daniel.haxx.se episode 8

Monday, October 27th, 2014

Today I hesitated to make my new weekly video episode. I looked at the viewers number and how they basically have dwindled the last few weeks. I’m not making this video series interesting enough for a very large crowd of people. I’m re-evaluating if I should do them at all, or if I can do something to spice them up…

… or perhaps just not look at the viewers numbers at all and just do what think is fun?

I decided I’ll go with the latter for now. After all, I enjoy making these and they usually give me some interesting feedback and discussions even if the numbers are really low. What good is a number anyway?

This week’s episode:

Personal

Firefox

Fun

HTTP/2

TALKS

  • I’m offering two talks for FOSDEM

curl

  • release next Wednesday
  • bug fixing period
  • security advisory is pending

wget

Stricter HTTP 1.1 framing good bye

Sunday, October 26th, 2014

I worked on a patch for Firefox bug 237623 to make sure Firefox would use a stricter check for “HTTP 1.1 framing”, checking that Content-Length is correct and that there’s no broken chunked encoding pieces. I was happy to close an over 10 years old bug when the fix landed in June 2014.

The fix landed and has not caused any grief all the way since June through to the actual live release (Nightlies, Aurora, Beta etc). This change finally shipped in Firefox 33 and I had more or less already started to forget about it, and now things went south really fast.

The amount of broken servers ended up too massive for us and we had to backpedal. The largest amount of problems can be split up in these two categories:

  1. Servers that deliver gzipped content and sends a Content-Length: for the uncompressed data. This seems to be commonly done with old mod_deflate and mod_fastcgi versions on Apache, but we also saw people using IIS reporting this symptom.
  2. Servers that deliver chunked-encoding but who skip the final zero-size chunk so that the stream actually never really ends.

We recognize that not everyone can have the servers fixed – even if all these servers should still be fixed! We now make these HTTP 1.1 framing problems get detected but only cause a problem if a certain pref variable is set (network.http.enforce-framing.http1), and since that is disabled by default they will be silently ignored much like before. The Internet is a more broken and more sad place than I want to accept at times.

We haven’t fully worked out how to also make the download manager (ie the thing that downloads things directly to disk, without showing it in the browser) happy, which was the original reason for bug 237623…

Although the code may now no longer alert anything about HTTP 1.1 framing problems, it will now at least mark the connection not due for re-use which will be a big boost compared to before since these broken framing cases really hurt persistent connections use. The partial transfer return codes for broken SPDY and HTTP/2 transfers remain though and I hope to be able to remain stricter with these newer protocols.

This partial reversion will land ASAP and get merged into patch releases of Firefox 33 and later.

Finally, to top this off. Here’s a picture of an old HTTP 1.1 frame so that you know what we’re talking about.

An old http1.1 frame

Changing networks with Firefox running

Friday, September 26th, 2014

Short recap: I work on network code for Mozilla. Bug 939318 is one of “mine” – yesterday I landed a fix (a patch series with 6 individual patches) for this and I wanted to explain what goodness that should (might?) come from this!

diffstat

diffstat reports this on the complete patch series:

29 files changed, 920 insertions(+), 162 deletions(-)

The change set can be seen in mozilla-central here. But I guess a proper description is easier for most…

The bouncy road to inclusion

This feature set and associated problems with it has been one of the most time consuming things I’ve developed in recent years, I mean in relation to the amount of actual code produced. I’ve had it “landed” in the mozilla-inbound tree five times and yanked out again before it landed correctly (within a few hours), every time of course reverted again because I had bugs remaining in there. The bugs in this have been really tricky with a whole bunch of timing-dependent and race-like problems and me being unfamiliar with a large part of the code base that I’m working on. It has been a highly frustrating journey during periods but I’d like to think that I’ve learned a lot about Firefox internals partly thanks to this resistance.

