How to save base64 image in Blob with Carrierwave in Rails4? - ruby-on-rails

Question

Like described in this Tutorial, I'm converting a canvas into a DataUrl and this DataUrl into a Blob. Then I make an ajax post request and would like to save the image in the Database using Carrierwave.
This is my JS code:
uploadButton.on('click', function(e) {
var dataURL = mycanvas.toDataURL("image/png;base64;");
// Get our file
var file= dataURLtoBlob(dataURL);
// Create new form data
var fd = new FormData();
// Append our Canvas image file to the form data
fd.append("image", file);
// And send it
$.ajax({
url: "/steps",
type: "POST",
data: fd,
processData: false,
contentType: false,
});
});
// Convert dataURL to Blob object
function dataURLtoBlob(dataURL) {
// Decode the dataURL
var binary = atob(dataURL.split(',')[1]);
// Create 8-bit unsigned array
var array = [];
for(var i = 0; i < binary.length; i++) {
array.push(binary.charCodeAt(i));
}
// Return our Blob object
return new Blob([new Uint8Array(array)], {type: 'image/png'});
}
When I add the following code to my controller, then the Image get's saved but of course not through carrierwave.
File.open("#{Rails.root}/public/uploads/somefilename.png", 'wb') do |f|
f.write(params[:image].read)
end
Updated Info:
These are the params for my ajax post request:
Parameters: {"image"=>#<ActionDispatch::Http::UploadedFile:0x007feac3e9a8a8 #tempfile=#<Tempfile:/var/folders/0k/q3kc7bpx3_51kc_5d2r1gqcc0000gn/T/RackMultipart20140211-1346-gj7kb7>, #original_filename="blob", #content_type="image/png", #headers="Content-Disposition: form-data; name=\"image\"; filename=\"blob\"\r\nContent-Type: image/png\r\n">}
And these are the params for a standard file upload:
Parameters: {"utf8"=>"✓", "image"=>{"image"=>#<ActionDispatch::Http::UploadedFile:0x007feac20c2e20 #tempfile=#<Tempfile:/var/folders/0k/q3kc7bpx3_51kc_5d2r1gqcc0000gn/T/RackMultipart20140211-1346-1ui8wq1>, #original_filename="burger.jpg", #content_type="image/jpeg", #headers="Content-Disposition: form-data; name=\"image[image]\"; filename=\"xy.jpg\"\r\nContent-Type: image/jpeg\r\n">}}
If I do Image.create(params[:image]) I have transaction rollback...
Error for transaction rollback:
Unprocessable Entity
ActiveRecord::RecordInvalid (Validation failed: image You are not allowed to upload "" files, allowed types: jpg, jpeg, gif, png)

Answer 1

I just wanted to add, you can add the file type in your view while appending your blob.
// Get our file
var file = dataURLtoBlob(dataURL);
// Create new form data
var fd = new FormData();
// Append our Canvas image file to the form data
fd.append("image", file, "blob.jpg");
Note the ending when we define the filename.
Hope this helps someone.
Source: https://developer.mozilla.org/en-US/docs/Web/API/FormData/append

Answer 2

You are whitelisting the filetypes permitted. By default, Carrierwave will attempt to determine the filetype by the filename extension - which isn't being passed since this is actually a Blob object. As such, you're getting a validation error about the file's 'type'. To fix this, simply append the expected filename extension for blob objects:
if params[:image].try(:original_filename) == 'blob'
params[:image].original_filename << '.png'
end
Image.create!(image: params[:image])