Global middleware

[teamon]

Super useful, especially when using existing libraries like elixir-google-api

# global for all tesla-based clients
config :tesla, middleware: [MySuperMetrics]

# for specific client
config :tesla, GoogleApi.Datastore.V1.Connection, middleware: [MySuperMetrics]

# inserting middleware before/after stack
config :tesla, middleware: [
  pre: [ModuleA], 
  post: [ModuleB]
]

[teamon]

There is a decision to be made: should config middleware be checked at compile or run time?

• compile time: no runtime overhead but requires recompilation of client module (i.e, change tesla config and mix deps.compile --force google-elixir-api)
• runtime: config read on every request but does not require recompilation and can be modified on a live system

[chulkilee]

If the client module has a list of middleware (inside module or using build_client) - then at which position this "global" middleware put in?

[teamon]

This is a good question to which I'm not sure about the answer yet.
Right now it is:

stack = client.pre ++ module.__middleware__ ++ client.post ++ adapter

(see https://github.com/teamon/tesla/blob/master/lib/tesla.ex#L118)

[teamon]

Adding custom middleware is possible with custom client, I no longer see much gain with global middleware.