Phát triển web với PHP và MySQL - p 38 pot

E-commerce and Security P ART III 346 3 Recipient’s Mail Server 2 Sender’s Browser Recipient’s Mail Client Web Server 1 F IGURE 15.5 In our encrypted email application, the message is se

<p>Your message could not be encrypted, so has not been sent.

<p>Sorry.”;

}

?>

In order to make this code work for you, you will need to change a few things Email will be

sent to the address in $to_email

The line

putenv(“GNUPGHOME=/tmp/.gnupg”);

will need to be changed to reflect the location of your GPG keyring On our system, the Web

server runs as the user nobody, and has the home directory /tmp/

We are using the function tempnam()to create a unique temporary filename You can specify

both the directory and a filename prefix We are going to create and delete these files in around

one second, so it is not very important what we call them We are specifying a prefix of ‘pgp’,

but letting PHP use the system temporary directory

The statement

$command = “/usr/local/bin/gpg -a “.

“ recipient ‘Luke Welling <luke@tangledweb.com.au>’ “.

“ encrypt -o $outfile $infile”;

sets up the command and parameters that will be used to call gpg It will need to be modified

to suit you As with when we used it on the command line, you need to tell GPG which key to

use to encrypt the message

The statement

system($command, $result);

executes the instructions stored in $commandand stores the return value in $result

We could ignore the return value, but it lets us have an if statement and tell the user that

some-thing went wrong

When we have finished with the temporary files that we use, we delete them using the

unlink()function This means that our user’s unencrypted email is being stored on the server

for a short time It is even possible that if the server failed during execution, the file could be

left on the server

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L ISTING 15.2 Continued

While we are thinking about the security of our script, it is important to consider all flows of information within our system GPG will encrypt our email and allow our recipient to decrypt

it, but how does the information originally come from the sender? If we are providing a Web interface to send GPG encrypted mail, the flow of information will look something like Figure 15.5

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3 Recipient’s Mail Server

2

Sender’s Browser

Recipient’s Mail Client

Web Server 1

F IGURE 15.5

In our encrypted email application, the message is sent via the Internet three times.

In this figure, each arrow represents our message being sent from one machine to another Each time the message is sent, it travels through the Internet and might pass through a number

of intermediary networks and machines

The script we are looking at here exists on the machine labeled Web Server in the diagram At the Web server, the message will be encrypted using the recipient’s public key It will then be sent via SMTP to the recipient’s mail server The recipient will connect to his mail server, probably using POP or IMAP, and download the message using a mail reader Here he will decrypt the message using his private key

The data transfers in Figure 15.5 are labeled 1, 2, and 3 For stages 2 and 3, the information being transmitted is a GPG encrypted message and is of little value to anybody who does not have the private key For transfer 1, the message being transmitted is the text that the sender entered in the form

If our information is important enough that we need to encrypt it for the second and third leg

of its journey, it is a bit silly to send it unencrypted for the first leg Therefore, this script belongs on a server that uses SSL

If we connect to our script using a port other than 443, it will provide a warning This is the default port for SSL If your server uses a non-default port for SSL, you might need to modify this code

Rather than providing an error message, we could deal with this situation in other ways We could redirect the user to the same URL via an SSL connection We could also choose to ignore it because it is not usually important if the form was delivered using a secure connec-tion What is usually important is the details that the user has typed into the form are sent to us securely We could simply have given a complete URL as the action of our form

Currently, our open form tag looks like this:

<form method = post action = send_private_mail.php>

We could alter it to send data via SSL even if the user connected without SSL like this:

<form method = post action = “https://webserver/send_private_mail.php”>

If we hard code the complete URL like this, we can be assured that visitors’ data will be sent

using SSL, but we will need to modify the code every time we use it on another server or even

in another directory

Although in this case, and many others, it is not important that the empty form is sent to the

user via SSL, it is usually a good idea to do so Seeing the little padlock symbol in the status

bar of their browsers reassures people that their information is going to be sent securely They

should not need to look at your HTML source and see what the action attribute of the form is

Further Reading

The specification for SSL version 3.0 is available from Netscape:

http://home.netscape.com/eng/ssl3/

If you would like to know more about how networks and networking protocols work, a classic

introductory text is Andrew S Tanenbaum’s Computer Networks.

