Mysql Situation where user crashes - php

So I have a 2 page registration page where on the first page the user inputs all his/her data and then clicks continue. On the 2nd page, they choose certain options and then click continue there, this will then take them somewhere else where their payments can be handled (not related to me at all).
I also have a Insert.php file that simply inserts all the user's data into the database. When clicking submit on page2, it actually redirects them to Insert.php, which inserts and then redirects them to the external payment page. I had to do this because for some reason the ajax call just wouldn't work.
My question is, what if right after they click submit on the 2nd page, their computer crashes or they close the browser? Will mysql understand that the connection has been terminated and not save anything or will it save partial data (as much as it could before the user crashed), and if so how do I delete the partial data?
At this point I'm just trying to do as much error handling as I can to prevent any serious problems down the road.

When they click submit, if the browser sends all the post fields, the code you have will happily carry on executing. As far as the server is concerned, nothing of any importance happened.
I would suggest having some post/get checking in the code (as always) which will make sure that all the data has been passed. If it has, it will save properly for the user.
Edit: If you are worried about only some elements of the form being sent before a crash, you can do something like this:
if(!empty($_POST['someElement']) && !empty($_POST['someElement2']) && !empty($_POST['someElement2']))
{
//All your elements are fully submitted, you can save the data safely
}

Related

How to automatically resubmit form

My site uses a combo of sessions and get/post.
When user hits back button, it says "confirm you want to resubmit form" or a similar message, depending on the browser. Then the user has to also refresh the page.
How can I make it automatically resubmit form. I don't want users seeing this message and getting stuck when they hit back.
I have PHP + HTML
you can use get method in post method resubmit message is appear and if you want to use post method then on server page use header such as header('location:index.php') and change index page that you want.
Not answering your question, but do reconsider.
POST actions should change the state of the server. GET actions should be transparent. If you're using a POST to submit data to commit to a database or launch nuclear missiles or whatever, the resubmit warning exists for a reason: imagine your embarrassment when you launch two nuclear missiles, but was only trying to launch one.
GET actions, on the other hand, by their specification, should never meaningfully impact the world, so the resubmission is safe. If there is something the user is allowed to go back to, it's a GET page. A POST page should not be returnable-to using the back button (or rather, the user should be made aware of it).
If you have to suppress this warning, you are doing something wrong.

PHP - return the same page with changes

I have html page where you can insert some information and then submit this form, which will change information in database. I do it normally, that submit button call php file in server.
But what I want, is that this php file will return to me the same html page of which I sent request, with modified changes. e.g: there will be "Database update successfully" text added etc.
How can I do it without AJAX ?
Thanks
In the PHP file, do a call to the header() function to redirect the user. For example:
header('Location: url.php');
To change the content of that page they are redirected to, you could pass something in the URL that your page will check for. For example:
header('Location: url.php?submitted=1');
There are other ways to implement this, but this seems the most straightforward to me. Note that you don't want to call header() until the end of your submission page.
Use POST/REDIRECT/GET
Excerpt:
The user submits the form
This is pretty straight forward. The user completes the form and submits it by pressing the submit button or enter on their keyboard.
We store the form data in a session
After processing the data we discover an error so we need to redisplay the form with an error message but we also want to populate
it with their data so they don't have to refill the entire form just
to fix potentially one little mistake. So we store their data in a
session ($_SESSION). Session variables carry over from page-to-page
for as long as the session is valid or until they are deleted. This is
an ideal place to put their information since redirecting will cause
their information to be immediately discarded by the server.
We redirect the user back to the same page using a 303 redirect
Once we have saved the user's information in their session we need to redirect them back to the same page. In order for this to work
properly we need to use a 303 redirect. This means we need to send a
303 header with our redirect. A 303 redirect will cause the browser to
reload the page without the initial HTTP POST request to be
resubmitted. This includes when the user uses the back or refresh
buttons.
We re-populate the form using the data stored in the session
When the page is sent to the user we re-populate it with their information we saved in their session.
Only by generating the whole page in CGI first, unless you go through some horribly convoluted method of getting value of one of the fields to be set to document.innerHTML or something like that in Javascript. But you'll go through hell to get the quoting issues resolved. Use AJAX, it was created for precisely this purpose and exactly to avoid the utter hell associated with what you need.
Alternatively: the "modified piece" of the page may be an iframe, and you can set the target attribute of the form, so that the PHP returns only the iframe content.

