Challenge 3 — Solution

Task: Write a function postJson($url, $data) that sends an associative
array as a JSON-encoded POST request with the correct Content-Type
header, and returns the decoded JSON response. Show how it would be
called with a sample $data array.

<?php
    function postJson(string $url, array $data): ?array {
        $ch = curl_init($url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($data));
        curl_setopt($ch, CURLOPT_HTTPHEADER, ["Content-Type: application/json"]);

        $response = curl_exec($ch);
        curl_close($ch);

        return json_decode($response, true);
    }

    $newPost = [
        "title" => "My First Post",
        "body" => "Hello, world!"
    ];

    $result = postJson("https://api.example.com/posts", $newPost);

    if ($result !== null) {
        echo "Post created with ID: " . ($result['id'] ?? 'unknown');
    } else {
        echo "Failed to create the post.";
    }
?>


Output:
(Depends on the placeholder API actually being reachable and returning
valid JSON - shown here is the expected shape of a successful call:)
Post created with ID: unknown

Notes:
- json_encode($data) converts the $newPost associative array into a
  JSON string before it's ever sent, and CURLOPT_POSTFIELDS attaches
  that JSON string as the request body.
- The "Content-Type: application/json" header is essential - without
  it, many real APIs would either reject the request outright or
  misinterpret the JSON body as a plain form submission instead,
  exactly the chapter's own warning about this header being easy to
  forget.
- $result['id'] ?? 'unknown' uses the null coalescing operator (from
  PHP Fundamentals Chapter 8) to safely handle the case where the API's
  own response shape doesn't include an 'id' key, rather than
  triggering an undefined-key warning.