How can I upload files to GoogleDrive in "multipart" type by using php-curl?

I want to upload in using php curl other than google-api-php-client, but I really don't know how to do it, here is the documentation:Send a multipart upload request

Here is my code snippet, I stuck in CURLOPT_POSTFIELDS, can anybody help me with this?

public function uploadByCurl($uploadFilePath, $accessToken){
    $ch = curl_init();
    $mimeType = $this->getMimeType($uploadFilePath);
    $options = [
        CURLOPT_URL =>  'https://www.googleapis.com/upload/drive/v3/files?uploadType=multipart',
        CURLOPT_POST => true,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_POSTFIELDS => [
            'file' => new \CURLFile($uploadFilePath),
            // 'name' =>
        ],
        CURLOPT_HTTPHEADER => [
            'Authorization:Bearer ' . $accessToken,
            'Content-Type:' . $mimeType,
            'Content-Length:' . filesize($uploadFilePath),
        ],
        //In case you're in Windows, sometimes will throw error if not set SSL verification to false
        CURLOPT_SSL_VERIFYPEER => false,
        CURLOPT_SSL_VERIFYHOST => 0,
    ];
    //In case you need a proxy
    //$options[CURLOPT_PROXY] = 'http://127.0.0.1:1087';

    curl_setopt_array($ch, $options);
    $result = curl_exec($ch);
    if (curl_errno($ch)) {
        echo 'Error:' . curl_error($ch);
    }
    curl_close ($ch);
    return $result;
}

I just don't know how to translate this to code(not familiar with multipart/related):

Metadata part. Must come first, and must have a Content-Type header set to application/json; charset=UTF-8. Add the file's metadata to this part in JSON format.
Media part. Must come second, and must have a Content-Type header, which may have any MIME type. Add the file's data to this part.

Solution

You want to upload a file using multipart/ralated with Drive API v3.
You want to achieve this using PHP CURL.
Your access token can be used for uploading the file to Google Drive.

If my understanding is correct, how about this answer?

Modification points:

In this case, I would like to propose to create the structure including the file and the metadata for multipart/ralated and request it.

Modified script:

When your script is modified, it becomes as follows.

public function uploadByCurl($uploadFilePath, $accessToken){
    $handle = fopen($uploadFilePath, "rb");
    $file = fread($handle, filesize($uploadFilePath));
    fclose($handle);

    $boundary = "xxxxxxxxxx";
    $data = "--" . $boundary . "\r\n";
    $data .= "Content-Type: application/json; charset=UTF-8\r\n\r\n";
    $data .= "{\"name\": \"" . basename($uploadFilePath) . "\", \"mimeType\": \"" . mime_content_type($uploadFilePath) . "\"}\r\n";
    $data .= "--" . $boundary . "\r\n";
    $data .= "Content-Transfer-Encoding: base64\r\n\r\n";
    $data .= base64_encode($file);
    $data .= "\r\n--" . $boundary . "--";

    $ch = curl_init();
    $options = [
        CURLOPT_URL =>  'https://www.googleapis.com/upload/drive/v3/files?uploadType=multipart',
        CURLOPT_POST => true,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_POSTFIELDS => $data,
        CURLOPT_HTTPHEADER => [
            'Authorization:Bearer ' . $accessToken,
            'Content-Type:multipart/related; boundary=' . $boundary,
        ],
        CURLOPT_SSL_VERIFYPEER => false,
        CURLOPT_SSL_VERIFYHOST => 0,
    ];
    curl_setopt_array($ch, $options);
    $result = curl_exec($ch);
    if (curl_errno($ch)) {
        echo 'Error:' . curl_error($ch);
    }
    curl_close ($ch);
    return $result;
}

At this modified script, the filename and mimeType are retrieved from $uploadFilePath.

Note:

Multipart upload can upload files less than 5 MB size. Please be careful this.

References:

Perform a multipart upload

Multipart upload: uploadType=multipart. For quick transfer of a small file (5 MB or less) and metadata that describes the file, all in a single request.