From 591534a3c3fcabd2c5b879a9bcd7085c06c0f713 Mon Sep 17 00:00:00 2001
From: Alexander Pevzner <pzz@apevzner.com>
Date: Mon, 2 Dec 2024 14:04:24 +0300
Subject: [PATCH] Don't start USB low-level I/O operation, if context.Context
 already expired

This is a king of small optimization. There is no reason to start I/O
operation at this case, because it will be canceled immediately after
start.
---
 usbio_libusb.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/usbio_libusb.go b/usbio_libusb.go
index 721ae81..229909d 100644
--- a/usbio_libusb.go
+++ b/usbio_libusb.go
@@ -762,6 +762,11 @@ func (iface *UsbInterface) SoftReset() error {
 func (iface *UsbInterface) Send(ctx context.Context,
 	data []byte) (n int, err error) {
 
+	// Don't even bother to send, if context already expired
+	if ctx.Err() != nil {
+		return 0, ctx.Err()
+	}
+
 	// Allocate a libusb_transfer.
 	xfer, doneChan, err := libusbTransferAlloc()
 	if err != nil {
@@ -806,6 +811,11 @@ func (iface *UsbInterface) Send(ctx context.Context,
 func (iface *UsbInterface) Recv(ctx context.Context,
 	data []byte) (n int, err error) {
 
+	// Don't even bother to recv, if context already expired
+	if ctx.Err() != nil {
+		return 0, ctx.Err()
+	}
+
 	// Some versions of Linux kernel don't allow bulk transfers to
 	// be larger that 16kb per URB, and libusb uses some smart-ass
 	// mechanism to avoid this limitation.