PHP, cURL, and HTTP POST example?

<?php
//
// A very simple PHP example that sends a HTTP POST to a remote site
//

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL,"http://www.example.com/tester.phtml");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS,
            "postvar1=value1&postvar2=value2&postvar3=value3");

// In real life you should use something like:
// curl_setopt($ch, CURLOPT_POSTFIELDS, 
//          http_build_query(array('postvar1' => 'value1')));

// Receive server response ...
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

$server_output = curl_exec($ch);

curl_close ($ch);

// Further processing ...
if ($server_output == "OK") { ... } else { ... }
?>

1.Step by step

• Initialize the cURL session:

$url = "www.domain.com";
$ch = curl_init($url);

• If your request has headers like bearer token or defining JSON contents you have to set HTTPHEADER options to cURL:

$token = "generated token code";
curl_setopt(
    $ch, 
    CURLOPT_HTTPHEADER, 
    array(
        'Content-Type: application/json', // for define content type that is json
        'bearer: '.$token, // send token in header request
        'Content-length: 100' // content length for example 100 characters (can add by strlen($fields))
    )
);

• If you want to include the header in the output set CURLOPT_HEADER to true:

curl_setopt($ch, CURLOPT_HEADER, false);

• Set RETURNTRANSFER option to true to return the transfer as a string instead of outputting it directly:

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

• To check the existence of a common name in the SSL peer certificate can be set to 0(to not check the names), 1(not supported in cURL 7.28.1), 2(default value and for production mode):

curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);

• For posting fields as an array by cURL:

$fields = array(
    "username" => "user1",
    "password" => "passuser1",
    "gender" => 1
);
curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);

• Execute cURL and return the string. depending on your resource this returns output like result=OK:

$result = curl_exec($ch);

• Close cURL resource, and free up system resources:

curl_close($ch);

2.Use as a class

• The whole call_cURL class that can be extended:

class class_name_for_call_cURL {
    protected function getUrl() {
        return "www.domain.com";
    }

    public function call_cURL() {
        $token = "generated token code";

        $fields = array(
            "username" => "user1",
            "password" => "passuser1",
            "gender" => 1
        );

        $url = $this->getUrl();
        $output = $this->_execute($fields, $url, $token);
        
        // if you want to get json data
        // $output = json_decode($output);
            
        if ($output == "OK") {
            return true;
        } else {
             return false;
        }
    }

    private function _execute($postData, $url, $token) {
        // for sending data as json type
        $fields = json_encode($postData);

        $ch = curl_init($url);
        curl_setopt(
            $ch, 
            CURLOPT_HTTPHEADER, 
            array(
                'Content-Type: application/json', // if the content type is json
                'bearer: '.$token // if you need token in header
            )
        );
        curl_setopt($ch, CURLOPT_HEADER, false);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);

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

        return $result;
    }
}

• Using the class and call cURL:

$class = new class_name_for_call_cURL();
var_dump($class->call_cURL()); // output is true/false

3.One function

• A function for using anywhere that needed:

function get_cURL() {

        $url = "www.domain.com";
        $token = "generated token code";

        $postData = array(
            "username" => "user1",
            "password" => "passuser1",
            "gender" => 1
        );

        // for sending data as json type
        $fields = json_encode($postData);

        $ch = curl_init($url);
        curl_setopt(
            $ch, 
            CURLOPT_HTTPHEADER, 
            array(
                'Content-Type: application/json', // if the content type is json
                'bearer: '.$token // if you need token in header
            )
        );
        curl_setopt($ch, CURLOPT_HEADER, false);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);

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

        return $result;
}

• This function is usable just by:

var_dump(get_cURL());

I'm surprised nobody suggested file_get_contents:

$url = "http://www.example.com";
$parameters = array('username' => 'user1', 'password' => 'passuser1', 'gender' => '1');
$options = array('http' => array(
    'header'  => 'Content-Type: application/x-www-form-urlencoded\r\n',
    'method'  => 'POST',
    'content' => http_build_query($parameters)
));

$context  = stream_context_create($options);
$result = file_get_contents($url, false, $context);

it's simple, it works; I use it in an environment where I control the code at both ends.

even better, use json_decode (and set up your code to return JSON)

$result = json_decode(file_get_contents($url, false, $context), TRUE);

this approach invokes curl behind the scenes, but you don't jump through as many hoops.

Answer refined from this original answer elsewhere on Stack Overflow: PHP sending variables to file_get_contents()

If the form is using redirects, authentication, cookies, SSL (https), or anything else other than a totally open script expecting POST variables, you are going to start gnashing your teeth really quick. Take a look at Snoopy, which does exactly what you have in mind while removing the need to set up a lot of the overhead.

Examples of sending form and raw data:

$curlHandler = curl_init();

curl_setopt_array($curlHandler, [
    CURLOPT_URL => 'https://postman-echo.com/post',
    CURLOPT_RETURNTRANSFER => true,

    /**
     * Specify POST method
     */
    CURLOPT_POST => true,

    /**
     * Specify array of form fields
     */
    CURLOPT_POSTFIELDS => [
        'foo' => 'bar',
        'baz' => 'biz',
    ],
]);

$response = curl_exec($curlHandler);

curl_close($curlHandler);

echo($response);

If you try to login on site with cookies.

This code:

if ($server_output == "OK") { ... } else { ... }

It May not works if you try to login, because many sites return status 200, but the post is not successful.

The easy way to check if the login post is successful is to check if it setting cookies again. If in output have a Set-Cookies string, this means the posts are not successful and it starts a new session.

Also, the post can be successful, but the status can redirect instead of 200.

To be sure the post is successful try this:

Follow location after the post, so it will go to the page where the post does redirect to:

curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);

And than check if new cookies existing in the request:

if (!preg_match('/^Set-Cookie:\s*([^;]*)/mi', $server_output)) 

{echo 'post successful'; }

else { echo 'not successful'; }

Easiest is to send data as application/json. This will take an array as input and properly encodes it into a json string:

$data = array(
    'field1' => 'field1value',
    'field2' => 'field2value',
)

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($data));

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type:application/json',
));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$resultStr = curl_exec($ch);
return json_decode($resultStr, true);