The Multipart middleware converts a Faraday::Request#body Hash of key/value pairs into a multipart form request, but only under these conditions:

• The request's Content-Type is "multipart/form-data"
• Content-Type is unspecified, AND one of the values in the Body responds to #content_type.

Faraday contains a couple helper classes for multipart values:

• Faraday::Multipart::FilePart wraps binary file data with a Content-Type. The file data can be specified with a String path to a local file, or an IO object.
• Faraday::Multipart::ParamPart wraps a String value with a Content-Type, and optionally a Content-ID.

Add this line to your application's Gemfile:

gem 'faraday-multipart'

And then execute:

bundle install

Or install it yourself as:

gem install faraday-multipart

First of all, you'll need to add the multipart middleware to your Faraday connection:

require 'faraday'
require 'faraday/multipart'

conn = Faraday.new(...) do |f|
  f.request :multipart, **options
  # ...
end

If you need to specify a different content type for the multipart request, you can do so by providing the content_type option but it must start with multipart/ otherwise it will default to multipart/form-data:

conn = Faraday.new(...) do |f|
  f.request :multipart, content_type: 'multipart/mixed'
  # ...
end

Payload can be a mix of POST data and multipart values.

# regular POST form value
payload = { string: 'value' }

# filename for this value is File.basename(__FILE__)
payload[:file] = Faraday::Multipart::FilePart.new(__FILE__, 'text/x-ruby')

# specify filename because IO object doesn't know it
payload[:file_with_name] = Faraday::Multipart::FilePart.new(
  File.open(__FILE__),
  'text/x-ruby',
  File.basename(__FILE__)
)

# Sets a custom Content-Disposition:
# nil filename still defaults to File.basename(__FILE__)
payload[:file_with_header] = Faraday::Multipart::FilePart.new(
  __FILE__,
  'text/x-ruby',
  nil,
  'Content-Disposition' => 'form-data; foo=1'
)

# Upload raw json with content type
payload[:raw_data] = Faraday::Multipart::ParamPart.new(
  { a: 1 }.to_json,
  'application/json'
)

# optionally sets Content-ID too
payload[:raw_with_id] = Faraday::Multipart::ParamPart.new(
  { a: 1 }.to_json,
  'application/json',
  'foo-123'
)

conn.post('/', payload)

Sometimes, the server you're calling will expect an array of documents or other values for the same key. The multipart middleware will automatically handle this scenario for you:

payload = {
  files: [
    Faraday::Multipart::FilePart.new(__FILE__, 'text/x-ruby'),
    Faraday::Multipart::FilePart.new(__FILE__, 'text/x-pdf')
  ],
  url: [
    'http://mydomain.com/callback1',
    'http://mydomain.com/callback2'
  ]
}

conn.post(url, payload)
#=> POST url[]=http://mydomain.com/callback1&url[]=http://mydomain.com/callback2
#=>   and includes both files in the request under the `files[]` name

However, by default these will be sent with files[] key and the URLs with url[], similarly to arrays in URL parameters. Some servers (e.g. Mailgun) expect each document to have the same parameter key instead. You can instruct the multipart middleware to do so by providing the flat_encode option:

require 'faraday'
require 'faraday/multipart'

conn = Faraday.new(...) do |f|
  f.request :multipart, flat_encode: true
  # ...
end

payload = ... # see example above

conn.post(url, payload)
#=> POST url=http://mydomain.com/callback1&url=http://mydomain.com/callback2
#=>   and includes both files in the request under the `files` name

This works for both UploadIO and normal parameters alike.

After checking out the repo, run bin/setup to install dependencies.

Then, run bin/test to run the tests.

To install this gem onto your local machine, run rake build.

To release a new version, make a commit with a message such as "Bumped to 0.0.2", and change the Unreleased heading in CHANGELOG.md to a heading like "0.0.2 (2022-01-01)", and then use GitHub Releases to author a release. A GitHub Actions workflow then publishes a new gem to RubyGems.org.

Bug reports and pull requests are welcome on GitHub.

The gem is available as open source under the terms of the MIT License.