Return asset ids as response header

[developmentseed]

Return asset ids as response header

[vincentsarago]

I propose adding a response header like X-ASSETS that returns a comma-separated or JSON-encoded list of asset ids that were used to create the response tile. For many sources, the asset id includes enough information to extract a date range and other helpful metadata.

with the new cogeo-mosaic BaseBackend method this might be a bit tricky. Especially if we want list of asset ids that were used to create the response tile. An easy solution would be for tile to return the whole list of assets passed to the tiler but this won't mean that they were used.

ref: https://github.com/developmentseed/cogeo-mosaic/blob/c989249ecda0ab090e5fff86e6aba2ba8c882f3f/cogeo_mosaic/backends/base.py#L59-L72

    def tile(
        self, x: int, y: int, z: int, **kwargs: Any,
    ) -> Tuple[numpy.ndarray, numpy.ndarray]:
        """Get Tile from multiple observation."""

        assets = self.assets_for_tile(x, y, z)
        if not assets:
            raise NoAssetFoundError(f"No assets found for tile {z}-{x}-{y}")

        def _reader(asset: str, x: int, y: int, z: int, **kwargs: Any):
            with self.reader(asset) as src_dst:
                return src_dst.tile(x, y, z, **kwargs)

        return mosaic_reader(assets, _reader, x, y, z, **kwargs)

so in ☝️ do return mosaic_reader(assets, _reader, x, y, z, **kwargs), assets

we could also try to change mosaic_reader and https://github.com/cogeotiff/rio-tiler/blob/master/rio_tiler/mosaic/reader.py#L19-L52 but not sure it will work.

[kylebarron]

An easy solution would be for tile to return the whole list of assets passed to the tiler but this won't mean that they were used

That's actually what I expected, but maybe it's worth considering trying to return only what was used