MXS-1220: Implement /sessions/ resource

The /sessions/ resource was not implemented due to changes in the core
polling mechanics. With the new worker thread messaging system, sessions
can be listed in a safe manner.

include/maxscale/session.h

@@ -423,4 +423,13 @@ void session_clear_stmt(MXS_SESSION *session);
  */
 json_t* session_to_json(const MXS_SESSION *session, const char* host);
 
+/**
+ * @brief Convert all sessions to JSON
+ *
+ * @param host Hostname of this server
+ *
+ * @return A JSON array with all sessions
+ */
+json_t* session_list_to_json(const char* host);
+
 MXS_END_DECLS

server/core/resource.cc

@@ -228,8 +228,7 @@ HttpResponse cb_get_monitor(const HttpRequest& request)
 
 HttpResponse cb_all_sessions(const HttpRequest& request)
 {
-    // TODO: Implement this
+    return HttpResponse(MHD_HTTP_OK, session_list_to_json(request.host()));
-    return HttpResponse(MHD_HTTP_OK);
 }
 
 HttpResponse cb_get_session(const HttpRequest& request)

server/core/session.cc

@@ -1059,3 +1059,23 @@ json_t* session_to_json(const MXS_SESSION *session, const char *host)
 
     return rval;
 }
+
+struct SessionListData
+{
+    json_t* json;
+    const char* host;
+};
+
+bool seslist_cb(DCB* dcb, void* data)
+{
+    SessionListData* d = (SessionListData*)data;
+    json_array_append_new(d->json, session_to_json(dcb->session, d->host));
+    return true;
+}
+
+json_t* session_list_to_json(const char* host)
+{
+    SessionListData data = {json_array(), host};
+    dcb_foreach(seslist_cb, &data);
+    return data.json;
+}