Category Archives: Firefox

decent durable defect density displayed

Here’s an encouraging graph from our regular Coverity scans of the curl source code, showing that we’ve maintained a fairly low “defect density” over the last two years, staying way below the average density level.
defect density over timeClick the image to view it slightly larger.

Defect density is simply the number of found problems per 1,000 lines of code. As a little (and probably unfair) comparison, right now when curl is flat on 0, Firefox is at 0.47, c-ares at 0.12 and libssh2 at 0.21.

Coverity is still the primary static code analyzer for C code that I’m aware of. None of the flaws Coverity picked up in curl during the last two years were detected by clang-analyzer for example.

HTTP/2 adoption, end of 2015

http2 front imageWhen I asked my surrounding in March 2015 to guess the expected HTTP/2 adoption by now, we as a group ended up with about 10%. OK, the question was vaguely phrased and what does it really mean? Let’s take a look at some aspects of where we are now.

Perhaps the biggest flaw in the question was that it didn’t specify HTTPS. All the browsers of today only implement HTTP/2 over HTTPS so of course if every HTTPS site in the world would support HTTP/2 that would still be far away from all the HTTP requests. Admittedly, browsers aren’t the only HTTP clients…

During the fall of 2015, both nginx and Apache shipped release versions with HTTP/2 support. nginx made it slightly harder for people by forcing users to select either SPDY or HTTP/2 (which was a technical choice done by them, not really enforced by the protocols) and also still telling users that SPDY is the safer choice.

Let’s Encrypt‘s finally launching their public beta in the early December also helps HTTP/2 by removing one of the most annoying HTTPS obstacles: the cost and manual administration of server certs.

Amount of Firefox responses

This is the easiest metric since Mozilla offers public access to the metric data. It is skewed since it is opt-in data and we know that certain kinds of users are less likely to enable this (if you’re more privacy aware or if you’re using it in enterprise environments for example). This also then measures the share by volume of requests; making the popular sites get more weight.

Firefox 43 counts no less than 22% of all HTTP responses as HTTP/2 (based on data from Dec 8 to Dec 16, 2015).

Out of all HTTP traffic Firefox 43 generates, about 63% is HTTPS which then makes almost 35% of all Firefox HTTPS requests are HTTP/2!

Firefox 43 is also negotiating HTTP/2 four times as often as it ends up with SPDY.

Amount of browser traffic

One estimate of how large share of browsers that supports HTTP/2 is the number. Roughly 70% on a global level. Another metric is the one published by KeyCDN at the end of October 2015. When they enabled HTTP/2 by default for their HTTPS customers world wide, the average number of users negotiating HTTP/2 turned out to be 51%. More than half!

Cloudflare however, claims the share of supported browsers are at a mere 26%. That’s a really big difference and I personally don’t buy their numbers as they’re way too negative and give some popular browsers very small market share. For example: Chrome 41 – 49 at a mere 15% of the world market, really?

I think the key is rather that it all boils down to what you measure – as always.

Amount of the top-sites in the world

Netcraft bundles SPDY with HTTP/2 in their October report, but it says that “29% of SSL sites within the thousand most popular sites currently support SPDY or HTTP/2, while 8% of those within the top million sites do.” (note the “of SSL sites” in there)

That’s now slightly old data that came out almost exactly when Apache first release its HTTP/2 support in a public release and Nginx hadn’t even had it for a full month yet.

Facebook eventually enabled HTTP/2 in November 2015.

Amount of “regular” sites

There’s still no ideal service that scans a larger portion of the Internet to measure adoption level. The site is about to change to a chrome-based spider (from IE) and once that goes live I hope that we will get better data.

W3Tech’s report says 2.5% of web sites in early December – less than SPDY!

I like how looks so far and I’ve provided them with my personal opinions and feedback on what I think they should do to make that the preferred site for this sort of data.

Using the shodan search engine, we could see that mid December 2015 there were about 115,000 servers on the Internet using HTTP/2.  That’s 20,000 (~24%) more than isthewebhttp2yet site says. It doesn’t really show percentages there, but it could be interpreted to say that slightly over 6% of HTTP/1.1 sites also support HTTP/2.

