PHP 5 Recipes A Problem-Solution Approach 2005 phần 9 ppsx

Selection:

<option value="nogo">make a selection...</option>

<option value="1"<?php if ($_POST['myselection'] == 1){?>➥

selected="selected"<?php } ?>>Choice 1</option>

<option value="2"<?php if ($_POST['myselection'] == 2){?>➥

selected="selected"<?php } ?>>Choice 2</option>

<option value="3"<?php if ($_POST['myselection'] == 3){?>➥

selected="selected"<?php } ?>>Choice 3</option>

</select><br /><br />

Your Email: <input type="text" name="youremail" maxlength="150"➥

value="<?php echo $_POST['youremail']; ?>" /><br />

</form>

<?php

}

</div>

</body>

</html>

Figure 13-1 shows the potential output if you input a valid name field but leave the selection and e-mail address empty.

Figure 13-1. Telling users to properly enter information

How It Works

In this example, you have seen how you may want to handle your validation. Keep in mind

that your objective is to ensure that users know what they did wrong and keep their properly

submitted information for ease of use. To ensure that the user of this form sees the error messages, the Cascading Style Sheet (CSS) class called error will be used every time an error

message is displayed. The error message will display in bold and red, thus directing the users

to realize what they did wrong.

By providing the value fields, and in the case of the select box a selected argument if you

have valid data, the form fields will retain any current, proper information. If there is no current, proper data to use, nothing will display. This form has now become decidedly easy to

use, is quite secure, and ensures a happy, well-directed user.

498 13-5 ■ REDISPLAYING FORMS WITH PRESERVED INFORMATION AND ERROR MESSAGES

5092_Ch13_FINAL 8/26/05 9:58 AM Page 498

Preventing Multiple Submissions of a Form

One possible occurrence that happens often is that users become impatient when waiting for

your script to do what it is doing, and hence they click the submit button on a form repeatedly.

This can wreak havoc on your script because, while the user may not see anything happening,

your script is probably going ahead with whatever it has been programmed to do.

Of particular danger are credit card number submittals. If a user continually hits the submit button on a credit card submittal form, their card may be charged multiple times if the

developer has not taken the time to validate against such an eventuality.

13-6. Preventing Multiple Submissions on the Server Side

You can deal with multiple submittal validation in essentially two ways. The first occurs on the

server. Server side refers to a script located on the server that is receiving the data; client side is

more browser related (and explained in the next example). Because the server has no actual

access to the browser, validating multiple submissions can be a bit trickier. While you can

accomplish this goal in a number of ways from a server-side perspective, we prefer to use a

session-based method. Basically, once the submit button has been clicked, the server logs the

request from the individual user. If the user attempts to resubmit a request, the script notes a

request is already in motion from this user and denies the subsequent request. Once the script

has finished processing, the session is unset, and you have no more worries.

For the following example, you will need a test.txt text file that you can create and place

relative to the script. (Or you can ensure that you have write privileges on the working directory, and the script will attempt to create it for you.) Keep in mind that the file must have the

proper privileges set for writing (CHMOD to 777 to keep things simple).

The Code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"➥

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>Sample 13.6</title>

</head>

<body>

<p>Example:</p>

Your Name: <input type="text" name="yourname" maxlength="150” /><br />

</form>

</div>

</body>

</html>

<?php

//Start the session state.

session_start ();

13-6 ■ PREVENTING MULTIPLE SUBMISSIONS ON THE SERVER SIDE 499

5092_Ch13_FINAL 8/26/05 9:58 AM Page 499

//Set a session started value for this user.

if (!isset ($_SESSION['processing'])){

$_SESSION['processing'] = false;

}

//Now you ensure you haven't already started processing the request.

if ($_SESSION['processing'] == false){

//Now, you let the script know that you are processing.

$_SESSION['processing'] = true;

//Create a loop that shows the effect of some heavy processing.

for ($i = 0; $i < 2000000; $i++){

//Thinking...

