Category Archives: Livecoding

The Joy of Coding (Ep. 11): Cleaning up the View Source Patch

For this episode, Richard Milewski and I figured out the syncing issue I’d been having in Episode 9, so I had my head floating in the bottom right corner while I hacked. Now you can see what I do with my face while hacking, if that’s a thing you had been interested in.

I’ve also started mirroring the episodes to YouTube, if YouTube is your choice platform for video consumption.

So, like last week, I was under a bit of time pressure because of a meeting scheduled for 2:30PM (actually the meeting I was supposed to have the week before – it just got postponed), so that gave me 1.5 hours to move forward with the View Source work we’d started back in Episode 8.

I started the episode by explaining that the cache key stuff we’d figured out in Episode 9 was really important, and that a bug had been filed by the Necko team to get the issue fixed. At the time of the video, there was a patch up for review in that bug, and when we applied it, we were able to retrieve source code out of the network cache after POST requests! Success!

Now that we had verified that our technique was going to work, I spent the rest of the episode cleaning up the patches we’d written. I started by doing a brief self-code-review to smoke out any glaring problems, and then started to fix those problems.

We got a good chunk of the way before I had to cut off the camera.

I know back when I started working on this particular bug, I had said that I wanted to take you through right to the end on camera – but the truth of the matter is, the priority of the bug went up, and I was moving too slowly on it, since I was restricting myself to a few hours on Wednesdays. So unfortunately, after my meeting, I went back to hacking on the bug off-camera, and yesterday I put up a patch for review. Here’s the review request, if you’re interested in seeing where I got to!

I felt good about the continuity experiment, and I think I’ll try it again for the next few episodes – but I think I’ll choose a lower-priority bug; that way, I think it’s more likely that I can keep the work contained within the episodes.

How did you feel about the continuity between episodes? Did it help to engage you, or did it not matter? I’d love to hear your comments!

Episode Agenda

References

Bug 1025146 – [e10s] Never load the source off of the network when viewing source – Notes

The Joy of Coding (Ep. 10): The Mystery of the Cache Key

In this episode, I kept my camera off, since I was having some audio-sync issues1.

I was also under some time-pressure, because I had a meeting scheduled for 2:30 ET2, giving me exactly 1.5 hours to do what I needed to do.

And what did I need to do?

I needed to figure out why an nsISHEntry, when passed to nsIWebPageDescriptor’s loadPage, was not enough to get the document out from the HTTP cache in some cases. 1.5 hours to figure it out – the pressure was on!

I don’t recall writing a single line of code. Instead, I spent most of my time inside XCode, walking through various scenarios in the debugger, trying to figure out what was going on. And I eventually figured it out! Read this footnote for the TL;DR:3

Episode Agenda

References

Bug 1025146 – [e10s] Never load the source off of the network when viewing source – Notes

  1. I should have those resolved for Episode 11! ↩

  2. And when the stream finished, I found out the meeting had been postponed to next week, meaning that next week will also be a short episode. 🙁 ↩

  3. Basically, the nsIChannel used to retrieve data over the network is implemented by HttpChannelChild in the content process. HttpChannelChild is really just a proxy to a proper nsIChannel on the parent-side. On the child side, HttpChannelChild does not implement nsICachingChannel, which means we cannot get a cache key from it when creating a session history entry. With no cache key, comes no ability to retrieve the document from the network cache via nsIWebDescriptor’s loadPage. ↩

The Joy of Coding (Ep. 9): More View Source Hacking!

In this episode1, I continued the work we had started in Episode 8, by trying to make it so that we don’t hit the network when viewing the source of a page in multi-process Firefox.

It was a little bit of a slog – after some thinking, I decided to undo some of the work we had done in the previous episode, and then I set up the messaging infrastructure for talking to the remote browser in the view source window.

I also rebased and landed a patch that we had written in the previous episode, after fixing up some nits2.

