Daniel Fone

Ruby/Rails Engineer

Upload Progress in Ruby with curb

May 2014

A friend was telling me how difficult it was to get the progress of a file upload in ruby using the standard Net::HTTP library or any of the popular HTTP wrapper gems. He wanted to get simple details similar to curl.

$ curl --progress-bar --form --upload=@1mb.txt http://requestb.in/ztmawczt > /dev/null
######################################################                    75.5%

Fortunately, there is the curb gem which provides ruby bindings around libcurl. Using this gem, we can use the on_progress method to do something like this:

curl.on_progress do |download_size, downloaded, upload_size, uploaded|
  print "\r#{uploaded}/#{upload_size}"
  true
end

The documentation is a little sparse, and there are two major caveats to watch out for:

  1. You MUST return true from this block if you want the upload to continue
  2. Any exceptions that occur in the block will be swallowed and reraised as an Curl::Err::AbortedByCallbackError. This makes development a little bit painful, but you use your own begin ... rescue ... end inside the block to help debug if needed.

I’ve published a full working example on github.

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