Form submits twice

I have a form that processes a payment, but approximately one in every 300 payments comes though twice, my logs show that there were two requests for all these occurrences.
I implemented some JavaScript that disables the submit button after it's clicked, and it seems to work fine for me, but I'm still getting double submissions every now and then.
Does anyone know anything else that could be causing the form to be submitted twice?
As Dagon says, server-side checks are your friend here. Give each instance of the form a randomly generated key (guid would be nice), and store that in the database. Don't accept forms that contain a key that already exists in the db.
Also, are you simply displaying HTML after your form processing logic executes? If so, try redirecting after you process the form.
It is a way: after user presses form submit button, disable it with javascript. That should prevent user from double submitting the form accidently. It works for all sites we implement it like because. Because sometimes user gets impatient and clicks form submit button several times, thats why you get double requests. What you need to make sure it works for all the browsers (disabling the button I mean).
Also you could do it on server side, it just is harder.
We use similar to the upvoted answer in Enable/disable submit button with jQuery and Coldfusion server code

php form submit and the resend information screen

I want to ask a best practice question.
Suppose I have a form in php with 3 fields say name, email and comment.
I submit the form via POST. In PHP I try and insert the date into the database.
Suppose the insertion fails.
I should now show the user an error and display the form filled in with the data he previously inserted so he can correct his error. Showing the form in it's initial state won't do.
So I display the form and the 3 fields are now filled in from PHP with echo or such. Now if I click refresh I get a message saying "Are you sure you want to resend information?".
OK.
Suppose after I insert the data I don't carry on but I redirect to the same page but with the necessary parameters in the query string. This makes the message go away but I have to carry 3 parameters in the query string.
So my question is:
How is it better to do this? I want to not carry around lots of parameters in the query string but also not get that error. How can this be done? Should I use cookies to store the form information.
Your first scenario seems the most valid.
i.e.
User submits the form
Some problem prevents submission, so form is re-displayed
If user "refreshes" they see the usual message about re-sending information (although their most likely path of progression is to re-submit the form that you are kindly re-populating for them).
The "Are you sure you want to resend information?" message is perfectly valid in the event of someone refreshing the page after a form submission, so don't write code to specifically break this behaviour.
I think generally people would temporarily store the submitted data in a session variable, and send the data back to the client.
Maybe it is besides the point but you mentioned "wrong dates", and I think many would say you should arrange things so that the user cannot unintentionally send you wrong dates.

Prevent Back button from showing POST confirmation alert

I have an application that supplies long list of parameters to a web page, so I have to use POST instead of GET. The problem is that when page gets displayed and user clicks the Back button, Firefox shows up a warning:
To display this page, Firefox must send information that will repeat any action (such as a search or order confirmation) that was performed earlier.
Since application is built in such way that going Back is a quite common operation, this is really annoying to end users.
Basically, I would like to do it the way this page does:
http://www.pikanya.net/testcache/
Enter something, submit, and click Back button. No warning, it just goes back.
Googling I found out that this might be a bug in Firefox 3, but I'd like to somehow get this behavior even after they "fix" it.
I guess it could be doable with some HTTP headers, but which exactly?
See my golden rule of web programming here:
Stop data inserting into a database twice
It says: “Never ever respond with a body to a POST-request. Always do the work, and then respond with a Location: header to redirect to the updated page so that browser requests it with GET”
If browser ever asks user about re-POST, your web app is broken. User should not ever see this question.
One way round it is to redirect the POST to a page which redirects to a GET - see Post/Redirect/Get on wikipedia.
Say your POST is 4K of form data. Presumably your server does something with that data rather than just displaying it once and throwing it away, such as saving it in a database. Keep doing that, or if it's a huge search form create a temporary copy of it in a database that gets purged after a few days or on a LRU basis when a space limit is used. Now create a representation of the data which can be accessed using GET. If it's temporary, generate an ID for it and use that as the URL; if it's a permanent set of data it probably has an ID or something that can be used for the URL. At the worst case, an algorithm like tiny url uses can collapse a big URL to a much smaller one. Redirect the POST to GET the representation of the data.
As a historical note, this technique was established practice in 1995.
One way to avoid that warning/behavior is to do the POST via AJAX, then send the user to another page (or not) separately.
I have been using the Session variable to help in this situation. Here's the method I use that has been working great for me for years:
//If there's something in the POST, move it to the session and then redirect right back to where we are
if ($_POST) {
$_SESSION['POST']=$_POST;
redirect($_SERVER["REQUEST_URI"]);
}
//If there's something in the SESSION POST, move it back to the POST and clear the SESSION POST
if ($_SESSION['POST']) {
$_POST=$_SESSION['POST'];
unset($_SESSION['POST']);
}
Technically you don't even need to put it back into a variable called $_POST. But it helps me in keeping track of what data has come from where.
I have an application that supplies long list of parameters to a web page, so I have to use POST instead of GET. The problem is that when page gets displayed and user clicks the Back button, Firefox shows up a warning:
Your reasoning is wrong. If the request is without side effects, it should be GET. If it has side effects, it should be POST. The choice should not be based on the number of parameters you need to pass.
As another solution you may stop to use redirecting at all.
You may process and render the processing result at once with no POST confirmation alert. You should just manipulate the browser history object:
history.replaceState("", "", "/the/result/page")
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