wsrpc/clientctx.go

// Client handler
package wsrpc

import (
	"context"
	"errors"
	"log"
	"reflect"
	"strings"
	"sync"

	"github.com/google/uuid"
	"golang.org/x/net/websocket"
)

// Vars
var (
	ErrNParam            = errors.New("Invalid number of parameters")
	ErrNReturn           = errors.New("Number of outputs mismatch")
	ErrBadImplementation = errors.New("Bad implementation")

	errorInterface = reflect.TypeOf((*error)(nil)).Elem()
)

// CallObj object
// Message
type CallObj struct {
	OP     string `json:"op"`     // operation
	ID     string `json:"id"`     // Id of the call
	Method string `json:"method"` // could be param 0 instead?

	// Payload
	Params   []interface{} `json:"params"`
	Response interface{}   `json:"response"`
	Error    string        `json:"error,omitempty"`
}

// DataObj common structure for dymanic json object
//type DataObj map[string]interface{}

// ListenerFunc function type to handle browser events
type ListenerFunc func(...interface{}) (interface{}, error)

// Request request type for handling requests channels

// ClientCtx main client struct
type ClientCtx struct {
	context.Context
	Close func()

	locker sync.Mutex
	WS     *websocket.Conn
	// stuff
	listeners map[string]ListenerFunc
	requests  map[string]chan CallObj
	message   chan CallObj
}

// NewClient new client (should have background context here)
func NewClient(ws *websocket.Conn) *ClientCtx {
	ctx, cancelFunc := context.WithCancel(context.Background())
	return &ClientCtx{
		Context:   ctx,
		Close:     cancelFunc,
		WS:        ws,
		listeners: map[string]ListenerFunc{},
		requests:  map[string]chan CallObj{},
	}

}

// Process received messages
func (c *ClientCtx) Process() {
	for {
		select {
		case <-c.Done():
			return // Break loop
		default:
		}
		var data = CallObj{}
		err := websocket.JSON.Receive(c.WS, &data)
		if err != nil { // Close receive
			c.Close()
			return
		}

		switch data.OP {
		case "call":
			params := data.Params
			var idn = data.Method
			var reqID = data.ID
			var fn, ok = c.listeners[idn]
			if !ok {
				websocket.JSON.Send(c.WS, CallObj{
					OP:    "response",
					ID:    reqID,
					Error: "Method not found",
				})
				break
			}
			go func() { // async send
				errStr := ""
				ret, err := fn(params...)
				if err != nil {
					errStr = err.Error()
				}
				var responseObj = CallObj{
					OP:       "response",
					ID:       reqID,
					Response: ret,
					Error:    errStr,
				}
				websocket.JSON.Send(c.WS, responseObj)
			}()
		case "response":
			c.locker.Lock()
			mchan, ok := c.requests[data.ID]
			delete(c.requests, data.ID)
			c.locker.Unlock()
			if ok {
				mchan <- data
			}
		}
	}
}

// Call a client method and estabilishes a request id
func (c *ClientCtx) Call(method string, params ...interface{}) (interface{}, error) {
	u := uuid.New()
	uuidStr := u.String()

	var callObj = CallObj{
		OP:     "call",
		ID:     uuidStr,
		Method: method,
		Params: params,
	}

	resCh := make(chan CallObj, 1)
	// Store the channel
	c.locker.Lock()
	c.requests[uuidStr] = resCh
	c.locker.Unlock()

	// IO send
	// Send to dispatcher instead?
	websocket.JSON.Send(c.WS, &callObj)

	// Hang until response
	res := <-resCh // Wait for response

	// Got Response
	var err error
	if res.Error != "" {
		err = errors.New(res.Error)
	}
	return res.Response, err
}

//Define export a method to ws client
func (c *ClientCtx) Define(name string, listener ListenerFunc) {
	c.listeners[name] = listener
}

//Export a struct of funcs
func (c *ClientCtx) Export(obj interface{}) {
	// Reflect here
	typ := reflect.TypeOf(obj)
	val := reflect.ValueOf(obj)

	for i := 0; i < typ.NumField(); i++ {
		fTyp := typ.Field(i)
		if fTyp.Type.Kind() != reflect.Func {
			log.Println("Ignore non func value")
			continue
		}
		tag, ok := fTyp.Tag.Lookup("wsexport")
		if !ok {
			continue
		}
		tagParts := strings.Split(tag, ",")

		exportName := tagParts[0]
		fnVal := val.Field(i)
		// Slow?
		c.listeners[exportName] = func(params ...interface{}) (interface{}, error) {
			if len(params) != fnVal.Type().NumIn() {
				return nil, ErrNParam
			}
			if fnVal.Type().NumOut() != 2 {
				return nil, ErrNReturn
			}
			if !fnVal.Type().Out(1).Implements(errorInterface) {
				return nil, ErrBadImplementation

			}

			vparam := []reflect.Value{}
			for _, p := range params {
				vparam = append(vparam, reflect.ValueOf(p))
			}
			r := fnVal.Call(vparam)
			return r[0].Interface(), r[1].Interface().(error)
		}

		// It is a func, check for tag
	}

}