max-concurrency hook property support

hook/hook.go

@@ -381,6 +381,7 @@ type Hook struct {
 	PassEnvironmentToCommand            []Argument      `json:"pass-environment-to-command,omitempty"`
 	PassArgumentsToCommand              []Argument      `json:"pass-arguments-to-command,omitempty"`
 	JSONStringParameters                []Argument      `json:"parse-parameters-as-json,omitempty"`
+	MaxConcurrency                      int             `json:"max-concurrency,omiempty"`
 	TriggerRule                         *Rules          `json:"trigger-rule,omitempty"`
 	TriggerRuleMismatchHttpResponseCode int             `json:"trigger-rule-mismatch-http-response-code,omitempty"`
 }

webhook.go

@@ -43,6 +43,8 @@ var (
 
 	watcher *fsnotify.Watcher
 	signals chan os.Signal
+
+	limits = make(map[string]chan struct{})
 )
 
 func matchLoadedHook(id string) *hook.Hook {
@@ -108,7 +110,15 @@ func main() {
 				if matchLoadedHook(hook.ID) != nil {
 					log.Fatalf("error: hook with the id %s has already been loaded!\nplease check your hooks file for duplicate hooks ids!\n", hook.ID)
 				}
-				log.Printf("\tloaded: %s\n", hook.ID)
+
+				msg := fmt.Sprintf("\tloaded: %s", hook.ID)
+
+				// initialize concurrency map
+				if hook.MaxConcurrency > 0 {
+					limits[hook.ID] = make(chan struct{}, hook.MaxConcurrency)
+					msg = fmt.Sprintf("%s (max: %d)", msg, hook.MaxConcurrency)
+				}
+				log.Println(msg)
 			}
 
 			loadedHooksFromFiles[hooksFilePath] = newHooks
@@ -208,6 +218,18 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 	if matchedHook := matchLoadedHook(id); matchedHook != nil {
 		log.Printf("%s got matched\n", id)
 
+		// check if we have concurrency limits
+		if _, ok := limits[id]; ok {
+			if len(limits[id]) == cap(limits[id]) {
+				log.Printf("reached concurrency limit for: %s (max=%d)", id, len(limits[id]))
+				w.WriteHeader(http.StatusTooManyRequests)
+				fmt.Fprintf(w, "Error occurred while evaluating hook rules.")
+				return
+			}
+			defer func() { <-limits[id] }()
+			limits[id] <- struct{}{}
+		}
+
 		body, err := ioutil.ReadAll(r.Body)
 		if err != nil {
 			log.Printf("error reading the request body. %+v\n", err)