From fd14ba67d5f6dfcc7dab413e6275d56f82fc699f Mon Sep 17 00:00:00 2001
From: Tim Hellhake <tim-hellhake@users.noreply.github.com>
Date: Sat, 23 Sep 2023 21:40:15 +0200
Subject: [PATCH] Make exclusive access optional

---
 serial.go            |  9 +++++++++
 serial_linux_test.go | 44 ++++++++++++++++++++++++++++++++++++++++++++
 serial_unix.go       |  4 +++-
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/serial.go b/serial.go
index abfd7f9..8b878d2 100644
--- a/serial.go
+++ b/serial.go
@@ -101,6 +101,7 @@ type Mode struct {
 	Parity            Parity           // Parity (see Parity type for more info)
 	StopBits          StopBits         // Stop bits (see StopBits type for more info)
 	InitialStatusBits *ModemOutputBits // Initial output modem bits status (if nil defaults to DTR=true and RTS=true)
+	AccessMode        AccessMode       // Access mode on unix systems (Default: Exclusive)
 }
 
 // Parity describes a serial port parity setting
@@ -131,6 +132,14 @@ const (
 	TwoStopBits
 )
 
+// AccessMode whether to access the port exclusively
+type AccessMode int
+
+const (
+	Exclusive = 0
+	Shared    = 1
+)
+
 // PortError is a platform independent error type for serial ports
 type PortError struct {
 	code     PortErrorCode
diff --git a/serial_linux_test.go b/serial_linux_test.go
index 1a7e1a3..3e37806 100644
--- a/serial_linux_test.go
+++ b/serial_linux_test.go
@@ -12,6 +12,7 @@ package serial
 import (
 	"context"
 	"os/exec"
+	"syscall"
 	"testing"
 	"time"
 
@@ -62,3 +63,46 @@ func TestDoubleCloseIsNoop(t *testing.T) {
 	require.NoError(t, port.Close())
 	require.NoError(t, port.Close())
 }
+
+func TestAccessModeDefault(t *testing.T) {
+	AccessModeExclusive(t, &Mode{})
+}
+
+func TestAccessModeExclusive(t *testing.T) {
+	mode := &Mode{
+		AccessMode: Exclusive,
+	}
+
+	AccessModeExclusive(t, mode)
+}
+
+func AccessModeExclusive(t *testing.T, mode *Mode) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cmd := startSocatAndWaitForPort(t, ctx)
+	go cmd.Wait()
+
+	port, err := Open("/tmp/faketty", mode)
+	require.NoError(t, err)
+	_, err2 := Open("/tmp/faketty", mode)
+	require.Error(t, err2, syscall.ENOENT)
+	require.NoError(t, port.Close())
+}
+
+func TestAccessModeShared(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cmd := startSocatAndWaitForPort(t, ctx)
+	go cmd.Wait()
+
+	mode := &Mode{
+		AccessMode: Shared,
+	}
+
+	port, err := Open("/tmp/faketty", mode)
+	require.NoError(t, err)
+	port2, err2 := Open("/tmp/faketty", mode)
+	require.NoError(t, err2)
+	require.NoError(t, port.Close())
+	require.NoError(t, port2.Close())
+}
diff --git a/serial_unix.go b/serial_unix.go
index f6ec896..1bb745b 100644
--- a/serial_unix.go
+++ b/serial_unix.go
@@ -275,7 +275,9 @@ func nativeOpen(portName string, mode *Mode) (*unixPort, error) {
 
 	unix.SetNonblock(h, false)
 
-	port.acquireExclusiveAccess()
+	if mode.AccessMode == Exclusive {
+		port.acquireExclusiveAccess()
+	}
 
 	// This pipe is used as a signal to cancel blocking Read
 	pipe := &unixutils.Pipe{}