Subject: Re: bug#56855: 27.1; sendmail-send-it considers it an error if sendmail wrote to stdout/stderr

From: Justus Winter <[email-masked]>
Date: Tue, 02 Aug 2022 07:59:06 +0200

Matt Armstrong <[email-masked]> writes:

> Justus Winter <[email-masked]> writes:
>
>> sendmail-send-it considers it an error if sendmail wrote to
>> stdout/stderr, despite the fact that the process returned success.
>
> [...]
>
>> I read documentation of various sendmail implementations, and all
>> agreed that returning success meant that the operation succeeded.  I
>> found no justification for emacs thinking that the operation failed if
>> the process printed to stdout or stderr.
>
> This is perhaps surprising.  It is also behavior that has come to be
> expected, especially in more traditional Unix programs.  E.g. crontab
> also considers jobs that print to stderr to have an error, regardless of
> exit status.

>From man cron(8) I see:

       When  executing  commands,  any  output  is  mailed to the owner of the
       crontab (or to the user named in the MAILTO environment variable in the
       crontab,  if  such  exists)  from the owner of the crontab (or from the
       email address  given  in  the  MAILFROM  environment  variable  in  the
       crontab,  if  such  exists).

Note how it says nothing about considering it an error.  In fact, I did
an experiment on my cron implementation (ISC cron 3.0pl1-149 as packaged
by Debian), and it did send me any output written to stdout or stderr
regardless of the exit status, and it did *not* notify me of a failing
command if no output was written.  Clearly, sending mails is orthogonal
to the exit status as far as cron is concerned.

> From the sendmail(8) manpage we have this statement:
>
>     Sendmail is not intended as a user interface routine; other programs
>     provide user-friendly front ends; sendmail is used only to deliver
>     pre-formatted messages.
>
> An implementation of the "sendmail program" should probably emulate the
> original sendmail as closely as possible.  It prints no messages when it
> succeeds.

I don't read the snippet you quoted as promising to never send text to
stderr if the process succeeds.  Now, I don't know which version of the
manpage you consider authoritative, but I found
e.g. https://linux.die.net/man/8/sendmail.sendmail which does contain
your snippet, and then clearly states:

      Sendmail returns an exit status describing what it did. The codes
      are defined in <sysexits.h>:

      EX_OK

      Successful completion on all addresses.

And:

      % grep EX_OK /usr/include/sysexits.h
      #define EX_OK            0       /* successful termination */

> On this we do have roughly 35 years of historical precedent, since the
> original Sendmail began in the mid-80s.  :-)

Well, happily, we're also 35 years wiser than to trust the original
sendmail with anything.

> This may seem like a historical wart, but I have personally found this
> behavior to be helpful, especially in programs that are typically run
> non-interactively and "out of sight" like a crontab or sendmail wrapper
> script.  E.g. when a shell script prints to stderr there may indeed have
> been a problem, but a bug in the script may still have caused it to exit
> with zero regardless.  It is usually easy to arange for such programs to
> print nothing when they succeed.

I don't understand that argument.  I agree that seeing the output is
beneficial, but then you say that it is easy to suppress that output,
the same output that seeing you deemed beneficial just a few lines
earlier.

In fact, I think we should ask what the best thing is for the user.  I
think that (a) emacs should correctly indicate whether sending the mail
succeeded or not, and (b) any warnings should be presented to the user.

Currently, emacs fails at (a) and your workaround violates (b).

>> I use msmtp with the authentication password encrypted using OpenPGP.
>> Then, I use 'gpg --no-tty -q -d ...' as msmtp's passwordeval function.
>> Now, my OpenPGP key has expired, but that doesn't stop GnuPG from
>> decrypting the secret, and in fact it returns the status code 0.  It
>> also prints
>>
>>   gpg: Note: secret key 08CC70F8D8CC765A expired at Mon 25 Jul 2022 05:31:26 PM CEST
>>
>> to stderr, which is picked up by emacs, it says
>>
>>   sending...failed to gpg: Note: secret key 08CC70F8D8CC765A expired at Mon 25 Jul 2022 05:31:26 PM CEST
>>
>> in the status buffer while the compose buffer stays open.  Note that
>> despite this, the message has been sent successfully, while emacs
>> indicates that the sending has failed.
>
> Can you configure your msmtp to behave like sendmail and refrain from
> printing human readable messages upon success?  Perhaps the --logger-fd
> or --logger-file arguments to gpg could be used to direct the output you
> do not wish to read to /dev/null?

Yes I can, but the question is: should I have to?

Best,
Justus