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Upload error handling

PHP course · Intermediate · Lesson 80/115

Learn to read $_FILES['file']['error'] codes and give meaningful error messages.

Upload error codes

Every upload carries an error code. This code lives in $_FILES['avatar']['error']. If the code is 0 (UPLOAD_ERR_OK) the upload succeeded; any other value means a problem.

Knowing the codes helps you show the right message. For example, 'file too large' and 'no file sent' are different situations that need different messages.

PHP defines these codes as UPLOAD_ERR_* constants. Using the constants (e.g. UPLOAD_ERR_OK instead of 0) makes the code more readable.

Common constants

The most common error constants are:

  • UPLOAD_ERR_OK (0): no error, upload succeeded
  • UPLOAD_ERR_INI_SIZE (1): upload_max_filesize exceeded
  • UPLOAD_ERR_PARTIAL (3): file was only partially uploaded
  • UPLOAD_ERR_NO_FILE (4): no file was selected

You translate these to messages with a match or an array. For example $messages = [UPLOAD_ERR_OK => 'No error', ...]. Then read with $messages[$code] ?? 'Unknown'; this gives each code a clear explanation.

Exercise The errorMessage function

Write an errorMessage(int $code): string function. Inside it, define the $messages array keyed by UPLOAD_ERR_OK, UPLOAD_ERR_INI_SIZE, UPLOAD_ERR_PARTIAL and UPLOAD_ERR_NO_FILE (values: 'No error', 'ini size limit exceeded', 'Partial upload', 'No file'). Then return $messages[$code] ?? 'Unknown: ' . $code. Finally call echo errorMessage(...) . "\n" for UPLOAD_ERR_OK, UPLOAD_ERR_INI_SIZE and UPLOAD_ERR_NO_FILE.

Show example solution 
' + code. Echo three codes in order.
Example solution:
<?php
// Build message from error code
function errorMessage(int $code): string {
    $messages = [
        UPLOAD_ERR_OK => "No error",
        UPLOAD_ERR_INI_SIZE => "ini size limit exceeded",
        UPLOAD_ERR_PARTIAL => "Partial upload",
        UPLOAD_ERR_NO_FILE => "No file",
    ];
    return $messages[$code] ?? "Unknown: " . $code;
}

echo errorMessage(UPLOAD_ERR_OK) . "\n";
echo errorMessage(UPLOAD_ERR_INI_SIZE) . "\n";
echo errorMessage(UPLOAD_ERR_NO_FILE) . "\n";

Test yourself

  1. Match constants and meanings

    UPLOAD_ERR_OK
    No error
    UPLOAD_ERR_INI_SIZE
    ini limit exceeded
    UPLOAD_ERR_PARTIAL
    Partial upload
    UPLOAD_ERR_NO_FILE
    No file sent

  2. Which constant means a successful upload?

    • UPLOAD_ERR_INI_SIZE
    • UPLOAD_ERR_OK
    • UPLOAD_ERR_PARTIAL
    • UPLOAD_ERR_NO_FILE
    Show answer

    UPLOAD_ERR_OK — Correct. UPLOAD_ERR_OK means no error.

  3. Success check

    if ($file['error'] === ____) { return 'OK'; }
    Show answer 
    if ($file['error'] === UPLOAD_ERR_OK) { return 'OK'; }

All lessons in Intermediate

1 Classes

  1. Defining a class
  2. Defining properties
  3. Defining methods
  4. In-class access with $this
  5. Instantiating with new
  6. Summary - Classes

2 Constructor

  1. The __construct method
  2. Passing parameters to the constructor
  3. Initializing properties
  4. Class type declaration
  5. The __destruct method
  6. Summary - Constructor

3 Inheritance

  1. Inheritance with extends
  2. Accessing parent with parent::
  3. Method override
  4. protected property and method
  5. Inheritance chain
  6. Summary - Inheritance

4 Project: Utility library

  1. Project: Utility library
  2. Class skeleton
  3. Adding methods
  4. Using with file inclusion
  5. Project final - Library

5 Visibility

  1. public access
  2. protected access
  3. private access
  4. Encapsulation
  5. Getter and setter methods
  6. Summary - Visibility

6 Static members

  1. static property
  2. static method
  3. In-class access with self::
  4. Late static binding with static::
  5. static vs instance
  6. Summary - Static members

7 Class constants

  1. Class constants with const
  2. Accessing constants
  3. Class name with ::class
  4. Class constants vs static
  5. Constant use cases
  6. Summary - Class constants

8 Project: Quiz app

  1. Project: Quiz app
  2. Designing a question class
  3. Checking answers
  4. Computing the score
  5. Project final - Quiz app

9 Interfaces

  1. Defining interfaces
  2. Implementing with implements
  3. Multiple interfaces
  4. Polymorphism
  5. interface vs abstract
  6. Summary - Interfaces

10 Abstract classes

  1. Defining abstract classes
  2. abstract methods
  3. Abstract class inheritance
  4. Template method pattern
  5. Constructor and abstract
  6. Summary - Abstract classes

11 Traits

  1. Defining traits
  2. Using traits with use
  3. Multiple traits
  4. Resolving method conflicts
  5. Trait vs inheritance
  6. Summary - Traits

12 Project: Blog app

  1. Project: Blog app
  2. Creating a post class
  3. Adding posts with a form
  4. Displaying the post list
  5. Project final - Blog

13 File handling

  1. Reading with file_get_contents()
  2. Writing with file_put_contents()
  3. Opening files with fopen()
  4. fwrite() and fread()
  5. Closing files with fclose()
  6. Summary - File handling

14 File upload

  1. The $_FILES superglobal
  2. move_uploaded_file()
  3. Validating file type
  4. File size limit
  5. Upload error handling
  6. Summary - File upload

15 Sessions

  1. Starting a session with session_start()
  2. Storing data with $_SESSION
  3. Reading from a session
  4. unset() and session_destroy()
  5. Login/logout logic
  6. Summary - Sessions

16 Cookies

  1. Creating cookies with setcookie()
  2. Reading cookies with $_COOKIE
  3. Cookie expiration
  4. Deleting cookies
  5. Session vs cookie
  6. Summary - Cookies

17 Project: Contact form

  1. Project: Contact form
  2. Form skeleton
  3. Validating data
  4. Integrating file upload
  5. Project final - Contact form

18 Error handling

  1. The try/catch block
  2. Throwing exceptions with throw
  3. The Exception class
  4. error_reporting configuration
  5. Custom exception classes
  6. Summary - Error handling

19 Date and time

  1. Formatting dates with date()
  2. Timestamps with time()
  3. Parsing dates with strtotime()
  4. The DateTime class
  5. DateInterval and DatePeriod
  6. Summary - Date and time

20 Intermediate final

  1. Challenge - OOP app
  2. Challenge - File and session
  3. Challenge - Multi-step registration form
  4. Challenge - Error handling
  5. Challenge - Mini API