losing connection on server / localhost

MiServer is Dyalog's APL-based web development framework

losing connection on server / localhost

Postby Gantois on Thu Feb 23, 2017 1:45 am

Hi,

The problem occurs in my app whenever the user has no action in browser for some period of time and then return to site. My server app do not recognize the values of some variables that had been initialized for the user and were being used. (the value becames null and one app error occurs)

Perhaps I have to control the timeout using instructions in "onSessionEnd" to avoid this kind of error. But, I don't know if this really is the problem and how to solve it.

Could someone help me?

Thanks,
Marco
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Re: losing connection on server / localhost

Postby Brian|Dyalog on Thu Feb 23, 2017 4:10 pm

Hi Marco,

Depending on what your application is doing, there may be several pieces that need to work together for managing session timeouts.

First, there's the SessionTimeout setting in Config/Server.xml - the default setting is '30m' for 30 minutes.

If have any cleanup work (closing files, etc) that needs to be done when the session times out, then you'd create your own server class based on the MiServer class and override the onSessionEnd method
Code: Select all
:Class MarcoServer : MiServer

    ∇ Make config
      :Access Public
      :Implements Constructor :Base config
    ∇

    ∇ onSessionEnd session
      :Access Public Override
    ⍝ The argument is a pointer to the session object so you can reference anything that you set within the session
    ⍝ Do any cleanup here...
    ∇

:EndClass


MiServer keeps an instance in the session of each page the user accessed. So, if your page has any cleanup it needs to do, you can use a public _Close method within the page. If your page doesn't have any specific cleanup to do, you don't need to write the _Close method.

The easiest way to check if the user's session has timed out is to check for the existence of a variable you set. If it's not there, the session is new, then do whatever initialization or redirection is needed and then set the variable. If the variable exists, then just carry on as normal.

The code below includes a stub function for _Close and a simple example of checking and setting a session variable. I set my SessionTimeout to 30s (30 seconds) and experimented with refreshing the page both before and after the timeout.

Code: Select all
:Class SessionExample : MiPage

    ∇ _Close
      :Access public
      ⍝ do any page cleanup (untie files, write log message, etc) here
    ∇

    ∇ Compose
      :Access public
      :If 0=_Request.Session.⎕NC'initialized'
          _Request.Session.initialized←1
          Add'Hello!'
      :Else
          Add'Welcome back!'
      :EndIf
    ∇

:EndClass


I hope this helps!

/Brian
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Re: losing connection on server / localhost

Postby woody on Sun Feb 26, 2017 2:40 pm

Marcos,

Yes, I have faced this "User Session Management" issue, as well.

One of the key points is to SAVE the Req.Session.ID (MS 2.x) along with the user login data.

So, when a user authenticates ... (login ID and PW are valid) ... you also store that user's Session ID ... and perhaps a ⎕TS time stamp also... just for good measure.

Next ... you may need to know if a user is ACTIVE ... or has left the session.

This might be another value.. the ⎕TS of the valid user's last transaction to your page.

The underlying data model might start to look like this:


USER_SESSIONS

User_ID .... Session_ID .... Session_Start_TS ..... Last_Trans_TS


Your cleanup routine (per Brian's post) might reference USER_SESSIONS to help with the cleanup.

Also, if a user returns... and their CURRENT req.Session.ID IS FOUND in your USER_SESSIONS table, then you know the user has returned and continues to working in their SAME MiServer APL Session.

However, if a user returns... and MiServer has terminated their old session due to TIMEOUT ... then, the user's Session ID will NOT be found in the USER_SESSIONS table ... and you would UPDATE that user's record (by the User_ID) to have the user's CURRENT req.Session.ID Login ⎕TS and last Transaction ⎕TS.

Your cleanup routine can inspect this table ... and perhaps DELETE the rows where the ⎕TS from last Transaction is older than 30 minutes... (or whatever setting you decide to use).

The user session is handled nicely by MiServer... by establishing a COOKIE in the user's browser. This cookie value is reviewed by MiServer... so the returning user is either processed in their current MiServer session .... or ... if the sessionID from the cookie is no longer active ... the user is given a NEW SESSION (and a new Cookie).

In our MiServer apps, I use APL Files to hold important user values ... so when a user returns... and establishes a NEW Session ... I read in the data values from the APL File, and re-establish the needed session variables.

This way, the user never knows the MiServer session has gone away.

One last thought...
You will need to decide how long you will allow a user to remain authenticated without session activity. The best idea is to leverage the built-in MiServer req.Session.ID to drive your cleanup of the USER_SESSIONS table.

So.. if a user comes to your site ... and their current Session ID is NOT found in the USER_SESSIONS table (e.g. APL file) ... THEN.. you should PROMPT THEM to LOGIN again.

And then update (or insert) the user's login record in USER_SESSIONS.

User_ID .... Session_ID .... Session_Start_TS ..... Last_Trans_TS


Cheers,

//W
Woodley Butler
Automatonics, Inc.
"Find your head in the APL Cloud"
http://www.APLcloud.com
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Re: losing connection on server / localhost

Postby Gantois on Fri Mar 03, 2017 4:33 pm

Brian and Woodley,

I will think about how to apply these recommendations in my app, to make modifications and tests.

Thanks very much,
Cheers
Marco
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Posts: 70
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