NSURL on iOS 17 fails to parse double protocols for PMTiles

[KiwiKilian]

MapLibre iOS Version

6.10.0

iOS Version

iOS 17.5

Device

Simulator

What happened?

Using PMTiles like https://example.com/some.pmtiles within a MLNVectorTileSource on iOS 17 simulator fails (no crash) with the following error:

'MapLibre error', 'Requesting: https//example.com/some.pmtiles failed with error: Error Domain=NSURLErrorDomain Code=-1002 "unsupported URL"

Note the missing : in the parsed URL.

Steps to reproduce

To break down the problem, it's enough to parse the URL. I've also included the proposal from @bdon for a more appropriate scheme (pmtiles+https://):

NSURL *url = [NSURL URLWithString:@"pmtiles://https://example.com/some.pmtiles"];
NSLog(@"%@", url.absoluteString);
NSURL *urlAlternative = [NSURL URLWithString:@"pmtiles+https://example.com/some.pmtiles"];
NSLog(@"%@", urlAlternative.absoluteString);

We also used a basic PMTiles example within MapLibre React Native. It basically it creates an MLNVectorTileSource

[MLNVectorTileSource alloc] initWithIdentifier:self.id configurationURL:[NSURL URLWithString:self.url]

• iOS 15.5
  • Example crashes due to Crash "Base Vertex Instance Drawing is only supported on MTLGPUFamilyApple3 and later." #3098
  • pmtiles://https://example.com/some.pmtiles
  • pmtiles+https://example.com/some.pmtiles
• iOS 16.4
  • Example works
  • pmtiles://https://example.com/some.pmtiles
  • pmtiles+https://example.com/some.pmtiles
• iOS 17.0 and iOS 17.5 ❌
  • Example is broken due to (URL changed for readability, note the missing :):

    'MapLibre error', 'Requesting: https//example.com/some.pmtiles failed with error: Error Domain=NSURLErrorDomain Code=-1002 "unsupported URL"

  • pmtiles://https//example.com/some.pmtiles ❌ missing :
  • pmtiles+https://example.com/some.pmtiles
• iOS 18.2
  • Example works
  • pmtiles://https://example.com/some.pmtiles
  • pmtiles+https://example.com/some.pmtiles

So it seems NSURL is only in iOS 17.x problematic, as I don't have any device running iOS 17 I can only reproduce using the simulator.

The problem does not occur when using a pmtiles://https:// scheme within a style JSON set as styleURL – through this use case the URLs aren't parsed as NSURL. The problem only occurs when creating a MLNVectorTileSource.

[KiwiKilian]

There are currently two proposals to fixing this:

• Adding a NSString constructor (@louwers)
  • This seems like a short term quick fix
• Changing the PMTiles protocol scheme (@bdon) PMTiles URLs in MapLibre are not valid URLs protomaps/PMTiles#509
  • This looks to me as the long term, spec compliant solution, but I'm no URL-parser-expert

[louwers]

I was able to reproduce this. I'll make a PR with a suggested solution.

[louwers]

@KiwiKilian We already have a good workaround available, since the TileJSON constructor already uses NSString.

Please see below. Is this an acceptable solution for you?

- (void)addFoursquarePOIsPMTilesLayer {
    // NOTE: the line below works on iOS 18 and up
    // However, on iOS 17 the second : is stripped from the URL
    // that is why we are using the TileJSON constructor as a workaround for this problem below
    //    MLNVectorTileSource *foursquareSource = [[MLNVectorTileSource alloc] initWithIdentifier:@"foursquare-10M" configurationURL:pmtilesURL];

    MLNVectorTileSource *foursquareSource =
      [[MLNVectorTileSource alloc] initWithIdentifier:@"foursquare-10M"
                                     tileURLTemplates:@[@"pmtiles://https://oliverwipfli.ch/data/foursquare-os-places-10M-2024-11-20.pmtiles"]
                                              options:nil];

    // Add the source to the map style
    [self.mapView.style addSource:foursquareSource];

    // Initialize the circle style layer
    MLNCircleStyleLayer *circleLayer = [[MLNCircleStyleLayer alloc] initWithIdentifier:@"foursquare-10M" source:foursquareSource];
    circleLayer.sourceLayerIdentifier = @"place";
    circleLayer.maximumZoomLevel = 11;

    // Set the circle color
    circleLayer.circleColor = [NSExpression expressionForConstantValue:[UIColor colorWithRed:0.8 green:0.2 blue:0.2 alpha:1.0]];
    
    // Set the circle opacity with interpolation
    circleLayer.circleOpacity = [NSExpression expressionWithMLNJSONObject:@[
        @"interpolate",
        @[@"linear"],
        @[@"zoom"],
        @6, @0.5,
        @11, @0.5,
        @14, @1.0
    ]];

    // Set the circle radius with interpolation
    circleLayer.circleRadius = [NSExpression expressionWithMLNJSONObject:@[
        @"interpolate",
        @[@"linear"],
        @[@"zoom"],
        @6, @1,
        @11, @3,
        @16, @4,
        @18, @8
    ]];

    // Add the layer to the map style
    [self.mapView.style addLayer:circleLayer];
}

[KiwiKilian]

The workaround solves the problem, but it feels a bit hacky, as it's not an actual tileURLTemplates. It requires us to check, if the URL starts with pmtiles:// and then use the other constructor:

- (nullable MLNSource*)makeSource
{
    if (self.url != nil) {
      if([self.url hasPrefix:@"pmtiles://"]) {
        return [[MLNVectorTileSource alloc] initWithIdentifier:self.id tileURLTemplates:@[self.url] options:nil];
      } else {
        return [[MLNVectorTileSource alloc] initWithIdentifier:self.id configurationURL:[NSURL URLWithString:self.url]];
      }
    }
    return [[MLNVectorTileSource alloc] initWithIdentifier:self.id tileURLTemplates:self.tileUrlTemplates options:[self getOptions]];
}

Of course we could also direct users to use the tileUrlTemplates – but it feels wrong, when the main problem is the usage of malformed URLs for PMTiles. Longterm, I would prefer a cleaner solution.

[louwers]

Why do you add this explicit check? Is there any downside from always using that approach?

[KiwiKilian]

I would have guessed the two constructors are there for a reason? From the docs:

configurationURL
A URL to a TileJSON configuration file describing the source’s contents and other metadata.

https://maplibre.org/maplibre-native/ios/latest/documentation/maplibre/mlnvectortilesource/initwithidentifier:configurationurl:#parameters

tileURLTemplates
An array of tile URL template strings. Only the first string is used; any additional strings are ignored.

https://maplibre.org/maplibre-native/ios/latest/documentation/maplibre/mlnvectortilesource/initwithidentifier:tileurltemplates:options:#parameters

So don't they work partially different? The first one fetching a JSON and applying the options from there, while the other one just tries to load tiles from the URL and passing the options manually?

Therefore I think its cleaner to properly use these constructors as intended?

[louwers]

You're completely right. It just happens to work for PMTiles because the same URL can be used for both a TileJSON or a tile.

I'll look into adding an NSString constructor then.