As I write this, it has not even been 24 hours since it got into m-c so there’s of course still a risk there’s an ugly bug or two left, but then I also hope to fix the pending problems without having to revert and re-apply the whole series…

Many ways to connect to networks

Firefox Nightly screenshotIn many network setups today, you get an environment and a network “experience” that is crafted for that particular place. For example you may connect to your work over a VPN where you get your company DNS and you can access sites and services you can’t even see when you connect from the wifi in your favorite coffee shop. The same thing goes for when you connect to that captive portal over wifi until you realize you used the wrong SSID and you switch over to the access point you were supposed to use.

For every one of these setups, you get different DHCP setups passed down and you get a new DNS server and so on.

These days laptop lids are getting closed (and the machine is put to sleep) at one place to be opened at a completely different location and rarely is the machine rebooted or the browser shut down.

Switching between networks

Switching from one of the networks to the next is of course something your operating system handles gracefully. You can even easily be connected to multiple ones simultaneously like if you have both an Ethernet card and wifi.

Enter browsers. Or in this case let’s be specific and talk about Firefox since this is what I work with and on. Firefox – like other browsers – will cache images, it will cache DNS responses, it maintains connections to sites a while even after use, it connects to some sites even before you “go there” and so on. All in the name of giving the users an as good and as fast experience as possible.

The combination of keeping things cached and alive, together with the fact that switching networks brings new perspectives and new “truths” offers challenges.

Realizing the situation is new

The changes are not at all mind-bending but are basically these three parts:

  1. Make sure that we detect network changes, even if just the set of available interfaces change. Send an event for this.
  2. Make sure the necessary parts of the code listens and understands this “network topology changed” event and acts on it accordingly
  3. Consider coming back from “sleep” to be a network changed event since we just cannot be sure of the network situation anymore.

The initial work has been made for Windows only but it allows us to smoothen out any rough edges before we continue and make more platforms support this.

The network changed event can be disabled by switching off the new “network.notify.changed” preference. If you do end up feeling a need for that, I really hope you file a bug explaining the details so that we can work on fixing it!

Act accordingly

So what is acting properly? What if the network changes in a way so that your active connections suddenly can’t be used anymore due to the new rules and routing and what not? We attack this problem like this: once we get a “network changed” event, we “allow” connections to prove that they are still alive and if not they’re torn down and re-setup when the user tries to reload or whatever. For plain old HTTP(S) this means just seeing if traffic arrives or can be sent off within N seconds, and for websockets, SPDY and HTTP2 connections it involves sending an actual ping frame and checking for a response.

The internal DNS cache was a bit tricky to handle. I initially just flushed all entries but that turned out nasty as I then also killed ongoing name resolves that caused errors to get returned. Now I instead added logic that flushes all the already resolved names and it makes names “in transit” to get resolved again so that they are done on the (potentially) new network that then can return different addresses for the same host name(s).

This should drastically reduce the situation that could happen before when Firefox would basically just freeze and not want to do any requests until you closed and restarted it. (Or waited long enough for other timeouts to trigger.)

The ‘N seconds’ waiting period above is actually 5 seconds by default and there’s a new preference called “network.http.network-changed.timeout” that can be altered at will to allow some experimentation regarding what the perfect interval truly is for you.

Firefox BallInitially on Windows only

My initial work has been limited to getting the changed event code done for the Windows back-end only (since the code that figures out if there’s news on the network setup is highly system specific), and now when this step has been taken the plan is to introduce the same back-end logic to the other platforms. The code that acts on the event is pretty much generic and is mostly in place already so it is now a matter of making sure the event can be generated everywhere.

My plan is to start on Firefox OS and then see if I can assist with the same thing in Firefox on Android. Then finally Linux and Mac.

I started on Windows since Windows is one of the platforms with the largest amount of Firefox users and thus one of the most prioritized ones.

More to do

There’s separate work going on for properly detecting captive portals. You know the annoying things hotels and airports for example tend to have to force you to do some login dance first before you are allowed to use the internet at that location. When such a captive portal is opened up, that should probably qualify as a network change – but it isn’t yet.

Daladevelop hackathon

Monday, September 15th, 2014

On Saturday the 13th of September, I took part in a hackathon in Falun Sweden organized by Daladevelop.

