Requests for comment/Json Config pages in wiki

Many extension require fairly complex configurations. So far I know that two teams - Zero and Logging - very successfully used the approach of storing JSON blobs as wikitext on Meta, e.g. m:Zero:250-99 and m:Schema:Echo. Both have developed custom code to edit, validate, store, and visualize that data, yet they both share lots of common code (Zero code was actually based on event logging code, but they have since diverged).

I propose for the common aspects of that code to be extracted into a separate extension JsonConfig, designed in a way to be useful not just to Zero & logging, but to allow a very easy way for any extension to store its own configuration.

Implemented Features
These features have already been implemented in Zero and/or logging, and might be useful for other extensions:
 * Visualization shows JSON as an easy to view table rather than code, with some extra highlighting. For example if the value is not provided and a default is used, it is shown in gray, or when the value is the same as default, it shows as purple. For example, see this and this.
 * Code Editor simplifies JSON editing
 * Custom Validation performs complex checks such as checking that the value is in the proper format or that a user ID exists.
 * MemCached caching stores json blobs in memcached under custom keys and expiration policies, and resets them on save.
 * Custom API allows all mobile zero users to load the appropriate slimmed-down configuration based on request's header, or netmapper to wget the list of all IPs configured as part of the Zero configurations.
 * Localization of most basic interface elements has been done in many languages, and it would reduce translation work if most common messages would be done just once in one place.

Unimplemented Nice-To-Haves
These features would be desirable to more than one type of configs:
 * Validate against JSON Schema - most extensions might not need complex validation rules, or might want to combine schema plus extra validation.
 * Custom editor - Zero team has been thinking about implementing a more complex editor, possibly based on JSON Schema.

General Usage
Lets say we decide to store the IPs of all legitimate proxies, whose X-Forwarded-For header can be trusted.

In this case Opera-Mini server info would be stored as Config:Proxy:Opera page:

Implementation details
JsonConfig is implemented as two parts - storage/parsing and editing/visualizing. The editor/visualizer is only available when JsonConfig runs on meta wiki, and allows complex presentation of the Config namespace wiki pages. The storage/parsing is available on all wikis, allowing quick access to cache as well as validation and parsing of the cached json blob.