Category Archives: cURL and libcurl

curl and/or libcurl related

curl up in Nuremberg!

I’m very happy to announce that the curl project is about to run our first ever curl meeting and developers conference.

March 18-19, Nuremberg Germany

Everyone interested in curl, libcurl and related matters is invited to participate. We only ask of you to register and pay the small fee. The fee will be used for food and more at the event.

You’ll find the full and detailed description of the event and the specific location in the curl wiki.

The agenda for the weekend is purposely kept loose to allow for flexibility and unconference-style adding things and topics while there. You will thus have the chance to present what you like and affect what others present. Do tell us what you’d like to talk about or hear others talk about! The sign-up for the event isn’t open yet, as we first need to work out some more details.

We have a dedicated mailing list for discussing the meeting, called curl-meet, so please consider yourself invited to join in there as well!

Thanks a lot to SUSE for hosting!

Feel free to help us make a cool logo for the event!


(The 19th birthday of curl is suitably enough the day after, on March 20.)

poll on mac 10.12 is broken

When Mac OS X first launched they did so without an existing poll function. They later added poll() in Mac OS X 10.3, but we quickly discovered that it was broken (it returned a non-zero value when asked to wait for nothing) so in the curl project we added a check in configure for that and subsequently avoided using poll() in all OS X versions to and including Mac OS 10.8 (Darwin 12). The code would instead switch to the alternative solution based on select() for these platforms.

With the release of Mac OS X 10.9 “Mavericks” in October 2013, Apple had fixed their poll() implementation and we’ve built libcurl to use it since with no issues at all. The configure script picks the correct underlying function to use.

Enter macOS 10.12 (yeah, its not called OS X anymore) “Sierra”, released in September 2016. Quickly we discovered that poll() once against did not act like it should and we are back to disabling the use of it in preference to the backup solution using select().

The new error looks similar to the old problem: when there’s nothing to wait for and we ask poll() to wait N milliseconds, the 10.12 version of poll() returns immediately without waiting. Causing busy-loops. The problem has been reported to Apple and its Radar number is 28372390. (There has been no news from them on how they plan to act on this.)

poll() is defined by POSIX and The Single Unix Specification it specifically says:

If none of the defined events have occurred on any selected file descriptor, poll() waits at least timeout milliseconds for an event to occur on any of the selected file descriptors.

We pushed a configure check for this in curl, to be part of the upcoming 7.51.0 release. I’ll also show you a small snippet you can use stand-alone below.

Apple is hardly alone in the broken-poll department. Remember how Windows’ WSApoll is broken?

Here’s a little code snippet that can detect the 10.12 breakage:

#include <poll.h>
#include <stdio.h>
#include <sys/time.h>

int main(void)
  struct timeval before, after;
  int rc;
  size_t us;

  gettimeofday(&before, NULL);
  rc = poll(NULL, 0, 500);
  gettimeofday(&after, NULL);

  us = (after.tv_sec - before.tv_sec) * 1000000 +
    (after.tv_usec - before.tv_usec);

  if(us < 400000) {
    puts("poll() is broken");
    return 1;
  else {
    puts("poll() works");
  return 0;

screenshotted curl credits

If you have more or better screenshots, please share!


This shot is taken from the ending sequence of the PC version of the game Grand Theft Auto V. 44 minutes in! See the youtube version.


Sky HD is a satellite TV box.


This is a Philips TV. The added use of c-ares I  consider a bonus!


The infotainment display of a BMW car.


Playstation 4 lists open source products it uses.


This is a screenshot from an Iphone open source license view. The iOS 10 screen however, looks like this:


curl in iOS 10 with an older year span than in the much older screenshot?

Instagram credits screenshot

Instagram on an Iphone.

Spotify credits screenshot

Spotify on an Iphone.


Virtualbox (thanks to Anders Nilsson)

curl-battle-net (thanks Anders Nilsson)


Freebox (thanks Alexis La Goutte)


The Youtube app on Android. (Thanks Ray Satiro)


The Youtube app on iOS (Thanks Anthony Bryan)

25,000 curl questions on stackoverflow

stackoverflow-logoOver time, I’ve reluctantly come to terms with the fact that a lot of questions and answers about curl is not done on the mailing lists we have setup in the project itself.

