How can I output a php image resource using Laminas MVC?

Question

I currently output an image like this (inside a controller class):

    ob_start();
    header("Content-Type: image/gif");
    imagegif($image_resource);
    imagedestroy($image_resource);
    $content_string = ob_get_clean();
    $this->getResponse()->setContent($content_string);

Is there a better way without actually capturing the output buffer? since this is not very testable...

Answer 1

The Only way to capture the image without output-buffer is to write the image to a file:

$tmpFile = tmpfile();
$path = stream_get_meta_data($tmpFile)['uri'];
imagegif($image_resource, $tmpFile);
$content_string = file_get_contents($path);
imagedestroy($image_resource);
fclose($tmpFile);

$this->getResponse()->setContent($content_string);

I created a temporary file with the tmpfile() method, and got the filename via stream_get_metadata() function. Then I loaded the content of the file into the string variable and closed the filehandle to the tmpfile so it gets removed.

A more optimized way from the comments proposed writing to a php://memory file instead. The is a small explanation in another question on when to use php://memory and php://temp

// open in memory file
$handle = fopen('php://memory', 'r+');
imagegif($im, $handle);
// reset file handle
fseek($handle, 0);

// get filesize
$stat = fstat($handle);
$size = $stat['size'];

// read the created file into variable
$fileContent = fread($handle, $size);
fclose($handle);

// write filecontent to the response object
$this->getResponse()->setContent($content_string);

Personally i would use the output buffer but move the code into a separate function or class. That way you can isolate and mock its behavior for testing purposes:

/** @var GDImage|resource $image */
function getImage($image): string
{
   ob_start();
   imagegif($image);
   $returnData = ob_get_contents();
   ob_end_clean();
   imagedestroy($image);
   return $returnData;
}
$content_string = getImage($image_resource);
$this->getResponse()->setContent($content_string);

In any way i would advise you to set the header on the response object instead of writing it manually:

$this->getResponse()->getHeaders()->addHeaders([
    'Content-Type' => 'image/gif',
]);
$this->getResponse()->setContent($content_string);

This way the headers get output to the browser by the framework at the correct time and you will not have any problems with output buffering.