[whatwg] HTML5 web messaging - postMessage

[Jack (Zhan, Hua Ping)]

http://jackiszhp.info/postMessage.html


The postMessage design outlined in the W3C document edited by Ian
Hickson is not good!
The design of the cross document messaging by Ian Hickson (Google,
Inc.) is very bad.
Even the last version is not good either. The design can be sketched
here as follows.

The sender:
var o = document.getElementsByTagName('iframe')[0];
o.contentWindow.postMessage('Hello world', 'http://b.example.org/');


The receiver:
window.addEventListener('message', receiver, false);
function receiver(e) {
  if (e.origin == 'http://example.com') {
    if (e.data == 'Hello world') {
      e.source.postMessage('Hello', e.origin);
    } else {
      alert(e.data);
    }
  }
}


This design was messed up by pulling "origin" (a word that some people
put too much attention more than should).
Even worse, it requires "o.contentWindow", this is really no
professional sense. Because of this design, if I open two tabs with
the same url http://www.google.com/ they are not able to communicate.

My proposal is discard the "o.contentWindow" part requirement.


My better proposal

the sender:
window.postMessage(messageObject,targetDomain optional,windowIDs optional);

Either targetDomain or windowIDs should present.
I propose to use ID rather than name (though window can have a name),
since window.name is not required to be unique within the browser.


then the user agent(i.e. the browser, such as firefox) will do the following

var e={source: {href: get the sender's window.location.href,
                windowID: unique windowID within this browser
               },
       target: {domain: targetDomain as the sender requested,
                windows: the array of windowID
               },
       data: JSON.parse(JSON.stringtify(messageObject)),
       ts: the timestamp when the post is requested
      };
if(windowIDs presents){
  postEvent to those windows.
} else {
  traverse the list of all windows
  for (each window){
    if(the domain of the window matches the target domain of the message) {
    postEvent(e);
  }
}


the receiver
/*
return true to indicate to continue to receive message from this sender
return false to indicate to deny messages from this sender forever
  (as long as the browser can remember this)
*/
function receiver(e) {
  if (e.source is accepted) {
    take the e.data to do whatever as desired.
    return true;
  }
  return false;
}

window.addEventListener('message', receiver, false);



if the receiver wants to respond to the sender
window.postMessage(messageObject,targetDomain optional,windowIDs optional);
        targetDomain can be found from e.source.href
        windowID can be found from e.source.windowID
        messageObject is the message object intended to be sent.





About domain match
the specification of the target domain can be


www.google.com
or google.com  this should match *.google.com
or com      this should match *.com
or ""  as for all
or https://www.google.com
or http://www.google.com:9876/abc/

For the last case, if a
window.location.href=="http://www.google.com:9876/def/", then they do
not match.

About Security
As long as the receiver check who is the sender which is identified by
the user agent, there is no security issue at all.
About context sharing within the browser
Whether session data should be shared among the different processes of
the same browser. such as cookies. It seems that firefox does not
allow 2 different processes unless use different profile.

Here, one more setting, whether the windowIDs should be unique across
different process. Within the same process among different tabs, they
must be unique. If no more than one process is allowed, then such
setting is not relevant.





Challenge
A bad design waste people's energy & time, to promote the better
solution. I am offering a reward for the 1st one who implement my
proposal. If you can do this before march 1st, 2013, I will give you
$10.




jackiszhp at gmail.com






pdf version
Last update: 2013.01.27 21:30