MXS-1390: Add missing self-link to module command output

The module commands now produce functional self-links. The links most
often require parameters so they are not of great use.

include/maxscale/json_api.h

@@ -39,16 +39,30 @@ MXS_BEGIN_DECLS
 /**
  * @brief Create a JSON object
  *
- * The caller should add a `data` field to the returned object.
- *
  * @param host Hostname of this server
  * @param self Endpoint of this resource
- * @param data The JSON data, either an array or an object
+ * @param data The JSON data, either an array or an object, stored in
+ *             the `data` field of the returned object
  *
  * @return A valid top-level JSON API object
  */
 json_t* mxs_json_resource(const char* host, const char* self, json_t* data);
 
+
+/**
+ * @brief Create a JSON metadata object
+ *
+ * This should be used to transport non-standard data to the client.
+ *
+ * @param host Hostname of this server
+ * @param self Endpoint of this resource
+ * @param data The JSON data, either an array or an object, stored in
+ *             the `meta` field of the returned object
+ *
+ * @return A valid top-level JSON API object
+ */
+json_t* mxs_json_metadata(const char* host, const char* self, json_t* data);
+
 /**
  * @brief Create an empty relationship object
  *

server/core/json_api.cc

@@ -39,6 +39,14 @@ json_t* mxs_json_resource(const char* host, const char* self, json_t* data)
     return rval;
 }
 
+json_t* mxs_json_metadata(const char* host, const char* self, json_t* data)
+{
+    json_t* rval = json_object();
+    json_object_set_new(rval, CN_LINKS, self_link(host, self));
+    json_object_set_new(rval, CN_META, data);
+    return rval;
+}
+
 json_t* mxs_json_relationship(const char* host, const char* endpoint)
 {
     json_t* rel = json_object();

server/core/resource.cc

@@ -667,14 +667,15 @@ HttpResponse cb_modulecmd(const HttpRequest& request)
             {
                 if (output)
                 {
-                    rc = MHD_HTTP_OK;
+                    /**
-
+                     * Store the command output in the meta field. This allows
-                    /** Store the command output in the meta field. This allows
                      * all the commands to conform to the JSON API even though
-                     * the content of the field can vary from command to command. */
+                     * the content of the field can vary from command to command.
-                    json_t* obj = json_object();
+                     */
-                    json_object_set_new(obj, CN_META, output);
+                    rc = MHD_HTTP_OK;
-                    output = obj;
+                    std::string self = "/"; // The uri_segment doesn't have the leading slash
+                    self += request.uri_segment(0, request.uri_part_count());
+                    output = mxs_json_metadata(request.host(), self.c_str(), output);
                 }
                 else
                 {