20-something hacker enthusiasts gathered in a rather large and comfortable room in this place, an almost three hour drive from my home. A number of talks and lectures were held through the day and the difficulty level ranged from newbie to more advanced. My own contribution was a talk about curl followed by one about HTTP/2. Blabbermouth as I am, I exhausted the friendly audience by talking a good total of almost 90 minutes straight. I got a whole range of clever and educated questions and I think and hope we all had a good time as a result.

The organizers ran a quiz for two-person teams. I teamed up with Andreas Olsson in team Emacs, and after having identified x86 assembly, written binary, spotted perl, named Ada Lovelace, used the term lightfoot and provided about 15 more answers we managed to get first prize and the honor of having beaten the others. Great fun!

HTTP/2 interop pains

Tuesday, September 2nd, 2014

At around 06:49 CEST on the morning of August 27 2014, Google deployed an HTTP/2 draft-14 implementation on their front-end servers that handle logins to Google accounts (and possibly others). Those at least take care of all the various login stuff you do with Google, G+, gmail, etc.

The little problem with that was just that their implementation of HTTP2 is in disagreement with all existing client implementations of that same protocol at that draft level. Someone immediately noticed this problem and filed a bug against Firefox.

The Firefox Nightly and beta versions have HTTP2 enabled by default and so users quickly started to notice this and a range of duplicate bug reports have been filed. And keeps being filed as more users run into this problem. As far as I know, Chrome does not have this enabled by default so much fewer Chrome users get this ugly surprise.

The Google implementation has a broken cookie handling (remnants from the draft-13 it looks like by how they do it). As I write this, we’re on the 7th day with this brokenness. We advice bleeding-edge users of Firefox to switch off HTTP/2 support in the mean time until Google wakes up and acts.

You can actually switch http2 support back on once you’ve logged in and it then continues to work fine. Below you can see what a lovely (wildly misleading) error message you get if you try http2 against Google right now with Firefox:

google-http2-draft14-cookies

This post is being debated on hacker news.

Updated: 20:14 CEST: There’s a fix coming, that supposedly will fix this problem on Thursday September 4th.

Update 2: In the morning of September 4th (my time), Google has reverted their servers to instead negotiate SPDY 3.1 and Firefox is fine with this.

Http2 interim meeting NYC

Sunday, June 8th, 2014

On June 5th, around thirty people sat down around a huge table in a conference room on the 4th floor in the Google offices in New York City, with a heavy rain pouring down outside.

It was time for another IETF http2 interim meeting. The attendees were all participants in the HTTPbis work group and came from a wide variety of companies and countries. The major browser vendors were represented there, and so were operators and big service providers and some proxy people. Most of the people who have been speaking up on the mailing list over the last year or so, unfortunately with a couple of people notably absent. (And before anyone asks, yes we are a group where the majority is old males like me.)

Most people present knew many of the others already, which helped to create a friendly familiar spirit and we quickly got started on the Thursday morning working our way through the rather long lits of issues to deal with. When we had our previous interim meeting in London, I think most of us though we would’ve been further along today but recent development and discussions on the list had actually brought back a lot of issues we though we were already done with and we now reiterated a whole slew of subjects. We weren’t allowed to take photographs indoors so you won’t see any pictures of this opportunity from me here.

Google offices building logo

We did close many issues and I’ll just quickly mention some of the noteworthy ones here…

Extensions

We started out with the topic of “extensions”. Should we revert the decision from Zurich (where it was decided that we shouldn’t allow extensions in http2) or was the current state of the protocol the right one? The arguments for allowing extensions included that we’d keep getting requests for new things to add unless we have a way and that some of the recent stuff we’ve added really could’ve been done as extensions instead. An argument against it is that it makes things much simpler and reliable if we just document exactly what the protocol has and is, and removing “optional” behavior from the protocol has been one of the primary mantas along the design process.

