How to Send Raw Image Data via Multipart/Form-Data in cURL for PHP?

Sending Raw Image Data via Multipart/Form-Data in cURL for PHP

When interacting with an API that expects image data via multipart/form-data, posting the image correctly can be challenging. In PHP, this process involves setting multipart/form-data headers and handling raw image data.

Form Structure

On the client side, the HTML form can be created as shown:

Server-Side Processing

On the server side, the PHP code to post the image data would be:

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_POST, 1);
$filePath = '/path/to/image.png';
$fields = [
    'name' => new \CurlFile($filePath, 'image/png', 'filename.png')
];
curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookieJar);
curl_setopt($ch, CURLOPT_HEADER, 1);
curl_setopt($ch, CURLINFO_HEADER_OUT, 1);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: multipart/form-data'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

// Get the response and check the content type
$response = curl_exec($ch);
$requestContentType = curl_getinfo($ch, CURLINFO_CONTENT_TYPE);
echo "<br>request Content Type was:".$requestContentType."<br>";

curl_close($ch);

echo "<br><b>SERVER POST IMAGE RESPONSE:</b><br>";
echo $response;

Using a CurlFile Object

In PHP versions before 5.6, using @$filePath without setting CURLOPT_SAFE_UPLOAD would work. However, in PHP 7 and above, it's necessary to use a CurlFile object to handle file uploads safely. This ensures that the raw image data is correctly transferred.

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