From 70ba95529ba0a8831a9aae846f7bb4ad1dc405d8 Mon Sep 17 00:00:00 2001
From: Tim Culverhouse <tim@timculverhouse.com>
Date: Mon, 29 Jul 2024 07:58:19 -0500
Subject: [PATCH] writer: add WriteStringLocked

Fix a race condition in the writer when we are querying background color
from the terminal widget. We do this by adding a mutex in the writer and
only locking during the flush method, and adding a helper
WriteStringLocked which protects access as well.

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
---
 vaxis.go  |  2 +-
 writer.go | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/vaxis.go b/vaxis.go
index dd6b68c..e90895c 100644
--- a/vaxis.go
+++ b/vaxis.go
@@ -1006,7 +1006,7 @@ func (vx *Vaxis) QueryBackground() Color {
 	if !vx.CanReportBackgroundColor() {
 		return Color(0)
 	}
-	vx.tw.WriteString(osc11)
+	vx.tw.WriteStringLocked(osc11)
 	resp := <-vx.chBg
 	var r, g, b int
 	_, err := fmt.Sscanf(resp, "11;rgb:%x/%x/%x", &r, &g, &b)
diff --git a/writer.go b/writer.go
index 500ca8a..bcf8450 100644
--- a/writer.go
+++ b/writer.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"sync"
 )
 
 // writer is a buffered writer for a terminal. If the terminal supports
@@ -13,6 +14,7 @@ type writer struct {
 	buf *bytes.Buffer
 	w   io.Writer
 	vx  *Vaxis
+	mut sync.Mutex
 }
 
 func newWriter(vx *Vaxis) *writer {
@@ -66,6 +68,15 @@ func (w *writer) Len() int {
 	return w.buf.Len()
 }
 
+// WriteStringLocked writes to the underlying terminal while the mutex is held.
+// This does not handle any mouse nor synchronization state and is intended to
+// be used for one-off synchronized sequence writes to the terminal
+func (w *writer) WriteStringLocked(s string) (n int, err error) {
+	w.mut.Lock()
+	defer w.mut.Unlock()
+	return w.w.Write([]byte(s))
+}
+
 func (w *writer) Flush() (n int, err error) {
 	if w.buf.Len() == 0 {
 		// If we didn't write any visual changes, make sure we make any
@@ -95,5 +106,7 @@ func (w *writer) Flush() (n int, err error) {
 	if w.vx.caps.synchronizedUpdate {
 		w.buf.WriteString(decrst(synchronizedUpdate))
 	}
+	w.mut.Lock()
+	defer w.mut.Unlock()
 	return w.w.Write(w.buf.Bytes())
 }
-- 
2.45.2