Next

That wraps up our discussion of e-commerce and security issues In the next section, we’ll

look at some more advanced PHP techniques including interacting with other machines on the

Internet, generating images on-the-fly, and using session control

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IN THIS PART

16 Interacting with the File System and the Server 351

17 Using Network and Protocol Functions 369

18 Managing the Date and Time 391

19 Generating Images 401

20 Using Session Control in PHP 429

21 Other Useful Features 447

IV

CHAPTER 16 Interacting with the File

System and the Server

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In Chapter 2, “Storing and Retrieving Data,” we saw how to read data from and write data to files on the Web server In this chapter, we will cover other PHP functions that enable us to interact with the file system on the Web server

We will discuss

• Uploading files with PHP

• Using directory functions

• Interacting with files on the server

• Executing programs on the server

• Using server environment variables

In order to discuss the uses of these functions, we will look at an example

Consider a situation in which you would like your client to be able to update some of a Web site’s content—for instance, the current news about their company (Or maybe you want a friendlier interface than FTP for yourself.) One approach to this is to let the client upload the content files as plain text These files will then be available on the site, through a template you have designed with PHP, as we did in Chapter 6, “Object Oriented PHP.”

Before we dive into the file system functions, let’s briefly look at how file upload works

Introduction to File Upload

One very useful piece of PHP functionality is support for HTTP upload Instead of files com-ing from the server to the browser uscom-ing HTTP, they go in the opposite direction, that is, from the browser to the server Usually you implement this with an HTML form interface The one we’ll use in our example is shown in Figure 16.1

F IGURE 16.1

The HTML form we use for file upload has different fields and field types from those of a normal HTML form.

As you can see, the form has a box where the user can enter a filename, or click the Browse

button to browse files available to him locally You might not have seen a file upload form

before We’ll look at how to implement this in a moment

After a filename has been entered, the user can click Send File, and the file will be uploaded to

the server, where a PHP script is waiting for it

HTML for File Upload

In order to implement file upload, we need to use some HTML syntax that exists specially for

this purpose The HTML for this form is shown in Listing 16.1

L ISTING 16.1 upload.html—HTML Form for File Upload

<html>

<head>

<title>Administration - upload new files</title>

</head>

<body>

<h1>Upload new news files</h1>

<form enctype=”multipart/form-data” action=”upload.php” method=post>

<input type=”hidden” name=”MAX_FILE_SIZE” value=”1000”>

Upload this file: <input name=”userfile” type=”file”>

<input type=”submit” value=”Send File”>

</form>

</body>

</html>

Note that this form uses POST File uploads will also work with the PUT method supported by

Netscape Composer and Amaya They will not work with GET

The extra features in this form are

• In the <form>tag, you must set the attribute enctype=”multipart/form-data”to let the server know that a file is coming along with the regular form information

• You must have a form field that sets the maximum size file that can be uploaded This is

a hidden field, and is shown here as

<input type=”hidden” name=”MAX_FILE_SIZE” value=”1000”>

The name of this form field must be MAX_FILE_SIZE The value is the maximum size (in bytes) of files you will allow people to upload

• You need an input of type file, shown here as

<input name=”userfile” type=”file”>

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You can choose whatever name you like for the file, but keep it in mind as you will use this name to access your file from the receiving PHP script

Writing the PHP to Deal with the File

Writing the PHP to catch the file is pretty straightforward

When the file is uploaded, it will go into a temporary location on the Web server This is the Web server’s default temporary directory If you do not move or rename the file before your script finishes execution, it will be deleted

Given that your HTML form has a field in it called userfile, you will end up with four vari-ables being passed to PHP:

• The value stored in $userfileis where the file has been temporarily stored on the Web server

• The value stored in $userfile_nameis the file’s name on the user’s system

• The value stored in $userfile_sizeis the size of the file in bytes

• The value stored in $userfile_typeis the MIME type of the file, for example,

text/plainor image/gif You can also access these variables via the $HTTP_POST_FILESarray, as follows:

• $HTTP_POST_FILES[‘userfile’][‘tmp_name’]

• $HTTP_POST_FILES[‘userfile’][‘name’]

• $HTTP_POST_FILES[‘userfile’][‘size’]

• $HTTP_POST_FILES[‘userfile’][‘type’]

Given that you know where the file is and what it’s called, you can now copy it to somewhere useful At the end of your script’s execution, the temporary file will be deleted Hence, you must move or rename the file if you want to keep it

In our example, we’re going to use the uploaded files as recent news articles, so we’ll strip out any tags that might be in them, and move them to a more useful directory A script that does this is shown in Listing 16.2

L ISTING 16.2 upload.php—PHP to Catch the Files from the HTML Form

<head>

<title>Uploading </title>

</head>

<body>

<h1>Uploading file </h1>

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