I'm currently developing a backend server which is based on the Phoenix framework. However, I don't understand one thing: I can define specific routes which are called whenever I use a certain HTTP verb to access said route. Since I couldn't perform any pre-flight request, I also added a OPTIONS route for each file which leads to the following scope block inside my router.ex file:
post "/someroute", SomeController, :some_handler
options "/someroute, SomeController, :options
All of this code is inside the router.ex file which is contained in the lib/_web folder and defines the routes of the backend as well as their respective handlers by using a DSL. While I know that some_handler is a function which is contained in some controller, I unfortunately have no idea where the function :options (or its atom) is defined. Does anyone have an idea where I can find something like the implementation of :options?
In this case, options is a macro (just like get or post). Macros have the benefit of allowing you to write out DSL's in a more readable way, but the drawback is that they are far more opaque than normal functional code because they generate the code. Look inside deps/phoenix/lib/phoenix/router.ex and you'll see that this isn't even a simple macro, it's looped:
for verb <- @http_methods do
@doc """
Generates a route to handle a #{verb} request to the given path.
#{verb}("/events/:id", EventController, :action)
See `match/5` for options.
"""
defmacro unquote(verb)(path, plug, plug_opts, options \\ []) do
add_route(:match, unquote(verb), path, plug, plug_opts, options)
end
end