How to POST a File String with cURL in PHP: A Step-by-Step Guide

POSTing a File String with cURL in PHP

In web development, transmitting files along with form data is a common requirement. While cURL offers a straightforward method to POST files from the file system, this article explores a technique to POST a file directly as a string, bypassing the need for temporary file creation.

Constructing the POST Data

The key lies in manually constructing the multipart/form-data request body. Begin by separating form fields from file uploads. For each non-file field, create a form-data section with the field name and value.

Next, for each file to be uploaded, create a form-data section with the file name, mime type, and actual file content.

Setting Headers

To simulate a browser-like POST, set the appropriate headers:

<code class="php">'Content-Type: multipart/form-data; boundary=' . $delimiter
'Content-Length: ' . strlen($data)</code>

where $delimiter is a unique string that separates each section of the form data.

Making the Request

<code class="php">$handle = curl_init($url);
curl_setopt($handle, CURLOPT_POST, true);
curl_setopt($handle, CURLOPT_HTTPHEADER , array(
    'Content-Type: multipart/form-data; boundary=' . $delimiter,
    'Content-Length: ' . strlen($data)));  
curl_setopt($handle, CURLOPT_POSTFIELDS, $data);
curl_exec($handle);</code>

By constructing the multipart/form-data body and setting the necessary headers, cURL can seamlessly POST a file represented as a string, providing a more flexible and efficient approach compared to working with physical files.

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