A primary such external site with curl related questions is of course stackoverflow – hardly news to programmers of today. The questions tagged with curl is of course only a very tiny fraction of the vast amount of questions and answers that accumulate on that busy site.

The pile of questions tagged with curl on stackoverflow has just surpassed the staggering number of 25,000. Of course, these questions involve persons who ask about particular curl behaviors (and a large portion is about PHP/CURL) but there’s also a significant amount of tags for questions where curl is only used to do something and that other something is actually what the question is about. And ‘libcurl’ is used as a separate tag and is often used independently of the ‘curl’ one. libcurl is tagged on almost 2,000 questions.

curl-symbolBut still. 25,000 questions. Wow.

I visit that site every so often and answer to some questions but I often end up feeling a great “distance” between me and questions there, and I have a hard time to bridge that gap. Also, stackoverflow the site and the format isn’t really suitable for debugging or solving problems within curl so I often end up trying to get the user move over to file an issue on curl’s github page or discuss the curl problem on a mailing list instead. Forums more suitable for plenty of back-and-forth before the solution or fix is figured out.

Now, any bets for how long it takes until we reach 100K questions?

A sea of curl stickers

To spread the word, to show off the logo, to share the love, to boost the brand, to allow us to fill up our own and our friend’s laptop covers I ordered a set of curl stickers to hand out to friends and fans whenever I meet any going forward. They arrived today, and I thought I’d give you a look. (You can still purchase your own set of curl stickers from

The sticker is 74 x 26 mm at its max.

curl stickers en masse

a bunch of curl stickers

My first 20 years of HTTP

During the autumn 1996 I took my first swim in the ocean known as HTTP. Twenty years ago now.

I had previously worked with writing an IRC bot in C, and IRC is a pretty simple text based protocol over TCP so I could use some experiences from that when I started to look into HTTP. That IRC bot was my first real application distributed to the world that was using TCP/IP. It was portable to most unixes and Amiga and it was open source.

1996 was the year the movie Independence Day premiered and the single hit song that plagued the world more than others that year was called Macarena. AOL, Webcrawler and Netscape were the most popular websites on the Internet. There were less than 300,000 web sites on the Internet (compared to some 900 million today).

I decided I should spice up the bot and make it offer a currency exchange rate service so that people who were chatting could ask the bot what 200 SEK is when converted to USD or what 50 AUD might be in DEM. – Right, there was no Euro currency yet back then!

I simply had to fetch the currency rates at a regular interval and keep them in the same server that ran the bot. I just needed a little tool to download the rates over HTTP. How hard can that be? I googled around (this was before Google existed so that was not the search engine I could use!) and found a tool named ‘httpget’ that made pretty much what I wanted. It truly was tiny – a few hundred nokia-1610lines of code.

I don’t have an exact date saved or recorded for when this happened, only the general time frame. You know, we had no smart phones, no Google calendar and no digital cameras. I sported my first mobile phone back then, the sexy Nokia 1610 – viewed in the picture on the right here.

The HTTP/1.0 RFC had just recently came out – which was the first ever real spec published for HTTP. RFC 1945 was published in May 1996, but I was blissfully unaware of the youth of the standard and I plunged into my little project. This was the first published HTTP spec and it says:

HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification reflects common usage of the protocol referred too as "HTTP/1.0". This specification describes the features that seem to be consistently implemented in most HTTP/1.0 clients and servers.

Many years after that point in time, I have learned that already at this time when I first searched for a HTTP tool to use, wget already existed. I can’t recall that I found that in my searches, and if I had found it maybe history would’ve made a different turn for me. Or maybe I found it and discarded for a reason I can’t remember now.

I wasn’t the original author of httpget; Rafael Sagula was. But I started contributing fixes and changes and soon I was the maintainer of it. Unfortunately I’ve lost my emails and source code history from those earliest years so I cannot easily show my first steps. Even the oldest changelogs show that we very soon got help and contributions from users.

The earliest saved code archive I have from those days, is from after we had added support for Gopher and FTP and renamed the tool ‘urlget’. was released on January 20 1998 which thus was more than a year later my involvement in httpget started.

The original httpget/urlget/curl code was stored in CVS and it was licensed under the GPL. I did most of the early development on SunOS and Solaris machines as my first experiments with Linux didn’t start until 97/98 something.


