Stdin pipe not closed in Msg.WriteToSendmailWithContext

[inliquid]

Not sure if it's an issue or my bad understanding of how cli MUA works, so I open a question here in discussions. In my target setup I'm using exim to send mails to users. I don't have working exim setup on my dev machine, so I decided to write a small program to log all calls to "exim" to a file while testing everything.

Here is how it looks like:

func main() {
	logger.Info.Println("-> Program started")
	defer logger.Info.Println("<- Program exited")

	logger.Info.Println("Args:", os.Args)

	s := bufio.NewScanner(os.Stdin)
	for s.Scan() {
		if s.Text() == "." {
			logger.Info.Println(`Got "." ending, stopped reding`)
			break
		}
		logger.Info.Println("Read line:", s.Text())
	}
	if err := s.Err(); err != nil {
		logger.Error.Panicln("Can't read os.Stdin:", err)
	}
}

It uses own logger based on standard logger. This program is compiled as exim and put in PATH. Not sure if original exim interprets "." as message ending, but added this just in case.

What I observed, effectively, is that WriteToSendmailWithContext hangs unless there is timeout set on given context. In last case such call return an error. In logs I can see that reading from os.Stdin stops somewhere before last line and that's it:

[INFO] 2022/05/24 18:11:27.876387 -> Program started
[INFO] 2022/05/24 18:11:27.876387 Args: [exim -oi -t]
[INFO] 2022/05/24 18:11:27.876387 Read line: Date: Tue, 24 May 2022 18:11:27 +0300
[INFO] 2022/05/24 18:11:27.876387 Read line: MIME-Version: 1.0
[INFO] 2022/05/24 18:11:27.876387 Read line: Message-ID: <20156.7468985450408456538.1653405087@inflow-pc>
[INFO] 2022/05/24 18:11:27.876387 Read line: Subject: Test message
[INFO] 2022/05/24 18:11:27.876387 Read line: User-Agent: go-mail v0.1.7 // https://github.com/wneessen/go-mail
[INFO] 2022/05/24 18:11:27.876387 Read line: X-Mailer: go-mail v0.1.7 // https://github.com/wneessen/go-mail
[INFO] 2022/05/24 18:11:27.876387 Read line: From: ***
[INFO] 2022/05/24 18:11:27.876387 Read line:  ***
[INFO] 2022/05/24 18:11:27.876387 Read line: To: ***
[INFO] 2022/05/24 18:11:27.876387 Read line: Content-Type: text/html; charset=UTF-8
[INFO] 2022/05/24 18:11:27.876387 Read line: Content-Transfer-Encoding: quoted-printable
[INFO] 2022/05/24 18:11:27.876387 Read line: 

I looked at implementation and I think problem (if I get it right) is that there is no indication that message is done. There is neither a single dot on a line "." (not sure if it's a correct way of terminating message on sendmail-like cli) , nor closed stdin, because its Close method is called in deferred closure. Instead, I think si.Close() should be called right before ec.Wait() so that stdin would be closed just after message written to it, but before program is exited.

[wneessen]

Thanks for the report. You are right. While the sendmail binary will not be waiting for a "." we should force the closing of STDIN so that the connection to receiving end can be completed with a EOF.

I've added the forcefully close in commit 070eb39 and merged it into main. Please give it a try. I've also realized that sendmail is located in /usr/sbin on most common unix systems therefore the default path has been adjusted accordingly.

[inliquid]

Thank you for quick update! May I ask to tag latest changes so that go modules system will see updates without the need to explicitly pull it via go get <...>@master

[wneessen]

Done: https://github.com/wneessen/go-mail/releases/tag/v0.1.9-beta.1

[inliquid]

It should be in semver format like v0.1.9, it won't pick it with suffix unfortunately.

[wneessen]

Corrected: https://github.com/wneessen/go-mail/releases/tag/v0.1.9