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Content-Type with header()

PHP course · Advanced · Lesson 51/92

Learn to set the JSON response header with header('Content-Type: application/json').

The header function sets the response header

The header function sends an HTTP response header. The browser or client reads these headers to understand the content type and how to handle it. The most common header is Content-Type.

The header must be called before any output is sent. Otherwise the server raises a headers already sent warning. So header calls always come before output.

The application/ media type

For structured data format responses, the Content-Type header takes a media type starting with application/. This prefix marks the content as application data, so the client picks the correct parser.

The client reads the Content-Type header and interprets the body accordingly. When the header and body match, the API works cleanly; otherwise the client errors. So you always set the header before any output.

Exercise Set the header and print the data

Convert the array in $data to a structured data format string and print it. First set a Content-Type: application/... header with the header function (the format name is shown in the lesson title). Then encode the array and print it.

Show example solution 
application/...'), then print with echo encode($data).
Example solution:
header('Content-Type: application/...');
echo encode($data);

Test yourself

  1. What Content-Type for a structured data format response?

    • A media type starting with application/
    • text/html
    • image/png
    • text/plain
    Show answer

    A media type starting with application/ — Correct. Structured data format responses use a media type starting with application/.

  2. Set the Content-Type header

    $data = ['status' => 'ok'];
____('Content-Type: application/...');
echo encode($data);
    Show answer 
    $data = ['status' => 'ok'];
header('Content-Type: application/...');
echo encode($data);

  3. Match the header concepts

    header()
    sends an HTTP header
    Content-Type
    declares the content type
    application/
    data format media prefix
    before output
    header call timing

All lessons in Advanced

1 PDO basics

  1. What is PDO?
  2. Connecting with PDO
  3. Running queries with query()
  4. Single row with fetch()
  5. All rows with fetchAll()
  6. Fetch mode constants
  7. Summary - PDO basics

2 Prepared statements

  1. Prepared statements with prepare()
  2. Running with execute()
  3. Binding parameters with bindParam()
  4. Binding values with bindValue()
  5. SQL injection and prevention
  6. Named placeholders
  7. Summary - Prepared statements

3 CRUD operations

  1. Inserting records with INSERT
  2. Reading records with SELECT
  3. Updating records with UPDATE
  4. Deleting records with DELETE
  5. Affected rows with rowCount()
  6. Transaction management
  7. Summary - CRUD operations

4 Project: Blog with PDO

  1. Project: Blog with PDO
  2. Database structure
  3. Adding and listing posts
  4. Editing and deleting posts
  5. Project final - Blog with PDO

5 Namespaces

  1. Defining namespaces
  2. Importing with use
  3. Aliases
  4. Global namespace
  5. Multi-level namespaces
  6. PSR-4 autoloading
  7. Summary - Namespaces

6 Composer

  1. What is Composer?
  2. The composer.json file
  3. Adding packages with require
  4. Autoload (PSR-4)
  5. Installing packages from Packagist
  6. composer update and install
  7. Summary - Composer

7 Regex

  1. Matching with preg_match()
  2. Replacing with preg_replace()
  3. All matches with preg_match_all()
  4. Character classes
  5. Quantifiers
  6. Capture groups
  7. Summary - Regex

8 JSON and API

  1. Encoding with json_encode()
  2. Parsing with json_decode()
  3. JSON error handling
  4. Content-Type with header()
  5. REST API basics
  6. HTTP methods
  7. Summary - JSON and API

9 Project: REST API

  1. Project: REST API
  2. Routing structure
  3. CRUD endpoints
  4. JSON response format
  5. Project final - REST API

10 Security

  1. Hashing with password_hash()
  2. Verifying with password_verify()
  3. SQL injection prevention
  4. XSS prevention
  5. CSRF token generation
  6. Security headers
  7. Summary - Security

11 Middleware

  1. The middleware pattern
  2. Request/Response cycle
  3. Middleware chain
  4. Auth middleware
  5. Logging middleware
  6. PSR-15 basics
  7. Summary - Middleware

12 Testing basics

  1. What is PHPUnit?
  2. Writing your first test
  3. Assertions
  4. Test layout (AAA)
  5. Test doubles (mock, stub)
  6. setUp and tearDown
  7. Summary - Testing basics

13 Design patterns

  1. The Singleton pattern
  2. The Factory pattern
  3. The Observer pattern
  4. The Strategy pattern
  5. The Decorator pattern
  6. The Adapter pattern
  7. Summary - Design patterns

14 Advanced final

  1. Challenge - PDO and API
  2. Challenge - Security app
  3. Challenge - Design patterns
  4. Challenge - Writing tests
  5. Challenge - Mini framework