Now let's write the main JS code in order to add menu items into Chrome extension. Create background.js file in the same directory as manifest.json with the content below:

if (chrome && chrome.browserAction){
     var baseUrl = "https://www.example.com"
     chrome.runtime.onInstalled.addListener(function() {
         chrome.tabs.create({ url: baseUrl + "/extension-installed/" });
     });

     chrome.runtime.setUninstallURL(baseUrl + "/extension-uninstalled/");

     // open a new page on left clicking on the extension itself
     chrome.browserAction.onClicked.addListener(function(activeTab) {
         chrome.tabs.create({ url: baseUrl + "/my-home-page" });
     });

     chrome.contextMenus.create({
         "id": "first_item",
         "title": "This is the first item",
         "contexts": ["browser_action"]
     });

     chrome.contextMenus.create({
         "id": "second_item",
         "title": "This is the second item",
         "contexts": ["browser_action"]
     });

     chrome.contextMenus.onClicked.addListener(function(info)
     {
         urls = {
             first_item: baseUrl + "/first-item",
             second_item: baseUrl + "/second-item"
         };
         chrome.tabs.create({url: urls[info.menuItemId]});
     });
 }

There are many events that based on that event you can do an action. Let's review some of the codes above.

chrome.runtime.onInstalled.addListener: on extension installation open a url using chrome.tabs. As you recall from the previous post we have added tabs to the permission section of manifest.

chrome.runtime.setUninstallURL: open a url on extension uninstallation.

chrome.browserAction.onClicked.addListener: open a url when your extension in toolbar is clicked (at the right of the address bar).

chrome.contextMenus.create: create an item with specific id and title. contexts sections tells the browser to show the menu just when user right click on the extension in toolbar. You can add page to have the extension menu item on the main page of browser itself.

chrome.contextMenus.onClicked.addListener: When one of the menu items is clicked open the corresponding URL.

Now to test it go to chrome://extensions/. Make sure developer mode is enabled. Click on Load unpacked and select your extension folder and open it. It will be installed by now.

Enjoy working with Chrome Extension! :)

#chrome #xtension

How to check MongoDB replication lag in Icinga2 and get notified when it is over 15 seconds?

We assume here that you have a replica set in place. First download the python script for our nagios plugin:

cd /usr/lib/nagios/plugins
 git clone git://github.com/mzupan/nagios-plugin-mongodb.git

Now the Icinga2 part. You first need to create a command for replication lag check:

cd /etc/icinga2/conf.d/commands

Create a new file replication_lag.conf:

object CheckCommand "check_replication_lag" {
     import "plugin-check-command"
     command = [ PluginDir + "/nagios-plugin-mongodb/check_mongodb.py", "-A", "replication_lag" ]
     arguments = {
         "-H" = "$mongo_host$"
         "-P" = "$mongo_port$"
     }
 }

Create a new file in services folder called replication_lag.conf:

apply Service for (display_name => config in host.vars.replication) {
     import "generic-service"
     check_command = "check_replication_lag"
     vars += config
     assign where host.vars.replication
 }

This service gets enabled where it finds replication in host config. Now in secondary mongoDB hosts configuration add the below part:

vars.replication["Secondary DB"] = {
     mongo_host = "slave.example.com"
     mongo_port = 27017
 }

#sysadmin #icinga2 #mongodb #replication #replication_lag #nagios_plugin

I have a script that checks a source folder for new files in case there are files in the source folder, it will move those files to destination.

The problem I encountered recently was that files are huge and it may be in the middle of the copying into source by another process so my script tries to move an incomplete file to a destination. Let's say the file is 4GB in size and just only 1GB of the file has been copied. I have to wait until file is 4GB and other handler using that file, then I should safely move the file.

You can use lsof command in order to check which processes are using the source file:

if [[ `lsof -- /var/my-folder/my-big-file.tar.gz` ]]
then
     echo "File is being used by a process."
     exit 1
 fi

NOTE: you can give file directly to lsof using -- or you can use grep command as follow:

lsof | grep /var/my-folder/my-big-file.tar.gz

NOTE2: if you are in a loop use break instead of exit.

