Mixed image formats doesn't work with s3/local directories tiles cache

[AnguIar]

Context

Mapproxy has the ability to use mixed image formats (https://mapproxy.org/docs/nightly/configuration.html#format).
It works fine when the tiles stored in a geopackage file, but doesn't work when using s3/local directory hierarchy.

Expected Behavior

Tiles should be rendered to the client.

Actual Behavior

Nothing is rendered. All tiles are empty.

Possible Fix

S3:
When making a request (as shown here) the file's extension is .mixed. Since the original file extension isn't known, we need to consider checking for the correct extension and use it.
Worst case scenario is making two requests per tile in order to find out the extension.

FS:
It's the same for FS - this line.

Steps to Reproduce

Create a directory with mixed tiles in it, upload to it S3 / use it locally and try to configure Mapproxy to use it.

Your Environment

• Version used: 1.15.1.post20221002
• Environment name and version: Pyhon 3.8
• Operating System and version: Ubuntu 20.04

[shimoncohen]

@weskamm @simonseyock Could you please reopen this issue? The PR was reverted.

[gu-LGB]

I had asked to revert the PR on this ticket. The background is that our services with the .mixed cache format only displayed white tiles. Here is my config - it may help to understand the problem: dop20.zip

I will also ask Mr Weskamm again to reopen this ticket.

[shimoncohen]

Thank you very much!
Does your cache contains all of the files with the .mixed extension? Because IMO the point of this PR is to use the correct extensions for each file e.g. jpeg and png (As breaking changes of course).

[gu-LGB]

Yes, I only have .mixed files:

[simonseyock]

We would prefer to maintain backwards compatibility. That means we would want to be able to read .mixed files, but only write .jpeg and .png files. If that is very difficult, we could discuss if there is an upgrade path to convert existing files. (Not all caches can be refetched).

[gu-LGB]

Both good ideas. We also have caches that cannot be refetched.

[shimoncohen]

I understand, I'll try to keep the fix backwards compatible for fetching the .mixed files.