Code Samples

Friday, June 22, 2018

jQuery AJAX fetch only headers and decide wheather to get the content | Use jQuery to send a HEAD request with AJAX and get the size of a file | Getting response headers data from an AJAX request with javascript

Response headers can contain valuable information and may help to keep your API responses simpler by separating the actual response data from accessory metadata.



For instance, when querying the API for a list of posts, the response body includes just the content but there are also some other valualbe information sent as headers:



The jQuery code for the AJAX request would look something like this:

$.ajax({
    type: 'HEAD',
    url: 'http://example.com/api.php',
    complete: function (xhr) {
        var contentLength = xhr.getResponseHeader('Content-Length');
        // OR YOU CAN SEE ALL INFORMATION USING
        var headers = xhr.getAllResponseHeaders();
    }
});


Which will output as below:

http://localhost/text-finder/download.pdf >> application/pdf
date: Fri, 22 Jun 2018 06:35:52 GMT
last-modified: Sun, 11 Feb 2018 16:39:41 GMT
server: Apache/2.4.33 (Win32) OpenSSL/1.0.2n PHP/5.6.35
etag: "5ae6f-564f2687e28f8"
content-type: application/pdf
connection: Keep-Alive
accept-ranges: bytes
keep-alive: timeout=5, max=100
content-length: 372335



http://localhost/text-finder/test2.html/forum >> text/html; charset=utf-8
date: Fri, 22 Jun 2018 06:35:52 GMT
server: Apache/2.4.33 (Win32) OpenSSL/1.0.2n PHP/5.6.35
vary: accept-language,accept-charset
content-language: en
connection: Keep-Alive
accept-ranges: bytes
content-type: text/html; charset=utf-8
keep-alive: timeout=5, max=97

Get URL and URL Parts in JavaScript | Get an Absolute URL with JavaScript | How to get the exact href value only without their domain | How to check if any Link is for some specific domain | Link attribute HOST > PATHNAME > Filter links by domain | host name

I'm having trouble in getting the exact value of href only

It's a little known (maybe) fact that most browsers convert Anchor node elements into Location objects as well. So you can access all parts available to Location too;

Suppose consider below html code:

<body>
HELLO '59 IS PRESENT <a href="test2.html">HI</a>
<a href="https://stackoverflow.com/questions/domain">Another LINK</a>
</body>

In above html, two link exists, one for self domain and another for stackoverflow, now if I look through them, below output would be generated:

PROTOCOL=http:, HOST=localhost, PORT=
LINK PATH=/test2.html

PROTOCOL=https:, HOST=stackoverflow.com, PORT=
LINK PATH=/questions/domain

A regex to match a substring that isn't followed by a certain other substring > Find Any Word Not Followed by a Specific Word > Regex Negative Lookbehind

The problem is I need to match a word say "match" in a string. It is very easy using the expression /(match)/gi

Above expression is very easy. Now original problem is need to match word "match" not starting with any other word like 10 or 20 or any word. To do so we need to use negative lookbehind. Below is a complete regex that will match word match but not start with 10 or 20 or '.

/(?<!(10|20))(?<!')(match)/gi

Meaning of the above regex is will match a word match but not followed by 10 or 20 or ' 

Output of this regex is as below

Explanation of this regex:

Sunday, June 17, 2018

Grails on Groovy > Invalidate Session > Error Handling - Session already invalidated

Problem is that in my grails application, when I invalidating the existing http session using session.invalidate() and creating a new session using request.getSession(true) is working fine for some time.

But this new session is not getting reflected everywhere in grails application. Due to this I do get 'Session already invalidated'.

I don't want to do request.getSession() everywhere, actually I would not get notified when this required or not. I am just using 'session'.

Grails holds the reference to a session object and every time you ask it for a session it returns the same reference.. so if you invalidate a session and then ask for the session it will return the same invalidated session, and cause 'session already invalidated' exception..

Execute following line Just after you do session.invalidate

import org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest

session.invalidate()
GrailsWebRequest.lookup(request).session = null

Grails on Groovy > Grails Filter to Redirect HTTP to HTTPS > Redirecting WWW to Root with Grails > Grails Append Something to URL before Redirect > URL Modification On Grails Filters

The problem is need to modify http to https as well as add www to domain name if not exists. To do so have to modify in our Grails Filters. 



For Grails applications, a filter can be used to improved security by redirecting traffic from regular HTTP to encrypted HTTPS.  The convention is that filters are written in Groovy using filenames ending in Filters, and the files go into the grails-app/conf folder.


Redirecting from HTTP to HTTPS provides a better user experience than simply blocking HTTP requests, as redirecting seamlessly forwards users to the web pages they expect to see.



