[pangea] dynamic call module

[florianlenz]

Feature / Issue

Pangea needs a lot of custom calls to fetch initial state from panthalassa. For example:

• identity public key
• chat messages
• and much more (specially in the future)

Writing a method for fetching all of those data is very time consuming since we have to build bridges for ios and android. A dynamic "call" module would fix that problem. The dynamic call module will take a call id (e.g. MESSAGES) as the first parameter and an map of values as the second parameter (e.g. {chat: "partner-id-pub-key", amount: 50}). The call will then be validated by the module and fetch the messages based on the parameters. A call module should always return an map of values. There should be a call module interface and a call module registry, the registry would basically take care of finding the right module for a call id.

This is how the call module might look like:

type CallModule interface {
   // the call id this module relates to 
   CallID() string
   // validate the given parameters - might return an error when received invalid parameters
   Validate(map[string]interface{}) error
   // will handle the call and return the result
   Handle(map[string]interface{}) (map[string]interface{}, error)
}

This is how the call module registry might look like:

type CallModuleReg interface {
   Call(callID, map[string]interface{}) (map[string]interface{}, error)
}

You are free to come up with other ideas / solutions. Please just post them here in the GH issue.

Acceptance criteria

• [x] tests
• [x] documentation on how to use it in the code
• [x] call module interface and registry is done

[florianlenz]

Will be done at tuesday @kevowevo