On Dec 3rd 2015, Cloudflare enabled HTTP/2 for all its customers and they claimed they doubled the number of HTTP/2 servers on the net in that single move. (The shodan numbers seem to disagree with that statement.)

Amount of system lib support

iOS 9 supports HTTP/2 in its native HTTP library. That’s so far the leader of HTTP/2 in system libraries department. Does Mac OS X have something similar?

I had expected Window’s wininet or other HTTP libs to be up there as well but I can’t find any details online about it. I hear the Android HTTP libs are not up to snuff either but since okhttp is now part of Android to some extent, I guess proper HTTP/2 in Android is not too far away?

Amount of HTTP API support

I hear very little about HTTP API providers accepting HTTP/2 in addition or even instead of HTTP/1.1. My perception is that this is basically not happening at all yet.

Next-gen experiments

If you’re using a modern Chrome browser today against a Google service you’re already (mostly) using QUIC instead of HTTP/2, thus you aren’t really adding to the HTTP/2 client side numbers but you’re also not adding to the HTTP/1.1 numbers.

QUIC and other QUIC-like (UDP-based with the entire stack in user space) protocols are destined to grow and get used even more as we go forward. I’m convinced of this.


Everyone was right! It is mostly a matter of what you meant and how to measure it.


Recall the words on the Chromium blog: “We plan to remove support for SPDY in early 2016“. For Firefox we haven’t said anything that absolute, but I doubt that Firefox will support SPDY for very long after Chrome drops it.

libbrotli is brotli in lib form

Brotli is this new cool compression algorithm that Firefox now has support for in Content-Encoding, Chrome will too soon and Eric Lawrence wrote up this nice summary about.

So I’d love to see brotli supported as a Content-Encoding in curl too, and then we just basically have to write some conditional code to detect the brotli library, add the adaption code for it and we should be in a good position. But…

There is (was) no brotli library!

It turns out the brotli team just writes their code to be linked with their tools, without making any library nor making it easy to install and use for third party applications.

an unmotivated circle sawWe can’t have it like that! I rolled up my imaginary sleeves (imaginary since my swag tshirt doesn’t really have sleeves) and I now offer libbrotli to the world. It is just a bunch of files and a build system that sucks in the brotli upstream repo as a submodule and then it builds a decoder library (brotlidec) and an encoder library (brotlienc) out of them. So there’s no code of our own here. Just building on top of the great stuff done by others.

It’s not complicated. It’s nothing fancy. But you can configure, make and make install two libraries and I can now go on and write a curl adaption for this library so that we can get brotli support for it done. Ideally, this (making a library) is something the brotli project will do on their own at some point, but until they do I don’t mind handling this.

As always, dive in and try it out, file any issues you find and send us your pull-requests for everything you can help us out with!

daniel weekly 42, switching off Nagle


See you at ApacheCon on Friday!


14% HTTP/2 thanks to nginx ?

Brotli everywhere! Firefox, libbrotli

The –libcurl flaw is fixed (and it was GONE from github for a few hours)

http2 explained in Swedish

No, the cheat sheet cannot be in the man page. But…

bug of the week: the http/2 performance fix


option of the week: -k

Talking at the GOTO Conference next week

HTTP/2 – 115 days with the RFC

http2Back in March 2015, I asked friends for a forecast on how much HTTP traffic that will be HTTP/2 by the end of the year and we arrived at about 10% as a group. Are we getting there? Remember that RFC 7540 was published on May 15th, so it is still less than 4 months old!

The HTTP/2 implementations page now lists almost 40 reasonably up-to-date implementations.


Since then, all browsers used by the vast majority of people have stated that they have or will have HTTP/2 support soon (Firefox, Chrome, Edge, Safari and Opera – including Firefox and Chrome on Android and Safari on iPhone). Even OS support is coming: on iOS 9 the support is coming as we speak and the windows HTTP library is getting HTTP/2 support. The adoption rate so far is not limited by the clients.

Unfortunately, the WGet summer of code project to add HTTP/2 support failed.

