Bugfix 3871 workflow concurrency (#3903)

* recursion waitgroup fix

* cleanup

v2/cmd/nuclei/test.yaml

@@ -1,18 +0,0 @@
-id: basic-example
-
-info:
-  name: Test HTTP Template
-  author: pdteam
-  severity: info
-
-http:
-  - raw:
-      - |+
-        GET / HTTP/1.1
-        Host: {{Hostname}}
-
-    unsafe: true
-    matchers:
-      - type: dsl
-        dsl:
-          - true

v2/pkg/core/workflow_execute.go

@@ -25,14 +25,23 @@ func (e *Engine) executeWorkflow(input *contextargs.MetaInput, w *workflows.Work
 	ctxArgs.MetaInput = input
 	ctxArgs.CookieJar = workflowCookieJar
 
-	swg := sizedwaitgroup.New(w.Options.Options.TemplateThreads)
+	// we can know the nesting level only at runtime, so the best we can do here is increase template threads by one unit in case it's equal to 1 to allow
+	// at least one subtemplate to go through, which it's idempotent to one in-flight template as the parent one is in an idle state
+	templateThreads := w.Options.Options.TemplateThreads
+	if templateThreads == 1 {
+		templateThreads++
+	}
+	swg := sizedwaitgroup.New(templateThreads)
+
 	for _, template := range w.Workflows {
 		swg.Add()
+
 		func(template *workflows.WorkflowTemplate) {
+			defer swg.Done()
+
 			if err := e.runWorkflowStep(template, ctxArgs, results, &swg, w); err != nil {
 				gologger.Warning().Msgf(workflowStepExecutionError, template.Template, err)
 			}
-			swg.Done()
 		}(template)
 	}
 	swg.Wait()
@@ -126,10 +135,11 @@ func (e *Engine) runWorkflowStep(template *workflows.WorkflowTemplate, input *co
 						swg.Add()
 
 						go func(subtemplate *workflows.WorkflowTemplate) {
+							defer swg.Done()
+
 							if err := e.runWorkflowStep(subtemplate, input, results, swg, w); err != nil {
 								gologger.Warning().Msgf(workflowStepExecutionError, subtemplate.Template, err)
 							}
-							swg.Done()
 						}(subtemplate)
 					}
 				}

v2/pkg/templates/compile.go

@@ -42,7 +42,6 @@ func Parse(filePath string, preprocessor Preprocessor, options protocols.Executo
 
 	var reader io.ReadCloser
 	if utils.IsURL(filePath) {
-		//todo:instead of creating a new client each time, a default one should be reused (same as the standard library)
 		// use retryablehttp (tls verification is enabled by default in the standard library)
 		resp, err := retryablehttp.DefaultClient().Get(filePath)
 		if err != nil {