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Generation of multipart post fail if inconsistent encodings given as input

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
ruby
Domain
api, backend

Research direction

Start in lib/net/http/generic_request.rb at encode_multipart_form_data and reproduce the supplied mixed UTF-8 and ASCII-8BIT StringIO example. Trace the multipart assembly that raises Encoding::CompatibilityError, then verify that a multipart request containing differently encoded inputs can be generated and sent without that failure.

Written by the indexing model from the issue text.

Description

When attaching multipart entities of different encodings it is easy to get failures due to intermediary strings inside encode_multipart_form_data that care about encoding despite there being no need to care about them.

Example:

require "net/http"
require "stringio"

utf_string = "räksmörgås"
ascii_string = "räkmacka"
ascii_string.force_encoding("ASCII-8BIT")

form_data = {
  "foo"   => "bar",
  "utf8"  => StringIO.new(utf_string),
  "ascii" => StringIO.new(ascii_string)
}

url = URI("http://www.example.com")

request = Net::HTTP::Post.new(url)
request.set_form(form_data, "multipart/form-data")

Net::HTTP.start(url.hostname, url.port) do |http|
  http.request(request)
end

This results in

net-http-0.4.1/lib/net/http/generic_request.rb:354:in `block in encode_multipart_form_data': incompatible character encodings: UTF-8 and ASCII-8BIT (Encoding::CompatibilityError)
	from /home/linus/.gem/ruby/3.3.3/gems/net-http-0.4.1/lib/net/http/generic_request.rb:320:in `each'
	from /home/linus/.gem/ruby/3.3.3/gems/net-http-0.4.1/lib/net/http/generic_request.rb:320:in `encode_multipart_form_data'
	from /home/linus/.gem/ruby/3.3.3/gems/net-http-0.4.1/lib/net/http/generic_request.rb:303:in `send_request_with_body_data'
	from /home/linus/.gem/ruby/3.3.3/gems/net-http-0.4.1/lib/net/http/generic_request.rb:204:in `exec'
[...]

There are real use cases that are reasonable like posting both a text file and a pdf at the same time.

A workaround is to always encode absolutely everything as ascii-8bit before posting it.

Dominant language
Ruby
Stars
148
Forks
95
Avg merge
10h 54m
Merged PRs (30d)
4

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