744514 - observer-service, when observing "*", topic is unreliable (in callback)

Status: RESOLVED INVALID

(Add-on SDK Graveyard :: General, defect, P2)

Description

[Gregg Lind (Fx Strategy and Insights - Shield - Heartbeat )]

When 

   observer.add("*",somecallback);

the `Observer` will have '*' as its topic.  The callback can't see what the true topic was.

I am not sure that there is a good way around this, other than allowing a 4th argument to `callback`, which is filled with the true topic.  Drawback: this would be inconsistent with the previous MDN usage/idiom.

At the very least, it deserves a warning in the docs.  

Code:

    var log_it = function (subject,data){console.log("OBSERVED",subject,data,"TOPIC:", this.topic)};
    observer.add("*",log_it);

Comment 1

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

At this point, we'd rather just document this quirk.

Comment 2

[Gregg Lind (Fx Strategy and Insights - Shield - Heartbeat )]

That's fair.  I saw no obvious way to get it onto the object that goes into the callback, unless the object gets proxycopied or something on the way in, with an added ".thistopic".  

It's a bit annoying, and removes a lot of the usefulness of "*", but that's life!

Comment 3

[Gregg Lind (Fx Strategy and Insights - Shield - Heartbeat )]

This seems to be broken under the recent revisions/simplifications to `observer-server.js`.

Suggestions might be...

1)  link to the xpcom docs, which could listen to "*"
2)  emit to "*" and always listen on it?

Messy version illustrating examples:  https://gist.github.com/2838598

Comment 4

[Gregg Lind (Fx Strategy and Insights - Shield - Heartbeat )]

Reopening.  On Android, lots of functionality is done over the observer bus.  In particular, I want to handle *every kind of message* in one way or another, *and know* when a new type of message appears, as part of UX observation of the interface.

Add a fourth argument of the actual topic helps tremendously.  

See:  https://github.com/mozilla/addon-sdk/pull/592

(This needs a bit of doc update and testing.  It should be fully backward compatible.)

Comment 5

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

CCing Irakli since he's all over observer-service's history.

Comment 6

[Irakli Gozalishvili [:irakli] [:gozala] [@gozala]]

Attachment: Pointer to Github pull request: https://github.com/mozilla/addon-sdk/pull/592

Pointer to Github pull-request

Comment 7

[Irakli Gozalishvili [:irakli] [:gozala] [@gozala]]

Attachment: Pointer to Github pull request: https://github.com/mozilla/addon-sdk/pull/592#attch-to-bugzilla

Pointer to Github pull-request

Comment 8

[Erik Vold [:erikvold] (please needinfo? me)]

The observer-service was removed in bug 958908 system/events should be used instead now, which supports '*' as Irakli noted here https://github.com/mozilla/addon-sdk/pull/592#issuecomment-11359722