[9.x] Allow overriding transport type on Mailgun transporter

[jnoordsij]

In #41255 the Mailgun transport type was changed from api to https. This breaks my application, as I add some custom headers which were working fine with the API transporter, but are ignored on the messages.mime endpoint. This MR allows overriding the transport type you want to use for Mailgun, while leaving the default option unchanged.

If wanted, I can also provide a PR to add this config key to the laravel/laravel repo.

[driesvints]

Thanks @jnoordsij. I still feel this change was warranted as we used the /message.mime endpoint in Laravel v8.

Just to be clear: you weren't using these custom headers in Laravel 8, correct?

[driesvints]

A PR to laravel/laravel could be useful as well.

'mailgun' => [
    'transport' => 'mailgun',
    'scheme' => 'https',
],

No env is needed as this should be a hardcoded value that's the same across environments.

[jnoordsij]

Thanks @jnoordsij. I still feel this change was warranted as we used the /message.mime endpoint in Laravel v8.

Yeah, the change itself seems logical, its just even more flexible this way I feel.

Just to be clear: you weren't using these custom headers in Laravel 8, correct?

I was using them in Laravel 8, but had to rewrite the implementation in Laravel 9. I used to extend the Illuminate\Mail\Transport\MailgunTransport to alter the HTTP payload, but this transport was removed. As this was removed in Laravel 9, I had to rewrite things once already. Adding text headers for the testmode in Laravel 9 worked fine with the API endpoint, but I can't seem to get it working again with the messages.mime endpoint.

For reference, I tried to obtain the request body before sending it in both my Laravel 8 and Laravel 9 apps, and they seem to be quite different:

Laravel 8

--553506d1f480caca62c55a8678ed647e36bcd10a\r\n
Content-Disposition: form-data; name="to"\r\n
Content-Length: 20\r\n
\r\n
mailgun@example.com\r\n
--553506d1f480caca62c55a8678ed647e36bcd10a\r\n
Content-Disposition: form-data; name="message"; filename="message.mime"\r\n
Content-Length: 324\r\n
\r\n
Message-ID: <f1c214aed4da7e9153a3f9430c02f62d@swift.generated>\r\n
Date: Thu, 03 Mar 2022 10:41:04 +0100\r\n
Subject: Test message\r\n
From: Example <test@example.com>\r\n
To: mailgun@example.com\r\n
MIME-Version: 1.0\r\n
Content-Type: text/html; charset=utf-8\r\n
Content-Transfer-Encoding: quoted-printable\r\n
\r\n
<p>Hello world!</p>\r\n
--553506d1f480caca62c55a8678ed647e36bcd10a\r\n
Content-Disposition: form-data; name="o:testmode"\r\n
Content-Length: 3\r\n
\r\n
yes\r\n
--553506d1f480caca62c55a8678ed647e36bcd10a\r\n
Content-Disposition: form-data; name="o:tag"\r\n
Content-Length: 26\r\n
\r\n
App Name (local)\r\n
--553506d1f480caca62c55a8678ed647e36bcd10a--\r\n
"""

Laravel 9

'body' => 'From: Example <test@example.com>
To: mailgun@example.com
Subject: Test message
o:testmode: yes
X-Mailgun-Tag: App Name (local)
Message-ID: <628fcc053ba6161ff327e492274005d6@example.com>
MIME-Version: 1.0
Date: Thu, 03 Mar 2022 10:57:09 +0100
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable

<p>Hello world!</p>'

[driesvints]

@jnoordsij all of that is being handled by Symfony Mailer so there's nothing we can really do there.

[jnoordsij]

@jnoordsij all of that is being handled by Symfony Mailer so there's nothing we can really do there.

Yeah I figured, hence having the option to just stick with the api transporter for myself seems to be the best solution for now.