Posting multidimensional array with PHP and CURL

Question

Hi everyone, I'm having trouble posting form data via CURL to a receiving PHP script located on a different host.

I get an Array to string conversion error

This is print_r of the array I'm posting:

Array
(
    [name] => Array
    (
        [0] => Jason
        [1] => Mary
        [2] => Lucy
    )
    [id] => 12
    [status] => local
    [file] => @/test.txt
)

This is the line the error occurs on:

curl_setopt($this->ch, CURLOPT_POSTFIELDS, $post);

The third argument must be an array because I need the Content-Type header to be set to multipart/form-data as I am sending a file via this same array, therefore I cannot convert the array to a query string or use http_build_query().

Also I do not have access to the code on the receiving host so I cannot serialize and unserialize the array.

I'm assuming that the value of the name key being an array is the cause for this error, I'm also assuming that CURLOPT_POSTFIELDS doesn't support multidimensional arrays. Is there any other way around this or am I doomed?

Thanks in advance!

Answer 1

The concept of an array doesn't really exist when it comes to HTTP requests. PHP (and likely other server-side languages) has logic baked in that can take request data that looks like an array (to it) and puts it together as an array while populating $_GET, $_POST etc.

For instance, when you POST an array from a form, the form elements often look something like this:

<form ...>
  <input name="my_array[0]">
  <input name="my_array[1]">
  <input name="my_array[2]">
</form>

or even:

<form ...>
  <input name="my_array[]">
  <input name="my_array[]">
  <input name="my_array[]">
</form>

While PHP knows what to do with this data when it receives it (ie. build an array), to HTML and HTTP, you have three unrelated inputs that just happen to have similar (or the same, although this isn't technically valid HTML) names.

To do the reverse for your cURL request, you need to decompose your array into string representations of the keys. So with your name array, you could do something like:

foreach ($post['name'] as $id => $name)
{
  $post['name[' . $id . ']'] = $name;
}
unset($post['name']);

Which would result in your $post array looking like:

Array
(
    [name[0]] => Jason
    [name[1]] => Mary
    [name[2]] => Lucy
    [id] => 12
    [status] => local
    [file] => @/test.txt
)

And then each key in the array you are posting would be a scalar value, which cURL is expecting, and the array would be represented as you need to for HTTP.

Answer 2

I think you'll need to pass the options as a string:

curl_setopt($this->ch, CURLOPT_POSTFIELDS, 'name[]=Jason&name[]=Mary&name[]=Lucy...');

You should then be able to set the header manually via CURLOPT_HTTPHEADER.

Answer 3

You'd have to build the POST string manually, rather than passing the entire array in. You can then override curl's auto-chose content header with:

curl_setopt($c, CURLOPT_HTTPHEADER, array("Content-type: multipart/form-data"));

Serializing/json-ifying would be easier, but as you say, you have no control over the receiving end, so you've got a bit of extra work to do.