From 3da20cab8ad305953d9ccd42716b8f7b0b2a36e9 Mon Sep 17 00:00:00 2001
From: Mathias Fredriksson <mafredri@gmail.com>
Date: Thu, 23 Feb 2023 13:46:07 +0000
Subject: [PATCH] fix: Use SyscallConn for isTTY which is safe during file
 close

---
 internal/entryhuman/entry.go      | 23 ++++++++++++++++++++---
 internal/entryhuman/entry_test.go | 28 ++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/internal/entryhuman/entry.go b/internal/entryhuman/entry.go
index 4e741c9..76b679c 100644
--- a/internal/entryhuman/entry.go
+++ b/internal/entryhuman/entry.go
@@ -12,6 +12,7 @@ import (
 	"runtime/debug"
 	"strconv"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/fatih/color"
@@ -163,9 +164,25 @@ func isTTY(w io.Writer) bool {
 	if w == forceColorWriter {
 		return true
 	}
-	f, ok := w.(interface {
-		Fd() uintptr
-	})
+	// SyscallConn is safe during file close.
+	if sc, ok := w.(interface {
+		SyscallConn() (syscall.RawConn, error)
+	}); ok {
+		conn, err := sc.SyscallConn()
+		if err != nil {
+			return false
+		}
+		var isTerm bool
+		err = conn.Control(func(fd uintptr) {
+			isTerm = terminal.IsTerminal(int(fd))
+		})
+		if err != nil {
+			return false
+		}
+		return isTerm
+	}
+	// Fallback to unsafe Fd.
+	f, ok := w.(interface{ Fd() uintptr })
 	return ok && terminal.IsTerminal(int(f.Fd()))
 }
 
diff --git a/internal/entryhuman/entry_test.go b/internal/entryhuman/entry_test.go
index f7fc596..8ec0cac 100644
--- a/internal/entryhuman/entry_test.go
+++ b/internal/entryhuman/entry_test.go
@@ -91,4 +91,32 @@ func TestEntry(t *testing.T) {
 		})
 		assert.Equal(t, "entry", "\x1b[0m\x1b[0m0001-01-01 00:00:00.000 \x1b[91m[CRITICAL]\x1b[0m\t\x1b[36m<.:0>	\x1b[0m\t\"\"\t{\x1b[34m\"hey\"\x1b[0m: \x1b[32m\"hi\"\x1b[0m}", act)
 	})
+
+	t.Run("isTTY during file close", func(t *testing.T) {
+		t.Parallel()
+
+		tmpdir := t.TempDir()
+		f, err := ioutil.TempFile(tmpdir, "slog")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer f.Close()
+
+		done := make(chan struct{}, 2)
+		go func() {
+			_ = entryhuman.Fmt(f, slog.SinkEntry{
+				Level: slog.LevelCritical,
+				Fields: slog.M(
+					slog.F("hey", "hi"),
+				),
+			})
+			done <- struct{}{}
+		}()
+		go func() {
+			_ = f.Close()
+			done <- struct{}{}
+		}()
+		<-done
+		<-done
+	})
 }