}

//Every time you do this, write to a text file so you can test that

//the script isn't getting hit with multiple submissions.

if ($file = fopen ("test.txt","w+")){

fwrite ($file, "Processing");

} else {

echo "Error opening file.";

}

//Then you start doing the calculations.

echo $_POST['yourname'];

//Then, once you have finished calculating, you can kill the session.

unset ($_SESSION['processing']);

}

How It Works

Now, enter your name and continue to jam on the submit button. Rather than allow the script

to continually run time and time again, the script verifies your existence via a session and determines if it is already processing your server call. If the script sees you are already processing,

then it will not allow you to try again no matter how many times you click the same button.

Once the script has finished performing its action, it merely unsets the session variable, and you

could theoretically start again. By checking the session, the script ensures that it is the same user

attempting to access the script and can therefore block multiple attempts from the same user.

13-7. Preventing Multiple Submissions on the Client Side

Handling multiple submittals from a client-side perspective is actually much simpler than

doing it on the server side. With well-placed JavaScript, you can ensure that the browser will

not let the submittal go through more than once. The problem with this method, of course,

is that JavaScript is not always foolproof because of the user’s ability to turn it off. That being

said, however, most users will have JavaScript enabled, so this script will likely work for

500 13-7 ■ PREVENTING MULTIPLE SUBMISSIONS ON THE CLIENT SIDE

5092_Ch13_FINAL 8/26/05 9:58 AM Page 500

90 percent of web users. The following example uses JavaScript to cut off multiple submittals

from a client-side (browser) level.

Don’t forget to ensure that you have a valid test.txt file (CHMOD to 777), as specified in the

previous recipe.

The Code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"➥

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>Sample 13.7</title>

<!--

function checkandsubmit() {

//Disable the submit button.

document.test.submitbut.disabled = true;

//Then submit the form.

document.test.submit();

}

//-->

</script>

</head>

<body>

<form action="sample13_6_process.php" method="post" name="test"➥

onsubmit="return checkandsubmit ()">

<p>Example:</p>

Your Name: <input type="text" name="yourname" maxlength="150" /><br />

<input type="submit" value="Submit" style="margin-top: 10px;"➥

id="submitbut" name"submitbut" />

</form>

</div>

</body>

</html>

<?php

//Create a loop that shows the effect of some heavy processing.

for ($i = 0; $i < 2000000; $i++){

//Thinking...

}

//Every time you do this, let's write to a text file so you can test that

//out script isn't getting hit with multiple submissions.

if ($file = fopen ("test.txt","w+")){

fwrite ($file, "Processing");

} else {

13-7 ■ PREVENTING MULTIPLE SUBMISSIONS ON THE CLIENT SIDE 501

5092_Ch13_FINAL 8/26/05 9:58 AM Page 501

echo "Error opening file.";

}

//Then you start doing the calculations.

echo $_POST['yourname'];

How It Works

We realize that this particular piece of functionality is based on JavaScript and this is a book

about PHP, but PHP is a server-side language. Therefore, to do a little client-side validation,

you must use a language that can interact with the browser, such as JavaScript. In any case,

the way this script works is by actually disabling the submit button once the form has been

submitted. The button is clicked, which forces the browser to redirect first to the JavaScript

function checkandsubmit(), which immediately disables the submit button and then submits

the form for you. At this point, it does not matter how long the script takes to finish executing;

the submit button is disabled and hence cannot be clicked again until the page is revisited.

13-8. Performing File Uploads

Handling file uploads in PHP is not exactly difficult from a syntax point of view, but it is

important (extremely important in fact) to ensure that the file being uploaded is within the

upload constraints you lay out for it. In other words, an individual user could easily upload a

virus or some other form of malicious software if you are not careful about allowing them to

upload only what you want from them. A similar consideration is file size. You could easily

find your server under some heavy loads if you are not careful about what size of files are

being uploaded. The following example allows you to upload an image (of the file type JPG

only) that is smaller than 500KB in size.

Keep in mind that in order for this script to work, you must have a directory created (relative to the script) that is called uploads and is writable (again, using a CHMOD of 777 is the

simplest way of accomplishing this).

The Code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"➥

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<title>Sample 13.8</title>

</head>

<body>

<?php

//If you have received a submission.

if ($_POST['submitted'] == "yes"){

$goodtogo = true;

//Check for a blank submission.

502 13-8 ■ PERFORMING FILE UPLOADS

5092_Ch13_FINAL 8/26/05 9:58 AM Page 502

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