The discussion went back and forth for a long time, and after almost three hours we had kind of a draw. Nobody was firmly against “the other” alternative but the two sides also seemed to have roughly the same amount of support. Then it was yet again time for the coin toss to guide us. Martin brought out an Australian coin and … the next protocol draft will allow extensions. Again. This also forces implementation to have to read and skip all unknown frames it receives compared to the existing situation where no unknown frames can ever occur.

BLOCKED as an extension

A rather given first candidate for an extension was the BLOCKED frame. At the time BLOCKED was added to the protocol it was explicitly added into the spec because we didn’t have extensions – and it is now being lifted out into one.

ALTSVC as an extension

What received slightly more resistance was the move to move out the ALTSVC frame as well. It was argued that the frame isn’t mandatory to support and therefore easily can be made into an extension.

Simplified padding

Another small change of the wire format since draft-12 was the removal of the high byte for padding to simplify. It reduces the amount you can pad a single frame but you can easily pad more using other means if you really have to, and there were numbers presented that said that 255 bytes were enough with HTTP 1.1 already so probably it will be enough for version 2 as well.

Schedule

There will be a new draft out really soon: draft -13. Martin, our editor of the spec, says he’ll be able to ship it in a week. That is intended to be the last draft, intended for implementation and it will then be expected to get deployed rather widely to allow us all in the industry to see how it works and be able to polish details or wordings that may still need it.

We had numerous vendors and HTTP stack implementers in the room and when we discussed schedule for when various products will be able to see daylight. If we all manage to stick to the plans. we may just have plenty of products and services that support http2 by the September/October time frame. If nothing major is found in this latest draft, we’re looking at RFC status not too far into 2015.

Meeting summary

I think we’re closing in for real now and I have good hopes for the protocol and our progress to a really wide scale deployment across the Internet. The HTTPbis group is an awesome crowd to work with and I had a great time. Our hosts took good care of us and made sure we didn’t lack any services or supplies. Extra thanks go to those of you who bought me dinners and to those who took me out to good beer places!

My http2 document

Yeah, it will now become somewhat out of date and my plan is to update it once the next draft ships. I’ll also do another http2 presentation already this week so I hope to also post an updated slide set soonish. Stay tuned!

Wireshark

My plan is to cooperate with the other Wireshark hackers and help making sure we have the next draft version supported in Wireshark really soon after its published.

curl and nghttp2

Most of the differences introduced are in the binary format so nghttp2 will need to be updated again – it is the library curl uses for the wire format of http2. The curl parts will need some adjustments, for example for Content-Encoding gzip that no longer is implicit but there should be little to do in the curl code for this draft bump.

licensed to get shared

Tuesday, May 6th, 2014

As my http2 presentation is about to get its 16,000th viewer over at Slideshare I just have to take a moment and reflect over that fact.

Sixteen thousand viewers. I’ve uploaded slides there before over the years but no other presentation has gotten even close to this amount of attention even though some of them have been collecting views for years by now.

http2 presentation screenshot

I wrote my http2 explained document largely due to the popularity of my presentation and the stream of questions and curiosity that brought to life. Within just a couple of days, that 27 page document had been downloaded more than 2,000 times and by now over 5000 times. This is almost 7MB of PDF which I believe raises the bar for the ordinary casual browser to not download it without having an interest and intention to at least glance through it. Of course I realize a large portion of said downloads are never really read.

Someone suggested to me (possibly in jest) that I should convert these into ebooks and “charge 1 USD a piece to get some profit out of them”. I really won’t and I would have a struggle to do that. It has been said before but in my case it is indeed true: I stand on the shoulders of giants. I’ve just collected information and written down texts that mostly are ideas, suggestions and conclusions others have already made in various other forums, lists or documents. I wouldn’t feel right charging for that nor depriving anyone the rights and freedoms to create derivatives and continue building on what I’ve done. I’m just the curator and janitor here. Besides, I already have an awesome job at an awesome company that allows me to work full time on open source – every day.

The next phase started thanks to the open license. A friendly volunteer named Vladimir Lettiev showed up and translated the entire document into Russian and now suddenly the reach of the text is vastly expanded into a territory where it previously just couldn’t penetrate. With using people’s native languages, information can really trickle down to a much larger audience. Especially in regions that aren’t very Englishified.

