Repeat Content-Length header when making requests with EM-HTTP-Request

[nbrookie]

Hi there,

I am seeing an issue where the Content-Length header is being repeated when making real network requests with the EM-HTTP-Request library. Here is the scenario:

WebMock.allow_net_connect!

EM::HttpRequest.new("http://httpbin.org/post").post(body: "foo", head: {"Content-Length" => "3"})

# sends this request string --> "POST /post HTTP/1.1\r\nContent-Length: 3\r\nConnection: close\r\nHost: httpbin.org\r\nUser-Agent: EventMachine HttpClient\r\nAccept-Encoding: gzip, compressed\r\nContent-Length: 3\r\n\r\n"

# Notice the Content-Length header is repeated

I wrote a test that replicates the issue here if helpful

I think this boils down to the WebMock::RequestSignature#headers= where we call WebMock::Util::Headers.normalize_headers(headers) and that changes the case of the headers.

However in https://github.com/igrigorik/em-http-request/blob/master/lib/em-http/client.rb#L185, EventMachine assumes the request headers are downcased when attempting to assign a Content-Length, so we end up with both an capitalized and downcased version in the request headers.

Filing this because this presents an issue with Puma > 5.6.2 since they are now checking for invalid headers (see this line) and the Content-Length header that results here looks like Content-Length: 123, 123 which Puma rejects

This monkey patch appears to fix the issue:

module EventMachine
  class WebMockHttpClient
    def connection_completed
      @state = :response_header
      headers = request_signature.headers.inject({}) { |h, (k, v)| h[k.to_s.downcase] = v; h }
      send_request(headers, request_signature.body)
    end   
  end
end