x-messages

Experimenting with HTTP Headers and Rails Joseph Paul Silvashy -
@jpsilvashy - jpsilvashy.com

HTTP header crash course

HTTP headers define the operating parameters of an HTTP transaction.

Headers are used in both the request and the response.

Overview a basic GET request: Sends request headers Sends response
headers and content body Client (your browser) Server (web server, reverse proxy, application...)

Accept: text/html, [...] Accept-Encoding: gzip, deflate Accept-Language: en-US,en; q=0.5 User-Agent:
[...] GET http://example.com

Cache-Control: must-revalidate, private, max-age=0 Connection: keep-alive Content-Length: 3146 Content-Type: text/html;
charset=utf-8 Date: Thu, 24 Jan 2013 21:16:51 GMT <html> ... HTTP/1.1 200 OK

There are a lot of standard headers... http://en.wikipedia.org/wiki/List_of_HTTP_header_fields

There are a lot of standard headers... About 75! http://en.wikipedia.org/wiki/List_of_HTTP_header_fields

Accept Accept-Charset Accept-Encoding Accept-Language Accept-Datetime Authorization Cache-Control Connection Cookie Content-Length
Content-MD5 Content-Type Date Expect From Host If-Match If-Modified-Since If-None-Match If-Range If-Unmodified- Since Max-Forwards Pragma Proxy- Authorization Range Referer TE Upgrade User-Agent Via Warning Typical Response Headers

Typical Rails response Headers

Content-MD5 Content-Type Date Expect From Host If-Match If-Modified-Since If-None-Match If-Range If-Unmodified- Since Max-Forwards Pragma Proxy- Authorization Range Referer TE Upgrade User-Agent Via Warning Typical Response Headers

Cache-Control Connection Content-Length Content-Type Date Typical Response Headers from Rails

Which header is for human readable messages to the client?

Content-MD5 Content-Type Date Expect From Host If-Match If-Modified-Since If-None-Match If-Range If-Unmodified- Since Max-Forwards Pragma Proxy- Authorization Range Referer TE Upgrade User-Agent Via Warning Typical Response Headers Warning

Typical Response Headers Warning

Warning?

The Warning general-header field is used to carry additional information
about the status or transformation of a message which might not be reflected in the message. http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html Warning (From rfc2616 See §14.46):

299: Miscellaneous persistent warning. The warning text MAY include arbitrary
information to be presented to a human user, or logged. A system receiving this warning MUST NOT take any automated action. Warning (From rfc2616 See §14.46): http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

Flash messages in Rails are: Arbitrary information presented to a
human user.

Warning: “Thanks for signing up!”

Hey, what about non-standard headers?!

Typically non-standard headers are prefixed with an “X-”

Requests: X-CSRF-Token X-Requested-With Some non-standard headers Response: X-Frame-Options X-Runtime X-Rack-Cache
X-Request-Id X-Ua-Compatible

Non-standard headers are popular, most servers send at least one.

Typical Rails Response: HTTP/1.1 200 OK Cache-Control: max-age=0, private, must-revalidate
Connection: keep-alive Content-Length: 3146 Content-Type: text/html; charset=utf-8 Date: Thu, 24 Jan 2013 20:15:48 GMT Etag: "9cc373612927384b4a3997397061ba60" Set-Cookie: _myapp_session=abcd; path=/; HttpOnly (cont...)

Typical Rails Response (cont.): X-Rack-Cache: miss X-Request-Id: 52f48735303febd137f014fb4db5f767 X-Runtime: 0.010621
X-Ua-Compatible: IE=Edge,chrome=1

There is a problem with this.

“X-” headers are officially deprecated!

Creators of new parameters to be used in the context
of application protocols SHOULD NOT prefix their parameter names with "X-" or similar constructs. IETF Says: (From rfc6648 §3, June 2012 ) http://www.ietf.org/rfc/rfc6648.txt

Using headers as a transport for flash messages.

Who gives a shit!? Doesn’t Rails handle this for me?

Rails does this by rendering flash messages in the view.

Alternatively, we can send the flash messages in a header
for easy consumption by the client.

Example application: http://x-messages.herokuapp.com/

after_filter :x_messages after_filter { flash.discard if request.xhr? } def x_messages
response.headers['X-Messages'] = flash.to_hash.to_json flash.to_hash end application_controller.rb https://github.com/jpsilvashy/x-messages/blob/master/app/controllers/ application_controller.rb

application_helper.rb https://github.com/jpsilvashy/x-messages/blob/master/app/controllers/ application_controller.rb def render_x_messages content_tag :ul, :class => 'x-messages'
do x_messages.collect do |type, message| concat content_tag(:li, message, :class => "message-#{type}") end end end

application.html.erb https://github.com/jpsilvashy/x-messages/blob/master/app/views/layouts/ application.html.erb  <%= render_x_messages %>  <script> var x_messages = <%= x_messages.to_json.html_safe %> </script>

application.js https://github.com/jpsilvashy/x-messages/blob/master/app/views/layouts/ application.html.erb ... //= require alertify //= require x-messages

x-messages.js https://github.com/jpsilvashy/x-messages/blob/master/app/assets/ javascripts/x-messages.js var getXMessages = function(response) { var xMessagesHeader
= response.getResponseHeader('X-Messages'); if ((typeof xMessagesHeader !== "undefined") && (xMessagesHeader !== null)) { return $.parseJSON(xMessagesHeader) } }

https://github.com/jpsilvashy/x-messages/blob/master/app/assets/ javascripts/x-messages.js var handleMessages = function(messages) { $.each(messages, function(type, message)
{ alertify.log(message, type); }); } x-messages.js (cont.)

https://github.com/jpsilvashy/x-messages/blob/master/app/assets/ javascripts/x-messages.js $(document).ajaxComplete(function(event, response) { handleMessages(getXMessages(response)) }); $(function() { $('.x-messages').hide();
if ((typeof xMessages !== "undefined") && (xMessages !== null)) { handleMessages(xMessages); } }) x-messages.js (cont.)

Issues with implementation • Error messages still have to be
rendered to the views since we cannot retrieve the response headers with javascript in our views unless we render the flash as an array. So this is only valuable for XHR requests at the moment (I think this can be fixed). • We still has “X-” name for header. https://github.com/jpsilvashy/x-messages/issues

x-messages

x-messages

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