Manage the data cache with the last modified date

Currently the cache is persistent, once a file is downloaded and cached, it is never updated.

The idea here is to fetch the last modified date of a file on Nextcloud, compare it with the date of the cached file and only update the cache if necessary.

When you display the content of a directory on Nextcloud, the javascript in the webpage fetch an XML files formatted as this:

<d:multistatus xmlns:d="DAV:"
    xmlns:s="http://sabredav.org/ns"
    xmlns:oc="http://owncloud.org/ns"
    xmlns:nc="http://nextcloud.org/ns">
    <d:response>
        <d:href>/public.php/webdav/</d:href>
        <d:propstat>
            <d:prop>
                <d:getlastmodified>Tue, 30 Jan 2024 15:46:25 GMT</d:getlastmodified>
                <d:getetag>&quot;65b919d1847ee&quot;</d:getetag>
                <d:resourcetype>
                    <d:collection/>
                </d:resourcetype>
                <oc:fileid>94059696</oc:fileid>
                <oc:permissions>RMG</oc:permissions>
                <oc:size>21877340931</oc:size>
                <d:quota-available-bytes>0</d:quota-available-bytes>
                <nc:has-preview>false</nc:has-preview>
                <nc:mount-type>external</nc:mount-type>
                <nc:is-encrypted>0</nc:is-encrypted>
                <nc:share-attributes>[]</nc:share-attributes>
            </d:prop>
            <d:status>HTTP/1.1 200 OK</d:status>
        </d:propstat>
        <d:propstat>
            <d:prop>
                <d:getcontenttype/>
                <d:getcontentlength/>
                <x1:share-permissions xmlns:x1="http://open-collaboration-services.org/ns"/>
            </d:prop>
            <d:status>HTTP/1.1 404 Not Found</d:status>
        </d:propstat>
    </d:response>
   ...
    <d:response>
        <d:href>/public.php/webdav/test.RDS</d:href>
        <d:propstat>
            <d:prop>
                <d:getlastmodified>Mon, 29 Jan 2024 17:52:41 GMT</d:getlastmodified>
                <d:getetag>&quot;&quot;49263511c92d3095340908cbb0c30f6d-1&quot;&quot;</d:getetag>
                <d:getcontenttype>application/octet-stream</d:getcontenttype>
                <d:resourcetype/>
                <oc:fileid>123611282</oc:fileid>
                <oc:permissions>RMG</oc:permissions>
                <oc:size>148288540</oc:size>
                <d:getcontentlength>148288540</d:getcontentlength>
                <nc:has-preview>false</nc:has-preview>
                <nc:mount-type>external</nc:mount-type>
                <nc:share-attributes>[]</nc:share-attributes>
            </d:prop>
            <d:status>HTTP/1.1 200 OK</d:status>
        </d:propstat>
        <d:propstat>
            <d:prop>
                <d:quota-available-bytes/>
                <nc:is-encrypted/>
                <x1:share-permissions xmlns:x1="http://open-collaboration-services.org/ns"/>
            </d:prop>
            <d:status>HTTP/1.1 404 Not Found</d:status>
        </d:propstat>
    </d:response>
    <d:response>
        <d:href>/public.php/webdav/test.png</d:href>
        <d:propstat>
            <d:prop>
                <d:getlastmodified>Mon, 29 Jan 2024 17:52:41 GMT</d:getlastmodified>
                <d:getetag>&quot;&quot;3c933f8c774ce7b963ad9ea84fb4214b&quot;&quot;</d:getetag>
                <d:getcontenttype>image/png</d:getcontenttype>
                <d:resourcetype/>
                <oc:fileid>117938340</oc:fileid>
                <oc:permissions>RMG</oc:permissions>
                <oc:size>109015</oc:size>
                <d:getcontentlength>109015</d:getcontentlength>
                <nc:has-preview>false</nc:has-preview>
                <nc:mount-type>external</nc:mount-type>
                <nc:share-attributes>[]</nc:share-attributes>
            </d:prop>
            <d:status>HTTP/1.1 200 OK</d:status>
        </d:propstat>
        <d:propstat>
            <d:prop>
                <d:quota-available-bytes/>
                <nc:is-encrypted/>
                <x1:share-permissions xmlns:x1="http://open-collaboration-services.org/ns"/>
            </d:prop>
            <d:status>HTTP/1.1 404 Not Found</d:status>
        </d:propstat>
    </d:response>
</d:multistatus>

To be able to fetch this file, one needs to catch the cookie produced during the fetch of the folder content page and transmit it with the request.