Fix gravity count when FTL fails to return this value

[rdwebdesign]

What does this PR aim to accomplish?

Fixes the -2 Domains on the Lists issue.

How does this PR accomplish the above?

When FTL fails to count the number of domains on the lists, the value -2 is returned, but this value should not be printed.

This PR shows 0 in this case.

Link documentation PRs if any are needed to support this PR:

none

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[yubiuser]

I see were this is coming from, but I wonder if '-2' is not the better choose as it also indicates database failures/issues and not only empty gravity lists.

[rdwebdesign]

In my opinion it is wrong to show -2 as the number of domains for the user.

If we need to indicate a database failure, then we need to show an error message somewhere. In this case, -2 is the value of DB_FAILED constant, not the domain count:

// Get number of domains in a specified table of the gravity database We return
// the constant DB_FAILED and log to FTL.log if we encounter any error
int gravityDB_count(const enum gravity_tables list)
{
    ...

https://github.com/pi-hole/FTL/blob/148e558fd17f1f8de88bab29b914fc14f8ef2423/src/database/gravity-db.c#L1074-L1077

and

https://github.com/pi-hole/FTL/blob/61a211f1c187206f5ff901afae657968114fde15/src/FTL.h#L96-L98

[yubiuser]

Maybe we should show 0 and log an error to the message table as well? @DL6ER

[rdwebdesign]

Maybe we should show 0 and log an error to the message table as well?

Yes.
The message can be shown in the messages table (if FTL generates the message), or we can simply reorder the code and add the message to the title attribute (see line 432) using javascript:

$(".small-box:has(#gravity_size)").attr("title", "ERROR MESSAGE HERE");

[DL6ER]

-2 typically means some really hard error on the database. Either the database does not exist (yet) or there is really some heavy error like mandatory tables missing. Even when the database is locked, it should still be possible to access it read-only to get these numbers. Is there any related issue ticket we could check for errors having been reported to FTL.log ?

FWIW my feeling is that -2 instead of 0 is more meaningful as it transports more info (as also said by @yubiuser above) but we'd need to (a) document this properly in the API docs (I didn't check if we do but I guess wo don't) and (b) handle this on the dashboard to show something more obvious to the user.

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edit https://discourse.pi-hole.net/t/2-domains-on-blocklist-after-updating-pihole/73626/ is the context

[rdwebdesign]

FWIW my feeling is that -2 instead of 0 is more meaningful

This is 100% true for the API, but not for the user interface.

From the UX point of view, -2 should be converted to an error message in the web interface.
A negative count is confusing and we have a lot of cases (since v5) showing users don't understand -2 as a valid number here.

[Th3M3]

But would the user understand if and why it suddenly shows that there are 0 Domains on the lists ?

As I mentioned in my initial post on Discourse, pihole was still working and blocking queries as expected.
So in view of that 0 is misleading too, isn't it?

IMHO it would be most helpful, if

• a message at the Pi-hole diagnosis system indicate what went wrong
• the reason for showing -2 is documented somewhere (didn't searched the docs either tbh.)

[yubiuser]

So in view of that 0 is misleading too, isn't it?

Maybe we could show ---- or Error + a tooltip suggesting to run gravity.

[rdwebdesign]

I think I was able to achieve all goals.

Now in case of an error:

• no more confusion (the count won't show as -2 domains);
• no misleading 0 domains;
• the box will show an error message, containing the error code;
• the tooltip text will show a message suggesting to update gravity.

I'm don't think we need a message in diagnosis page, but in any case this should be done in FTL repo and is out of the scope of this PR.

[yubiuser]