Fix invalid assumption in code that multipart forms can be parsed in the same way as urlencoded forms.

Refactored code to use switch-case statement over the `Content-Type` header and log unsupported content types instead of silently failing.
Also made the `x-www-form-urlencoded` content type handler more specific (as opposed to the previous code which looked for `form` occurence in the value),
as we need to use different logic for multipart forms, which we'll hopefully implement soon.

The issue with multipart forms that we have to handle first is that the files are being written to temporary files, and as such, for async hooks
webhook cannot guarantee they'll be available after we close the request; that, and the fact that we don't have code that will properly serialize
and pass such Golang objects to the script, as there are several fields which might be interesting to the end user.

webhook.go

@@ -240,7 +240,8 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 			contentType = matchedHook.IncomingPayloadContentType
 		}
 
-		if strings.Contains(contentType, "json") {
+		switch {
+		case strings.Contains(contentType, "json"):
 			decoder := json.NewDecoder(strings.NewReader(string(body)))
 			decoder.UseNumber()
 
@@ -249,13 +250,15 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 			if err != nil {
 				log.Printf("[%s] error parsing JSON payload %+v\n", rid, err)
 			}
-		} else if strings.Contains(contentType, "form") {
+		case strings.Contains(contentType, "x-www-form-urlencoded"):
 			fd, err := url.ParseQuery(string(body))
 			if err != nil {
 				log.Printf("[%s] error parsing form payload %+v\n", rid, err)
 			} else {
 				payload = valuesToMap(fd)
 			}
+		default:
+			log.Printf("[%s] error parsing body payload due to unsupported content type header: %s\n", rid, contentType)
 		}
 
 		// handle hook
@@ -272,7 +275,7 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 			ok, err = matchedHook.TriggerRule.Evaluate(&headers, &query, &payload, &body, r.RemoteAddr)
 			if err != nil {
 				msg := fmt.Sprintf("[%s] error evaluating hook: %s", rid, err)
-				log.Print(msg)
+				log.Println(msg)
 				w.WriteHeader(http.StatusInternalServerError)
 				fmt.Fprint(w, "Error occurred while evaluating hook rules.")
 				return