carrierwave

https://github.com/carrierwaveuploader/carrierwave

Ruby

Classier solution for file uploads for Rails, Sinatra and other Ruby web frameworks

Mail::Part#add_content_id

Creates a new empty Content-ID field and inserts it in the correct order
into the Header.  The ContentIdField object will automatically generate
a unique content ID if you try and encode it or output it to_s without
specifying a content id.

It will preserve the content ID you specify if you do.

Source | Google | Stack overflow

Edit

git clone [email protected]:carrierwaveuploader/carrierwave.git

cd carrierwave

open

Contribute

# Make a new branch

git checkout -b -your-name--update-docs-Mail--Part-add_content_id-for-pr

# Commit to git

git add git commit -m "better docs for Mail::Part#add_content_id"

# Open pull request

gem install hub # on a mac you can `brew install hub`

hub fork

git push <your name> -your-name--update-docs-Mail--Part-add_content_id-for-pr

hub pull-request

# Celebrate!