The example below shows the redirect code

package com.pkm

import grails.util.Environment

import javax.servlet.http.HttpServletRequest

class SecurityFilters {
    String getDomainName(HttpServletRequest request) {
        return request.getRequestURL().substring(0, request.getRequestURL().indexOf("/", 8)) + request.contextPath
    }
    String getFullRequestURI(HttpServletRequest request) {
        String query = request.getQueryString()
        String request_uri = request.getAttribute("javax.servlet.forward.request_uri")
        if (request_uri == null) {
            return request.getRequestURL().toString().substring(0, request.getRequestURL().toString().length() - 1) + (query ? "?$query".toString() : "")
        }
        return request.getRequestURL().substring(0,request.getRequestURL().indexOf("/", 8)) + request_uri + (query ? "?$query".toString() : "")
    }

    def filters = {
        filter1(uri: "/**") {
            before = {
                Boolean isSecure = request.isSecure(), doRedirect = false
                String domain = getDomainName(request)
                String url = getFullRequestURI(request)

                println("SECURE=${isSecure.toString().capitalize()}" +
                        "\n\t >DOMAIN=${domain}" +
                        "\n\t\t>URL=${url}")

                /*if (!request.getServerName().toLowerCase().startsWith("www")) {
                    doRedirect = true
                    url = url.substring(0, url.indexOf("//")) + "//www." + url.substring(url.indexOf("//") + 2)
                }*/
                if (!request.isSecure() && !Environment.isDevelopmentMode()) {
                    doRedirect = true
                    url = "https://" + url.substring(url.indexOf("//") + 2)
                }
                if (!url.toLowerCase().endsWith("redirected=true-2")) {
                    doRedirect = true
                    url = url + (url.contains("?") ? "&redirected=true-2" : "?redirected=true-2")
                }
                if (doRedirect && request.isGet()) {
                    response.setStatus(302)
                    response.setHeader("Location", url)
                    response.flushBuffer()
                    return false
                }
            }
            after = { Map model ->

            }
            afterView = { Exception e ->

            }
        }
    }
}


If your server listens for https requests (or any requests on ports other than 80), you can add checks using the same format, replacing http and port 80 with the appropriate values. You can also redirect from any subdomain you want to the root site (or another subdomain), by simply swapping www with your subdomain.



And output would be like below. First request forwarded to second URL with additional parameters.

SECURE=False
  >DOMAIN=http://localhost:3346/CONTEXT_PATH
  >URL=http://localhost:3346/CONTEXT_PATH/home/index
SECURE=False
  >DOMAIN=http://localhost:3346/CONTEXT_PATH
  >URL=http://localhost:3346/CONTEXT_PATH/home/index?redirected=true-2

Grails on Groovy > Transform Collection / List to a Map with collectEntries > Get Map From Array List > Convert List To Corresponding Map Entity

Since Groovy 1.7.9 we can use the collectEntries method for a Collection to get a Map. We use a closure to transform the elements in the collection to a map entry. And the end result is a Map with all the map entries.

List<String> words = ["Grails", "On", "Groovy"]
Map map = words.collectEntries {
    [ (it): it.contains("G") ]
}
println(map)

Which will output as below:

[Grails:true, On:false, Groovy:true]

Grails on Groovy > Transactions > Transaction Block > Read Only Transactions > With New Transaction > Transactions With Read Only Stage

We all know that Grails services are transactional by default. When you create a service you see that there is a annotation @Transactional exists over class name. Transactional means all transactions will persist on database or no one will persist.


We can set transactions read only mode if we wish in a transactional block if we need. Below is a code snippet:

package com.pkm

import grails.transaction.Transactional
import org.springframework.transaction.TransactionStatus

@Transactional
class HomeService {
    TransactionStatus transactionStatus

    void callMe() {
        Table1 table1 = Table1.last()
        new Table2(table1: table1, subject: "S3", score: 3D).save()
        transactionStatus.setRollbackOnly()

        Table2.withNewTransaction { TransactionStatus tx ->
            table1 = Table1.last()
            new Table2(table1: table1, subject: "S4", score: 3D).save()
            tx.setRollbackOnly()
        }
    }
}



In above code block, we inject a bean named transactionStatus which actually maintain if a service definition is read only or not. We can set it to read only mode using transactionStatus.setRollbackOnly(). We can do the same job for when we do anything in withNewTransaction block. You can see there is another transactionStatus occur for that new region. So you can also set it to read only mode.

Pages

Friday, June 22, 2018

jQuery AJAX fetch only headers and decide wheather to get the content | Use jQuery to send a HEAD request with AJAX and get the size of a file | Getting response headers data from an AJAX request with javascript

Get URL and URL Parts in JavaScript | Get an Absolute URL with JavaScript | How to get the exact href value only without their domain | How to check if any Link is for some specific domain | Link attribute HOST > PATHNAME > Filter links by domain | host name

A regex to match a substring that isn't followed by a certain other substring > Find Any Word Not Followed by a Specific Word > Regex Negative Lookbehind

Sunday, June 17, 2018

Grails on Groovy > Invalidate Session > Error Handling - Session already invalidated

Grails on Groovy > Grails Filter to Redirect HTTP to HTTPS > Redirecting WWW to Root with Grails > Grails Append Something to URL before Redirect > URL Modification On Grails Filters

Grails on Groovy > Transform Collection / List to a Map with collectEntries > Get Map From Array List > Convert List To Corresponding Map Entity

Grails on Groovy > Transactions > Transaction Block > Read Only Transactions > With New Transaction > Transactions With Read Only Stage