make timings and metadata headers optional

[vincentsarago]

closes #229

[kylebarron]

I was just thinking the other day that these should be optional! For example the MDN article says

The Server-Timing header may expose potentially sensitive application and infrastructure information. Consider to control which metrics are returned when and to whom on the server side. For example, you could only show metrics to authenticated users and nothing to the public.

[vincentsarago]

@kylebarron I've added add_assets_in_headers option in the MosaicTilerFactory. Do it make senses to rename debug -> add_timings_in_headers then ?

[kylebarron]

You could just have an optional_headers argument that takes a list. Then it'll be more extensible for the future

[vincentsarago]

@kylebarron I'm not sure to fully understand what you mean.

are you saying something like 👇

cog = TilerFactory(optional_headers={"timings", ...}

[kylebarron]

Yeah basically. You could have an enum of available optional headers. It might also make sense to make the keys the same as the header names, e.g.

cog = TilerFactory(optional_headers={"Server-Timing", "X-Assets", ...}

(though should be case insensitive)

[vincentsarago]

Alright @kylebarron,

You could have an enum of available optional headers.

I don't see how this will be easy to do. basically right now we have "Server-Timing" for basic tilers and "Server-Timing", "X-Assets" for Mosaic tilers. First I'm not sure how to implement this using enums and second we will need two different enums (one only with "Server-Timing" and another with "Server-Timing" and "X-Assets").

I wanted to use attrs so we could have used the attribute validation but attrs makes things a bit more complex (#234)

I don't really want to spend more time on it but feel free to propose your own PR 🙏

Note:
for now I've went the way of 2 different attributes:

• add_timing_headers
• add_assets_headers

[kylebarron]

Not every factory needs to implement all the available optional headers... You can have a single enum listing the optional headers available, and just note in the docs (or maybe give a warning at runtime) if a non-mosaic tiler attempts to use the X-Assets header.

[vincentsarago]

You can have a single enum listing the optional headers available, and just note in the docs (or maybe give a warning at runtime) if a non-mosaic tiler attempts to use the X-Assets header.

seems like more code to me! but also no idea how enum will work for this case when we have multiple values provided as input

[kylebarron]

Well the enum part isn't important... All I was suggesting is something like this, instead of making a separate parameter for every optional header like add_timing_headers, add_assets_headers, ...

tilerfactory(
	...,
	optional_headers=['Server-Timing', 'X-Assets'])

from . import OptionalHeaders
tilerfactory(
	...,
	optional_headers=[OptionalHeaders.Server_Timing, OptionalHeaders.X_Assets])

[vincentsarago]

Alright it took me some time but I think I understand what you proposed! can you check the last commit and 👍 👎 @kylebarron