Example of PHP RESTful Web Service

contact.php

<?php

header("Access-Control-Allow-Origin: *");

$id = isset($_GET['id']) ? $_GET['id'] : NULL;

if ($id != NULL)
{
    $contact = findById($id);
    if ($contact != NULL) 
    {
        header('Content-type: text/json');
        header("HTTP/1.0 200 OK");
        echo json_encode($contact);
    } else {
        $error = ['code' => 4, 'message' => 'Contact with ID ' . $id . ' does not exist.'];
        header('Content-type: text/json');
        header("HTTP/1.0 404 Not Found");
        echo json_encode($error);
    }
    
}
else 
{
    $contacts = findAll();
    header('Content-type: text/json');
    header("HTTP/1.0 200 OK");
    echo json_encode($contacts);
}

function findById($id)
{
    $contacts = findAll();
    foreach($contacts as $contact) 
    {
        if ($contact['id'] == $id)
        {
            return $contact;
        }
    }
    
    return NULL;
}

function findAll()
{
    return [
        ['id' => 1, 'lastName' => 'Rizal', 'firstName' => 'Jose', 'mobileNumber' => '09161234561'],
        ['id' => 2, 'lastName' => 'Bonifacio', 'firstName' => 'Andres', 'mobileNumber' => '09161234562'],
        ['id' => 3, 'lastName' => 'Mabini', 'firstName' => 'Apolinario', 'mobileNumber' => '09161234563']
    ];
}