Fix null-pointer dereference MapRenderer Android

[louwers]

In the Android-specific MapRenderer class a std::unique_ptr<AndroidRendererBackend> is dereferenced that may be a nullptr. This can of course lead to a crash, which was reported in #2579

I am surprised this has not resulted in more crashes being reported, because I think the null-pointer dereference happens every time onSurfaceCreated is (initially) called, and a method is even called on the dereferenced null-pointer...

We should probably release 11.1.0 once this is released merged.

[TimSylvester]

Interesting, it looks like that means a render can occur before onSurfaceCreated is called or after a resetRenderer.

[louwers]

Interesting, it looks like that means a render can occur before onSurfaceCreated is called or after a resetRenderer.

I think onSurfaceCreated dereferences backend before it is initialized in that same method.

[kodebach]

I think onSurfaceCreated dereferences backend before it is initialized in that same method.

I rather suspect it's the other end of the lifecycle, i.e. render is called after Android has destroyed the surface. (see also #2579 (comment))

I don't know the maplibre code, so no idea if Android destroying the surface would cause the backend reference to become invalid. But based on our crash data that seems most likely to me.

[louwers]

Right. When render is called after resetRenderer, the backend is again a nullptr.

[louwers]

When the app goes to the background and onSurfaceDestroyed is called, the backend and renderer are reset. onSurfaceChanged calls onSurfaceCreated when no renderer exists, but onSurfaceCreated needs a valid backend to exist. I updated the reset() method to create a new backend to make sure there is always a valid one.

[elican-doenyas]

@louwers I experienced the same issue when I upgraded to use the latest map libre android sdk (v11.6.1). Looking into the issue, there seems to be a nullptr dereference on MapRenderer:render method. I believe this happens when the style.json does not include a renderer property in its metadata. I was able to resolve the issue by adding;

"maputnik:renderer": "mbgljs"

value to the metadata section of the style.json I am using.

Can you please verify this and possibly introduce a fix so it does not crash in the absence of this property? We were not aware that it was required as the metadata is listed as 'optional' in the style specs here: https://maplibre.org/maplibre-style-spec/root/#metadata

Note 1: Previously, our company was using the v10.2.0 maplibre android sdk, and it was working fine without this property in the style.

Note 2: The relevant crash log is attached.
maplibre-nullptr.txt

[louwers]

@elican-doenyas That is a different issue, please open a separate issue.