Then, I (re)-learned that flipping the “remote” attribute of a browser is not enough in order for it to run out-of-process; I have to remove it from the DOM, and then re-add it. And once it’s been re-added, I have to reload any frame scripts that I had loaded in the previous incarnation of the browser.

Anyhow, by the end of the episode, we were able to view the source from a remote browser inside a remote view source browser!3 That’s a pretty big deal!

Episode Agenda

References

Bug 1025146 – [e10s] Never load the source off of the network when viewing source – Notes

  1. A note that I also tried an experiment where I keep my camera running during the entire session, and place the feed into the bottom right-hand corner of the recording. It looks like there were some synchronization issues between audio and video, which are a bit irritating. Sorry about that! I’ll see what I can do about that. ↩

  2. and dropping a nit having conversed with :gabor about it ↩

  3. We were still loading it off the network though, so I need to figure out what’s going on there in the next episode. ↩

The Joy of Coding (Ep. 8): View Source Hacking

In this episode, I again started with some code review. I reviewed this patch for this bug by fellow Firefox hacker Gijs, and refreshed my memory on var hoisting. I’ve been using let for so long that it was really, really weird to see how var worked.

After that, I quickly gave an update on my plugin crash UI bug I had been working on the last episode – the patches are up, and are currently undergoing review, so there wasn’t much to do there.

Next, I started on a brand new bug1, explained the bug2, and then laid out my plan for attacking it.

Specifically, I’m going to try an experiment: I will only be working on that bug during Joy of Coding sessions. That way, there is continuity from video to video, and you won’t miss any of the development that goes on between episodes.

We sliced off a chunk to get done, and hit some minor roadblocks (as expected). The View Source code is old and crufty, and I have to do my best to make sure I don’t break any of the other applications that depend on it (like Thunderbird and SeaMonkey).

So that was the name of the game – looking to see how other applications use View Source, and trying to come up with a plan for making sure we don’t break them, while at the same time refactoring View Source to be easier to code against (and work with a frame script and messages).

It was a long slog3, but we got to a good point by the end. Let’s see how far we get next week!

Episode Agenda

References

Bug 1148807 – Method moveToAlertPosition in dialog.xml should check if opener is not null

Bug 1110887 – With e10s, plugin crash submit UI is broken – Notes

Bug 1025146 – [e10s] Never load the source off of the network when viewing source – Notes

  1. I say brand new, except that, as I explain in the video, I had already attacked this bug early on in my e10s work, and had only recently come back to it. ↩

  2. The View Source tool sometimes re-retrieves the source off of the network when opened from an e10s-browser ↩

  3. My longest episode ever, clocking in at over 2.5 hours. ↩

The Joy of Coding (Episode 7): Code review, and a Regression

In this episode, I started with some code review. I was reviewing a patch to make the Findbar (particularly, the Find As You Type feature) e10s-friendly.

With that review out of the way, I had to swap a bunch of information about the plugin crash UI for e10s in my head – and in particular, some non-determinism that we have to handle. I explained that stuff (and hopefully didn’t spend too much time on it).

Then, I showed how far I’d gotten with the plugin crash UI for e10s. I was able to submit a crash report, but I found I wasn’t able to type into the comment text area.

After a while, I noticed that I couldn’t type into the comment text area on Nightly, even without my patch. And then I reproduced it in Aurora. And then in Beta. Luckily, I couldn’t reproduce it in Release – but with Beta transitioning to Release in only a few days, I didn’t have a lot of time to get a bug on file to shine some light on it.

Luckily, our brilliant Steven Michaud was on the case, and has just landed a patch to fix this. Talk about fast work!

Episode Agenda

References:
Bug 1133981 – [e10s] Stop sending unsafe CPOWs after the findbar has been closed in a remote browser

Bug 1110887 – With e10s, plugin crash submit UI is broken – Notes

Bug 1147521 – Cannot type into comment area of plugin crash UI