(I have high hopes for getting a HTTP/2 enabled curl into Debian soon as they’ve just packaged a new enough nghttp2 library. If things go well, this leads the way for other distros too.)


Server-side we see Apache’s mod_h2 module ship in a public release soon (possibly in a httpd version 2.4 series release), nginx has this alpha patch I’ve already mentioned and Apache Traffic Server (ATS) has already shipped h2 support for a while and my friends tell me that 6.0 has fixed numerous of their initial bugs. IIS 10 for Windows 10 was released on July 29th 2015 and supports HTTP/2. H2O and nghttp2 have shipped HTTP/2 for a long time by now. I would say that the infrastructure offering is starting to look really good! Around the end of the year it’ll look even better than today.

Of course we’re still seeing HTTP/2 only deployed over HTTPS so HTTP/2 cannot currently get more popular than HTTPS is but there’s also no real reason for a site using HTTPS today to not provide HTTP/2 within the near future. I think there’s a real possibility that we go above 10% use already in 2015 and at least for browser traffic to HTTPS sites we should be able to that almost every single HTTPS site will go HTTP/2 during 2016.

The delayed start of letsencrypt has also delayed more and easier HTTPS adoption.

Still catching up

I’m waiting to see the intermediaries really catch up. Varnish, Squid and HAProxy I believe all are planning to support it to at least some extent, but I’ve not yet seen them release a version with HTTP/2 enabled.

I hear there’s still not a good HTTP/2 story on Android and its stock HTTP library, although you can in fact run libcurl HTTP/2 enabled even there, and I believe there are other stand-alone libs for Android that support HTTP/2 too, like OkHttp for example.

Firefox numbers

Firefox Nightly screenshotThe latest stable Firefox release right now is version 40. It counts 13% HTTP/2 responses among all HTTP responses. Counted as a share of the transactions going over HTTPS, the share is roughly 27%! (Since Firefox 40 counts 47% of the transactions as HTTPS.)

This is certainly showing a share of the high volume sites of course, but there are also several very high volume sites that have not yet gone HTTP/2, like Facebook, Yahoo, Amazon, Wikipedia and more…

The IPv6 comparison

Right, it is not a fair comparison, but… The first IPv6 RFC has been out for almost twenty years and the adoption is right now at about 8.4% globally.

HTTP Workshop 2015, day -1

http workshopI’ve traveled to a rainy and gray Münster, Germany, today and checked in to my hotel for the coming week and the HTTP Workshop. Tomorrow is the first day and I’m looking forward to it probably a little too much.

There is a whole bunch of attendees coming. Simply put, most of the world’s best brains and the most eager implementers of the HTTP stacks that are in use today and will be in use tomorrow (with a bunch of notable absentees of course but you know you’ll be missed). I’m happy and thrilled to be able to take part during this coming week.

daniel weekly

daniel weekly screenshot

My series of weekly videos, in lack of a better name called daniel weekly, reached episode 35 today. I’m celebrating this fact by also adding an RSS-feed for those of you who prefer to listen to me in an audio-only version.

As an avid podcast listener myself, I can certainly see how this will be a better fit to some. Most of these videos are just me talking anyway so losing the visual shouldn’t be much of a problem.

A typical episode

I talk about what I work on in my open source projects, which means a lot of curl stuff and occasional stuff from my work on Firefox for Mozilla. I also tend to mention events I attend and HTTP/networking developments I find interesting and grab my attention. Lots of HTTP/2 talk for example. I only ever express my own personal opinions.

It is generally an extremely geeky and technical video series.

Every week I mention a (curl) “bug of the week” that allows me to joke or rant about the bug in question or just mention what it is about. In episode 31 I started my “command line options of the week” series in which I explain one or a few curl command line options with some amount of detail. There are over 170 options so the series is bound to continue for a while. I’ve explained ten options so far.

I’ve set a limit for myself and I make an effort to keep the episodes shorter than 20 minutes. I’ve not succeed every time.


The 35 episodes have been viewed over 17,000 times in total. Episode two is the most watched individual one with almost 1,500 views.

Right now, my channel has 190 subscribers.

