stop ruby http request modifying header name

While it's possible to monkey patch Net::HTTPHeader and Net:HTTPGenericRequest to remove the downcase and capitalize, I found a different approach that allows selective case sensitivity rather than forcing everything.

The solution:

class CaseSensitiveString < String
    def downcase
        self
    end
    def capitalize
        self
    end
end

Then CaseSensitiveString.new('keyname') to create your keys when they are case sensitive. Use strings/symbols for other keys to maintain existing behaviour. This is much simpler than the monkey patching and works well with the rest-client library as well as Net::HTTP.

According to the HTTP spec (RFC 2616), header field names are case-insensitive. So the third-party server has a broken implementation.

If you really needed to, you could monkey-patch Net::HTTP to preserve case, because it downcases the field names when it stores them and then writes them with initial caps.

Here's the storage method you used (Net::HTTPHeader#[]=):

# File net/http.rb, line 1160
    def []=(key, val)
      unless val
        @header.delete key.downcase
        return val
      end
      @header[key.downcase] = [val]
    end

And here is where it writes the header (Net::HTTPGenericRequest#write_header):

# File lib/net/http.rb, line 2071
    def write_header(sock, ver, path)
      buf = "#{@method} #{path} HTTP/#{ver}\r\n"
      each_capitalized do |k,v|
        buf << "#{k}: #{v}\r\n"
      end
      buf << "\r\n"
      sock.write buf
    end

Those are likely the only methods you'd need to override, but I'm not 100% certain.

Building off of a previous answer, this will work for ruby 2.3:

class CaseSensitiveString < String
  def downcase
    self
  end

  def capitalize
    self
  end

  def to_s
    self
  end
end

The to_s method needs to be added because as of 2.3, HTTP::Header's capitalize method calls to_s on each header.