#MeraKrypto

Tuesday, April 29th, 2014

A whole range of significant Swedish network organizations (ISOC, SNUS, DFRI and SUNET) organized a full-day event today, managed by the great mr Olle E Johansson. The event, called “MeraKrypto” (MoreCrypto would be the exact translation), was a day with introductions to TLS and a lot of talks around TLS and other encryption and security related topics.

I was there and held a talk on the topic of “curl and TLS” and I basically talked some basics around what curl and libcurl are, how we do TLS, some common problems and hwo verifying the server cert is a common usage mistake and then I continued on to quickly mention how http2 and TLS relate..See my slides below, but please be aware that as usual you may not grasp the whole thing only by the (English) slides. The event was fully booked so there was around one hundred peeps in the audience and there were a lot of interested minds that asked good questions proving they really understood the topics.

The discussion almost got heated during the talk about how companies do MITMing of SSL sessions and this guy from Bluecoat pretty much single-handedly argued for the need for this and how “it fills a useful purpose”.

It was a great afternoon!

The event was streamed live and recorded on video. I’ll post a link as soon as it gets available to me.

curl and TLS #MeraKrypto from Daniel Stenberg

http2 explained

Saturday, April 26th, 2014

http2 front page

I’m hereby offering you all the first version of my document explaining http2, the protocol. It features explanations on the background, basic fundamentals, details on the wire format and something about existing implementations and what’s to expect for the future.

The full PDF currently boasts 27 pages at version 1.0, but I plan to keep up with the http2 development going further and I’m also kind of thinking that I will get at least some user feedback, and I’ll do subsequent updates to improve and extend the document over time. Of course time will tell how good that will work.

The document is edited in libreoffice and that file is available on github, but ODT is really not a format suitable for patches and merges so I hope we can sort out changes with filing issues and sending emails.

Wireshark dissector work

Thursday, April 24th, 2014

WiresharkRecently I cloned the Wireshark git repository and started updating the http2 dissector. That’s the piece of code that gets called to analyze a stream of data that Wireshark thinks is http2.

The current http2 dissector was left at draft-09 state, while the current draft at the time was number 11 and there have been several changes on the binary format since so any reasonably updated client or server would send or receive byte streams that Wireshark couldn’t properly display.

I never wrote any dissector code before but I must say Wireshark didn’t disappoint. It was straight forward and mostly downright easy to fix most of the wrong details. I’m not pretending to be a master at this nor is the dissector code anywhere near “finished” yet but I still enjoyed the API and how to write a thing like this.

I’ve since dissected plain-text http2 streams that I’ve done with curl+nghttp2 and I’ve also used the SSLKEYLOGFILE trick with Firefox to automatically decrypt the TLS session and have the dissector figure out the underlying http2 parts.

If there’s any little snag to mention, it is the fact that they insist on getting patches submitted directly to gerrit instead of any mailing list or similar. This required me to create a gerrit account, and really figure out how to push my stuff from git to there, instead of the more traditional and simpler approach of just sending my patch to a mailing list or possibly submitting it to a bug/patch tracker somewhere with my browser.

Call me old-style but in fact the hip way of today with a pull-request github style would also have been much easier. Here’s what my gerrit submission looks like. But I get it, gerrit does push a little more work over to the submitter and I figure that once a submitter such as myself finally has fixed all the nits in the patch it is very easy for the project to actually merge it. I actually got someone else to help me point out how to even find the link to view the code review after the first one was submitted on the site… (when I post this, my patch has not yet been accepted or merged into the wireshark git repo)

Here’s a basic screenshot showing a trace of Firefox requesting https://nghttp2.org using http2. Click it for the full thing.

wireshark-screenshot

.. and what happens this morning my time? There’s a brand new http2 draft-12 out with more changes on the on-the-wire format! Well to be honest, that really wasn’t a surprise. I’ll get the new stuff supported too, but I’ll do that in a separate patch as I prefer to hold off until I see a live stream by at least one implementation to test against.