The first web page I know we have saved on is from December 1998 and by then the project had been renamed to curl already. Roughly two years after the start of the journey.

RFC 2068 was the first HTTP/1.1 spec. It was released already in January 1997, so not that long after the 1.0 spec shipped. In our project however we stuck with doing HTTP 1.0 for a few years longer and it wasn’t until February 2001 we first started doing HTTP/1.1 requests. First shipped in curl 7.7. By then the follow-up spec to HTTP/1.1, RFC 2616, had already been published as well.

The IETF working group called HTTPbis was started in 2007 to once again refresh the HTTP/1.1 spec, but it took me a while until someone pointed out this to me and I realized that I too could join in there and do my part. Up until this point, I had not really considered that little me could actually participate in the protocol doings and bring my views and ideas to the table. At this point, I learned about IETF and how it works.

I posted my first emails on that list in the spring 2008. The 75th IETF meeting in the summer of 2009 was held in Stockholm, so for me still working  on HTTP only as a spare time project it was very fortunate and good timing. I could meet a lot of my HTTP heroes and HTTPbis participants in real life for the first time.

I have participated in the HTTPbis group ever since then, trying to uphold the views and standpoints of a command line tool and HTTP library – which often is not the same as the web browsers representatives’ way of looking at things. Since I was employed by Mozilla in 2014, I am of course now also in the “web browser camp” to some extent, but I remain a protocol puritan as curl remains my first “child”.

Mozilla’s search for a new logo

I’m employed by Mozilla. The same Mozilla that recently has announced that it is looking around for feedback on how to revamp its logo and graphical image.

It was with amusement I saw one of the existing suggestions for a new logo by using “://” (colon slash slash) the name:


… compared with the recently announced new curl logo:


Me being in both teams and being a general Internet protocol enthusiast I couldn’t be more happy if Mozilla would end up using a design so clearly based on the same underlying thoughts. After all,
Imitation is the sincerest of flattery as Charles Caleb Colton once so eloquently expressed it.

Removing the PowerShell curl alias?

PowerShell is a spiced up command line shell made by Microsoft. According to some people, it is a really useful and good shell alternative.

Already a long time ago, we got bug reports from confused users who couldn’t use curl from their PowerShell prompts and it didn’t take long until we figured out that Microsoft had added aliases for both curl and wget. The alias had the shell instead invoke its own command called “Invoke-WebRequest” whenever curl or wget was entered. Invoke-WebRequest being PowerShell’s own version of a command line tool for fiddling with URLs.

Invoke-WebRequest is of course not anywhere near similar to neither curl nor wget and it doesn’t support any of the command line options or anything. The aliases really don’t help users. No user who would want the actual curl or wget is helped by these aliases, and user who don’t know about the real curl and wget won’t use the aliases. They were and remain pointless. But they’ve remained a thorn in my side ever since. Me knowing that they are there and confusing users every now and then – not me personally, since I’m not really a Windows guy.

Fast forward to modern days: Microsoft released PowerShell as open source on github yesterday. Without much further ado, I filed a Pull-Request, asking the aliases to be removed. It is a minuscule, 4 line patch. It took way longer to git clone the repo than to make the actual patch and submit the pull request!

It took 34 minutes for them to close the pull request:

“Those aliases have existed for multiple releases, so removing them would be a breaking change.”

To be honest, I didn’t expect them to merge it easily. I figure they added those aliases for a reason back in the day and it seems unlikely that I as an outsider would just make them change that decision just like this out of the blue.

But the story didn’t end there. Obviously more Microsoft people gave the PR some attention and more comments were added. Like this:

“You bring up a great point. We added a number of aliases for Unix commands but if someone has installed those commands on WIndows, those aliases screw them up.

We need to fix this.”

So, maybe it will trigger a change anyway? The story is ongoing…

curl and h2 on mac

$ curl ‐‐http2
curl: (1) Unsupported protocol

curl on mac

curcurl-symboll has been shipped by default on Mac OS X since many years – I actually couldn’t even manage to figure out exactly how many. It is built and bundled with the operating system by Apple itself and on Apple’s own terms and even though I’m the main curl developer I’ve never discussed this with them or even been asked or told about their plans. I’m not complaining, our license allows this and I’m nothing but happy with them shipping curl to millions of Mac users.

