From 839d8d17a7c2ffc7bb605104bd5c163d0626d02d Mon Sep 17 00:00:00 2001
From: Pekka Vainio <pekka.vainio@iki.fi>
Date: Tue, 3 Mar 2026 15:32:26 +0200
Subject: [PATCH] fix: handle -1 from syscall.Read

---
 serial_posix.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/serial_posix.go b/serial_posix.go
index 6d25b2d..d20ff95 100644
--- a/serial_posix.go
+++ b/serial_posix.go
@@ -111,6 +111,14 @@ func (p *port) Read(b []byte) (n int, err error) {
 		return
 	}
 	n, err = syscall.Read(fd, b)
+	if n < 0 {
+		// underlying syscall.Read returns -1 on error, but we want to return 0 to be consistent with io.Reader interface.
+		if err == nil {
+			// This should not happen, but just in case.
+			err = fmt.Errorf("serial: read returned %v without error", n)
+		}
+		n = 0
+	}
 	return
 }