NOTE3: if you get command not found, install it using apt-get install lsof

#linux #sysadmin #lsof #grep

How to upgrade Axigen mail server?

The procedure is dead simple! Mail server itself notifies you about the new updates in its admin panel. Head over to the given link and download the the appropriate file related to your OS. Usually a .run file.

1- First make it executable:

chmod +x axigen-10.2.2.x86_64.rpm.run

NOTE: here my version update may differ from yours.

2- Now stop Axigen.

3- Run the installer and go in an interactive way. JUST be sure to skip the Axigen post-install configuration wizard.

4- Now start Axigen.

NOTE: in case you want to take backup copy the folder /var/opt/axigen in a safe place. This path may differ based on your OS and your distro.

#mail_server #axigen #upgrade #update

Have you heard about CORS (Cross Origin Resource Sharing)?

If you know it, but like me you don't know it as you should and every time the bowser gives you a new error in console you again get wandered in the wilderness, I'd suggest going to the awesome link below and read thoroughly line by line:

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

NOTE: this article is fantastic! Believe you me. You will understand eveything you need to know exactly what is CORS and how to handle it properly.


#browser #mozilla #CORS #cross_origin #cross_origin_resource_sharing

nginX by default does not set CORS headers for requests with error status codes like 401. There are 2 options here to add CORS headers:

1- If your nginX version is new you have the option of always to add to add_header:

add_header 'Access-Control-Allow-Origin' $http_origin always;

2- If you got error of invalid number of arguments in "add_header" directive, then use more_set_headers:

more_set_headers -s '401 400 403 404 500' 'Access-Control-Allow-Origin: $http_origin';

NOTE: when this error happens then in $.ajax or any similar method you wont have access to status codes. So be extremely catious!!!

#nginX #web_server #CORS #more_set_headers #add_header #ajax

How to upload a text content as a file in $.Ajax()?

FormData class is used to create a multipart/form-data inside of JS code. A sample code speaks thousand words:

var formData = new FormData();
 var blob = new Blob([YOUR_CONTENT_HERE], { type: "text/html"});
 formData.append("file", blob);

We have created a binary data from the text which is in the format of text/html, then I have appended the data as an input file with the name of file (which will be captured on server-side).

The Ajax part is utterly simple:

$.ajax({
     type: 'POST',
     url: 'https://www.example.com/storage',
     data: formData,
     processData: false,
     contentType: false
 }).done(function(data) {});

NOTE: DO NOT OMIT processData, contentType parameters.

#javascript #jQuery #ajax #FormData #Blob #upload

Does that happen for you too, to CD into a wrong directory and need to get back to the previous directory?

Let's say you are in a long path like /mnt/new_volume/backup/files/archive, now you switch to home of your directory. In order to get back to the previous directory, you just need to issue the below command:

cd -

#linux #cd

https://spyhce.com/blog/understanding-new-and-init

#python27 #python3 #__init__ #__new__ #old_style #new_style #OOP #class #super

How to convert ByteArray to PDF and then upload it via jQuery?

var docData = [ yourByteArray ];
 var blob = new Blob([new Uint8Array(docData)], { type: 'application/pdf' });

 // Now create form to upload the file
 var formData = new FormData();
 formData.append("file", blob);

 // Let's now upload the file
 $.ajax({
         type: 'POST',
         url: 'https://www.YOUR-UPLOAD-FILE-ENDPOINT.com/storage',
         beforeSend: request => set_ajax_headers(request),
         data: formData,
         processData: false,
         contentType: false
     }).done(function(data) {
         console.log('File is uploaded!');
     });

NOTE: function set_ajax_headers is a function that sets headers on the given request.

#javascript #ByteArray #PDF #Uint8Array #Blob #jQuery