Leaving OpenSSL

osxOriginally, curl on Mac was built against OpenSSL for the TLS and SSL support, but over time our friends at Apple have switched more and more of their software over to use their own TLS and crypto library Secure Transport instead of OpenSSL. A while ago Apple started bundling curl built to use the native mac TLS library instead of OpenSSL.

As you may know, when you build curl you can select from eleven different TLS libraries and one of them of course is Secure Transport. Support for this TLS back-end in curl was written by curl hackers, but it apparently got to a quality level good enough for Apple to decide to build curl with this back-end and ship it like that.

The Secure Transport back-end is rather capable and generally doesn’t cause many reasons for concern. There’s however one notable little glitch that people keep asking me about…

curl doesn’t support HTTP/2 on mac!

There are two obvious reasons why not, and they are:

1. No ALPN with Secure Transport

Secure Transport doesn’t offer any public API to enable HTTP/2 with ALPN when speaking HTTPS. Sure, we know Apple supports HTTP/2 already in several other aspects in their ecosystem and we can check their open code so we know there’s support for HTTP/2 and ALPN. There’s just no official APIs for us to use to switch it on!

So, if you insist on building curl to use Secure Transport instead of one of the many alternatives that actually support ALPN just fine, then you can’t negotiate HTTP/2 over TLS!

2. No nghttp2 with Mac OS

Even without ALPN support, you could actually still negotiate HTTP/2 over plain text TCP connections if you have a server that supports it. But even then curl depends on the awesome nghttp2 library to provide the frame level protocol encoding/decoding and more. If Apple would decide to enable HTTP/2 support for curl on Mac OS, they need to build it against nghttp2. I really think they should.

Homebrew and friends to the rescue!

Correct. You can still install your own separate curl binary (and libcurl library) from other sources, like for example Homebrew or Macports and they do offer versions built against other TLS back-ends and nghttp2 and then of course HTTP/2 works just fine with curl on mac.

Did I file a bug with Apple?

No, but I know for certain that there has been a bug report filed by someone else. Unfortunately it isn’t public so I can’t link nor browse it.

A workshop Monday

http workshopI decided I’d show up a little early at the Sheraton as I’ve been handling the interactions with hotel locally here in Stockholm where the workshop will run for the coming three days. Things were on track, if we ignore how they got the wrong name of the workshop on the info screens in the lobby, instead saying “Haxx Ab”…

Mark welcomed us with a quick overview of what we’re here for and quick run-through of the rough planning for the days. Our schedule is deliberately loose and open to allow for changes and adaptations as we go along.

Patrick talked about the 1 1/2 years of HTTP/2 working in Firefox so far, and we discussed a lot around the numbers and telemetry. What do they mean and why do they look like this etc. HTTP/2 is now at 44% of all HTTPS requests and connections using HTTP/2 are used for more than 8 requests on median (compared to slightly over 1 in the HTTP/1 case). What’s almost not used at all? HTTP/2 server push, Alt-Svc and HTTP 308 responses. Patrick’s presentation triggered a lot of good discussions. His slides are here.

RTT distribution for Firefox running on desktop and mobile, from Patrick’s slide set:


The lunch was lovely.

Vlad then continued to talk about experiences from implementing and providing server push at Cloudflare. It and the associated discussions helped emphasize that we need better help for users on how to use server push and there might be reasons for browsers to change how they are stored in the current “secondary cache”. Also, discussions around how to access pushed resources and get information about pushes from javascript were briefly touched on.

After a break with some sweets and coffee, Kazuho continued to describe cache digests and how this concept can help making servers do better or more accurate server pushes. Back to more discussions around push and what it actually solved, how much complexity it is worth and so on. I thought I could sense hesitation in the room on whether this is really something to proceed with.

We intend to have a set of lightning talks after lunch each day and we have already have twelve such suggested talks listed in the workshop wiki, but the discussions were so lively and extensive that we missed them today and we even had to postpone the last talk of today until tomorrow. I can already sense how these three days will not be enough for us to cover everything we have listed and planned…

We ended the evening with a great dinner sponsored by Mozilla. I’d say it was a great first day. I’m looking forward to day 2!