In this blog, I will discuss how the DownloadDataSettings servlet hosted on SUSI server functions. This post also covers a step by step demonstration on how to use this feature if you have hosted your own custom SUSI server and have admin rights to it. Given below is the endpoint where the request to download a particular file has to be made.
For systematic functionality and workflow, Users with admin login, are given a special access. This allows them to download the settings files and go through them easily when needed. There are various files which have email ids of registered users (accounting.json), user roles associated to them (authorization.json), groups they are a part of (groups.json) etc. To list all the files in the folder, use the given below end point:
How does the above servlet works? Prior to that, let us see how to to get admin rights on your custom SUSI.AI server.
For admin login, it is required that you have access to files and folders on server. Signup with an account and browse to
Find the email id with which you signed up for admin login and change userRole to “admin”. For example,
If you have signed up with an email id “firstname.lastname@example.org” and want to give admin access to it, modify the userRole to “admin”. See below.
Till now, server did not have any email id with admin login or user role equal to admin. Hence, this exercise is required only for the first admin. Later admins can use changeUserRole application and give/change/modify user roles for any of the users registered. By now you must have admin login session. Let’s see now how the download and file listing servlets work.
First, the server creates a path by locally referencing settings folder with the help of DAO.data_dir.getPath(). This will give a string path to the data directory containing all the data-settings files. Now the server just has to make a JSONArray and has to pass a String array to JSONArray’s constructor, which will eventually be containing the name of all the data/settings files. If the process is not successfull ,then, “accepted” = false will be sent as an error to the user. The base user role to access the servlet is ADMIN as only admins are allowed to download data/setting files,
The file name which you have to download has to be sent in a HTTP request as a get parameter. For example, if an admin has to download accounting.json to get the list of all the registered users, the request is to be made in the following way:
*BASE_URL is the URL where the server is hosted. For standard server, use BASE_URL = http://api.susi.ai.
In the initial steps, Server generates a path to data/settings folder and finds the file, name of which it receives in the request. If no filename is specified in the API call, by default, the server sends accounting.json file.
File settings = new File(DAO.data_dir.getPath()+"/settings");
String filePath = settings.getPath();
String fileName = post.get("file","accounting");
filePath += "/"+fileName+".json";
Next, the server will extract the file and using ServletOutputStream class, it will generate properties for it and set appropriate context for it. This context will, in turn, fetch the mime type for the file generated. If the mime type is returned as null, by default, mime type for the file will be set to application/octet-stream. For more information on mime type, please look at the following link. A complete list of mime types is compiled and documented here.
In the above code snippet, mime type and length of the file being downloaded is set. Next, we set the headers for the download response and use filename for that.
response.setHeader("Content-Disposition", "attachment; filename=" + fileName +".json");
All the manual work is done by now. The only thing left is to open a buffer stream, size of which has been defined as a class variable.
Here we use a byte array of size 4096 elements and write the file to client’s default download storage.
private static final int BUFSIZE = 4096;
byte byteBuffer = new byte[BUFSIZE];
DataInputStream in = new DataInputStream(new FileInputStream(file));
while ((in != null) && ((length = in.read(byteBuffer)) != -1))
All the above-mentioned steps are enclosed in a try-catch block, which catches an exception if any ,and logs it in the log file. This message is also sent to the client for appropriate user information along with the success or failure indication through a boolean flag. Do not forget to close the input and output buffers as it may lead to memory leaks and someone with proper knowledge of network and buffer stream would be able to steal any essential or secured data.