SUSI Server needed to have an API where users can upload and store images. This images will be useful in setting custom theme for the botbuilder or for chat.susi.ai. User can upload image from their systems instead of pasting the link of an image stored in cloud. Also we need an API to retrieve the stored image given its full path. This blog explains how the SUSI Server returns the image stored upon requesting.

Understanding where the image is stored

The images uploaded to the SUSI Server is stored in its local storage. The local storage is where all the json files and other data are stored. We store the images inside “image_uploads” folder. In the get image API, the client will provide the full path of the image i.e the user UUID and the image’s full name. Then we need to fetch this image from the local storage and return it.

Retrieving the image from local storage

The Retrieving image API has the endpoint “/cms/getImage.png”. The servlet file is “GetImageServlet.java”. The client has to send the full path of the image in the parameter “image”. A sample GET request is “http://127.0.0.1:4000/cms/getImage.png?image=963e84467b92c0916b27d157b1d45328/1529692996805_susi icon.png”.

We need to retrieve the given image from the correct path.

Query post = RemoteAccess.evaluate(request);
String image_path = post.get("image","");
File imageFile = new File(DAO.data_dir  + File.separator + "image_uploads" + File.separator+ image_path);
if (!imageFile.exists()) {response.sendError(503, "image does not exist"); return;}
String file = image_path.substring(image_path.indexOf("/")+1);

Writing the image in Byte Stream

Now that we have the image file, we need to write that image in a Byte array output stream. We read the pixels data from the image using “FileInputStream” method.

ByteArrayOutputStream data = new ByteArrayOutputStream();
byte[] b = new byte[2048];
InputStream is = new BufferedInputStream(new FileInputStream(imageFile));
int c;
try {
while ((c = is.read(b)) >  0) {data.write(b, 0, c);}
} catch (IOException e) {}

Returning the image to the client

Now that we have the image data in the Byte array, we can send that data to the client. Before that we have to set the response type. We set the response type accordingly if the image is png, gif, or jpg. For other types, we the response type as “octet-stream”. Finally we attach the image in the response object and send it.

if (file.endsWith(".png") || (file.length() == 0 && request.getServletPath().endsWith(".png"))) post.setResponse(response, "image/png");
else if (file.endsWith(".gif") || (file.length() == 0 && request.getServletPath().endsWith(".gif"))) post.setResponse(response, "image/gif");
else if (file.endsWith(".jpg") || file.endsWith(".jpeg") || (file.length() == 0 && request.getServletPath().endsWith(".jpg"))) post.setResponse(response, "image/jpeg");
else post.setResponse(response, "application/octet-stream");

ServletOutputStream sos = response.getOutputStream();
sos.write(data.toByteArray());
post.finalize();

Result:

Resources

• About byte array output stream: https://docs.oracle.com/javase/7/docs/api/java/io/ByteArrayOutputStream.html
• Buffered image in java: https://www.tutorialspoint.com/java_dip/java_buffered_image.htm
• Servlet output stream: https://docs.oracle.com/javaee/5/api/javax/servlet/ServletOutputStream.html