From a63b28875ff5b7f52b2c41992656afac36c66a34 Mon Sep 17 00:00:00 2001
From: Cristian Maglie <c.maglie@bug.st>
Date: Thu, 27 Jul 2017 13:53:59 +0200
Subject: [PATCH] linux: detect port disconnection during Read

See https://stackoverflow.com/a/34945814/1655275

> pselect signals that file descriptor is ready and
> ioctl(fd, FIONREAD, &len) returns zero len.

Failure to detect this condition has been revealed by
the testsuite:

=== RUN   TestDisconnectingPortDetection
2017/07/27 13:56:37 PR - Connecting to Probe
2017/07/27 13:56:37      > Searching for port 2341:8037
2017/07/27 13:56:37        Detected port '/dev/ttyACM0' 2341:8037
2017/07/27 13:56:37        Using '/dev/ttyACM0'
2017/07/27 13:56:37 Starting test (timeout 20s)
2017/07/27 13:56:37 PR - Turn ON target
2017/07/27 13:56:37 TR - Connecting to Target
2017/07/27 13:56:37      > Searching for port 2341:8036
2017/07/27 13:56:37        Detected port '/dev/ttyACM0' 2341:8037
[...cut...]
2017/07/27 13:56:46      > Searching for port 2341:8036
2017/07/27 13:56:46        Detected port '/dev/ttyACM0' 2341:8037
2017/07/27 13:56:46        Detected port '/dev/ttyACM1' 2341:8036
2017/07/27 13:56:46        Using '/dev/ttyACM1'
2017/07/27 13:56:46 T2 - Make a Read call
2017/07/27 13:56:46 T1 - Delay 200ms before disconnecting target
2017/07/27 13:56:46 T1 - Disconnect target
2017/07/27 13:56:46 PR - Turn OFF target
2017/07/27 13:56:46 T2 - Read returned: n=0 err=nil
--- FAIL: TestDisconnectingPortDetection (9.18s)
        Error Trace:    serial_test.go:100
	Error:		An error is expected but got nil. %s
	Messages:	Read returned no errors

this commit fix the problem above.
---
 serial_unix.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/serial_unix.go b/serial_unix.go
index f9e887c..c921389 100644
--- a/serial_unix.go
+++ b/serial_unix.go
@@ -77,6 +77,12 @@ func (port *unixPort) Read(p []byte) (int, error) {
 		if err == unix.EINTR {
 			continue
 		}
+		// Linux: when the port is disconnected during a read operation
+		// the port is left in a "readable with zero-length-data" state.
+		// https://stackoverflow.com/a/34945814/1655275
+		if n == 0 && err == nil {
+			return 0, &PortError{code: PortClosed}
+		}
 		if n < 0 { // Do not return -1 unix errors
 			n = 0
 		}