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)
@@ -57,40 +61,94 @@ 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 {
-			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
-				var opaque interface{}
-				if raw, err := json.Marshal(event); err != nil {
-					I.Events.Log(log.ERROR, "error serializing event %s: %v", event.Tag, err)
-				} else if err = json.Unmarshal(raw, &opaque); err != nil {
-					I.Events.Log(log.ERROR, "error serializing event %s: %v", event.Tag, err)
+		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
+					var opaque interface{}
+					if raw, err := json.Marshal(event); err != nil {
+						I.Events.Log(log.ERROR, "error serializing event %s: %v", event.Tag, err)
+					} else if err = json.Unmarshal(raw, &opaque); err != nil {
+						I.Events.Log(log.ERROR, "error serializing event %s: %v", event.Tag, err)
+					}
+
+					// lock vm if ready and available
+					locked := false
+					if I.script != nil {
+						I.script.Lock()
+						locked = true
+					}
+
+					if _, err := cb.Call(otto.NullValue(), opaque); err != nil {
+						I.Events.Log(log.ERROR, "error dispatching event %s: %v", event.Tag, err)
+					}
+
+					// unlock vm if ready and available
+					if locked {
+						I.script.Unlock()
+					}
 				}
 
-				// lock vm if ready and available
-				locked := false
-				if I.script != nil {
-					I.script.Lock()
-					locked = true
-				}
-
-				if _, err := cb.Call(otto.NullValue(), opaque); err != nil {
-					I.Events.Log(log.ERROR, "error dispatching event %s: %v", event.Tag, err)
-				}
-
-				// unlock vm if ready and available
-				if locked {
-					I.script.Unlock()
-				}
+			case <-closeChan:
+				return
 			}
+
 		}
-	}(filterExpr, cb)
+	}(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")
+	}
 
 	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