Core/Toolbox/IO/Sendfile.php
public function getContentType(): string
    {
        if (empty($this->content_type) && !empty($this->file)) {
            $this->content_type = $this->getMimeType($this->file);
        }

        return $this->content_type;
    }
public function getContentType(): string
    {
        if (empty($this->content_type) && !empty($this->file)) {
            $this->content_type = $this->getMimeType($this->file);
        }

        return $this->content_type;
    }
Returns content type of file

Tries to autodetect content type when no type is set.

@return string