JSON-RPC passthrough

Plugins may register their own JSON-RPC methods that are exposed through the JSON-RPC provided by lightningd. This provides users with a single interface to interact with, while allowing the addition of custom methods without having to modify the daemon itself.

JSON-RPC methods are registered as part of the getmanifest result. Each registered method must provide a name and a description. An optional long_description may also be
provided. This information is then added to the internal dispatch table, and used to return the help text when using lightning-cli help, and the methods can be called using the name.

For example, getmanifest result will register two methods, called hello and gettime:

  "rpcmethods": [
      "name": "hello",
      "usage": "[name]",
      "description": "Returns a personalized greeting for {greeting} (set via options)."
      "name": "gettime",
      "description": "Returns the current time in {timezone}",
      "usage": "",
      "long_description": "Returns the current time in the timezone that is given as the only parameter.\nThis description may be quite long and is allowed to span multiple lines."

The RPC call will be passed through unmodified, with the exception of the JSON-RPC call id, which is internally remapped to a unique integer instead, in order to avoid collisions. When passing the result back the id field is restored to its original value.

Note that if your result for an RPC call includes "format-hint": "simple", then lightning-cli will default to printing your output in "human-readable" flat form.