Preserving case in HTTP headers with Ruby's Net:HTTP

Question

Although the HTTP spec says that headers are case insensitive; Paypal, with their new adaptive payments API require their headers to be case-sensitive.

Using the paypal adaptive payments extension for ActiveMerchant ( http://github.com/lamp/paypal_adaptive_gateway ) it seems that although the headers are set in all caps, they are sent in mixed case.

Here is the code that sends the HTTP request:

headers = {
  "X-PAYPAL-REQUEST-DATA-FORMAT" => "XML",
  "X-PAYPAL-RESPONSE-DATA-FORMAT" => "JSON",
  "X-PAYPAL-SECURITY-USERID" => @config[:login],
  "X-PAYPAL-SECURITY-PASSWORD" => @config[:password],
  "X-PAYPAL-SECURITY-SIGNATURE" => @config[:signature],
  "X-PAYPAL-APPLICATION-ID" => @config[:appid]
}
build_url action

request = Net::HTTP::Post.new(@url.path)

request.body = @xml
headers.each_pair { |k,v| request[k] = v }
request.content_type = 'text/xml'

proxy = Net::HTTP::Proxy("127.0.0.1", "60723")

server = proxy.new(@url.host, 443)
server.use_ssl = true

server.start { |http| http.request(request) }.body

(i added the proxy line so i could see what was going on with Charles - http://www.charlesproxy.com/ )

When I look at the request headers in charles, this is what i see:

X-Paypal-Application-Id ...
X-Paypal-Security-Password...
X-Paypal-Security-Signature ...
X-Paypal-Security-Userid ...
X-Paypal-Request-Data-Format XML
X-Paypal-Response-Data-Format JSON
Accept */*
Content-Type text/xml
Content-Length 522
Host svcs.sandbox.paypal.com

I verified that it is not Charles doing the case conversion by running a similar request using curl. In that test the case was preserved.

Answer 1

The RFC does specify that header keys are case-insensitive , so unfortunately you seem to have hit an annoying requirement with the PayPal API.

Net::HTTP is what is changing the case, although I'm surprised they're not all getting downcased:

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

"Sets the header field corresponding to the case-insensitive key."

As the above is a simple class it could be monkey-patched. I will think further for a nicer solution.

Answer 2

Use following code to force case sensitive headers.

class CaseSensitivePost < Net::HTTP::Post
  def initialize_http_header(headers)
    @header = {}
    headers.each{|k,v| @header[k.to_s] = [v] }
  end

  def [](name)
    @header[name.to_s]
  end

  def []=(name, val)
    if val
      @header[name.to_s] = [val]
    else
      @header.delete(name.to_s)
    end
  end

  def capitalize(name)
    name
  end
end

Usage example:

post = CaseSensitivePost.new(url, {myCasedHeader: '1'})
post.body = body
http = Net::HTTP.new(host, port)
http.request(post)

Answer 3

I got several issues with the code proposed by @kaplan-ilya because the Net::HTTP library tries to detect the post content-type, and the I ended up with 2 content-type and other fields repeated with different cases.

So the code below should ensure than once a particular case has been choosen, it will stick to the same.

  class Post < Net::HTTP::Post
    def initialize_http_header(headers)
      @header = {}
      headers.each { |k, v| @header[k.to_s] = [v] }
    end

    def [](name)
      _k, val = header_insensitive_match name
      val
    end

    def []=(name, val)
      key, _val = header_insensitive_match name
      key = name if key.nil?
      if val
        @header[key] = [val]
      else
        @header.delete(key)
      end
    end

    def capitalize(name)
      name
    end

    def header_insensitive_match(name)
      @header.find { |key, _value| key.match Regexp.new(name.to_s, Regexp::IGNORECASE) }
    end
  end

Answer 4

If you are still looking for an answer that works. Newer versions have introduced some changes to underlying capitalize method by using to_s . Fix is to make the to_s and to_str return the self so that the returned object is an instance of ImmutableKey instead of the base string class.

class ImmutableKey < String 
         def capitalize 
               self 
         end 
         
         def to_s
          self 
         end 
         
         alias_method :to_str, :to_s
 end

Ref: https://jatindhankhar.in/blog/custom-http-header-and-ruby-standard-library/