How do I encode an image from storage to base64?

I'm trying to forward an image in storage via email as an attachment, but either the email is not sent (Response returns The attachment content must be base64) if I put data:$mimeType;base64, before the $image or it's sent, but the attachment is unviewable, either in preview mode, or after downloading it (it has the wrong size too).

Here's my code (I'm using purely REST API at this point)

TypeScript

Future _testEmail()async {
  String path = "storage/buckets/$bucketId/files/$docId/preview";
  var response = await _httpService.get(path);
    if (response?.statusCode == 200 && response?.data != null) {
      
      // grab data as Uint8List
      image = const Utf8Encoder().convert(response?.data);
      // encode to base64 for attaching
      final img = base64Encode(image);
      //get Mime Type
      final type = response?.headers.value("Content-Type");

      _sendEmail($firstName, $lastName, $recipient, img, type!);
    } else {
      debugPrint("Ooooooooppppppsssss!!!");
    }
}

TL;DR

Developers are having trouble encoding an image from storage to base64 for email attachments. The solution involves ensuring there's a space after the comma in the attachment content, and correctly encoding the image to base64 before attaching it to the email.

TypeScript

void _sendEmail(String firstName, String lastName, String recipient,
      String image, String mimeType) async {
    const path = "send";
    final ext = mimeType.split("/")[1];
    String fileName = (ext == 'png') ? "$name.png" : "$name.jpg";

    final data = {
      "personalizations": [
        {
          "to": [
            {
              "name": "Email Recipient",
              "email": recipient
            }
          ]
        }
      ],
      "from": {"email": "sender@gmail.com"},
      "subject": "Test Email with Attachment",
      "content": [
        {
          "type": "text/html",
          "value":
              "Sample email with attachment from $fname $lname."
        }
      ],
      "attachments": [
        {
          "content": "data:$mimeType;base64,$image", // generates the attachment must be base64
          // "content": image,                       // email is sent, but wrong size & unusable
          "filename": fileName,
          "type": mimeType
        }
      ]
    };

    
    final response = await _httpEmail.post(path, data);  // sending email via REST API

    if (response?.statusCode == 202 && response?.data != null) {
      print("Email sent!");
    } else {
      print("Status Code: ${response?.statusCode.toString()}");
      print("Response Data: ${response?.data.toString()}");
    }
  }