Pull Request for Issue #18543

Summary of Changes

This implements a basic fallbackdownloadurl support for com_joomlaupdate

Testing Instructions

Do NOT do this on a production site! This is for testing only!

• install 3.8.2
• apply this patch
• set this update server: https://www.jah-tz.de/downloads/core/updateserver/list.xml
• we propose a fake update to 3.8.3
• the update should fail as the primary download url is not a zip file
• joomla detects that and tries the fallback which is a zip download.
• joomla tells you that he is using the fallback.

Expected result

Joomla can be updated using a fallbackurl

Actual result

Joomla can not be updated using a fallbackurl and Joomla told you that we need to use a fallback.

Additional comments

@mbabker can you take a look into the implementation?

Given the magic that is done in the updater code this works for me but maybe you can give some feedback / review on this?

@brianteeman

Please take a look into the language strings. I hope that you understand what i want to say with the current strings. I know that this is not a good wording but I think we should told our users that we used a fallback url and that the download of the primary update package failed. Can you please review and suggest a better wording?

Technical Details

On the update server part we need to define the fallback like this:

	<update>
		<name>Joomla! 3.8</name>
		<description>Joomla! 3.8 CMS</description>
		<element>joomla</element>
		<type>file</type>
		<version>3.8.3</version>
		<infourl title="Joomla!">https://www.joomla.org/announcements/release-news/5716-joomla-3-8-2-release.html</infourl>
		<downloads>
			<fallbackdownloadurl type="full" format="zip">https://downloads.joomla.org/cms/joomla3/3-8-2/Joomla_3.8.2-Stable-Update_Package.zip</fallbackdownloadurl>
			<downloadurl type="full" format="zip">https://downloads.joomla.org/test.html</downloadurl>
		</downloads>
		<tags>
			<tag>stable</tag>
		</tags>
		<maintainer>Joomla! PLT</maintainer>
		<maintainerurl>https://www.joomla.org</maintainerurl>
		<section>STS</section>
		<targetplatform name="joomla" version="3.[78]" />
		<php_minimum>5.3.10</php_minimum>
	</update>

please note the following line:

<fallbackdownloadurl type="full" format="zip">https://downloads.joomla.org/cms/joomla3/3-8-2/Joomla_3.8.2-Stable-Update_Package.zip</fallbackdownloadurl>

Todo's after tests

• update the update server and place the update on a non AWS source
• issue a com_joomlaupdate update using a non AWS souce or 3.8.3 or share the joomlaupdate package with the russian community.