("rawon"); err != nil {
+		ctl.Close()
+		return nil, err
+	}
+	cons, err := os.Open(dev + "/cons")
+	if err != nil {
+		ctl.Close()
+		return nil, err
+	}
+
+	ch := make(chan rune, 32)
+	k := &Keyboardctl{C: ch, ctl: ctl, cons: cons}
+	go func() {
+		defer close(ch)
+		br := bufio.NewReader(cons)
+		var buf []byte
+		b := make([]byte, 1)
+		for {
+			n, err := br.Read(b)
+			if n == 0 || err != nil {
+				return
+			}
+			buf = append(buf, b[0])
+			// a rune may arrive a byte at a time
+			if r, sz := utf8.DecodeRune(buf); r != utf8.RuneError || sz > 1 {
+				ch <- r
+				buf = buf[:0]
+			} else if len(buf) >= utf8.UTFMax {
+				buf = buf[:0]
+			}
+		}
+	}()
+	return k, nil
+}
+
+func (k *Keyboardctl) Close() error {
+	k.cons.Close()
+	// dropping consctl is what restores rio's own line editing
+	return k.ctl.Close()
+}