RFC Proposal: Pluggable Mail Transports

8 years ago by Dolf Schimmel — view source

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Howdy,

I'm planning to create an RFC on this shortly, but would like to gauge the initial response first.

Currently whenever an email is sent through the mail() function it is sent by an invocation of a sendmail-compatible executable. However, there are scenario's in which an alternative transport than through a sendmail executable may be desired. For example when PHP has been locked down, preventing it from starting any executables. It would be nice if it would be possible to allow such an alternative e.g. through a PHP Extension. Of course there are many frameworks out there that setup an smtp connection themselves, but in a shared hosting environment it's unfeasible to tell users they can't use the mail() function.

This approach is akin to how sessions have a storage handler. PHP by default provides the 'file' and 'user' handlers. But the memcached extension provides a storage mechanism of its own which is then registered through php_session_register_module().

This would only implement an extra hook to allow for overriding the default sendmail mail transport (introducing a new ini setting) without bringing extra functionality to the php user land.

Also, this hook would allow to implement other feature requests, like #29629. [1]

The patch I'm proposing can be found here: https://github.com/php/php-src/pull/1778/files

Cheers,

Dolf

https://bugs.php.net/bug.php?id=29629

8 years ago by keisial@gmail.com — view source

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I don't think more than a direct SMTP transport will be needed (LMTP
perhaps?), but it seems a good idea that #29629 can finally be fixed.

8 years ago by johannes@schlueters.de — view source

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Howdy,

I'm planning to create an RFC on this shortly, but would like to gauge
the initial response first.

Currently whenever an email is sent through the mail() function it is
sent by an invocation of a sendmail-compatible executable. However,
there are scenario's in which an alternative transport than through a
sendmail executable may be desired. For example when PHP has been
locked down, preventing it from starting any executables. It would be
nice if it would be possible to allow such an alternative e.g. through
a PHP Extension. Of course there are many frameworks out there that
setup an smtp connection themselves, but in a shared hosting
environment it's unfeasible to tell users they can't use the mail()
function.

For one: Why can't they use the mail function? A hoster can easily
provide a sendmail-compatible program doing whatever is needed in the
environment.
The purpose of the function is to get rid of mail reliably and quickly
in order to have it queued somewhere. PHP shouldn't be the MTA. That's
a tough task (i.e. what to do when the SMTP server is down or slow? -
PHP shouldn't have to wait)
So I'd like to learn where mail() can't be used (aside from a dev
desktop where this might need "too much" system configuration)

And as a side note: If you really have a special case where providing a
sendmail tool is no option you could easily create an extension
replacing mail() with a custom function (mbstring functions, runkit and
other extensions show how this can be done)

The patch I'm proposing can be found here:
https://github.com/php/php-src/pull/1778/files

I haven't fully reviewed this. But you're not handing extension
unloading. In some SAPIs we have dl() available and serve multiple
requests. Thus in one request a mail module could be loaded by dl() on
shutdown the extension will be unloaded, but the pointer will still
exist in the handler table.

johannes

8 years ago by johannes@schlueters.de — view source

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They surely could. In fact that's how we've been doing it for a long
time now. But they also want to lock down things as much as possible. In
our case we decided to disallow PHP from doing any forking and put it in
a (noexec) filesystem namespace that doesn't contain any exectuables.

That is indeed a good point. Thanks!

The purpose of the function is to get rid of mail reliably and quickly
in order to have it queued somewhere. PHP shouldn't be the MTA. That's
a tough task (i.e. what to do when the SMTP server is down or slow? -
PHP shouldn't have to wait)
So I'd like to learn where mail() can't be used (aside from a dev
desktop where this might need "too much" system configuration)

Well, you're right in that PHP doesn't have to be an MTA. But, that
doesn't mean you don't want it to communicate directly with an MTA. The
MTA typically decides whether it will actually accept the email or
whether it considers it spam or whether a user has reached their quota,
just to name a few examples. It's way more convenient to let the user
know immediately whether their mail was accepted than it is to simply
queue it somewhere and generate a lot of bounce mails which will often
times go unread.

Also the sendmail tool can return an error. While I admit, that we don't
have a way to transport the error reason. The user will get a simple
"false" (which hardly anybody, a least that's my assumption, checks for)

The risk I'm seeing is that mail() is a blocking function and is often
called in a loop (foreach (subscriber) { mail } ) and we should
encourage offloading as quickly as possible.

If other disagree with me on hat I'm fine :)

johannes