Uploading Files Securely with PHP
Illustration by Don Barnett

Planning the class's features


From:

Uploading Files Securely with PHP

with David Powers

Video: Planning the class's features

In the previous chapter, we created a basic script to upload the single file. But it was far from perfect. Although there was a hidden form field to set the maximum size for an individual file, someone could easily create a form of their own to get around that restriction. No checks are made on the type of file being uploaded. If the files are stored in the public folder, this presents a security risk. There's no check on filenames. So they could contain spaces, causing problems on Linux servers or in URLs.
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  1. 4m 49s
    1. Welcome
      57s
    2. What you should know before watching this course
      2m 0s
    3. Using the exercise files
      1m 52s
  2. 33m 2s
    1. How PHP handles file uploads
      6m 16s
    2. Examining the $_FILES array
      5m 8s
    3. Setting the maximum file size
      5m 36s
    4. Preparing the upload folder
      3m 18s
    5. Moving the file to its destination
      6m 51s
    6. Limitations on file uploads
      5m 53s
  3. 47m 3s
    1. Planning the class's features
      3m 15s
    2. Creating and using a namespaced class
      5m 25s
    3. Creating the class constructor
      7m 26s
    4. Getting a reference to the uploaded file
      5m 9s
    5. Checking the error level
      5m 7s
    6. Displaying errors and other messages
      4m 51s
    7. Setting and checking the maximum file size
      7m 19s
    8. Strengthening the setMaxSize() method
      8m 31s
  4. 35m 30s
    1. Restricting acceptable MIME types
      5m 27s
    2. Removing spaces from file names
      5m 21s
    3. Restricting acceptable file-name extensions
      6m 10s
    4. Neutralizing potentially dangerous uploads
      5m 54s
    5. Renaming files with duplicate names
      7m 58s
    6. Moving the file to its destination
      4m 40s
  5. 10m 25s
    1. Understanding how the $_FILES array handles multiple files
      4m 42s
    2. Adapting the class to handle both single and multiple uploads
      5m 43s
  6. 38m 15s
    1. Overview of the UploadFile class
      5m 9s
    2. Setting up to use the class
      4m 11s
    3. Using the class
      8m 12s
    4. Reporting errors with multiple uploads
      4m 0s
    5. Displaying the server limits
      4m 51s
    6. Alerting the user about exceeding the server limits
      6m 14s
    7. Changing the class's defaults
      5m 38s
  7. 1m 38s
    1. Goodbye
      1m 38s

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Watch the Online Video Course Uploading Files Securely with PHP
2h 50m Intermediate Feb 24, 2014

Viewers: in countries Watching now:

The basic process of uploading files with PHP is very simple, but there are security implications that many people are unaware of. This course shows how to create a secure custom PHP class that can handle both single-file and multi-file uploads. Author David Powers shows you how to create a file upload class that checks the size, type, and names of files, renaming them when it encounters a duplicate file name. He'll show you how to make the class report on the outcome of the upload process and the nature of any errors that occur, and how to prevent the user from uploading files that exceed the server limits.

At the end of this course, you'll have a robust, flexible class that can be incorporated into many projects (including web forms) with just a few lines of code.

Topics include:
  • How PHP handles file uploads
  • Setting the maximum file size
  • Moving the file to its destination
  • Creating and using a namespaced class
  • Displaying error messages
  • Restricting unacceptable MIME types and file extensions
  • Using the class
  • Reporting errors
  • Altering the user
Subject:
Developer
Software:
PHP
Author:
David Powers

Planning the class's features

In the previous chapter, we created a basic script to upload the single file. But it was far from perfect. Although there was a hidden form field to set the maximum size for an individual file, someone could easily create a form of their own to get around that restriction. No checks are made on the type of file being uploaded. If the files are stored in the public folder, this presents a security risk. There's no check on filenames. So they could contain spaces, causing problems on Linux servers or in URLs.

Also, files with the same name as an existing one, automatically overwrite the original. The basic script handles only one file at a time. And it would be difficult to reuse without adapting the same script each time you want to use it. To solve these shortcomings, we're going to create a custom class. A class is basically a collection of related variables and functions that are designed to work together to perform a specific task, in this case to upload files.

Variables defined inside the class are known as properties. Functions inside a class are known as methods, but they're defined in exactly the same way as any other function. Calling the method as simply a convention. In php, you can set the visibility of properties and methods to public, protected or private. Public means they can be freely accessed. Protected or private hides them from strips outside the class definition, preventing values from being changed accidentally.

You use the class to create an object. You store this in a variable like any other value, but it gives you a strip access to the classes properties and methods. We'll be creating a class called UploadFile. The first requirement is that it should be easy to reuse. It needs to check the maximum size on the server side to avoid running out of disk space. The class should restrict uploads to specific mime types, and if that's too restrictive, it should neutralize potentially risky types.

For example, if an executable file is uploaded, adding a suffix to the file name will prevent it from being run automatically. Filenames need to be cleaned up by removing spaces. There also needs to be an option to check for duplicate file names ,and add a number to the file's base name to prevent existing files from being overwritten. The class also needs to handle multiple uploads seamlessly. To avoid conflicts with other scripts the class will use a namespace. This means the server must be running php 5.3 or later.

Official support for earlier versions of php ended in December 2010. So if your server is still running PHP 5.2 you're well overdo an upgrade. Like the original script, the class needs to inform the user of the outcome of the upload. And the class will need some helper methods such as converter's too and from megabytes. Which can also be used without creating an object. There's a lot of work to be done. So let's get on with building the class.

There are currently no FAQs about Uploading Files Securely with PHP.

 
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