Restore Teleporter functionality

[DL6ER]

What does this implement/fix?

Restore Teleporter functionality. Concerning compatibility, https://caniuse.com/url tells us it can be used in any sufficiently recent browser except IE and Opera Mini. If you have a better approach, I'd love to see it.

Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[yubiuser]

Nice work. However, while my header is attachment; filename="pi-hole_nanopi_teleporter_2023-10-12_22-19-38.zip", my suggested file name is _pi-hole_nanopi_teleporter_2023-10-12_22-19-38.zip_.

See the leading and trainling _

[rdwebdesign]

This is happening because the quotes are part of the string and they are replaced by _.

[rdwebdesign]

When the button is clicked, the API sends a payload containing the zip file. To download the file, code creates a "fake" link, triggers a Click event and removes the link after the download.

This is how the link looks like:

<a href="blob:http://192.168.0.20…-a302fce919ff" download='"pi-hole_pidev_teleporter_2023-10-16_23-54-13.zip"'>

(The value of download parameter is received with double-quotes ("pi-hole_pidev_teleporter_2023-10-16_23-54-13.zip").

Each browser deals with these quotes in slightly different ways:

• Firefox just removes them. The file name is correctly used.
• Chrome and Edge replace them with _. The file name starts and ends with underscores (_pi-hole_pidev_teleporter_2023-10-16_23-54-13.zip_).
• Safari (iOS) changes the file name into "pi-hole_pidev_teleporter_2023-10-16_23-54-13.zip".zip (very strange).

I didn't test other browsers.

These are the Response Headers received:

cache-control: no-cache, no-store, must-revalidate, private, max-age=0
connection: close
content-disposition: attachment; filename="pi-hole_pidev_teleporter_2023-10-16_23-54-13.zip"
content-length: 16104
content-security-policy: default-src 'self' 'unsafe-inline';
content-type: application/zip
date: Tue, 17 Oct 2023 02:54:13 GMT
expires: 0
pragma: no-cache
referrer-policy: strict-origin-when-cross-origin
x-content-type-options: nosniff
x-frame-options: DENY
x-xss-protection: 0

Do we need to send the filename with quotes and remove them on the javascript? Or can we send it without quotes?

https://github.com/pi-hole/FTL/blob/529d7f7a3013a472b9387256232e560571d77932/src/api/teleporter.c#L38-L40

Can we use this?

        snprintf(pi_hole_extra_headers, sizeof(pi_hole_extra_headers),
                 "Content-Disposition: attachment; filename=%s",
                 filename);

[yubiuser]

The final messages says

 Import successful
Processed files:

/etc/pihole/pihole.toml
/etc/pihole/dhcp.leases
/etc/pihole/gravity.db

However, it's not gravity.db that have been restored by only the lists, clients, groups,.... We may need to add a hint that users should run pihole -g.