The top-3 countries that watch my videos: USA, Sweden and UK.

Share of viewers that are female: 3.7%


SSL padlockI’ve written the http2 explained document and I’ve done several talks about HTTP/2. I’ve gotten a lot of questions about TLS in association with HTTP/2 due to this, and I want to address some of them here.

TLS is not mandatory

In the HTTP/2 specification that has been approved and that is about to become an official RFC any day now, there is no language that mandates the use of TLS for securing the protocol. On the contrary, the spec clearly explains how to use it both in clear text (over plain TCP) as well as over TLS. TLS is not mandatory for HTTP/2.

TLS mandatory in effect

While the spec doesn’t force anyone to implement HTTP/2 over TLS but allows you to do it over clear text TCP, representatives from both the Firefox and the Chrome development teams have expressed their intents to only implement HTTP/2 over TLS. This means HTTPS:// URLs are the only ones that will enable HTTP/2 for these browsers. Internet Explorer people have expressed that they intend to also support the new protocol without TLS, but when they shipped their first test version as part of the Windows 10 tech preview, that browser also only supported HTTP/2 over TLS. As of this writing, there has been no browser released to the public that speaks clear text HTTP/2. Most existing servers only speak HTTP/2 over TLS.

The difference between what the spec allows and what browsers will provide is the key here, and browsers and all other user-agents are all allowed and expected to each select their own chosen path forward.

If you’re implementing and deploying a server for HTTP/2, you pretty much have to do it for HTTPS to get users. And your clear text implementation will not be as tested…

A valid remark would be that browsers are not the only HTTP/2 user-agents and there are several such non-browser implementations that implement the non-TLS version of the protocol, but I still believe that the browsers’ impact on this will be notable.

Stricter TLS

When opting to speak HTTP/2 over TLS, the spec mandates stricter TLS requirements than what most clients ever have enforced for normal HTTP 1.1 over TLS.

It says TLS 1.2 or later is a MUST. It forbids compression and renegotiation. It specifies fairly detailed “worst acceptable” key sizes and cipher suites. HTTP/2 will simply use safer TLS.

Another detail here is that HTTP/2 over TLS requires the use of ALPN which is a relatively new TLS extension, RFC 7301, which helps us negotiate the new HTTP version without losing valuable time or network packet round-trips.

TLS-only encourages more HTTPS

Since browsers only speak HTTP/2 over TLS (so far at least), sites that want HTTP/2 enabled must do it over HTTPS to get users. It provides a gentle pressure on sites to offer proper HTTPS. It pushes more people over to end-to-end TLS encrypted connections.

This (more HTTPS) is generally considered a good thing by me and us who are concerned about users and users’ right to privacy and right to avoid mass surveillance.

Why not mandatory TLS?

The fact that it didn’t get in the spec as mandatory was because quite simply there was never a consensus that it was a good idea for the protocol. A large enough part of the working group’s participants spoke up against the notion of mandatory TLS for HTTP/2. TLS was not mandatory before so the starting point was without mandatory TLS and we didn’t manage to get to another stand-point.

When I mention this in discussions with people the immediate follow-up question is…

No really, why not mandatory TLS?

The motivations why anyone would be against TLS for HTTP/2 are plentiful. Let me address the ones I hear most commonly, in an order that I think shows the importance of the arguments from those who argued them.

1. A desire to inspect HTTP traffic

looking-glassThere is a claimed “need” to inspect or intercept HTTP traffic for various reasons. Prisons, schools, anti-virus, IPR-protection, local law requirements, whatever are mentioned. The absolute requirement to cache things in a proxy is also often bundled with this, saying that you can never build a decent network on an airplane or with a satellite link etc without caching that has to be done with intercepts.

Of course, MITMing proxies that terminate SSL traffic are not even rare these days and HTTP/2 can’t do much about limiting the use of such mechanisms.

2. Think of the little ones

small-big-dogSmall devices cannot handle the extra TLS burden“. Either because of the extra CPU load that comes with TLS or because of the cert management in a billion printers/fridges/routers etc. Certificates also expire regularly and need to be updated in the field.

