Get response headers from Curb

I intend to make a call from a Ruby on Rails application:

c = Curl::Easy.http_post("https://example.com", json_string_goes_here) do |curl|
  curl.headers['Accept'] = 'application/json'
  curl.headers['Content-Type'] = 'application/json'
  curl.headers['Api-Version'] = '2.2'
end

The response should have custom headers:

X-Custom1 : "some value"
X-Custom2 : "another value"

How do I iterate over the response headers to compare the values to what I was expecting?

Using Curl::Easy's header_str you can access the returned headers as a string. From the documentation:

Return the response header from the previous call to perform. This is populated by the default on_header handler - if you supply your own header handler, this string will be empty.

To test this I turned on the built-in Gem server using:

gem server

Here's some code to test this:

curl = Curl::Easy.http_get('http://0.0.0.0:8808')
curl.header_str
=> "HTTP/1.1 200 OK \r\nDate: 2013-01-10 09:07:42 -0700\r\nContent-Type: text/html\r\nServer: WEBrick/1.3.1 (Ruby/1.9.3/2012-11-10)\r\nContent-Length: 62164\r\nConnection: Keep-Alive\r\n\r\n"

Capturing the response, and breaking the remaining string into a hash making it easier to use, is simple:

http_response, *http_headers = curl.header_str.split(/[\r\n]+/).map(&:strip)
http_headers = Hash[http_headers.flat_map{ |s| s.scan(/^(\S+): (.+)/) }]

http_response # => "HTTP/1.1 200 OK"

http_headers 
=> {
                  "Date" => "2013-01-10 09:07:42 -0700",
          "Content-Type" => "text/html",
                "Server" => "WEBrick/1.3.1 (Ruby/1.9.3/2012-11-10)",
        "Content-Length" => "62164",
            "Connection" => "Keep-Alive"
    }

Testing again, in Pry:

[27] (pry) main: 0> curl = Curl::Easy.http_get('http://www.example.com')
#<Curl::Easy http://www.example.com>
[28] (pry) main: 0> curl.header_str
"HTTP/1.0 302 Found\r\nLocation: http://www.iana.org/domains/example/\r\nServer: BigIP\r\nConnection: Keep-Alive\r\nContent-Length: 0\r\n\r\n"
[29] (pry) main: 0> http_response, *http_headers = curl.header_str.split(/[\r\n]+/).map(&:strip)
[
    [0] "HTTP/1.0 302 Found",
    [1] "Location: http://www.iana.org/domains/example/",
    [2] "Server: BigIP",
    [3] "Connection: Keep-Alive",
    [4] "Content-Length: 0"
]
[30] (pry) main: 0> http_headers = Hash[http_headers.flat_map{ |s| s.scan(/^(\S+): (.+)/) }]
{
          "Location" => "http://www.iana.org/domains/example/",
            "Server" => "BigIP",
        "Connection" => "Keep-Alive",
    "Content-Length" => "0"
}