new: added removeEventListener builtin function (closes #1139)

session/script_builtin_runtime.go

@@ -2,8 +2,10 @@ package session
 
 import (
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 	"os"
+	"sync"
 
 	"github.com/bettercap/bettercap/v2/js"
 	"github.com/evilsocket/islazy/fs"
@@ -14,6 +16,8 @@ import (
 // see https://github.com/robertkrimen/otto/issues/213
 var jsRuntime = otto.New()
 
+var jsListeners = sync.Map{}
+
 func jsRunFunc(call otto.FunctionCall) otto.Value {
 	argv := call.ArgumentList
 	argc := len(argv)
@@ -57,12 +61,25 @@ func jsOnEventFunc(call otto.FunctionCall) otto.Value {
 		cb = argv[1]
 	}
 
+	listenerKey := fmt.Sprintf("%s:%s", filterExpr, cb.String())
+
+	if _, found := jsListeners.Load(listenerKey); found {
+		return js.ReportError("listener already exists")
+	}
+
+	// add to listeners
+	closeChan := make(chan bool)
+	jsListeners.Store(listenerKey, closeChan)
+
 	// start a go routine for this event listener
-	go func(expr string, cb otto.Value) {
+	go func(expr string, cb otto.Value, closeChan chan bool) {
 		listener := I.Events.Listen()
 		defer I.Events.Unlisten(listener)
+		defer close(closeChan)
 
-		for event := range listener {
+		for {
+			select {
+			case event := <-listener:
 				if expr == "" || event.Tag == expr {
 					// some objects don't do well with js, so convert them to a generic map
 					// before passing them to the callback
@@ -89,8 +106,49 @@ func jsOnEventFunc(call otto.FunctionCall) otto.Value {
 						I.script.Unlock()
 					}
 				}
+
+			case <-closeChan:
+				return
+			}
+
+		}
+	}(filterExpr, cb, closeChan)
+
+	return js.NullValue
+}
+
+func jsRemoveEventListenerFunc(call otto.FunctionCall) otto.Value {
+	argv := call.ArgumentList
+	argc := len(argv)
+	cb := otto.NullValue()
+	filterExpr := ""
+
+	// just one argument, a function to receive all events
+	if argc == 1 {
+		if argv[0].IsFunction() == false {
+			return js.ReportError("the single argument must be a function")
+		}
+		cb = argv[0]
+	} else {
+		if argc != 2 {
+			return js.ReportError("expected two arguments (event_name, callback), got %d", argc)
+		} else if argv[0].IsString() == false {
+			return js.ReportError("first argument must be a string")
+		} else if argv[1].IsFunction() == false {
+			return js.ReportError("second argument must be a function")
+		}
+
+		filterExpr = argv[0].String()
+		cb = argv[1]
+	}
+
+	listenerKey := fmt.Sprintf("%s:%s", filterExpr, cb.String())
+	if closer, found := jsListeners.Load(listenerKey); found {
+		closer.(chan bool) <- true
+		jsListeners.Delete(listenerKey)
+	} else {
+		return js.ReportError("listener not found")
 	}
-	}(filterExpr, cb)
 
 	return js.NullValue
 }

session/session.go

@@ -330,6 +330,7 @@ func (s *Session) Start() error {
 	plugin.Defines["saveJSON"] = jsSaveJSONFunc
 	plugin.Defines["saveToFile"] = jsSaveToFileFunc
 	plugin.Defines["onEvent"] = jsOnEventFunc
+	plugin.Defines["removeEventListener"] = jsRemoveEventListenerFunc
 	plugin.Defines["session"] = s
 
 	// load the script here so the session and its internal objects are ready