Sending multi-dimensional data and multiple files with CurlFile in one request

Let’s say we have a form like the one below. We want to send the data to our webserver via AJAX and from there to a script running on an external server.

So we have normal inputs, a multi-select field and a file dropzone where we can upload multiple files.

Assuming the AJAX POST request was successful we get the following data on PHP site:

// print_r($_POST)

Array
(
    [first_name] => John
    [last_name] => Doe
    [activities] => Array
        (
            [0] => soccer
            [1] => hiking
        )
)

and the files should look like this

// print_r($_FILES)

Array
(
    [upload] => Array
        (
            [name] => Array
                (
                    [0] => my_photo.jpg
                    [1] => my_life.pdf
                )

            [type] => Array
                (
                    [0] => image/jpg
                    [1] => application/pdf
                )

            [tmp_name] => Array
                (
                    [0] => /tmp/phpW5spji
                    [1] => /tmp/phpWgnUeY
                )

            [error] => Array
                (
                    [0] => 0
                    [1] => 0
                )

            [size] => Array
                (
                    [0] => 647548
                    [1] => 643223
                )

        )

)

So far, so good. Now we want to send this data and files to the external server using cURL with the CurlFile Class

Since cURL only accepts a simple but not a multi-dimensional array, we have to flatten the $_POST array first.

To do this, you could use this function for example which gives you the following:

// print_r($new_post_array)

Array
(
    [first_name] => John
    [last_name] => Doe
    [activities[0]] => soccer
    [activities[1]] => hiking
)

The next step is to create CurlFile Objects for the uploaded files. This is done by the following loop:

$files = array();

foreach ($_FILES["upload"]["error"] as $key => $error) {
    if ($error == UPLOAD_ERR_OK) {

        $files["upload[$key]"] = curl_file_create(
            $_FILES['upload']['tmp_name'][$key],
            $_FILES['upload']['type'][$key],
            $_FILES['upload']['name'][$key]
        );
    }
}

curl_file_create is a helper function of the CurlFile Class and creates the CurlFile objects. We save each object in the $files array with keys named “upload[0]” and “upload[1]” for our two files.

We now have to combine the flattened post array and the files array and save it as $data like this:

$data = $new_post_array + $files;

The last step is to send the cURL request:

$ch = curl_init();

curl_setopt_array($ch, array(
    CURLOPT_POST => 1,
    CURLOPT_URL => "https://api.externalserver.com/upload.php",
    CURLOPT_RETURNTRANSFER => 1,
    CURLINFO_HEADER_OUT => 1,
    CURLOPT_POSTFIELDS => $data
));

$result = curl_exec($ch);

curl_close ($ch);

Since $data is now a simple (flat) array, cURL automatically sends this POST request with Content Type: multipart/form-data

In upload.php on the external server you can now get the post data and files with $_POST and $_FILES as you would normally do.