Handle ambiguous sticker names and values

[h7x4]

There is an edgecase for stickers with names and values containing =, making the server output hard to parse.

$ nc localhost 6600
OK MPD 0.24.0
sticker set playlist TestPlaylist "test=1" "value=2"
OK
sticker list playlist TestPlaylist
sticker: test=1=value=2
OK

First solution that comes to mind would be to wrap the name and value in quotes, but then you could maybe put "=" inside your string or something (I guess we could escape quotes as well?). Not sure what the best solution is here. Newlines maybe?

I feel like this is in the grey area of being a bug, considering it's up to the client developer to choose sensible tag names. But one client might interfere with another, so maybe it should be considered so.

[geneticdrift]

Adding for reference:
The issue of escaping = in sticker names was raised in the PR and was left out eventually.

This is the relevant part of a longer comment:

"escape sticker name" - I'm not happy with this one. The escaping syntax for sticker names is not documented, and I'd rather restrict the allowed sticker names than adding some escaping rules. I mean, why would anybody really need = in a sticker name? Not restricting sticker names might have been an oversight in the initial design.

Agree. Not a significant issue.

[jcorporation]

I have already some pull requests for improved sticker handling open. After they are merged, I could look into this. I think restricting the sticker names is the best approach. Should we only disallow = or should we allow only [a-zA-Z0-9] and some special charakters like .-_?

[geneticdrift]

restricting the sticker names is the best approach

Could be a backward compatibility problem if sticker names that are already in the database become invalid.

So maybe just documenting the restrictions and not enforcing them?

From the docs:

Client developers should create a standard for common sticker names, to ensure interoperability.

This never happened as far as I know, so clients may only be concerned with their own sticker names.

New restrictions can then be applied only to MPD officially standardized sticker names if and when that happens.

[jcorporation]

I had tried to create a standard: https://github.com/jcorporation/mpd-stickers

At the moment it is only a collection of used sticker namens.

As MPD has now a feature to enable specific protocol features, it can be implemented as opt-in for new clients.

#2123