Of course there will be a least acceptable system performance required to do TLS decently and there will always be systems that fall below that threshold.

3. Certificates are too expensive

The price of certificates for servers are historically often brought up as an argument against TLS even it isn’t really HTTP/2 related and I don’t think it was ever an argument that was particularly strong against TLS within HTTP/2. Several CAs now offer zero-cost or very close to zero-cost certificates these days and with the upcoming efforts like, chances are it’ll become even better in the not so distant future.

pile-of-moneyRecently someone even claimed that HTTPS limits the freedom of users since you need to give personal information away (he said) in order to get a certificate for your server. This was not a price he was willing to pay apparently. This is however simply not true for the simplest kinds of certificates. For Domain Validated (DV) certificates you usually only have to prove that you “control” the domain in question in some way. Usually by being able to receive email to a specific receiver within the domain.

4. The CA system is broken

TLS of today requires a PKI system where there are trusted certificate authorities that sign certificates and this leads to a situation where all modern browsers trust several hundred CAs to do this right. I don’t think a lot of people are happy with this and believe this is the ultimate security solution. There’s a portion of the Internet that advocates for DANE (DNSSEC) to address parts of the problem, while others work on gradual band-aids like Certificate Transparency and OCSP stapling to make it suck less.

please trust me

My personal belief is that rejecting TLS on the grounds that it isn’t good enough or not perfect is a weak argument. TLS and HTTPS are the best way we currently have to secure web sites. I wouldn’t mind seeing it improved in all sorts of ways but I don’t believe running protocols clear text until we have designed and deployed the next generation secure protocol is a good idea – and I think it will take a long time (if ever) until we see a TLS replacement.

Who were against mandatory TLS?

Yeah, lots of people ask me this, but I will refrain from naming specific people or companies here since I have no plans on getting into debates with them about details and subtleties in the way I portrait their arguments. You can find them yourself if you just want to and you can most certainly make educated guesses without even doing so.

What about opportunistic security?

A text about TLS in HTTP/2 can’t be complete without mentioning this part. A lot of work in the IETF these days are going on around introducing and making sure opportunistic security is used for protocols. It was also included in the HTTP/2 draft for a while but was moved out from the core spec in the name of simplification and because it could be done anyway without being part of the spec. Also, far from everyone believes opportunistic security is a good idea. The opponents tend to say that it will hinder the adoption of “real” HTTPS for sites. I don’t believe that, but I respect that opinion because it is a guess as to how users will act just as well as my guess is they won’t act like that!

Opportunistic security for HTTP is now being pursued outside of the HTTP/2 spec and allows clients to upgrade plain TCP connections to instead do “unauthenticated TLS” connections. And yes, it should always be emphasized: with opportunistic security, there should never be a “padlock” symbol or anything that would suggest that the connection is “secure”.

Firefox supports opportunistic security for HTTP and it will be enabled by default from Firefox 37.


Пост доступен на сайте Восстановление: TLS в HTTP/2. (Russian)

TLS in HTTP/2 (Kazakh)

More HTTP framing attempts

Previously, in my exciting series “improving the HTTP framing checks in Firefox” we learned that I landed a patch, got it backed out, struggled to improve the checks and finally landed the fixed version only to eventually get that one backed out as well.

And now I’ve landed my third version. The amendment I did this time:

When receiving HTTP content that is content-encoded and compressed I learned that when receiving deflate compression there is basically no good way for us to know if the content gets prematurely cut off. They seem to lack the footer too often for it to make any sense in checking for that. gzip streams however end with a footer so they are easier to reliably detect when they are incomplete. (As was discovered before, the Content-Length: is far too often not updated by the server so it is instead wrongly showing the uncompressed size.)

This (deflate vs gzip) knowledge is now used by the patch, meaning that deflate compressed downloads can be cut off without the browser noticing…

Will this version of the fix actually stick? I don’t know. There’s lots of bad voodoo out there in the HTTP world and I’m putting my finger right in the middle of some of it with this change. I’m pretty sure I’ve not written my last blog post on this topic just yet… If it sticks this time, it should show up in Firefox 39.