How do you set up a file upload route correctly for a JSON-REST API?

wuarmin · June 2, 2025, 6:22pm

Thanks @timriley!
The output for the upload-endpoint is:

>>> content_type: "multipart/form-data; boundary=------------------------l66OQWe0cxN8bD2hp6nkC9"
>>> config.formats.values: [:multipart]
>>> config.formats.mapping: {"application/octet-stream" => :all, "*/*" => :all, "multipart/form-data" => :multipart}
>>> accepted_mime_types(config): ["multipart/form-data"]

So the issue lies here:

github.com/rack/rack

lib/rack/mime.rb

e63769278


      
          end
          module_function :mime_type
          
          # Returns true if the given value is a mime match for the given mime match
          # specification, false otherwise.
          #
          #    Rack::Mime.match?('text/html', 'text/*') => true
          #    Rack::Mime.match?('text/plain', '*') => true
          #    Rack::Mime.match?('text/html', 'application/json') => false
          
          def match?(value, matcher)
            v1, v2 = value.split('/', 2)
            m1, m2 = matcher.split('/', 2)
          
            (m1 == '*' || v1 == m1) && (m2.nil? || m2 == '*' || m2 == v2)
          end
          module_function :match?
          
          # List of most common mime-types, selected various sources
          # according to their usefulness in a webserving scope for Ruby
          # users.

Here’s the debug output:

>>> v1: "multipart" v2: "form-data; boundary=------------------------NYJ4v948lVEtMlrLscIhv8"
>>> m1: "multipart" m2: "form-data"

The m2-v2-match fails.

@timriley: What do you think? I think we should fix this at Rack? I opened an issue there:

github.com/rack/rack

Rack::Mime.match? returns false when Content-Type includes valid parameters like boundary

opened 06:47PM - 02 Jun 25 UTC

wuarmin

Hey 👋, we have noticed that ```ruby Rack::Mime.match?("multipart/form-data; bou…ndary=------------------------NYJ4v948lVEtMlrLscIhv8”, “multipart/form-data”) ``` returns `false`. Is this expected? Here's the implementation: https://github.com/rack/rack/blob/e6376927801774e25a3c1e5b977ff2fd2209e799/lib/rack/mime.rb#L30 This issue surfaced in a Hanami app, where `Rack::Mime.match? is used internally to validate incoming content types. File uploads using `multipart/form-data` with a boundary parameter are being rejected because the match fails. thanks

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How do you set up a file upload route correctly for a JSON-REST API?

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