1523947 - ThreadActor.sources will force emitting newSource events for the returned sources

Status: NEW

(DevTools :: Debugger, task, P3)

Description

[Alexandre Poirot [:ochameau]]

ThreadActor.sources method:
https://searchfox.org/mozilla-central/rev/c07aaf12f13037c1f5a343d31f8291549e57373f/devtools/server/actors/thread.js#1238
onSources: function(request) {
for (const source of this.dbg.findSources()) {
this.sources.createSourceActor(source);
}

TabSources.createSourceActor will call TabSources.sources, which will inconditionally emit a newSource event:
https://searchfox.org/mozilla-central/rev/c07aaf12f13037c1f5a343d31f8291549e57373f/devtools/server/actors/utils/TabSources.js#142
source: function({ source, isInlineSource, contentType }) {
...
this.emit("newSource", actor);

Which is received by the ThreadActor, piping this event back to the frontend, also, inconditionally:
https://searchfox.org/mozilla-central/rev/c07aaf12f13037c1f5a343d31f8291549e57373f/devtools/server/actors/thread.js#1875-1886
onNewSourceEvent: function(source) {
...
const type = "newSource";
this.conn.send({
from: this._parent.actorID,
type,
source: source.form(),
});

And, on top of that, we emit the newSource event twice from here, but that's another story (bug 1269919).

That means that we end up emitting each source form 3 times:

• once in the array returned by ThreadActor.sources request,
• and two additional times from this onNewSourceEvent method.

This means calling SourceActor.form 3 times, building its non-naive JSON 3 times and piping it through RDP 3 times.

It would be great to only pipe it once, but this may require some tweaks in the frontend if we were depending on this extra verbosity of the actor.

Comment 1

[Jason Laster [:jlast]]

This is important because the client calls fetchSources in several places and we could accidentally send the same results down.