Make templates pluggable

[francislavoie]

Context: https://caddy.community/t/including-files-scripts/15050/4

Right now, the templates module is inflexible in that only functions the functions registered by Caddy itself are available.

A good refactor would be to make it possible to pass an optional array of modules in the http.handlers.templates.functions.* namespace which get invoked at Provision() time to register additional functions.

[kroppt]

I am interested in working on this.

The TemplateContext is responsible for parsing and executing templates. It knows which functions are valid. It's a part of the http.handlers.templates module. That module then must get custom functions at Provision time for hand-off to that context.

Modules would be defined under http.handlers.templates.functions (e.g. http.handlers.templates.functions.bash) which allows for a definition of how to execute the function (e.g. call exec.Command with bash and the script filepath). Adding new function types can be done by adding a module under http.handlers.templates.functions.*, which can be added to a server as a Caddy plugin.

Is my understanding of the problem correct?

[francislavoie]

Yep, that's right!

I think you can use caddy.GetModules("http.handlers.templates.functions") to fetch a list of all the registered modules in that namespace, and if they conform to the right interface, you can load them in.

caddy/modules.go

Line 202 in af73215

func GetModules(scope string) []ModuleInfo {

That way, plugging in new functions would be zero-config, they would just added in if they're registered.

[mholt]

FYI for future searchers, this is probably being superseded by #5939.