#ZEN

Suppose you have developed your own web app with InterSystems technologies stack and now want to perform a captcha validation on the client side in order to determine whether or not the user is human and make it safer. There are some modern frameworks to address the captcha issue, however most part of them needs internet access to generate codes and sometimes are complex to implement. Take this as basic example considering that image recognition has gotten too good. That's why you nowadays you tend to see more pattern recognition captchas than mere reading ones. (I.e.

What is a portlet?

The simple answer is: a custom widget. A portlet can exist by itself on a DeepSee dashboard, it can be used along side standard DeepSee widgets, or along side other portlets. The rendering of the custom widget is completely user defined. This means you can embed a web page, create a form to perform any sort of action needed based on the data on your dashboard, use third party charting libraries, or simply display data from outside of a DeepSee cube.

How to get started

This article is little explanation to a GitGub project.

This code snippet provides a ZEN page that downloads a stream from its database directly:

/// We assume that you have stored your data within this schema:
/// MyApp.Model.Storage: Filename,FileSize,Content,ContentType
Class zen.downloadStream Extends (%ZEN.Component.page,%CSP.StreamServer)
{
 
    /// Wrapper to get the id of the download, we assume that the id is passed to this zen page
    /// as a URI parameter, i.e.: MyApp.Downloads.cls?OID=1234
    ClassMethod GetId()
    {
        Quit $Get(%request.Data("OID",1))
    }
     
    /// Set the appropriate header for the file.
    ClassMethod OnPreHTTP() As %Boolean
    {
        Set tId = ..GetId()
     
        If ##Class(MyApp.Model.Storage).%ExistsId(tId) {
            Set tStream = ##Class(MyApp.Model.Storage).%OpenId(tId)
            // You could "guess" the content type by its file extension
            // or you can store it (before) in the database separately (like in this example).
            // Set Extension = $Piece(tStream.Filename,".",$Length(tStream.Filename,"."))
            // Set ContentType = ..FileClassify(Extension)
     
            Set %response.ContentType = tStream.ContentType
            Do %response.SetHeader("content-disposition","attachment; filename="_tStream.Filename)
            Do %response.SetHeader("Content-Length",tStream.FileSize)
        }
        Else {
            Set %response.Status="404 File Not Found"
            Quit 0
        }
        Quit $$$OK
    }
     
    ClassMethod OnPage() As %Status
    {
        Set Download = ##Class(MyApp.Model.Storage).%OpenId(..GetId())
        Do Download.Content.OutputToDevice()
        Quit $$$OK
    }
 
}

Link to code on GitHub

If you are developing applications that use CSP or Zen, or potentially any of the other InterSystems web-related stuff that's built on top of CSP, then it's important to know how to keep one particular secret.

A central part of the CSP security architecture is a server-side session key. "Server-side" because its value should never be revealed to the client that is issuing the web requests. If it is revealed, a malicious client might be able to use it to bypass your security and make your server do things you don't want it to.