webservices: fix REST web services for cm

Bug 1631810: Web services fixes

* fix json_decode() invalid param warnings
* dont pass functionaname if it's empty

behatnotneeded

Change-Id: I83acba2795fa901613b985a5b82586281b1e5f3c

htdocs/webservice/rest/lib.php

@@ -184,7 +184,7 @@ class webservice_rest_client {
             }
 
             // default to parsing HTTP parameters
-            $this->serverurl = $this->serverurl. '?'.$this->auth . '&wsfunction='. $functionname;
+            $this->serverurl = $this->serverurl . '?' . $this->auth . ($functionname ? '&wsfunction=' . $functionname : '');
             $result = webservice_download_file_content($this->serverurl, $this->headers, $params,
                                                          false, 300, 20, get_config('disablesslchecks'), null, false, true);
             log_debug("REST client response: ".var_export($result, true));

htdocs/webservice/rest/locallib.php

@@ -164,8 +164,12 @@ class webservice_rest_server extends webservice_base_server {
             // in oauth, structures are flattened using json
             if ($oauth_token) {
                 foreach ($this->parameters as $key => $value) {
-                    if (json_decode($value, true) !== NULL) {
-                        $this->parameters[$key] = json_decode($value, true);
+                    if (!is_string($value)) {
+                        continue;
+                    }
+                    $decoded = json_decode($value, true);
+                    if (json_last_error() === JSON_ERROR_NONE) {
+                        $this->parameters[$key] = $decoded;
                     }
                 }
             }