json_emitter.go

/*
Copyright (c) 2017 Ashley Jeffs

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, sub to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package io

import (
	"encoding/json"

	"github.com/Jeffail/leaps/lib/api"
	"github.com/Jeffail/leaps/lib/api/events"
)

//------------------------------------------------------------------------------

// ReadWriteJSONCloser - An interface for writing and reading JSON content.
type ReadWriteJSONCloser interface {
	ReadJSON(v interface{}) error
	WriteJSON(v interface{}) error
	Close() error
}

//------------------------------------------------------------------------------

// JSONEmitter - Instantiated for each incoming connection, which implements the
// ReadWriteJSONCloser interface. JSONEmitter implements the leaps API by
// allowing components to register their own request and event handlers. All
// incoming messages are expected to be of the JSON format:
//
//   {
//     "type": "<type_string>",
//     "body": {...}
//   }
//
// Handlers for request types are given the unparsed JSON body of the request.
type JSONEmitter struct {
	requestHandlers  map[string][]api.RequestHandler
	responseHandlers map[string][]api.ResponseHandler
	closeHandlers    []api.EventHandler

	rw ReadWriteJSONCloser
}

// NewJSONEmitter - Constructs a new JSONEmitter around a ReadWriteJSONCloser.
func NewJSONEmitter(rw ReadWriteJSONCloser) *JSONEmitter {
	return &JSONEmitter{
		requestHandlers:  make(map[string][]api.RequestHandler),
		responseHandlers: make(map[string][]api.ResponseHandler),
		rw:               rw,
	}
}

// OnReceive - Register a handler for a particular incoming event type.
func (w *JSONEmitter) OnReceive(reqType string, reqHandler api.RequestHandler) {
	w.requestHandlers[reqType] = append(w.requestHandlers[reqType], reqHandler)
}

// OnSend - Register a handler for a particular outgoing event type.
func (w *JSONEmitter) OnSend(resType string, resHandler api.ResponseHandler) {
	w.responseHandlers[resType] = append(w.responseHandlers[resType], resHandler)
}

// OnClose - Register an event handler for a close event.
func (w *JSONEmitter) OnClose(eventHandler api.EventHandler) {
	w.closeHandlers = append(w.closeHandlers, eventHandler)
}

// Close - Close the underlying network connection.
func (w *JSONEmitter) Close() error {
	return w.rw.Close()
}

// Send - Send data to the connected client.
func (w *JSONEmitter) Send(resType string, data interface{}) error {
	if handlers, ok := w.responseHandlers[resType]; ok {
		for _, h := range handlers {
			if !h(data) {
				return nil
			}
		}
	}
	return w.rw.WriteJSON(struct {
		Type string      `json:"type"`
		Body interface{} `json:"body"`
	}{
		Type: resType,
		Body: data,
	})
}

// ListenAndEmit - Begins reading to the underlying io.ReadWriteJSONCloser and
// emitting events accordingly.
func (w *JSONEmitter) ListenAndEmit() {
	defer func() {
		for _, h := range w.closeHandlers {
			h()
		}
	}()
	for {
		var req struct {
			Type string          `json:"type"`
			Body json.RawMessage `json:"body"`
		}
		if err := w.rw.ReadJSON(&req); err != nil {
			return
		}
		if handlers, ok := w.requestHandlers[req.Type]; ok {
			for _, h := range handlers {
				if err := h(req.Body); err != nil {
					w.Send("error", events.ErrorMessage{
						Error: events.APIError{T: err.Type(), Err: err.Error()},
					})
				}
			}
		} else {
			w.Send("error", events.ErrorMessage{
				Error: events.APIError{T: "command_err", Err: "command not recognised"},
			})
		}
	}
}

//------------------------------------------------------------------------------